From c23a03ad8191ca928d96b668f8800a4ab22b2e13 Mon Sep 17 00:00:00 2001
From: Paul Masurel <paul.masurel@gmail.com>
Date: Thu, 8 Oct 2020 16:36:51 +0900
Subject: [PATCH] Large API Change in the Directory API. (#901)

Tantivy used to assume that all files could be somehow memory mapped. After this change, Directory return a `FileSlice` that can be reduced and eventually read into an `OwnedBytes` object. Long and blocking io operation are still required by they do not span over the entire file.
---
 CHANGELOG.md                             |   1 +
 Cargo.toml                               |   2 -
 examples/iterating_docs_and_positions.rs |   8 +-
 src/collector/facet_collector.rs         |   6 +-
 src/common/bitpacker.rs                  |  24 +--
 src/common/composite_file.rs             |  66 +++---
 src/core/inverted_index_reader.rs        |  96 +++++----
 src/core/searcher.rs                     |  43 ++--
 src/core/segment.rs                      |   7 +-
 src/core/segment_reader.rs               | 117 +++++-----
 src/directory/directory.rs               |  13 +-
 src/directory/error.rs                   |  10 +
 src/directory/file_slice.rs              | 264 +++++++++++++++++++++++
 src/directory/footer.rs                  |  25 ++-
 src/directory/managed_directory.rs       |  68 +++---
 src/directory/mmap_directory.rs          |  77 +++----
 src/directory/mod.rs                     |   7 +-
 src/directory/owned_bytes.rs             | 239 ++++++++++++++++++++
 src/directory/ram_directory.rs           |  25 ++-
 src/directory/read_only_source.rs        | 137 ------------
 src/directory/tests.rs                   |  81 ++++---
 src/fastfield/bytes/mod.rs               |   4 +-
 src/fastfield/bytes/reader.rs            |  17 +-
 src/fastfield/delete.rs                  |  24 ++-
 src/fastfield/mod.rs                     | 122 +++++------
 src/fastfield/reader.rs                  |  37 ++--
 src/fastfield/readers.rs                 |  48 +++--
 src/fieldnorm/reader.rs                  |  30 +--
 src/indexer/index_writer.rs              |  41 +++-
 src/indexer/merger.rs                    |  18 +-
 src/lib.rs                               |  88 ++++----
 src/positions/mod.rs                     |  27 ++-
 src/positions/reader.rs                  |  74 ++++---
 src/postings/block_segment_postings.rs   |  67 +++---
 src/postings/mod.rs                      |  89 ++++----
 src/postings/postings_writer.rs          |   2 +-
 src/postings/segment_postings.rs         |  18 +-
 src/postings/skip.rs                     |  78 +++----
 src/postings/stacker/expull.rs           |   6 +-
 src/query/automaton_weight.rs            |   4 +-
 src/query/bm25.rs                        |  28 +--
 src/query/phrase_query/phrase_query.rs   |   2 +-
 src/query/phrase_query/phrase_weight.rs  |   8 +-
 src/query/range_query.rs                 |   4 +-
 src/query/term_query/term_query.rs       |  18 +-
 src/query/term_query/term_scorer.rs      |   2 +-
 src/query/term_query/term_weight.rs      |  12 +-
 src/reader/mod.rs                        |   6 +-
 src/schema/term.rs                       |   2 +-
 src/snippet/mod.rs                       |  22 +-
 src/space_usage/mod.rs                   |  46 ++--
 src/store/mod.rs                         |  18 +-
 src/store/reader.rs                      |  54 ++---
 src/store/writer.rs                      |   3 +-
 src/termdict/mod.rs                      | 162 ++++++--------
 src/termdict/term_info_store.rs          |  57 +++--
 src/termdict/termdict.rs                 |  47 ++--
 tests/failpoints/mod.rs                  |  13 +-
 58 files changed, 1497 insertions(+), 1117 deletions(-)
 create mode 100644 src/directory/file_slice.rs
 create mode 100644 src/directory/owned_bytes.rs
 delete mode 100644 src/directory/read_only_source.rs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 199e9c215..2f3f0dea7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@ Tantivy 0.14.0
 - Remove dependency to atomicwrites #833 .Implemented by @pmasurel upon suggestion and research from @asafigan). 
 - Migrated tantivy error from the now deprecated `failure` crate to `thiserror` #760. (@hirevo)
 - API Change. Accessing the typed value off a `Schema::Value` now returns an Option instead of panicking if the type does not match. 
+- Large API Change in the Directory API. Tantivy used to assume that all files could be somehow memory mapped. After this change, Directory return a `FileSlice` that can be reduced and eventually read into an `OwnedBytes` object. Long and blocking io operation are still required by they do not span over the entire file.
 
 Tantivy 0.13.2
 ===================
diff --git a/Cargo.toml b/Cargo.toml
index efd59bdf5..d44fc2283 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -33,7 +33,6 @@ notify = {version="4", optional=true}
 uuid = { version = "0.8", features = ["v4", "serde"] }
 crossbeam = "0.7"
 futures = {version = "0.3",  features=["thread-pool"] }
-owning_ref = "0.4"
 tantivy-query-grammar = { version="0.14.0-dev", path="./query-grammar" }
 stable_deref_trait = "1"
 rust-stemmers = "1"
@@ -41,7 +40,6 @@ downcast-rs = "1"
 bitpacking = {version="0.8", default-features = false, features=["bitpacker4x"]}
 census = "0.4"
 fnv = "1"
-owned-read = "0.4"
 thiserror = "1.0"
 htmlescape = "0.3"
 fail = "0.4"
diff --git a/examples/iterating_docs_and_positions.rs b/examples/iterating_docs_and_positions.rs
index d55186bf6..3055895e4 100644
--- a/examples/iterating_docs_and_positions.rs
+++ b/examples/iterating_docs_and_positions.rs
@@ -45,7 +45,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // A `Term` is a text token associated with a field.
         // Let's go through all docs containing the term `title:the` and access their position
@@ -58,7 +58,7 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut segment_postings) =
-            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)
+            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)?
         {
             // this buffer will be used to request for positions
             let mut positions: Vec<u32> = Vec::with_capacity(100);
@@ -106,7 +106,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // This segment posting object is like a cursor over the documents matching the term.
         // The `IndexRecordOption` arguments tells tantivy we will be interested in both term frequencies
@@ -115,7 +115,7 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut block_segment_postings) =
-            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)
+            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)?
         {
             loop {
                 let docs = block_segment_postings.docs();
diff --git a/src/collector/facet_collector.rs b/src/collector/facet_collector.rs
index 98b844fb6..9e86472cb 100644
--- a/src/collector/facet_collector.rs
+++ b/src/collector/facet_collector.rs
@@ -7,7 +7,6 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use crate::TantivyError;
 use std::cmp::Ordering;
 use std::collections::btree_map;
 use std::collections::BTreeMap;
@@ -266,10 +265,7 @@ impl Collector for FacetCollector {
         _: SegmentLocalId,
         reader: &SegmentReader,
     ) -> crate::Result<FacetSegmentCollector> {
-        let field_name = reader.schema().get_field_name(self.field);
-        let facet_reader = reader.facet_reader(self.field).ok_or_else(|| {
-            TantivyError::SchemaError(format!("Field {:?} is not a facet field.", field_name))
-        })?;
+        let facet_reader = reader.facet_reader(self.field)?;
 
         let mut collapse_mapping = Vec::new();
         let mut counts = Vec::new();
diff --git a/src/common/bitpacker.rs b/src/common/bitpacker.rs
index 22a21bcd5..640d8adcf 100644
--- a/src/common/bitpacker.rs
+++ b/src/common/bitpacker.rs
@@ -1,6 +1,7 @@
 use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use std::io;
-use std::ops::Deref;
+
+use crate::directory::OwnedBytes;
 
 pub(crate) struct BitPacker {
     mini_buffer: u64,
@@ -60,20 +61,14 @@ impl BitPacker {
 }
 
 #[derive(Clone)]
-pub struct BitUnpacker<Data>
-where
-    Data: Deref<Target = [u8]>,
-{
+pub struct BitUnpacker {
     num_bits: u64,
     mask: u64,
-    data: Data,
+    data: OwnedBytes,
 }
 
-impl<Data> BitUnpacker<Data>
-where
-    Data: Deref<Target = [u8]>,
-{
-    pub fn new(data: Data, num_bits: u8) -> BitUnpacker<Data> {
+impl BitUnpacker {
+    pub fn new(data: OwnedBytes, num_bits: u8) -> BitUnpacker {
         let mask: u64 = if num_bits == 64 {
             !0u64
         } else {
@@ -90,7 +85,7 @@ where
         if self.num_bits == 0 {
             return 0u64;
         }
-        let data: &[u8] = &*self.data;
+        let data: &[u8] = self.data.as_slice();
         let num_bits = self.num_bits;
         let mask = self.mask;
         let addr_in_bits = idx * num_bits;
@@ -109,8 +104,9 @@ where
 #[cfg(test)]
 mod test {
     use super::{BitPacker, BitUnpacker};
+    use crate::directory::OwnedBytes;
 
-    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker<Vec<u8>>, Vec<u64>) {
+    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker, Vec<u64>) {
         let mut data = Vec::new();
         let mut bitpacker = BitPacker::new();
         let max_val: u64 = (1u64 << num_bits as u64) - 1u64;
@@ -122,7 +118,7 @@ mod test {
         }
         bitpacker.close(&mut data).unwrap();
         assert_eq!(data.len(), ((num_bits as usize) * len + 7) / 8 + 7);
-        let bitunpacker = BitUnpacker::new(data, num_bits);
+        let bitunpacker = BitUnpacker::new(OwnedBytes::new(data), num_bits);
         (bitunpacker, vals)
     }
 
diff --git a/src/common/composite_file.rs b/src/common/composite_file.rs
index 34cfe2a59..775bd62a9 100644
--- a/src/common/composite_file.rs
+++ b/src/common/composite_file.rs
@@ -1,14 +1,15 @@
 use crate::common::BinarySerializable;
 use crate::common::CountingWriter;
 use crate::common::VInt;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{TerminatingWrite, WritePtr};
 use crate::schema::Field;
 use crate::space_usage::FieldUsage;
 use crate::space_usage::PerFieldSpaceUsage;
 use std::collections::HashMap;
-use std::io::Write;
-use std::io::{self, Read};
+use std::io::{self, Read, Write};
+
+use super::HasLen;
 
 #[derive(Eq, PartialEq, Hash, Copy, Ord, PartialOrd, Clone, Debug)]
 pub struct FileAddr {
@@ -103,25 +104,26 @@ impl<W: TerminatingWrite + Write> CompositeWrite<W> {
 /// for each field.
 #[derive(Clone)]
 pub struct CompositeFile {
-    data: ReadOnlySource,
+    data: FileSlice,
     offsets_index: HashMap<FileAddr, (usize, usize)>,
 }
 
 impl CompositeFile {
     /// Opens a composite file stored in a given
-    /// `ReadOnlySource`.
-    pub fn open(data: &ReadOnlySource) -> io::Result<CompositeFile> {
+    /// `FileSlice`.
+    pub fn open(data: &FileSlice) -> io::Result<CompositeFile> {
         let end = data.len();
-        let footer_len_data = data.slice_from(end - 4);
+        let footer_len_data = data.slice_from(end - 4).read_bytes()?;
         let footer_len = u32::deserialize(&mut footer_len_data.as_slice())? as usize;
         let footer_start = end - 4 - footer_len;
-        let footer_data = data.slice(footer_start, footer_start + footer_len);
+        let footer_data = data
+            .slice(footer_start, footer_start + footer_len)
+            .read_bytes()?;
         let mut footer_buffer = footer_data.as_slice();
         let num_fields = VInt::deserialize(&mut footer_buffer)?.0 as usize;
 
         let mut file_addrs = vec![];
         let mut offsets = vec![];
-
         let mut field_index = HashMap::new();
 
         let mut offset = 0;
@@ -150,19 +152,19 @@ impl CompositeFile {
     pub fn empty() -> CompositeFile {
         CompositeFile {
             offsets_index: HashMap::new(),
-            data: ReadOnlySource::empty(),
+            data: FileSlice::empty(),
         }
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read(&self, field: Field) -> Option<ReadOnlySource> {
+    pub fn open_read(&self, field: Field) -> Option<FileSlice> {
         self.open_read_with_idx(field, 0)
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<ReadOnlySource> {
+    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<FileSlice> {
         self.offsets_index
             .get(&FileAddr { field, idx })
             .map(|&(from, to)| self.data.slice(from, to))
@@ -192,46 +194,44 @@ mod test {
     use std::path::Path;
 
     #[test]
-    fn test_composite_file() {
+    fn test_composite_file() -> crate::Result<()> {
         let path = Path::new("test_path");
         let mut directory = RAMDirectory::create();
         {
             let w = directory.open_write(path).unwrap();
             let mut composite_write = CompositeWrite::wrap(w);
-            {
-                let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
-                VInt(32431123u64).serialize(&mut write_0).unwrap();
-                write_0.flush().unwrap();
-            }
-
-            {
-                let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
-                VInt(2).serialize(&mut write_4).unwrap();
-                write_4.flush().unwrap();
-            }
-            composite_write.close().unwrap();
+            let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
+            VInt(32431123u64).serialize(&mut write_0)?;
+            write_0.flush()?;
+            let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
+            VInt(2).serialize(&mut write_4)?;
+            write_4.flush()?;
+            composite_write.close()?;
         }
         {
-            let r = directory.open_read(path).unwrap();
-            let composite_file = CompositeFile::open(&r).unwrap();
+            let r = directory.open_read(path)?;
+            let composite_file = CompositeFile::open(&r)?;
             {
                 let file0 = composite_file
                     .open_read(Field::from_field_id(0u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file0_buf = file0.as_slice();
-                let payload_0 = VInt::deserialize(&mut file0_buf).unwrap().0;
+                let payload_0 = VInt::deserialize(&mut file0_buf)?.0;
                 assert_eq!(file0_buf.len(), 0);
                 assert_eq!(payload_0, 32431123u64);
             }
             {
                 let file4 = composite_file
                     .open_read(Field::from_field_id(4u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file4_buf = file4.as_slice();
-                let payload_4 = VInt::deserialize(&mut file4_buf).unwrap().0;
+                let payload_4 = VInt::deserialize(&mut file4_buf)?.0;
                 assert_eq!(file4_buf.len(), 0);
                 assert_eq!(payload_4, 2u64);
             }
         }
+        Ok(())
     }
 }
diff --git a/src/core/inverted_index_reader.rs b/src/core/inverted_index_reader.rs
index e62f65cf5..dec2bf684 100644
--- a/src/core/inverted_index_reader.rs
+++ b/src/core/inverted_index_reader.rs
@@ -1,5 +1,7 @@
+use std::io;
+
 use crate::common::BinarySerializable;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::positions::PositionReader;
 use crate::postings::TermInfo;
 use crate::postings::{BlockSegmentPostings, SegmentPostings};
@@ -14,7 +16,7 @@ use crate::termdict::TermDictionary;
 ///
 /// It is safe to delete the segment associated to
 /// an `InvertedIndexReader`. As long as it is open,
-/// the `ReadOnlySource` it is relying on should
+/// the `FileSlice` it is relying on should
 /// stay available.
 ///
 ///
@@ -22,9 +24,9 @@ use crate::termdict::TermDictionary;
 /// the `SegmentReader`'s [`.inverted_index(...)`] method
 pub struct InvertedIndexReader {
     termdict: TermDictionary,
-    postings_source: ReadOnlySource,
-    positions_source: ReadOnlySource,
-    positions_idx_source: ReadOnlySource,
+    postings_file_slice: FileSlice,
+    positions_file_slice: FileSlice,
+    positions_idx_file_slice: FileSlice,
     record_option: IndexRecordOption,
     total_num_tokens: u64,
 }
@@ -33,22 +35,21 @@ impl InvertedIndexReader {
     #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_pass_by_value))] // for symmetry
     pub(crate) fn new(
         termdict: TermDictionary,
-        postings_source: ReadOnlySource,
-        positions_source: ReadOnlySource,
-        positions_idx_source: ReadOnlySource,
+        postings_file_slice: FileSlice,
+        positions_file_slice: FileSlice,
+        positions_idx_file_slice: FileSlice,
         record_option: IndexRecordOption,
-    ) -> InvertedIndexReader {
-        let total_num_tokens_data = postings_source.slice(0, 8);
-        let mut total_num_tokens_cursor = total_num_tokens_data.as_slice();
-        let total_num_tokens = u64::deserialize(&mut total_num_tokens_cursor).unwrap_or(0u64);
-        InvertedIndexReader {
+    ) -> io::Result<InvertedIndexReader> {
+        let (total_num_tokens_slice, postings_body) = postings_file_slice.split(8);
+        let total_num_tokens = u64::deserialize(&mut total_num_tokens_slice.read_bytes()?)?;
+        Ok(InvertedIndexReader {
             termdict,
-            postings_source: postings_source.slice_from(8),
-            positions_source,
-            positions_idx_source,
+            postings_file_slice: postings_body,
+            positions_file_slice,
+            positions_idx_file_slice,
             record_option,
             total_num_tokens,
-        }
+        })
     }
 
     /// Creates an empty `InvertedIndexReader` object, which
@@ -56,9 +57,9 @@ impl InvertedIndexReader {
     pub fn empty(record_option: IndexRecordOption) -> InvertedIndexReader {
         InvertedIndexReader {
             termdict: TermDictionary::empty(),
-            postings_source: ReadOnlySource::empty(),
-            positions_source: ReadOnlySource::empty(),
-            positions_idx_source: ReadOnlySource::empty(),
+            postings_file_slice: FileSlice::empty(),
+            positions_file_slice: FileSlice::empty(),
+            positions_idx_file_slice: FileSlice::empty(),
             record_option,
             total_num_tokens: 0u64,
         }
@@ -88,11 +89,12 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         block_postings: &mut BlockSegmentPostings,
-    ) {
-        let offset = term_info.postings_offset as usize;
-        let end_source = self.postings_source.len();
-        let postings_slice = self.postings_source.slice(offset, end_source);
-        block_postings.reset(term_info.doc_freq, postings_slice);
+    ) -> io::Result<()> {
+        let postings_slice = self
+            .postings_file_slice
+            .slice_from(term_info.postings_offset as usize);
+        block_postings.reset(term_info.doc_freq, postings_slice.read_bytes()?);
+        Ok(())
     }
 
     /// Returns a block postings given a `Term`.
@@ -103,9 +105,11 @@ impl InvertedIndexReader {
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<BlockSegmentPostings> {
-        self.get_term_info(term)
+    ) -> io::Result<Option<BlockSegmentPostings>> {
+        Ok(self
+            .get_term_info(term)
             .map(move |term_info| self.read_block_postings_from_terminfo(&term_info, option))
+            .transpose()?)
     }
 
     /// Returns a block postings given a `term_info`.
@@ -116,10 +120,10 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
+    ) -> io::Result<BlockSegmentPostings> {
         let offset = term_info.postings_offset as usize;
-        let postings_data = self.postings_source.slice_from(offset);
-        BlockSegmentPostings::from_data(
+        let postings_data = self.postings_file_slice.slice_from(offset);
+        BlockSegmentPostings::open(
             term_info.doc_freq,
             postings_data,
             self.record_option,
@@ -135,20 +139,23 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         option: IndexRecordOption,
-    ) -> SegmentPostings {
-        let block_postings = self.read_block_postings_from_terminfo(term_info, option);
+    ) -> io::Result<SegmentPostings> {
+        let block_postings = self.read_block_postings_from_terminfo(term_info, option)?;
         let position_stream = {
             if option.has_positions() {
-                let position_reader = self.positions_source.clone();
-                let skip_reader = self.positions_idx_source.clone();
+                let position_reader = self.positions_file_slice.clone();
+                let skip_reader = self.positions_idx_file_slice.clone();
                 let position_reader =
-                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx);
+                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx)?;
                 Some(position_reader)
             } else {
                 None
             }
         };
-        SegmentPostings::from_block_postings(block_postings, position_stream)
+        Ok(SegmentPostings::from_block_postings(
+            block_postings,
+            position_stream,
+        ))
     }
 
     /// Returns the total number of tokens recorded for all documents
@@ -167,24 +174,31 @@ impl InvertedIndexReader {
     /// For instance, requesting `IndexRecordOption::Freq` for a
     /// `TextIndexingOptions` that does not index position will return a `SegmentPostings`
     /// with `DocId`s and frequencies.
-    pub fn read_postings(&self, term: &Term, option: IndexRecordOption) -> Option<SegmentPostings> {
+    pub fn read_postings(
+        &self,
+        term: &Term,
+        option: IndexRecordOption,
+    ) -> io::Result<Option<SegmentPostings>> {
         self.get_term_info(term)
             .map(move |term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     pub(crate) fn read_postings_no_deletes(
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<SegmentPostings> {
+    ) -> io::Result<Option<SegmentPostings>> {
         self.get_term_info(term)
             .map(|term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     /// Returns the number of documents containing the term.
-    pub fn doc_freq(&self, term: &Term) -> u32 {
-        self.get_term_info(term)
+    pub fn doc_freq(&self, term: &Term) -> io::Result<u32> {
+        Ok(self
+            .get_term_info(term)
             .map(|term_info| term_info.doc_freq)
-            .unwrap_or(0u32)
+            .unwrap_or(0u32))
     }
 }
diff --git a/src/core/searcher.rs b/src/core/searcher.rs
index 8e8775efd..925e4c4e7 100644
--- a/src/core/searcher.rs
+++ b/src/core/searcher.rs
@@ -11,8 +11,8 @@ use crate::store::StoreReader;
 use crate::termdict::TermMerger;
 use crate::DocAddress;
 use crate::Index;
-use std::fmt;
 use std::sync::Arc;
+use std::{fmt, io};
 
 /// Holds a list of `SegmentReader`s ready for search.
 ///
@@ -32,17 +32,17 @@ impl Searcher {
         schema: Schema,
         index: Index,
         segment_readers: Vec<SegmentReader>,
-    ) -> Searcher {
-        let store_readers = segment_readers
+    ) -> io::Result<Searcher> {
+        let store_readers: Vec<StoreReader> = segment_readers
             .iter()
             .map(SegmentReader::get_store_reader)
-            .collect();
-        Searcher {
+            .collect::<io::Result<Vec<_>>>()?;
+        Ok(Searcher {
             schema,
             index,
             segment_readers,
             store_readers,
-        }
+        })
     }
 
     /// Returns the `Index` associated to the `Searcher`
@@ -75,13 +75,14 @@ impl Searcher {
 
     /// Return the overall number of documents containing
     /// the given term.
-    pub fn doc_freq(&self, term: &Term) -> u64 {
-        self.segment_readers
-            .iter()
-            .map(|segment_reader| {
-                u64::from(segment_reader.inverted_index(term.field()).doc_freq(term))
-            })
-            .sum::<u64>()
+    pub fn doc_freq(&self, term: &Term) -> crate::Result<u64> {
+        let mut total_doc_freq = 0;
+        for segment_reader in &self.segment_readers {
+            let inverted_index = segment_reader.inverted_index(term.field())?;
+            let doc_freq = inverted_index.doc_freq(term)?;
+            total_doc_freq += u64::from(doc_freq);
+        }
+        Ok(total_doc_freq)
     }
 
     /// Return the list of segment readers
@@ -148,22 +149,22 @@ impl Searcher {
     }
 
     /// Return the field searcher associated to a `Field`.
-    pub fn field(&self, field: Field) -> FieldSearcher {
-        let inv_index_readers = self
+    pub fn field(&self, field: Field) -> crate::Result<FieldSearcher> {
+        let inv_index_readers: Vec<Arc<InvertedIndexReader>> = self
             .segment_readers
             .iter()
             .map(|segment_reader| segment_reader.inverted_index(field))
-            .collect::<Vec<_>>();
-        FieldSearcher::new(inv_index_readers)
+            .collect::<crate::Result<Vec<_>>>()?;
+        Ok(FieldSearcher::new(inv_index_readers))
     }
 
     /// Summarize total space usage of this searcher.
-    pub fn space_usage(&self) -> SearcherSpaceUsage {
+    pub fn space_usage(&self) -> io::Result<SearcherSpaceUsage> {
         let mut space_usage = SearcherSpaceUsage::new();
-        for segment_reader in self.segment_readers.iter() {
-            space_usage.add_segment(segment_reader.space_usage());
+        for segment_reader in &self.segment_readers {
+            space_usage.add_segment(segment_reader.space_usage()?);
         }
-        space_usage
+        Ok(space_usage)
     }
 }
 
diff --git a/src/core/segment.rs b/src/core/segment.rs
index 113706e78..efd1bcbb7 100644
--- a/src/core/segment.rs
+++ b/src/core/segment.rs
@@ -4,7 +4,7 @@ use crate::core::SegmentId;
 use crate::core::SegmentMeta;
 use crate::directory::error::{OpenReadError, OpenWriteError};
 use crate::directory::Directory;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use crate::indexer::segment_serializer::SegmentSerializer;
 use crate::schema::Schema;
 use crate::Opstamp;
@@ -78,10 +78,9 @@ impl Segment {
     }
 
     /// Open one of the component file for a *regular* read.
-    pub fn open_read(&self, component: SegmentComponent) -> Result<ReadOnlySource, OpenReadError> {
+    pub fn open_read(&self, component: SegmentComponent) -> Result<FileSlice, OpenReadError> {
         let path = self.relative_path(component);
-        let source = self.index.directory().open_read(&path)?;
-        Ok(source)
+        self.index.directory().open_read(&path)
     }
 
     /// Open one of the component file for *regular* write.
diff --git a/src/core/segment_reader.rs b/src/core/segment_reader.rs
index d89a3755c..e2ce45291 100644
--- a/src/core/segment_reader.rs
+++ b/src/core/segment_reader.rs
@@ -1,10 +1,9 @@
-use crate::common::CompositeFile;
 use crate::common::HasLen;
 use crate::core::InvertedIndexReader;
 use crate::core::Segment;
 use crate::core::SegmentComponent;
 use crate::core::SegmentId;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::fastfield::DeleteBitSet;
 use crate::fastfield::FacetReader;
 use crate::fastfield::FastFieldReaders;
@@ -16,11 +15,12 @@ use crate::space_usage::SegmentSpaceUsage;
 use crate::store::StoreReader;
 use crate::termdict::TermDictionary;
 use crate::DocId;
+use crate::{common::CompositeFile, error::DataCorruption};
 use fail::fail_point;
-use std::collections::HashMap;
 use std::fmt;
 use std::sync::Arc;
 use std::sync::RwLock;
+use std::{collections::HashMap, io};
 
 /// Entry point to access all of the datastructures of the `Segment`
 ///
@@ -50,7 +50,7 @@ pub struct SegmentReader {
     fast_fields_readers: Arc<FastFieldReaders>,
     fieldnorm_readers: FieldNormReaders,
 
-    store_source: ReadOnlySource,
+    store_file: FileSlice,
     delete_bitset_opt: Option<DeleteBitSet>,
     schema: Schema,
 }
@@ -106,19 +106,26 @@ impl SegmentReader {
     }
 
     /// Accessor to the `FacetReader` associated to a given `Field`.
-    pub fn facet_reader(&self, field: Field) -> Option<FacetReader> {
+    pub fn facet_reader(&self, field: Field) -> crate::Result<FacetReader> {
         let field_entry = self.schema.get_field_entry(field);
         if field_entry.field_type() != &FieldType::HierarchicalFacet {
-            return None;
+            return Err(crate::TantivyError::InvalidArgument(format!(
+                "Field {:?} is not a facet field.",
+                field_entry.name()
+            )));
         }
-        let term_ords_reader = self.fast_fields().u64s(field)?;
+        let term_ords_reader = self.fast_fields().u64s(field).ok_or_else(|| {
+            DataCorruption::comment_only(format!(
+                "Cannot find data for hierarchical facet {:?}",
+                field_entry.name()
+            ))
+        })?;
         let termdict = self
             .termdict_composite
             .open_read(field)
-            .map(|source| TermDictionary::from_source(&source))
-            .unwrap_or_else(TermDictionary::empty);
-        let facet_reader = FacetReader::new(term_ords_reader, termdict);
-        Some(facet_reader)
+            .map(TermDictionary::open)
+            .unwrap_or_else(|| Ok(TermDictionary::empty()))?;
+        Ok(FacetReader::new(term_ords_reader, termdict))
     }
 
     /// Accessor to the segment's `Field norms`'s reader.
@@ -129,7 +136,7 @@ impl SegmentReader {
     /// They are simply stored as a fast field, serialized in
     /// the `.fieldnorm` file of the segment.
     pub fn get_fieldnorms_reader(&self, field: Field) -> crate::Result<FieldNormReader> {
-        self.fieldnorm_readers.get_field(field).ok_or_else(|| {
+        self.fieldnorm_readers.get_field(field)?.ok_or_else(|| {
             let field_name = self.schema.get_field_name(field);
             let err_msg = format!(
                 "Field norm not found for field {:?}. Was it marked as indexed during indexing?",
@@ -140,33 +147,33 @@ impl SegmentReader {
     }
 
     /// Accessor to the segment's `StoreReader`.
-    pub fn get_store_reader(&self) -> StoreReader {
-        StoreReader::from_source(self.store_source.clone())
+    pub fn get_store_reader(&self) -> io::Result<StoreReader> {
+        StoreReader::open(self.store_file.clone())
     }
 
     /// Open a new segment for reading.
     pub fn open(segment: &Segment) -> crate::Result<SegmentReader> {
-        let termdict_source = segment.open_read(SegmentComponent::TERMS)?;
-        let termdict_composite = CompositeFile::open(&termdict_source)?;
+        let termdict_file = segment.open_read(SegmentComponent::TERMS)?;
+        let termdict_composite = CompositeFile::open(&termdict_file)?;
 
-        let store_source = segment.open_read(SegmentComponent::STORE)?;
+        let store_file = segment.open_read(SegmentComponent::STORE)?;
 
         fail_point!("SegmentReader::open#middle");
 
-        let postings_source = segment.open_read(SegmentComponent::POSTINGS)?;
-        let postings_composite = CompositeFile::open(&postings_source)?;
+        let postings_file = segment.open_read(SegmentComponent::POSTINGS)?;
+        let postings_composite = CompositeFile::open(&postings_file)?;
 
         let positions_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONS) {
-                CompositeFile::open(&source)?
+            if let Ok(positions_file) = segment.open_read(SegmentComponent::POSITIONS) {
+                CompositeFile::open(&positions_file)?
             } else {
                 CompositeFile::empty()
             }
         };
 
         let positions_idx_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
-                CompositeFile::open(&source)?
+            if let Ok(positions_skip_file) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
+                CompositeFile::open(&positions_skip_file)?
             } else {
                 CompositeFile::empty()
             }
@@ -184,13 +191,14 @@ impl SegmentReader {
 
         let delete_bitset_opt = if segment.meta().has_deletes() {
             let delete_data = segment.open_read(SegmentComponent::DELETE)?;
-            Some(DeleteBitSet::open(delete_data))
+            let delete_bitset = DeleteBitSet::open(delete_data)?;
+            Some(delete_bitset)
         } else {
             None
         };
 
         Ok(SegmentReader {
-            inv_idx_reader_cache: Arc::new(RwLock::new(HashMap::new())),
+            inv_idx_reader_cache: Default::default(),
             max_doc: segment.meta().max_doc(),
             num_docs: segment.meta().num_docs(),
             termdict_composite,
@@ -198,7 +206,7 @@ impl SegmentReader {
             fast_fields_readers: fast_field_readers,
             fieldnorm_readers,
             segment_id: segment.id(),
-            store_source,
+            store_file,
             delete_bitset_opt,
             positions_composite,
             positions_idx_composite,
@@ -218,14 +226,14 @@ impl SegmentReader {
     /// is returned.
     /// Similarly if the field is marked as indexed but no term has been indexed for the given
     /// index. an empty `InvertedIndexReader` is returned (but no warning is logged).
-    pub fn inverted_index(&self, field: Field) -> Arc<InvertedIndexReader> {
+    pub fn inverted_index(&self, field: Field) -> crate::Result<Arc<InvertedIndexReader>> {
         if let Some(inv_idx_reader) = self
             .inv_idx_reader_cache
             .read()
             .expect("Lock poisoned. This should never happen")
             .get(&field)
         {
-            return Arc::clone(inv_idx_reader);
+            return Ok(Arc::clone(inv_idx_reader));
         }
         let field_entry = self.schema.get_field_entry(field);
         let field_type = field_entry.field_type();
@@ -235,41 +243,42 @@ impl SegmentReader {
             warn!("Field {:?} does not seem indexed.", field_entry.name());
         }
 
-        let postings_source_opt = self.postings_composite.open_read(field);
+        let postings_file_opt = self.postings_composite.open_read(field);
 
-        if postings_source_opt.is_none() || record_option_opt.is_none() {
+        if postings_file_opt.is_none() || record_option_opt.is_none() {
             // no documents in the segment contained this field.
             // As a result, no data is associated to the inverted index.
             //
             // Returns an empty inverted index.
             let record_option = record_option_opt.unwrap_or(IndexRecordOption::Basic);
-            return Arc::new(InvertedIndexReader::empty(record_option));
+            return Ok(Arc::new(InvertedIndexReader::empty(record_option)));
         }
 
         let record_option = record_option_opt.unwrap();
-        let postings_source = postings_source_opt.unwrap();
+        let postings_file = postings_file_opt.unwrap();
 
-        let termdict_source = self.termdict_composite.open_read(field).expect(
-            "Failed to open field term dictionary in composite file. Is the field indexed?",
-        );
+        let termdict_file: FileSlice = self.termdict_composite.open_read(field)
+            .ok_or_else(||
+               DataCorruption::comment_only(format!("Failed to open field {:?}'s term dictionary in the composite file. Has the schema been modified?", field_entry.name()))
+            )?;
 
-        let positions_source = self
+        let positions_file = self
             .positions_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
-        let positions_idx_source = self
+        let positions_idx_file = self
             .positions_idx_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
         let inv_idx_reader = Arc::new(InvertedIndexReader::new(
-            TermDictionary::from_source(&termdict_source),
-            postings_source,
-            positions_source,
-            positions_idx_source,
+            TermDictionary::open(termdict_file)?,
+            postings_file,
+            positions_file,
+            positions_idx_file,
             record_option,
-        ));
+        )?);
 
         // by releasing the lock in between, we may end up opening the inverting index
         // twice, but this is fine.
@@ -278,7 +287,7 @@ impl SegmentReader {
             .expect("Field reader cache lock poisoned. This should never happen.")
             .insert(field, Arc::clone(&inv_idx_reader));
 
-        inv_idx_reader
+        Ok(inv_idx_reader)
     }
 
     /// Returns the segment id
@@ -306,8 +315,8 @@ impl SegmentReader {
     }
 
     /// Summarize total space usage of this segment.
-    pub fn space_usage(&self) -> SegmentSpaceUsage {
-        SegmentSpaceUsage::new(
+    pub fn space_usage(&self) -> io::Result<SegmentSpaceUsage> {
+        Ok(SegmentSpaceUsage::new(
             self.num_docs(),
             self.termdict_composite.space_usage(),
             self.postings_composite.space_usage(),
@@ -315,12 +324,12 @@ impl SegmentReader {
             self.positions_idx_composite.space_usage(),
             self.fast_fields_readers.space_usage(),
             self.fieldnorm_readers.space_usage(),
-            self.get_store_reader().space_usage(),
+            self.get_store_reader()?.space_usage(),
             self.delete_bitset_opt
                 .as_ref()
                 .map(DeleteBitSet::space_usage)
                 .unwrap_or(0),
-        )
+        ))
     }
 }
 
@@ -337,7 +346,7 @@ mod test {
     use crate::DocId;
 
     #[test]
-    fn test_alive_docs_iterator() {
+    fn test_alive_docs_iterator() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         schema_builder.add_text_field("name", TEXT | STORED);
         let schema = schema_builder.build();
@@ -345,26 +354,26 @@ mod test {
         let name = schema.get_field("name").unwrap();
 
         {
-            let mut index_writer = index.writer_for_tests().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(name => "tantivy"));
             index_writer.add_document(doc!(name => "horse"));
             index_writer.add_document(doc!(name => "jockey"));
             index_writer.add_document(doc!(name => "cap"));
-
             // we should now have one segment with two docs
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
 
         {
-            let mut index_writer2 = index.writer(50_000_000).unwrap();
+            let mut index_writer2 = index.writer(50_000_000)?;
             index_writer2.delete_term(Term::from_field_text(name, "horse"));
             index_writer2.delete_term(Term::from_field_text(name, "cap"));
 
             // ok, now we should have a deleted doc
-            index_writer2.commit().unwrap();
+            index_writer2.commit()?;
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let docs: Vec<DocId> = searcher.segment_reader(0).doc_ids_alive().collect();
         assert_eq!(vec![0u32, 2u32], docs);
+        Ok(())
     }
 }
diff --git a/src/directory/directory.rs b/src/directory/directory.rs
index 900d398c5..024746dc3 100644
--- a/src/directory/directory.rs
+++ b/src/directory/directory.rs
@@ -3,7 +3,7 @@ use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use crate::directory::WatchCallback;
 use crate::directory::WatchHandle;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use std::fmt;
 use std::io;
 use std::io::Write;
@@ -11,7 +11,6 @@ use std::marker::Send;
 use std::marker::Sync;
 use std::path::Path;
 use std::path::PathBuf;
-use std::result;
 use std::thread;
 use std::time::Duration;
 
@@ -117,19 +116,19 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// change.
     ///
     /// Specifically, subsequent writes or flushes should
-    /// have no effect on the returned `ReadOnlySource` object.
+    /// have no effect on the returned `FileSlice` object.
     ///
     /// You should only use this to read files create with [Directory::open_write].
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError>;
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError>;
 
     /// Removes a file
     ///
     /// Removing a file will not affect an eventual
-    /// existing ReadOnlySource pointing to it.
+    /// existing FileSlice pointing to it.
     ///
     /// Removing a nonexistent file, yields a
     /// `DeleteError::DoesNotExist`.
-    fn delete(&self, path: &Path) -> result::Result<(), DeleteError>;
+    fn delete(&self, path: &Path) -> Result<(), DeleteError>;
 
     /// Returns true iff the file exists
     fn exists(&self, path: &Path) -> bool;
@@ -139,7 +138,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     ///
     /// Right after this call, the file should be created
     /// and any subsequent call to `open_read` for the
-    /// same path should return a `ReadOnlySource`.
+    /// same path should return a `FileSlice`.
     ///
     /// Write operations may be aggressively buffered.
     /// The client of this trait is responsible for calling flush
diff --git a/src/directory/error.rs b/src/directory/error.rs
index 1f0a7fc9b..f3856288e 100644
--- a/src/directory/error.rs
+++ b/src/directory/error.rs
@@ -57,6 +57,11 @@ pub enum OpenWriteError {
     },
 }
 
+impl OpenWriteError {
+    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+        Self::IOError { io_error, filepath }
+    }
+}
 /// Type of index incompatibility between the library and the index found on disk
 /// Used to catch and provide a hint to solve this incompatibility issue
 pub enum Incompatibility {
@@ -137,6 +142,11 @@ pub enum OpenReadError {
     IncompatibleIndex(Incompatibility),
 }
 
+impl OpenReadError {
+    pub(crate) fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+        Self::IOError { io_error, filepath }
+    }
+}
 /// Error that may occur when trying to delete a file
 #[derive(Debug, Error)]
 pub enum DeleteError {
diff --git a/src/directory/file_slice.rs b/src/directory/file_slice.rs
new file mode 100644
index 000000000..f1ea23ecb
--- /dev/null
+++ b/src/directory/file_slice.rs
@@ -0,0 +1,264 @@
+use crate::common::HasLen;
+use crate::directory::OwnedBytes;
+use stable_deref_trait::{CloneStableDeref, StableDeref};
+use std::sync::Arc;
+use std::{io, ops::Deref};
+
+pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+
+/// Objects that represents files sections in tantivy.
+///
+/// These read objects are only in charge to deliver
+/// the data in the form of a constant read-only `&[u8]`.
+/// Whatever happens to the directory file, the data
+/// hold by this object should never be altered or destroyed.
+pub trait FileSliceTrait: 'static + Send + Sync + HasLen {
+    fn read_bytes(&self) -> io::Result<OwnedBytes>;
+    fn slice(&self, from: usize, to: usize) -> FileSlice;
+}
+
+impl FileSliceTrait for &'static [u8] {
+    fn read_bytes(&self) -> io::Result<OwnedBytes> {
+        Ok(OwnedBytes::new(*self))
+    }
+
+    fn slice(&self, from: usize, to: usize) -> FileSlice {
+        FileSlice::from(&self[from..to])
+    }
+}
+
+impl HasLen for &'static [u8] {
+    fn len(&self) -> usize {
+        self.as_ref().len()
+    }
+}
+
+/// Logical slice of read only file in tantivy.
+//
+/// In other words, it is more or less equivalent to the triplet `(file, start_byteoffset, stop_offset)`.
+///
+/// FileSlice is a simple wrapper over an `Arc<Box<dyn FileSliceTrait>>`. It can
+/// be cloned cheaply.
+///
+/// The underlying behavior is therefore specific to the `Directory` that created it.
+/// Despite its name, a `FileSlice` may or may not directly map to an actual file
+/// on the filesystem.
+#[derive(Clone)]
+pub struct FileSlice(Arc<Box<dyn FileSliceTrait>>);
+
+impl FileSlice {
+    /// Creates a FileSlice, wrapping over a FileSliceTrait.
+    pub fn new<D>(data: D) -> Self
+    where
+        D: Deref<Target = [u8]> + Send + Sync + 'static,
+    {
+        FileSlice::from(SlicedDeref::new(data))
+    }
+
+    /// Creates an empty FileSlice
+    pub fn empty() -> FileSlice {
+        let data: &'static [u8] = &[];
+        FileSlice::from(data)
+    }
+
+    /// Returns a `OwnedBytes` with all of the data in the `FileSlice`.
+    ///
+    /// The behavior is strongly dependant on the implementation of the underlying
+    /// `Directory` and the `FileSliceTrait` it creates.
+    /// In particular, it is  up to the `Directory` implementation
+    /// to handle caching if needed.
+    pub fn read_bytes(&self) -> io::Result<OwnedBytes> {
+        self.0.read_bytes()
+    }
+
+    /// Splits the file slice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    ///
+    /// This operation is cheap and must not copy any underlying data.
+    pub fn split(self, left_len: usize) -> (FileSlice, FileSlice) {
+        let left = self.slice_to(left_len);
+        let right = self.slice_from(left_len);
+        (left, right)
+    }
+
+    /// Splits the file slice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    pub fn split_from_end(self, right_len: usize) -> (FileSlice, FileSlice) {
+        let left_len = self.len() - right_len;
+        self.split(left_len)
+    }
+
+    /// Creates a FileSlice that is just a view over a slice of the data.
+    pub fn slice(&self, start: usize, stop: usize) -> FileSlice {
+        assert!(
+            start <= stop,
+            "Requested negative slice [{}..{}]",
+            start,
+            stop
+        );
+        assert!(stop <= self.len());
+        self.0.slice(start, stop)
+    }
+
+    /// Like `.slice(...)` but enforcing only the `from`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(from_offset, self.len())`
+    pub fn slice_from(&self, from_offset: usize) -> FileSlice {
+        self.slice(from_offset, self.len())
+    }
+
+    /// Like `.slice(...)` but enforcing only the `to`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(0, to_offset)`
+    pub fn slice_to(&self, to_offset: usize) -> FileSlice {
+        self.slice(0, to_offset)
+    }
+}
+
+impl HasLen for FileSlice {
+    fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl<S: FileSliceTrait> From<S> for FileSlice {
+    fn from(file: S) -> Self {
+        FileSlice(Arc::new(Box::new(file)))
+    }
+}
+
+impl From<Arc<BoxedData>> for FileSlice {
+    fn from(data: Arc<BoxedData>) -> Self {
+        let slice_deref: SlicedDeref = SlicedDeref::from(data);
+        FileSlice::from(slice_deref)
+    }
+}
+
+/// `SliceDeref` wraps an `Arc<BoxData>` to implement `FileSliceTrait` .
+/// It keeps track of (start, stop) boundaries.
+#[derive(Clone)]
+pub struct SlicedDeref {
+    data: Arc<BoxedData>,
+    start: usize,
+    stop: usize,
+}
+
+impl SlicedDeref {
+    /// Wraps a new `Deref<Target = [u8]>`
+    pub fn new<D>(data: D) -> Self
+    where
+        D: Deref<Target = [u8]> + 'static + Send + Sync,
+    {
+        let len = data.len();
+        SlicedDeref {
+            data: Arc::new(Box::new(data)),
+            start: 0,
+            stop: len,
+        }
+    }
+}
+
+impl From<Arc<BoxedData>> for SlicedDeref {
+    fn from(data: Arc<BoxedData>) -> Self {
+        let len = data.len();
+        SlicedDeref {
+            data,
+            start: 0,
+            stop: len,
+        }
+    }
+}
+
+unsafe impl StableDeref for SlicedDeref {}
+unsafe impl CloneStableDeref for SlicedDeref {}
+
+impl FileSliceTrait for SlicedDeref {
+    fn read_bytes(&self) -> io::Result<OwnedBytes> {
+        Ok(OwnedBytes::new(self.clone()))
+    }
+
+    fn slice(&self, from: usize, to: usize) -> FileSlice {
+        assert!(to <= self.len());
+        FileSlice::from(SlicedDeref {
+            data: self.data.clone(),
+            start: self.start + from,
+            stop: self.start + to,
+        })
+    }
+}
+
+impl HasLen for SlicedDeref {
+    fn len(&self) -> usize {
+        self.stop - self.start
+    }
+}
+
+impl Deref for SlicedDeref {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        &self.data.deref()[self.start..self.stop]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{FileSlice, FileSliceTrait, SlicedDeref};
+    use crate::common::HasLen;
+    use std::io;
+
+    #[test]
+    fn test_file_slice() -> io::Result<()> {
+        let file_slice = FileSlice::new(b"abcdef".as_ref());
+        assert_eq!(file_slice.len(), 6);
+        assert_eq!(file_slice.slice_from(2).read_bytes()?.as_slice(), b"cdef");
+        assert_eq!(file_slice.slice_to(2).read_bytes()?.as_slice(), b"ab");
+        assert_eq!(
+            file_slice
+                .slice_from(1)
+                .slice_to(2)
+                .read_bytes()?
+                .as_slice(),
+            b"bc"
+        );
+        {
+            let (left, right) = file_slice.clone().split(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"");
+            assert_eq!(right.read_bytes()?.as_slice(), b"abcdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"ab");
+            assert_eq!(right.read_bytes()?.as_slice(), b"cdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcdef");
+            assert_eq!(right.read_bytes()?.as_slice(), b"");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcd");
+            assert_eq!(right.read_bytes()?.as_slice(), b"ef");
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_file_slice_trait_slice_len() {
+        let blop: &'static [u8] = b"abc";
+        let owned_bytes: Box<dyn FileSliceTrait> = Box::new(blop);
+        assert_eq!(owned_bytes.len(), 3);
+    }
+
+    #[test]
+    fn test_slice_deref() -> io::Result<()> {
+        let slice_deref = SlicedDeref::new(&b"abcdef"[..]);
+        assert_eq!(slice_deref.len(), 6);
+        assert_eq!(slice_deref.read_bytes()?.as_ref(), b"abcdef");
+        assert_eq!(slice_deref.slice(1, 4).read_bytes()?.as_ref(), b"bcd");
+        Ok(())
+    }
+}
diff --git a/src/directory/footer.rs b/src/directory/footer.rs
index 33f6d06d4..3a696896f 100644
--- a/src/directory/footer.rs
+++ b/src/directory/footer.rs
@@ -1,9 +1,8 @@
-use crate::common::{BinarySerializable, CountingWriter, FixedSize, VInt};
+use crate::common::{BinarySerializable, CountingWriter, FixedSize, HasLen, VInt};
 use crate::directory::error::Incompatibility;
-use crate::directory::read_only_source::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{AntiCallToken, TerminatingWrite};
 use crate::Version;
-use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use crc32fast::Hasher;
 use std::io;
 use std::io::Write;
@@ -64,26 +63,26 @@ impl Footer {
         let mut counting_write = CountingWriter::wrap(&mut write);
         self.serialize(&mut counting_write)?;
         let written_len = counting_write.written_bytes();
-        write.write_u32::<LittleEndian>(written_len as u32)?;
+        (written_len as u32).serialize(write)?;
         Ok(())
     }
 
-    pub fn extract_footer(source: ReadOnlySource) -> Result<(Footer, ReadOnlySource), io::Error> {
-        if source.len() < 4 {
+    pub fn extract_footer(file: FileSlice) -> io::Result<(Footer, FileSlice)> {
+        if file.len() < 4 {
             return Err(io::Error::new(
                 io::ErrorKind::UnexpectedEof,
                 format!(
                     "File corrupted. The file is smaller than 4 bytes (len={}).",
-                    source.len()
+                    file.len()
                 ),
             ));
         }
-        let (body_footer, footer_len_bytes) = source.split_from_end(u32::SIZE_IN_BYTES);
-        let footer_len = LittleEndian::read_u32(footer_len_bytes.as_slice()) as usize;
-        let body_len = body_footer.len() - footer_len;
-        let (body, footer_data) = body_footer.split(body_len);
-        let mut cursor = footer_data.as_slice();
-        let footer = Footer::deserialize(&mut cursor)?;
+        let (body_footer, footer_len_file) = file.split_from_end(u32::SIZE_IN_BYTES);
+        let mut footer_len_bytes = footer_len_file.read_bytes()?;
+        let footer_len = u32::deserialize(&mut footer_len_bytes)? as usize;
+        let (body, footer) = body_footer.split_from_end(footer_len);
+        let mut footer_bytes = footer.read_bytes()?;
+        let footer = Footer::deserialize(&mut footer_bytes)?;
         Ok((footer, body))
     }
 
diff --git a/src/directory/managed_directory.rs b/src/directory/managed_directory.rs
index 7d4e6198c..13c6cf762 100644
--- a/src/directory/managed_directory.rs
+++ b/src/directory/managed_directory.rs
@@ -5,7 +5,7 @@ use crate::directory::DirectoryLock;
 use crate::directory::GarbageCollectionResult;
 use crate::directory::Lock;
 use crate::directory::META_LOCK;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use crate::directory::{WatchCallback, WatchHandle};
 use crate::error::DataCorruption;
 use crate::Directory;
@@ -86,12 +86,7 @@ impl ManagedDirectory {
                 directory: Box::new(directory),
                 meta_informations: Arc::default(),
             }),
-            Err(OpenReadError::IOError { io_error, filepath }) => {
-                Err(crate::TantivyError::OpenReadError(OpenReadError::IOError {
-                    io_error,
-                    filepath,
-                }))
-            }
+            io_err @ Err(OpenReadError::IOError { .. }) => Err(io_err.err().unwrap().into()),
             Err(OpenReadError::IncompatibleIndex(incompatibility)) => {
                 // For the moment, this should never happen  `meta.json`
                 // do not have any footer and cannot detect incompatibility.
@@ -241,8 +236,14 @@ impl ManagedDirectory {
                 io_error,
                 filepath: path.to_path_buf(),
             })?;
+        let bytes = data
+            .read_bytes()
+            .map_err(|io_error| OpenReadError::IOError {
+                filepath: path.to_path_buf(),
+                io_error,
+            })?;
         let mut hasher = Hasher::new();
-        hasher.update(data.as_slice());
+        hasher.update(bytes.as_slice());
         let crc = hasher.finalize();
         Ok(footer
             .versioned_footer
@@ -273,24 +274,17 @@ impl ManagedDirectory {
 }
 
 impl Directory for ManagedDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
-        let read_only_source = self.directory.open_read(path)?;
-        let (footer, reader) = Footer::extract_footer(read_only_source).map_err(|io_error| {
-            OpenReadError::IOError {
-                io_error,
-                filepath: path.to_path_buf(),
-            }
-        })?;
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
+        let file_slice = self.directory.open_read(path)?;
+        let (footer, reader) = Footer::extract_footer(file_slice)
+            .map_err(|io_error| OpenReadError::wrap_io_error(io_error, path.to_path_buf()))?;
         footer.is_compatible()?;
         Ok(reader)
     }
 
     fn open_write(&mut self, path: &Path) -> result::Result<WritePtr, OpenWriteError> {
         self.register_file_as_managed(path)
-            .map_err(|io_error| OpenWriteError::IOError {
-                io_error,
-                filepath: path.to_path_buf(),
-            })?;
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
         Ok(io::BufWriter::new(Box::new(FooterProxy::new(
             self.directory
                 .open_write(path)?
@@ -414,39 +408,37 @@ mod tests_mmap_specific {
     }
 
     #[test]
-    fn test_checksum() {
+    fn test_checksum() -> crate::Result<()> {
         let test_path1: &'static Path = Path::new("some_path_for_test");
         let test_path2: &'static Path = Path::new("other_test_path");
 
         let tempdir = TempDir::new().unwrap();
         let tempdir_path = PathBuf::from(tempdir.path());
 
-        let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
-        let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
-        let mut write = managed_directory.open_write(test_path1).unwrap();
-        write.write_all(&[0u8, 1u8]).unwrap();
-        write.terminate().unwrap();
+        let mmap_directory = MmapDirectory::open(&tempdir_path)?;
+        let mut managed_directory = ManagedDirectory::wrap(mmap_directory)?;
+        let mut write = managed_directory.open_write(test_path1)?;
+        write.write_all(&[0u8, 1u8])?;
+        write.terminate()?;
 
-        let mut write = managed_directory.open_write(test_path2).unwrap();
-        write.write_all(&[3u8, 4u8, 5u8]).unwrap();
-        write.terminate().unwrap();
+        let mut write = managed_directory.open_write(test_path2)?;
+        write.write_all(&[3u8, 4u8, 5u8])?;
+        write.terminate()?;
 
-        let read_source = managed_directory.open_read(test_path2).unwrap();
-        assert_eq!(read_source.as_slice(), &[3u8, 4u8, 5u8]);
+        let read_file = managed_directory.open_read(test_path2)?.read_bytes()?;
+        assert_eq!(read_file.as_slice(), &[3u8, 4u8, 5u8]);
         assert!(managed_directory.list_damaged().unwrap().is_empty());
 
         let mut corrupted_path = tempdir_path.clone();
         corrupted_path.push(test_path2);
-        let mut file = OpenOptions::new()
-            .write(true)
-            .open(&corrupted_path)
-            .unwrap();
-        file.write_all(&[255u8]).unwrap();
-        file.flush().unwrap();
+        let mut file = OpenOptions::new().write(true).open(&corrupted_path)?;
+        file.write_all(&[255u8])?;
+        file.flush()?;
         drop(file);
 
-        let damaged = managed_directory.list_damaged().unwrap();
+        let damaged = managed_directory.list_damaged()?;
         assert_eq!(damaged.len(), 1);
         assert!(damaged.contains(test_path2));
+        Ok(())
     }
 }
diff --git a/src/directory/mmap_directory.rs b/src/directory/mmap_directory.rs
index b360eb25b..be6942615 100644
--- a/src/directory/mmap_directory.rs
+++ b/src/directory/mmap_directory.rs
@@ -1,12 +1,12 @@
 use crate::core::META_FILEPATH;
 use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenDirectoryError, OpenReadError, OpenWriteError};
-use crate::directory::read_only_source::BoxedData;
 use crate::directory::AntiCallToken;
+use crate::directory::BoxedData;
 use crate::directory::Directory;
 use crate::directory::DirectoryLock;
+use crate::directory::FileSlice;
 use crate::directory::Lock;
-use crate::directory::ReadOnlySource;
 use crate::directory::WatchCallback;
 use crate::directory::WatchCallbackList;
 use crate::directory::WatchHandle;
@@ -42,21 +42,17 @@ pub(crate) fn make_io_err(msg: String) -> io::Error {
 /// Returns None iff the file exists, can be read, but is empty (and hence
 /// cannot be mmapped)
 fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
-    let file = File::open(full_path).map_err(|e| {
-        if e.kind() == io::ErrorKind::NotFound {
-            OpenReadError::FileDoesNotExist(full_path.to_owned())
+    let file = File::open(full_path).map_err(|io_err| {
+        if io_err.kind() == io::ErrorKind::NotFound {
+            OpenReadError::FileDoesNotExist(full_path.to_path_buf())
         } else {
-            OpenReadError::IOError {
-                io_error: e,
-                filepath: full_path.to_owned(),
-            }
+            OpenReadError::wrap_io_error(io_err, full_path.to_path_buf())
         }
     })?;
 
-    let meta_data = file.metadata().map_err(|e| OpenReadError::IOError {
-        io_error: e,
-        filepath: full_path.to_owned(),
-    })?;
+    let meta_data = file
+        .metadata()
+        .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_owned()))?;
     if meta_data.len() == 0 {
         // if the file size is 0, it will not be possible
         // to mmap the file, so we return None
@@ -66,10 +62,7 @@ fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
     unsafe {
         memmap::Mmap::map(&file)
             .map(Some)
-            .map_err(|e| OpenReadError::IOError {
-                io_error: e,
-                filepath: full_path.to_owned(),
-            })
+            .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_path_buf()))
     }
 }
 
@@ -408,7 +401,7 @@ impl TerminatingWrite for SafeFileWriter {
 }
 
 impl Directory for MmapDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         debug!("Open Read {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -418,15 +411,13 @@ impl Directory for MmapDirectory {
                  on mmap cache while reading {:?}",
                 path
             );
-            OpenReadError::IOError {
-                io_error: make_io_err(msg),
-                filepath: path.to_owned(),
-            }
+            let io_err = make_io_err(msg);
+            OpenReadError::wrap_io_error(io_err, path.to_path_buf())
         })?;
         Ok(mmap_cache
             .get_mmap(&full_path)?
-            .map(ReadOnlySource::from)
-            .unwrap_or_else(ReadOnlySource::empty))
+            .map(FileSlice::from)
+            .unwrap_or_else(FileSlice::empty))
     }
 
     /// Any entry associated to the path in the mmap will be
@@ -465,29 +456,22 @@ impl Directory for MmapDirectory {
             .create_new(true)
             .open(full_path);
 
-        let mut file = open_res.map_err(|err| {
-            if err.kind() == io::ErrorKind::AlreadyExists {
-                OpenWriteError::FileAlreadyExists(path.to_owned())
+        let mut file = open_res.map_err(|io_err| {
+            if io_err.kind() == io::ErrorKind::AlreadyExists {
+                OpenWriteError::FileAlreadyExists(path.to_path_buf())
             } else {
-                OpenWriteError::IOError {
-                    io_error: err,
-                    filepath: path.to_owned(),
-                }
+                OpenWriteError::wrap_io_error(io_err, path.to_path_buf())
             }
         })?;
 
         // making sure the file is created.
-        file.flush().map_err(|io_error| OpenWriteError::IOError {
-            io_error,
-            filepath: path.to_owned(),
-        })?;
+        file.flush()
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
 
         // Apparetntly, on some filesystem syncing the parent
         // directory is required.
-        self.sync_directory().map_err(|e| OpenWriteError::IOError {
-            io_error: e,
-            filepath: path.to_owned(),
-        })?;
+        self.sync_directory()
+            .map_err(|io_err| OpenWriteError::wrap_io_error(io_err, path.to_path_buf()))?;
 
         let writer = SafeFileWriter::new(file);
         Ok(BufWriter::new(Box::new(writer)))
@@ -498,21 +482,16 @@ impl Directory for MmapDirectory {
         let mut buffer = Vec::new();
         match File::open(&full_path) {
             Ok(mut file) => {
-                file.read_to_end(&mut buffer)
-                    .map_err(|io_error| OpenReadError::IOError {
-                        io_error,
-                        filepath: path.to_owned(),
-                    })?;
+                file.read_to_end(&mut buffer).map_err(|io_error| {
+                    OpenReadError::wrap_io_error(io_error, path.to_path_buf())
+                })?;
                 Ok(buffer)
             }
             Err(io_error) => {
                 if io_error.kind() == io::ErrorKind::NotFound {
                     Err(OpenReadError::FileDoesNotExist(path.to_owned()))
                 } else {
-                    Err(OpenReadError::IOError {
-                        io_error,
-                        filepath: path.to_owned(),
-                    })
+                    Err(OpenReadError::wrap_io_error(io_error, path.to_path_buf()))
                 }
             }
         }
@@ -560,10 +539,10 @@ mod tests {
     // The following tests are specific to the MmapDirectory
 
     use super::*;
-    use crate::indexer::LogMergePolicy;
     use crate::schema::{Schema, SchemaBuilder, TEXT};
     use crate::Index;
     use crate::ReloadPolicy;
+    use crate::{common::HasLen, indexer::LogMergePolicy};
     use std::fs;
     use std::sync::atomic::{AtomicUsize, Ordering};
 
diff --git a/src/directory/mod.rs b/src/directory/mod.rs
index df5e55d81..09662cab5 100644
--- a/src/directory/mod.rs
+++ b/src/directory/mod.rs
@@ -9,10 +9,11 @@ mod mmap_directory;
 
 mod directory;
 mod directory_lock;
+mod file_slice;
 mod footer;
 mod managed_directory;
+mod owned_bytes;
 mod ram_directory;
-mod read_only_source;
 mod watch_event_router;
 
 /// Errors specific to the directory module.
@@ -21,8 +22,10 @@ pub mod error;
 pub use self::directory::DirectoryLock;
 pub use self::directory::{Directory, DirectoryClone};
 pub use self::directory_lock::{Lock, INDEX_WRITER_LOCK, META_LOCK};
+pub(crate) use self::file_slice::BoxedData;
+pub use self::file_slice::FileSlice;
+pub use self::owned_bytes::OwnedBytes;
 pub use self::ram_directory::RAMDirectory;
-pub use self::read_only_source::ReadOnlySource;
 pub use self::watch_event_router::{WatchCallback, WatchCallbackList, WatchHandle};
 use std::io::{self, BufWriter, Write};
 use std::path::PathBuf;
diff --git a/src/directory/owned_bytes.rs b/src/directory/owned_bytes.rs
new file mode 100644
index 000000000..7aa366ceb
--- /dev/null
+++ b/src/directory/owned_bytes.rs
@@ -0,0 +1,239 @@
+use stable_deref_trait::StableDeref;
+use std::mem;
+use std::ops::Deref;
+use std::sync::Arc;
+use std::{fmt, io};
+
+/// An OwnedBytes simply wraps an object that owns a slice of data and exposes
+/// this data as a static slice.
+///
+/// The backing object is required to be `StableDeref`.
+#[derive(Clone)]
+pub struct OwnedBytes {
+    data: &'static [u8],
+    box_stable_deref: Arc<dyn Deref<Target = [u8]> + Sync + Send>,
+}
+
+impl OwnedBytes {
+    /// Creates an empty `OwnedBytes`.
+    pub fn empty() -> OwnedBytes {
+        OwnedBytes::new(&[][..])
+    }
+
+    /// Creates an `OwnedBytes` intance given a `StableDeref` object.
+    pub fn new<T: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync>(
+        data_holder: T,
+    ) -> OwnedBytes {
+        let box_stable_deref = Arc::new(data_holder);
+        let data = unsafe { mem::transmute::<_, &'static [u8]>(box_stable_deref.deref().deref()) };
+        OwnedBytes {
+            box_stable_deref,
+            data,
+        }
+    }
+
+    /// Returns the underlying slice of data.
+    /// `Deref` and `AsRef` are also available.
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[u8] {
+        self.data
+    }
+
+    /// Returns the len of the slice.
+    #[inline(always)]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Splits the OwnedBytes into two OwnedBytes `(left, right)`.
+    ///
+    /// Left will hold `split_len` bytes.
+    ///
+    /// This operation is cheap and does not require to copy any memory.
+    /// On the other hand, both `left` and `right` retain a handle over
+    /// the entire slice of memory. In other words, the memory will only
+    /// be released when both left and right are dropped.
+    pub fn split(self, split_len: usize) -> (OwnedBytes, OwnedBytes) {
+        let right_box_stable_deref = self.box_stable_deref.clone();
+        let left = OwnedBytes {
+            data: &self.data[..split_len],
+            box_stable_deref: self.box_stable_deref,
+        };
+        let right = OwnedBytes {
+            data: &self.data[split_len..],
+            box_stable_deref: right_box_stable_deref,
+        };
+        (left, right)
+    }
+
+    /// Returns true iff this `OwnedBytes` is empty.
+    #[inline(always)]
+    pub fn is_empty(&self) -> bool {
+        self.as_slice().is_empty()
+    }
+
+    /// Drops the left most `advance_len` bytes.
+    ///
+    /// See also [.clip(clip_len: usize))](#method.clip).
+    #[inline(always)]
+    pub fn advance(&mut self, advance_len: usize) {
+        self.data = &self.data[advance_len..]
+    }
+}
+
+impl fmt::Debug for OwnedBytes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // We truncate the bytes in order to make sure the debug string
+        // is not too long.
+        let bytes_truncated: &[u8] = if self.len() > 8 {
+            &self.as_slice()[..10]
+        } else {
+            self.as_slice()
+        };
+        write!(f, "OwnedBytes({:?}, len={})", bytes_truncated, self.len())
+    }
+}
+
+impl Deref for OwnedBytes {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        self.as_slice()
+    }
+}
+
+impl io::Read for OwnedBytes {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            if data.len() >= buf.len() {
+                let buf_len = buf.len();
+                buf.copy_from_slice(&data[..buf_len]);
+                buf.len()
+            } else {
+                let data_len = data.len();
+                buf[..data_len].copy_from_slice(data);
+                data_len
+            }
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            buf.extend(data);
+            data.len()
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        let read_len = self.read(buf)?;
+        if read_len != buf.len() {
+            return Err(io::Error::new(
+                io::ErrorKind::UnexpectedEof,
+                "failed to fill whole buffer",
+            ));
+        }
+        Ok(())
+    }
+}
+
+impl AsRef<[u8]> for OwnedBytes {
+    fn as_ref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::{self, Read};
+
+    use super::OwnedBytes;
+
+    #[test]
+    fn test_owned_bytes_debug() {
+        let short_bytes = OwnedBytes::new(b"abcd".as_ref());
+        assert_eq!(
+            format!("{:?}", short_bytes),
+            "OwnedBytes([97, 98, 99, 100], len=4)"
+        );
+        let long_bytes = OwnedBytes::new(b"abcdefghijklmnopq".as_ref());
+        assert_eq!(
+            format!("{:?}", long_bytes),
+            "OwnedBytes([97, 98, 99, 100, 101, 102, 103, 104, 105, 106], len=17)"
+        );
+    }
+
+    #[test]
+    fn test_owned_bytes_read() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcdefghiklmnopqrstuvwxyz".as_ref());
+        {
+            let mut buf = [0u8; 5];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"abcde");
+            assert_eq!(bytes.as_slice(), b"fghiklmnopqrstuvwxyz")
+        }
+        {
+            let mut buf = [0u8; 2];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"fg");
+            assert_eq!(bytes.as_slice(), b"hiklmnopqrstuvwxyz")
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_right_at_the_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 5];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf, b"abcde");
+        assert_eq!(bytes.as_slice(), b"");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        assert_eq!(&buf, b"abcde");
+        Ok(())
+    }
+    #[test]
+    fn test_owned_bytes_read_incomplete() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 7];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf[..5], b"abcde");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_to_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = Vec::new();
+        bytes.read_to_end(&mut buf)?;
+        assert_eq!(buf.as_slice(), b"abcde".as_ref());
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_split() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        let (left, right) = bytes.split(3);
+        assert_eq!(left.as_slice(), b"abc");
+        assert_eq!(right.as_slice(), b"defghi");
+    }
+
+    #[test]
+    fn test_owned_bytes_split_boundary() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        {
+            let (left, right) = bytes.clone().split(0);
+            assert_eq!(left.as_slice(), b"");
+            assert_eq!(right.as_slice(), b"abcdefghi");
+        }
+        {
+            let (left, right) = bytes.split(9);
+            assert_eq!(left.as_slice(), b"abcdefghi");
+            assert_eq!(right.as_slice(), b"");
+        }
+    }
+}
diff --git a/src/directory/ram_directory.rs b/src/directory/ram_directory.rs
index 3b9a58182..0dc7dc572 100644
--- a/src/directory/ram_directory.rs
+++ b/src/directory/ram_directory.rs
@@ -1,9 +1,9 @@
-use crate::core::META_FILEPATH;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use crate::directory::AntiCallToken;
 use crate::directory::WatchCallbackList;
-use crate::directory::{Directory, ReadOnlySource, WatchCallback, WatchHandle};
+use crate::directory::{Directory, FileSlice, WatchCallback, WatchHandle};
 use crate::directory::{TerminatingWrite, WritePtr};
+use crate::{common::HasLen, core::META_FILEPATH};
 use fail::fail_point;
 use std::collections::HashMap;
 use std::fmt;
@@ -80,17 +80,17 @@ impl TerminatingWrite for VecWriter {
 
 #[derive(Default)]
 struct InnerDirectory {
-    fs: HashMap<PathBuf, ReadOnlySource>,
+    fs: HashMap<PathBuf, FileSlice>,
     watch_router: WatchCallbackList,
 }
 
 impl InnerDirectory {
     fn write(&mut self, path: PathBuf, data: &[u8]) -> bool {
-        let data = ReadOnlySource::new(Vec::from(data));
+        let data = FileSlice::new(Vec::from(data));
         self.fs.insert(path, data).is_some()
     }
 
-    fn open_read(&self, path: &Path) -> Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError> {
         self.fs
             .get(path)
             .ok_or_else(|| OpenReadError::FileDoesNotExist(PathBuf::from(path)))
@@ -153,9 +153,9 @@ impl RAMDirectory {
     /// If an error is encounterred, files may be persisted partially.
     pub fn persist(&self, dest: &mut dyn Directory) -> crate::Result<()> {
         let wlock = self.fs.write().unwrap();
-        for (path, source) in wlock.fs.iter() {
+        for (path, file) in wlock.fs.iter() {
             let mut dest_wrt = dest.open_write(path)?;
-            dest_wrt.write_all(source.as_slice())?;
+            dest_wrt.write_all(file.read_bytes()?.as_slice())?;
             dest_wrt.terminate()?;
         }
         Ok(())
@@ -163,7 +163,7 @@ impl RAMDirectory {
 }
 
 impl Directory for RAMDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         self.fs.read().unwrap().open_read(path)
     }
 
@@ -195,7 +195,14 @@ impl Directory for RAMDirectory {
     }
 
     fn atomic_read(&self, path: &Path) -> Result<Vec<u8>, OpenReadError> {
-        Ok(self.open_read(path)?.as_slice().to_owned())
+        let bytes =
+            self.open_read(path)?
+                .read_bytes()
+                .map_err(|io_error| OpenReadError::IOError {
+                    io_error,
+                    filepath: path.to_path_buf(),
+                })?;
+        Ok(bytes.as_slice().to_owned())
     }
 
     fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
diff --git a/src/directory/read_only_source.rs b/src/directory/read_only_source.rs
deleted file mode 100644
index 9949b9e77..000000000
--- a/src/directory/read_only_source.rs
+++ /dev/null
@@ -1,137 +0,0 @@
-use crate::common::HasLen;
-use stable_deref_trait::{CloneStableDeref, StableDeref};
-use std::ops::Deref;
-use std::sync::Arc;
-
-pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
-
-/// Read object that represents files in tantivy.
-///
-/// These read objects are only in charge to deliver
-/// the data in the form of a constant read-only `&[u8]`.
-/// Whatever happens to the directory file, the data
-/// hold by this object should never be altered or destroyed.
-pub struct ReadOnlySource {
-    data: Arc<BoxedData>,
-    start: usize,
-    stop: usize,
-}
-
-unsafe impl StableDeref for ReadOnlySource {}
-unsafe impl CloneStableDeref for ReadOnlySource {}
-
-impl Deref for ReadOnlySource {
-    type Target = [u8];
-
-    fn deref(&self) -> &[u8] {
-        self.as_slice()
-    }
-}
-
-impl From<Arc<BoxedData>> for ReadOnlySource {
-    fn from(data: Arc<BoxedData>) -> Self {
-        let len = data.len();
-        ReadOnlySource {
-            data,
-            start: 0,
-            stop: len,
-        }
-    }
-}
-
-impl ReadOnlySource {
-    pub(crate) fn new<D>(data: D) -> ReadOnlySource
-    where
-        D: Deref<Target = [u8]> + Send + Sync + 'static,
-    {
-        let len = data.len();
-        ReadOnlySource {
-            data: Arc::new(Box::new(data)),
-            start: 0,
-            stop: len,
-        }
-    }
-
-    /// Creates an empty ReadOnlySource
-    pub fn empty() -> ReadOnlySource {
-        ReadOnlySource::new(&[][..])
-    }
-
-    /// Returns the data underlying the ReadOnlySource object.
-    pub fn as_slice(&self) -> &[u8] {
-        &self.data[self.start..self.stop]
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset given
-    /// as an argument.
-    pub fn split(self, addr: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left = self.slice(0, addr);
-        let right = self.slice_from(addr);
-        (left, right)
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset `end - right_len`.
-    pub fn split_from_end(self, right_len: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left_len = self.len() - right_len;
-        self.split(left_len)
-    }
-
-    /// Creates a ReadOnlySource that is just a
-    /// view over a slice of the data.
-    ///
-    /// Keep in mind that any living slice extends
-    /// the lifetime of the original ReadOnlySource,
-    ///
-    /// For instance, if `ReadOnlySource` wraps 500MB
-    /// worth of data in anonymous memory, and only a
-    /// 1KB slice is remaining, the whole `500MBs`
-    /// are retained in memory.
-    pub fn slice(&self, start: usize, stop: usize) -> ReadOnlySource {
-        assert!(
-            start <= stop,
-            "Requested negative slice [{}..{}]",
-            start,
-            stop
-        );
-        assert!(stop <= self.len());
-        ReadOnlySource {
-            data: self.data.clone(),
-            start: self.start + start,
-            stop: self.start + stop,
-        }
-    }
-
-    /// Like `.slice(...)` but enforcing only the `from`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(from_offset, self.len())`
-    pub fn slice_from(&self, from_offset: usize) -> ReadOnlySource {
-        self.slice(from_offset, self.len())
-    }
-
-    /// Like `.slice(...)` but enforcing only the `to`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(0, to_offset)`
-    pub fn slice_to(&self, to_offset: usize) -> ReadOnlySource {
-        self.slice(0, to_offset)
-    }
-}
-
-impl HasLen for ReadOnlySource {
-    fn len(&self) -> usize {
-        self.stop - self.start
-    }
-}
-
-impl Clone for ReadOnlySource {
-    fn clone(&self) -> Self {
-        self.slice_from(0)
-    }
-}
-
-impl From<Vec<u8>> for ReadOnlySource {
-    fn from(data: Vec<u8>) -> ReadOnlySource {
-        ReadOnlySource::new(data)
-    }
-}
diff --git a/src/directory/tests.rs b/src/directory/tests.rs
index 74f2f2840..6767f0bc6 100644
--- a/src/directory/tests.rs
+++ b/src/directory/tests.rs
@@ -20,9 +20,9 @@ mod mmap_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
+    fn test_simple() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_simple(&mut directory);
+        super::test_simple(&mut directory)
     }
 
     #[test]
@@ -32,15 +32,17 @@ mod mmap_directory_tests {
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
+    fn test_rewrite_forbidden() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+        super::test_rewrite_forbidden(&mut directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
+    fn test_directory_delete() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_directory_delete(&mut directory);
+        super::test_directory_delete(&mut directory)?;
+        Ok(())
     }
 
     #[test]
@@ -72,9 +74,9 @@ mod ram_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
+    fn test_simple() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_simple(&mut directory);
+        super::test_simple(&mut directory)
     }
 
     #[test]
@@ -84,15 +86,17 @@ mod ram_directory_tests {
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
+    fn test_rewrite_forbidden() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+        super::test_rewrite_forbidden(&mut directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
+    fn test_directory_delete() -> crate::Result<()> {
         let mut directory = make_directory();
-        super::test_directory_delete(&mut directory);
+        super::test_directory_delete(&mut directory)?;
+        Ok(())
     }
 
     #[test]
@@ -123,35 +127,28 @@ fn ram_directory_panics_if_flush_forgotten() {
     assert!(write_file.write_all(&[4]).is_ok());
 }
 
-fn test_simple(directory: &mut dyn Directory) {
+fn test_simple(directory: &mut dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
-        let mut write_file = directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
-        write_file.write_all(&[4]).unwrap();
-        write_file.write_all(&[3]).unwrap();
-        write_file.write_all(&[7, 3, 5]).unwrap();
-        write_file.flush().unwrap();
-    }
-    {
-        let read_file = directory.open_read(test_path).unwrap();
-        let data: &[u8] = &*read_file;
-        assert_eq!(data, &[4u8, 3u8, 7u8, 3u8, 5u8]);
-    }
+    let mut write_file = directory.open_write(test_path)?;
+    assert!(directory.exists(test_path));
+    write_file.write_all(&[4])?;
+    write_file.write_all(&[3])?;
+    write_file.write_all(&[7, 3, 5])?;
+    write_file.flush()?;
+    let read_file = directory.open_read(test_path)?.read_bytes()?;
+    assert_eq!(read_file.as_slice(), &[4u8, 3u8, 7u8, 3u8, 5u8]);
     assert!(directory.delete(test_path).is_ok());
     assert!(!directory.exists(test_path));
+    Ok(())
 }
 
-fn test_rewrite_forbidden(directory: &mut dyn Directory) {
+fn test_rewrite_forbidden(directory: &mut dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
-        directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
-    }
-    {
-        assert!(directory.open_write(test_path).is_err());
-    }
+    directory.open_write(test_path)?;
+    assert!(directory.exists(test_path));
+    assert!(directory.open_write(test_path).is_err());
     assert!(directory.delete(test_path).is_ok());
+    Ok(())
 }
 
 fn test_write_create_the_file(directory: &mut dyn Directory) {
@@ -165,21 +162,20 @@ fn test_write_create_the_file(directory: &mut dyn Directory) {
     }
 }
 
-fn test_directory_delete(directory: &mut dyn Directory) {
+fn test_directory_delete(directory: &mut dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
     assert!(directory.open_read(test_path).is_err());
-    let mut write_file = directory.open_write(&test_path).unwrap();
-    write_file.write_all(&[1, 2, 3, 4]).unwrap();
-    write_file.flush().unwrap();
+    let mut write_file = directory.open_write(&test_path)?;
+    write_file.write_all(&[1, 2, 3, 4])?;
+    write_file.flush()?;
     {
-        let read_handle = directory.open_read(&test_path).unwrap();
-        assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+        let read_handle = directory.open_read(&test_path)?.read_bytes()?;
+        assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         // Mapped files can't be deleted on Windows
         if !cfg!(windows) {
             assert!(directory.delete(&test_path).is_ok());
-            assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+            assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         }
-
         assert!(directory.delete(Path::new("SomeOtherPath")).is_err());
     }
 
@@ -189,6 +185,7 @@ fn test_directory_delete(directory: &mut dyn Directory) {
 
     assert!(directory.open_read(&test_path).is_err());
     assert!(directory.delete(&test_path).is_err());
+    Ok(())
 }
 
 fn test_watch(directory: &mut dyn Directory) {
diff --git a/src/fastfield/bytes/mod.rs b/src/fastfield/bytes/mod.rs
index 1ce4fe416..9800881e1 100644
--- a/src/fastfield/bytes/mod.rs
+++ b/src/fastfield/bytes/mod.rs
@@ -85,7 +85,7 @@ mod tests {
         let field = searcher.schema().get_field("string_bytes").unwrap();
         let term = Term::from_field_bytes(field, b"lucene".as_ref());
         let term_query = TermQuery::new(term, IndexRecordOption::Basic);
-        let term_weight = term_query.specialized_weight(&searcher, true);
+        let term_weight = term_query.specialized_weight(&searcher, true)?;
         let term_scorer = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0f32)?;
         assert_eq!(term_scorer.doc(), 0u32);
         Ok(())
@@ -98,7 +98,7 @@ mod tests {
         let field = searcher.schema().get_field("string_bytes").unwrap();
         let term = Term::from_field_bytes(field, b"lucene".as_ref());
         let term_query = TermQuery::new(term, IndexRecordOption::Basic);
-        let term_weight = term_query.specialized_weight(&searcher, false);
+        let term_weight = term_query.specialized_weight(&searcher, false)?;
         let term_scorer_err = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0f32);
         assert!(matches!(
             term_scorer_err,
diff --git a/src/fastfield/bytes/reader.rs b/src/fastfield/bytes/reader.rs
index bf120152c..123d6a89b 100644
--- a/src/fastfield/bytes/reader.rs
+++ b/src/fastfield/bytes/reader.rs
@@ -1,6 +1,5 @@
-use owning_ref::OwningRef;
-
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::fastfield::FastFieldReader;
 use crate::DocId;
 
@@ -17,16 +16,16 @@ use crate::DocId;
 #[derive(Clone)]
 pub struct BytesFastFieldReader {
     idx_reader: FastFieldReader<u64>,
-    values: OwningRef<ReadOnlySource, [u8]>,
+    values: OwnedBytes,
 }
 
 impl BytesFastFieldReader {
     pub(crate) fn open(
         idx_reader: FastFieldReader<u64>,
-        values_source: ReadOnlySource,
-    ) -> BytesFastFieldReader {
-        let values = OwningRef::new(values_source).map(|source| &source[..]);
-        BytesFastFieldReader { idx_reader, values }
+        values_file: FileSlice,
+    ) -> crate::Result<BytesFastFieldReader> {
+        let values = values_file.read_bytes()?;
+        Ok(BytesFastFieldReader { idx_reader, values })
     }
 
     fn range(&self, doc: DocId) -> (usize, usize) {
@@ -38,7 +37,7 @@ impl BytesFastFieldReader {
     /// Returns the bytes associated to the given `doc`
     pub fn get_bytes(&self, doc: DocId) -> &[u8] {
         let (start, stop) = self.range(doc);
-        &self.values[start..stop]
+        &self.values.as_slice()[start..stop]
     }
 
     /// Returns the overall number of bytes in this bytes fast field.
diff --git a/src/fastfield/delete.rs b/src/fastfield/delete.rs
index 5dfd16056..b726a0e3a 100644
--- a/src/fastfield/delete.rs
+++ b/src/fastfield/delete.rs
@@ -1,5 +1,6 @@
 use crate::common::{BitSet, HasLen};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::directory::WritePtr;
 use crate::space_usage::ByteCount;
 use crate::DocId;
@@ -39,7 +40,7 @@ pub fn write_delete_bitset(
 /// Set of deleted `DocId`s.
 #[derive(Clone)]
 pub struct DeleteBitSet {
-    data: ReadOnlySource,
+    data: OwnedBytes,
     len: usize,
 }
 
@@ -58,21 +59,22 @@ impl DeleteBitSet {
         let mut wrt = directory.open_write(path).unwrap();
         write_delete_bitset(&bitset, max_doc, &mut wrt).unwrap();
         wrt.terminate().unwrap();
-        let source = directory.open_read(path).unwrap();
-        Self::open(source)
+        let file = directory.open_read(path).unwrap();
+        Self::open(file).unwrap()
     }
 
-    /// Opens a delete bitset given its data source.
-    pub fn open(data: ReadOnlySource) -> DeleteBitSet {
-        let num_deleted: usize = data
+    /// Opens a delete bitset given its file.
+    pub fn open(file: FileSlice) -> crate::Result<DeleteBitSet> {
+        let bytes = file.read_bytes()?;
+        let num_deleted: usize = bytes
             .as_slice()
             .iter()
             .map(|b| b.count_ones() as usize)
             .sum();
-        DeleteBitSet {
-            data,
+        Ok(DeleteBitSet {
+            data: bytes,
             len: num_deleted,
-        }
+        })
     }
 
     /// Returns true iff the document is still "alive". In other words, if it has not been deleted.
@@ -84,7 +86,7 @@ impl DeleteBitSet {
     #[inline(always)]
     pub fn is_deleted(&self, doc: DocId) -> bool {
         let byte_offset = doc / 8u32;
-        let b: u8 = (*self.data)[byte_offset as usize];
+        let b: u8 = self.data.as_slice()[byte_offset as usize];
         let shift = (doc & 7u32) as u8;
         b & (1u8 << shift) != 0
     }
diff --git a/src/fastfield/mod.rs b/src/fastfield/mod.rs
index 2e7808225..227cc1e2f 100644
--- a/src/fastfield/mod.rs
+++ b/src/fastfield/mod.rs
@@ -209,6 +209,7 @@ mod tests {
     use crate::schema::FAST;
     use crate::schema::{Document, IntOptions};
     use crate::{Index, SegmentId, SegmentReader};
+    use common::HasLen;
     use once_cell::sync::Lazy;
     use rand::prelude::SliceRandom;
     use rand::rngs::StdRng;
@@ -239,7 +240,7 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_small() {
+    fn test_intfastfield_small() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
         {
@@ -254,27 +255,24 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
-        {
-            assert_eq!(source.len(), 36 as usize);
-        }
-        {
-            let composite_file = CompositeFile::open(&source).unwrap();
-            let field_source = composite_file.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(field_source);
-            assert_eq!(fast_field_reader.get(0), 13u64);
-            assert_eq!(fast_field_reader.get(1), 14u64);
-            assert_eq!(fast_field_reader.get(2), 2u64);
-        }
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 36 as usize);
+        let composite_file = CompositeFile::open(&file)?;
+        let file = composite_file.open_read(*FIELD).unwrap();
+        let fast_field_reader = FastFieldReader::<u64>::open(file)?;
+        assert_eq!(fast_field_reader.get(0), 13u64);
+        assert_eq!(fast_field_reader.get(1), 14u64);
+        assert_eq!(fast_field_reader.get(2), 2u64);
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_large() {
+    fn test_intfastfield_large() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             fast_field_writers.add_document(&doc!(*FIELD=>4u64));
             fast_field_writers.add_document(&doc!(*FIELD=>14_082_001u64));
@@ -285,19 +283,15 @@ mod tests {
             fast_field_writers.add_document(&doc!(*FIELD=>1_002u64));
             fast_field_writers.add_document(&doc!(*FIELD=>1_501u64));
             fast_field_writers.add_document(&doc!(*FIELD=>215u64));
-            fast_field_writers
-                .serialize(&mut serializer, &HashMap::new())
-                .unwrap();
-            serializer.close().unwrap();
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
+            serializer.close()?;
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
+        assert_eq!(file.len(), 61 as usize);
         {
-            assert_eq!(source.len(), 61 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 4u64);
             assert_eq!(fast_field_reader.get(1), 14_082_001u64);
             assert_eq!(fast_field_reader.get(2), 3_052u64);
@@ -308,10 +302,11 @@ mod tests {
             assert_eq!(fast_field_reader.get(7), 1_501u64);
             assert_eq!(fast_field_reader.get(8), 215u64);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_null_amplitude() {
+    fn test_intfastfield_null_amplitude() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
 
@@ -327,22 +322,21 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 34 as usize);
         {
-            assert_eq!(source.len(), 34 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             for doc in 0..10_000 {
                 assert_eq!(fast_field_reader.get(doc), 100_000u64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_large_numbers() {
+    fn test_intfastfield_large_numbers() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
 
@@ -360,14 +354,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 80042 as usize);
         {
-            assert_eq!(source.len(), 80042 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 0u64);
             for doc in 1..10_001 {
                 assert_eq!(
@@ -376,10 +368,11 @@ mod tests {
                 );
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield() {
+    fn test_signed_intfastfield() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
@@ -400,14 +393,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 17709 as usize);
         {
-            assert_eq!(source.len(), 17709 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
 
             assert_eq!(fast_field_reader.min_value(), -100i64);
             assert_eq!(fast_field_reader.max_value(), 9_999i64);
@@ -420,10 +411,11 @@ mod tests {
                 assert_eq!(buffer[i], -100i64 + 53i64 + i as i64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield_default_val() {
+    fn test_signed_intfastfield_default_val() -> crate::Result<()> {
         let path = Path::new("test");
         let mut directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
@@ -442,13 +434,14 @@ mod tests {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
             assert_eq!(fast_field_reader.get(0u32), 0i64);
         }
+        Ok(())
     }
 
     // Warning: this generates the same permutation at each call
@@ -459,28 +452,26 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_permutation() {
+    fn test_intfastfield_permutation() -> crate::Result<()> {
         let path = Path::new("test");
         let permutation = generate_permutation();
         let n = permutation.len();
         let mut directory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             for &x in &permutation {
                 fast_field_writers.add_document(&doc!(*FIELD=>x));
             }
-            fast_field_writers
-                .serialize(&mut serializer, &HashMap::new())
-                .unwrap();
-            serializer.close().unwrap();
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
+            serializer.close()?;
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
 
             let mut a = 0u64;
             for _ in 0..n {
@@ -488,6 +479,7 @@ mod tests {
                 a = fast_field_reader.get(a as u32);
             }
         }
+        Ok(())
     }
 
     #[test]
@@ -633,9 +625,9 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
             let fast_field_reader = FastFieldReader::<u64>::open(data);
 
@@ -667,9 +659,9 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
             let fast_field_reader = FastFieldReader::<u64>::open(data);
 
diff --git a/src/fastfield/reader.rs b/src/fastfield/reader.rs
index 867163b99..ab5fa88ba 100644
--- a/src/fastfield/reader.rs
+++ b/src/fastfield/reader.rs
@@ -3,13 +3,12 @@ use crate::common::bitpacker::BitUnpacker;
 use crate::common::compute_num_bits;
 use crate::common::BinarySerializable;
 use crate::common::CompositeFile;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{Directory, RAMDirectory, WritePtr};
 use crate::fastfield::{FastFieldSerializer, FastFieldsWriter};
 use crate::schema::Schema;
 use crate::schema::FAST;
 use crate::DocId;
-use owning_ref::OwningRef;
 use std::collections::HashMap;
 use std::marker::PhantomData;
 use std::path::Path;
@@ -20,34 +19,27 @@ use std::path::Path;
 /// fast field is required.
 #[derive(Clone)]
 pub struct FastFieldReader<Item: FastValue> {
-    bit_unpacker: BitUnpacker<OwningRef<ReadOnlySource, [u8]>>,
+    bit_unpacker: BitUnpacker,
     min_value_u64: u64,
     max_value_u64: u64,
     _phantom: PhantomData<Item>,
 }
 
 impl<Item: FastValue> FastFieldReader<Item> {
-    /// Opens a fast field given a source.
-    pub fn open(data: ReadOnlySource) -> Self {
-        let min_value: u64;
-        let amplitude: u64;
-        {
-            let mut cursor = data.as_slice();
-            min_value =
-                u64::deserialize(&mut cursor).expect("Failed to read the min_value of fast field.");
-            amplitude =
-                u64::deserialize(&mut cursor).expect("Failed to read the amplitude of fast field.");
-        }
+    /// Opens a fast field given a file.
+    pub fn open(file: FileSlice) -> crate::Result<Self> {
+        let mut bytes = file.read_bytes()?;
+        let min_value = u64::deserialize(&mut bytes)?;
+        let amplitude = u64::deserialize(&mut bytes)?;
         let max_value = min_value + amplitude;
         let num_bits = compute_num_bits(amplitude);
-        let owning_ref = OwningRef::new(data).map(|data| &data[16..]);
-        let bit_unpacker = BitUnpacker::new(owning_ref, num_bits);
-        FastFieldReader {
+        let bit_unpacker = BitUnpacker::new(bytes, num_bits);
+        Ok(FastFieldReader {
             min_value_u64: min_value,
             max_value_u64: max_value,
             bit_unpacker,
             _phantom: PhantomData,
-        }
+        })
     }
 
     pub(crate) fn into_u64_reader(self) -> FastFieldReader<u64> {
@@ -157,12 +149,11 @@ impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(path).expect("Failed to open the file");
-        let composite_file =
-            CompositeFile::open(&source).expect("Failed to read the composite file");
-        let field_source = composite_file
+        let file = directory.open_read(path).expect("Failed to open the file");
+        let composite_file = CompositeFile::open(&file).expect("Failed to read the composite file");
+        let field_file = composite_file
             .open_read(field)
             .expect("File component not found");
-        FastFieldReader::open(field_source)
+        FastFieldReader::open(field_file).unwrap()
     }
 }
diff --git a/src/fastfield/readers.rs b/src/fastfield/readers.rs
index fe7dc5a22..177f23cd2 100644
--- a/src/fastfield/readers.rs
+++ b/src/fastfield/readers.rs
@@ -72,44 +72,48 @@ impl FastFieldReaders {
                 if !bytes_option.is_fast() {
                     continue;
                 }
-                let idx_reader = fast_fields_composite
+                let fast_field_idx_file = fast_fields_composite
                     .open_read_with_idx(field, 0)
-                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))
-                    .map(FastFieldReader::open)?;
+                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))?;
+                let idx_reader = FastFieldReader::open(fast_field_idx_file)?;
                 let data = fast_fields_composite
                     .open_read_with_idx(field, 1)
                     .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))?;
+                let bytes_fast_field_reader = BytesFastFieldReader::open(idx_reader, data)?;
                 fast_field_readers
                     .fast_bytes
-                    .insert(field, BytesFastFieldReader::open(idx_reader, data));
+                    .insert(field, bytes_fast_field_reader);
             } else if let Some((fast_type, cardinality)) = type_and_cardinality(field_type) {
                 match cardinality {
                     Cardinality::SingleValue => {
                         if let Some(fast_field_data) = fast_fields_composite.open_read(field) {
                             match fast_type {
                                 FastType::U64 => {
-                                    let fast_field_reader = FastFieldReader::open(fast_field_data);
+                                    let fast_field_reader = FastFieldReader::open(fast_field_data)?;
                                     fast_field_readers
                                         .fast_field_u64
                                         .insert(field, fast_field_reader);
                                 }
                                 FastType::I64 => {
-                                    fast_field_readers.fast_field_i64.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
+                                    let fast_field_reader =
+                                        FastFieldReader::open(fast_field_data.clone())?;
+                                    fast_field_readers
+                                        .fast_field_i64
+                                        .insert(field, fast_field_reader);
                                 }
                                 FastType::F64 => {
-                                    fast_field_readers.fast_field_f64.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
+                                    let fast_field_reader =
+                                        FastFieldReader::open(fast_field_data.clone())?;
+                                    fast_field_readers
+                                        .fast_field_f64
+                                        .insert(field, fast_field_reader);
                                 }
                                 FastType::Date => {
-                                    fast_field_readers.fast_field_date.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
+                                    let fast_field_reader =
+                                        FastFieldReader::open(fast_field_data.clone())?;
+                                    fast_field_readers
+                                        .fast_field_date
+                                        .insert(field, fast_field_reader);
                                 }
                             }
                         } else {
@@ -120,10 +124,10 @@ impl FastFieldReaders {
                         let idx_opt = fast_fields_composite.open_read_with_idx(field, 0);
                         let data_opt = fast_fields_composite.open_read_with_idx(field, 1);
                         if let (Some(fast_field_idx), Some(fast_field_data)) = (idx_opt, data_opt) {
-                            let idx_reader = FastFieldReader::open(fast_field_idx);
+                            let idx_reader = FastFieldReader::open(fast_field_idx)?;
                             match fast_type {
                                 FastType::I64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -131,7 +135,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::U64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -139,7 +143,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::F64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
@@ -147,7 +151,7 @@ impl FastFieldReaders {
                                         .insert(field, multivalued_int_fast_field);
                                 }
                                 FastType::Date => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
+                                    let vals_reader = FastFieldReader::open(fast_field_data)?;
                                     let multivalued_int_fast_field =
                                         MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
                                     fast_field_readers
diff --git a/src/fieldnorm/reader.rs b/src/fieldnorm/reader.rs
index d798c8679..bd8ed6628 100644
--- a/src/fieldnorm/reader.rs
+++ b/src/fieldnorm/reader.rs
@@ -1,6 +1,7 @@
 use super::{fieldnorm_to_id, id_to_fieldnorm};
 use crate::common::CompositeFile;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::schema::Field;
 use crate::space_usage::PerFieldSpaceUsage;
 use crate::DocId;
@@ -19,16 +20,21 @@ pub struct FieldNormReaders {
 
 impl FieldNormReaders {
     /// Creates a field norm reader.
-    pub fn open(source: ReadOnlySource) -> crate::Result<FieldNormReaders> {
-        let data = CompositeFile::open(&source)?;
+    pub fn open(file: FileSlice) -> crate::Result<FieldNormReaders> {
+        let data = CompositeFile::open(&file)?;
         Ok(FieldNormReaders {
             data: Arc::new(data),
         })
     }
 
     /// Returns the FieldNormReader for a specific field.
-    pub fn get_field(&self, field: Field) -> Option<FieldNormReader> {
-        self.data.open_read(field).map(FieldNormReader::open)
+    pub fn get_field(&self, field: Field) -> crate::Result<Option<FieldNormReader>> {
+        if let Some(file) = self.data.open_read(field) {
+            let fieldnorm_reader = FieldNormReader::open(file)?;
+            Ok(Some(fieldnorm_reader))
+        } else {
+            Ok(None)
+        }
     }
 
     /// Return a break down of the space usage per field.
@@ -56,13 +62,14 @@ impl FieldNormReaders {
 /// in a very short array.
 #[derive(Clone)]
 pub struct FieldNormReader {
-    data: ReadOnlySource,
+    data: OwnedBytes,
 }
 
 impl FieldNormReader {
-    /// Opens a field norm reader given its data source.
-    pub fn open(data: ReadOnlySource) -> Self {
-        FieldNormReader { data }
+    /// Opens a field norm reader given its file.
+    pub fn open(fieldnorm_file: FileSlice) -> crate::Result<Self> {
+        let data = fieldnorm_file.read_bytes()?;
+        Ok(FieldNormReader { data })
     }
 
     /// Returns the number of documents in this segment.
@@ -87,8 +94,7 @@ impl FieldNormReader {
     /// Returns the `fieldnorm_id` associated to a document.
     #[inline(always)]
     pub fn fieldnorm_id(&self, doc_id: DocId) -> u8 {
-        let fielnorms_data = self.data.as_slice();
-        fielnorms_data[doc_id as usize]
+        self.data.as_slice()[doc_id as usize]
     }
 
     /// Converts a `fieldnorm_id` into a fieldnorm.
@@ -111,7 +117,7 @@ impl FieldNormReader {
             .cloned()
             .map(FieldNormReader::fieldnorm_to_id)
             .collect::<Vec<u8>>();
-        let field_norms_data = ReadOnlySource::from(field_norms_id);
+        let field_norms_data = OwnedBytes::new(field_norms_id);
         FieldNormReader {
             data: field_norms_data,
         }
diff --git a/src/indexer/index_writer.rs b/src/indexer/index_writer.rs
index b36ac331c..0ad6a9034 100644
--- a/src/indexer/index_writer.rs
+++ b/src/indexer/index_writer.rs
@@ -108,9 +108,9 @@ fn compute_deleted_bitset(
         // Limit doc helps identify the first document
         // that may be affected by the delete operation.
         let limit_doc = doc_opstamps.compute_doc_limit(delete_op.opstamp);
-        let inverted_index = segment_reader.inverted_index(delete_op.term.field());
+        let inverted_index = segment_reader.inverted_index(delete_op.term.field())?;
         if let Some(mut docset) =
-            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)
+            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)?
         {
             let mut deleted_doc = docset.doc();
             while deleted_doc != TERMINATED {
@@ -979,7 +979,7 @@ mod tests {
         let num_docs_containing = |s: &str| {
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
 
         {
@@ -1015,7 +1015,7 @@ mod tests {
             .unwrap();
         let num_docs_containing = |s: &str| {
             let term_a = Term::from_field_text(text_field, s);
-            reader.searcher().doc_freq(&term_a)
+            reader.searcher().doc_freq(&term_a).unwrap()
         };
         {
             // writing the segment
@@ -1110,6 +1110,7 @@ mod tests {
                 .unwrap()
                 .searcher()
                 .doc_freq(&term_a)
+                .unwrap()
         };
         assert_eq!(num_docs_containing("a"), 0);
         assert_eq!(num_docs_containing("b"), 100);
@@ -1129,7 +1130,7 @@ mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
         let mut index_writer = index.writer_with_num_threads(4, 12_000_000).unwrap();
 
@@ -1180,7 +1181,15 @@ mod tests {
 
         // working with an empty index == no documents
         let term_b = Term::from_field_text(text_field, "b");
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_b), 0);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_b)
+                .unwrap(),
+            0
+        );
     }
 
     #[test]
@@ -1200,7 +1209,15 @@ mod tests {
 
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
@@ -1226,7 +1243,15 @@ mod tests {
         // Find original docs in the index
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
diff --git a/src/indexer/merger.rs b/src/indexer/merger.rs
index 9acf7f18c..6ad3f61e7 100644
--- a/src/indexer/merger.rs
+++ b/src/indexer/merger.rs
@@ -38,7 +38,7 @@ fn compute_total_num_tokens(readers: &[SegmentReader], field: Field) -> crate::R
                 count[fieldnorm_id as usize] += 1;
             }
         } else {
-            total_tokens += reader.inverted_index(field).total_num_tokens();
+            total_tokens += reader.inverted_index(field)?.total_num_tokens();
         }
     }
     Ok(total_tokens
@@ -510,7 +510,7 @@ impl IndexMerger {
             .readers
             .iter()
             .map(|reader| reader.inverted_index(indexed_field))
-            .collect();
+            .collect::<crate::Result<Vec<_>>>()?;
 
         for field_reader in &field_readers {
             let terms = field_reader.terms();
@@ -583,8 +583,8 @@ impl IndexMerger {
                 let term_info = heap_item.streamer.value();
                 let segment_reader = &self.readers[heap_item.segment_ord];
                 let inverted_index: &InvertedIndexReader = &*field_readers[segment_ord];
-                let segment_postings =
-                    inverted_index.read_postings_from_terminfo(term_info, segment_postings_option);
+                let segment_postings = inverted_index
+                    .read_postings_from_terminfo(term_info, segment_postings_option)?;
                 let delete_bitset_opt = segment_reader.delete_bitset();
                 let doc_freq = if let Some(delete_bitset) = delete_bitset_opt {
                     segment_postings.doc_freq_given_deletes(delete_bitset)
@@ -653,7 +653,7 @@ impl IndexMerger {
     ) -> crate::Result<HashMap<Field, TermOrdinalMapping>> {
         let mut term_ordinal_mappings = HashMap::new();
         for (field, field_entry) in self.schema.fields() {
-            let fieldnorm_reader = fieldnorm_readers.get_field(field);
+            let fieldnorm_reader = fieldnorm_readers.get_field(field)?;
             if field_entry.is_indexed() {
                 if let Some(term_ordinal_mapping) = self.write_postings_for_field(
                     field,
@@ -670,7 +670,7 @@ impl IndexMerger {
 
     fn write_storable_fields(&self, store_writer: &mut StoreWriter) -> crate::Result<()> {
         for reader in &self.readers {
-            let store_reader = reader.get_store_reader();
+            let store_reader = reader.get_store_reader()?;
             if reader.num_deleted_docs() > 0 {
                 for doc_id in reader.doc_ids_alive() {
                     let doc = store_reader.get(doc_id)?;
@@ -1533,7 +1533,7 @@ mod tests {
         let reader = index.reader()?;
         let searcher = reader.searcher();
         let mut term_scorer = term_query
-            .specialized_weight(&searcher, true)
+            .specialized_weight(&searcher, true)?
             .specialized_scorer(searcher.segment_reader(0u32), 1.0)?;
         assert_eq!(term_scorer.doc(), 0);
         assert_nearly_equals!(term_scorer.block_max_score(), 0.0079681855);
@@ -1548,7 +1548,7 @@ mod tests {
         assert_eq!(searcher.segment_readers().len(), 2);
         for segment_reader in searcher.segment_readers() {
             let mut term_scorer = term_query
-                .specialized_weight(&searcher, true)
+                .specialized_weight(&searcher, true)?
                 .specialized_scorer(segment_reader, 1.0)?;
             // the difference compared to before is instrinsic to the bm25 formula. no worries there.
             for doc in segment_reader.doc_ids_alive() {
@@ -1572,7 +1572,7 @@ mod tests {
 
         let segment_reader = searcher.segment_reader(0u32);
         let mut term_scorer = term_query
-            .specialized_weight(&searcher, true)
+            .specialized_weight(&searcher, true)?
             .specialized_scorer(segment_reader, 1.0)?;
         // the difference compared to before is instrinsic to the bm25 formula. no worries there.
         for doc in segment_reader.doc_ids_alive() {
diff --git a/src/lib.rs b/src/lib.rs
index 6fd4ce2ad..0bbd683fd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -383,31 +383,23 @@ mod tests {
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
         let mut index_writer = index.writer_for_tests()?;
-        {
-            index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.commit()?;
-        }
-        {
-            index_writer.add_document(doc!(text_field=>"a"));
-            index_writer.add_document(doc!(text_field=>"a a"));
-            index_writer.commit()?;
-        }
-        {
-            index_writer.add_document(doc!(text_field=>"c"));
-            index_writer.commit()?;
-        }
-        {
-            let reader = index.reader()?;
-            let searcher = reader.searcher();
-            let term_a = Term::from_field_text(text_field, "a");
-            assert_eq!(searcher.doc_freq(&term_a), 3);
-            let term_b = Term::from_field_text(text_field, "b");
-            assert_eq!(searcher.doc_freq(&term_b), 1);
-            let term_c = Term::from_field_text(text_field, "c");
-            assert_eq!(searcher.doc_freq(&term_c), 2);
-            let term_d = Term::from_field_text(text_field, "d");
-            assert_eq!(searcher.doc_freq(&term_d), 0);
-        }
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field=>"a"));
+        index_writer.add_document(doc!(text_field=>"a a"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field=>"c"));
+        index_writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let term_a = Term::from_field_text(text_field, "a");
+        assert_eq!(searcher.doc_freq(&term_a)?, 3);
+        let term_b = Term::from_field_text(text_field, "b");
+        assert_eq!(searcher.doc_freq(&term_b)?, 1);
+        let term_c = Term::from_field_text(text_field, "c");
+        assert_eq!(searcher.doc_freq(&term_c)?, 2);
+        let term_d = Term::from_field_text(text_field, "d");
+        assert_eq!(searcher.doc_freq(&term_d)?, 0);
         Ok(())
     }
 
@@ -504,13 +496,13 @@ mod tests {
             reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 5);
@@ -518,7 +510,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -540,14 +532,14 @@ mod tests {
             reader.reload()?;
             let searcher = reader.searcher();
             let seg_reader = searcher.segment_reader(0);
-            let inverted_index = seg_reader.inverted_index(term_abcd.field());
+            let inverted_index = seg_reader.inverted_index(term_abcd.field())?;
 
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 5);
@@ -555,7 +547,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 3);
@@ -577,19 +569,19 @@ mod tests {
             reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(term_abcd.field());
+            let inverted_index = segment_reader.inverted_index(term_abcd.field())?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(!advance_undeleted(&mut postings, segment_reader));
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -599,7 +591,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 4);
@@ -624,8 +616,8 @@ mod tests {
         let term = Term::from_field_u64(field, 1u64);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
@@ -648,8 +640,8 @@ mod tests {
         let term = Term::from_field_i64(value_field, negative_val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
@@ -672,8 +664,8 @@ mod tests {
         let term = Term::from_field_f64(value_field, val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
@@ -693,7 +685,7 @@ mod tests {
         let reader = index.reader()?;
         let searcher = reader.searcher();
         let segment_reader = searcher.segment_reader(0);
-        let inverted_index = segment_reader.inverted_index(absent_field); //< should not panic
+        let inverted_index = segment_reader.inverted_index(absent_field)?;
         assert_eq!(inverted_index.terms().num_terms(), 0);
         Ok(())
     }
@@ -743,14 +735,14 @@ mod tests {
             let index_reader = index.reader()?;
             let searcher = index_reader.searcher();
             let reader = searcher.segment_reader(0);
-            let inverted_index = reader.inverted_index(text_field);
+            let inverted_index = reader.inverted_index(text_field)?;
             let term_abcd = Term::from_field_text(text_field, "abcd");
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             let term_af = Term::from_field_text(text_field, "af");
             let mut postings = inverted_index
-                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.term_freq(), 3);
diff --git a/src/positions/mod.rs b/src/positions/mod.rs
index 46abdc3b0..8532b343d 100644
--- a/src/positions/mod.rs
+++ b/src/positions/mod.rs
@@ -38,11 +38,11 @@ const LONG_SKIP_INTERVAL: u64 = (LONG_SKIP_IN_BLOCKS * COMPRESSION_BLOCK_SIZE) a
 pub mod tests {
 
     use super::PositionSerializer;
-    use crate::directory::ReadOnlySource;
     use crate::positions::reader::PositionReader;
+    use crate::{common::HasLen, directory::FileSlice};
     use std::iter;
 
-    fn create_stream_buffer(vals: &[u32]) -> (ReadOnlySource, ReadOnlySource) {
+    fn create_stream_buffer(vals: &[u32]) -> (FileSlice, FileSlice) {
         let mut skip_buffer = vec![];
         let mut stream_buffer = vec![];
         {
@@ -53,10 +53,7 @@ pub mod tests {
             }
             serializer.close().unwrap();
         }
-        (
-            ReadOnlySource::from(stream_buffer),
-            ReadOnlySource::from(skip_buffer),
-        )
+        (FileSlice::new(stream_buffer), FileSlice::new(skip_buffer))
     }
 
     #[test]
@@ -65,7 +62,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &n in &[1, 10, 127, 128, 130, 312] {
             let mut v = vec![0u32; n];
             position_reader.read(0, &mut v[..]);
@@ -81,7 +78,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &offset in &[1u64, 10u64, 127u64, 128u64, 130u64, 312u64] {
             for &len in &[1, 10, 130, 500] {
                 let mut v = vec![0u32; len];
@@ -100,7 +97,7 @@ pub mod tests {
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
 
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         let mut buf = [0u32; 7];
         let mut c = 0;
 
@@ -122,7 +119,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut buf = [0u32; 256];
         position_reader.read(128, &mut buf);
         for i in 0..256 {
@@ -142,7 +139,8 @@ pub mod tests {
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
         let mut buf = [0u32; 1];
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 200_000);
+        let mut position_reader =
+            PositionReader::new(stream.clone(), skip.clone(), 200_000).unwrap();
         position_reader.read(230, &mut buf);
         position_reader.read(9, &mut buf);
     }
@@ -157,7 +155,7 @@ pub mod tests {
         }
         let (stream, skip) = create_stream_buffer(&v[..]);
         let mut buf = Vec::new();
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut offset = 0;
         for i in 1..24 {
             buf.resize(i, 0);
@@ -175,7 +173,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 1_000_000);
-        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024);
+        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024).unwrap();
         let mut buf = [0u32; 1];
         position_reader.read(0, &mut buf);
         assert_eq!(buf[0], CONST_VAL);
@@ -194,7 +192,8 @@ pub mod tests {
             128 * 1024 + 7,
             128 * 10 * 1024 + 10,
         ] {
-            let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), offset);
+            let mut position_reader =
+                PositionReader::new(stream.clone(), skip.clone(), offset).unwrap();
             let mut buf = [0u32; 1];
             position_reader.read(0, &mut buf);
             assert_eq!(buf[0], offset as u32);
diff --git a/src/positions/reader.rs b/src/positions/reader.rs
index 1bcbf4d1e..37fdae396 100644
--- a/src/positions/reader.rs
+++ b/src/positions/reader.rs
@@ -1,8 +1,13 @@
+use std::io;
+
 use crate::common::{BinarySerializable, FixedSize};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::positions::COMPRESSION_BLOCK_SIZE;
 use crate::positions::LONG_SKIP_INTERVAL;
 use crate::positions::LONG_SKIP_IN_BLOCKS;
+use bitpacking::{BitPacker, BitPacker4x};
+
 /// Positions works as a long sequence of compressed block.
 /// All terms are chained one after the other.
 ///
@@ -23,28 +28,28 @@ use crate::positions::LONG_SKIP_IN_BLOCKS;
 /// A given block obviously takes `(128 x  num_bit_for_the_block / num_bits_in_a_byte)`,
 /// so skipping a block without decompressing it is just a matter of advancing that many
 /// bytes.
-use bitpacking::{BitPacker, BitPacker4x};
-use owned_read::OwnedRead;
 
 struct Positions {
     bit_packer: BitPacker4x,
-    skip_source: ReadOnlySource,
-    position_source: ReadOnlySource,
-    long_skip_source: ReadOnlySource,
+    skip_file: FileSlice,
+    position_file: FileSlice,
+    long_skip_data: OwnedBytes,
 }
 
 impl Positions {
-    pub fn new(position_source: ReadOnlySource, skip_source: ReadOnlySource) -> Positions {
-        let (body, footer) = skip_source.split_from_end(u32::SIZE_IN_BYTES);
-        let num_long_skips = u32::deserialize(&mut footer.as_slice()).expect("Index corrupted");
-        let (skip_source, long_skip_source) =
+    pub fn new(position_file: FileSlice, skip_file: FileSlice) -> io::Result<Positions> {
+        let (body, footer) = skip_file.split_from_end(u32::SIZE_IN_BYTES);
+        let footer_data = footer.read_bytes()?;
+        let num_long_skips = u32::deserialize(&mut footer_data.as_slice())?;
+        let (skip_file, long_skip_file) =
             body.split_from_end(u64::SIZE_IN_BYTES * (num_long_skips as usize));
-        Positions {
+        let long_skip_data = long_skip_file.read_bytes()?;
+        Ok(Positions {
             bit_packer: BitPacker4x::new(),
-            skip_source,
-            long_skip_source,
-            position_source,
-        }
+            skip_file,
+            long_skip_data,
+            position_file,
+        })
     }
 
     /// Returns the offset of the block associated to the given `long_skip_id`.
@@ -54,19 +59,23 @@ impl Positions {
         if long_skip_id == 0 {
             return 0;
         }
-        let long_skip_slice = self.long_skip_source.as_slice();
+        let long_skip_slice = self.long_skip_data.as_slice();
         let mut long_skip_blocks: &[u8] = &long_skip_slice[(long_skip_id - 1) * 8..][..8];
         u64::deserialize(&mut long_skip_blocks).expect("Index corrupted")
     }
 
-    fn reader(&self, offset: u64) -> PositionReader {
+    fn reader(&self, offset: u64) -> io::Result<PositionReader> {
         let long_skip_id = (offset / LONG_SKIP_INTERVAL) as usize;
         let offset_num_bytes: u64 = self.long_skip(long_skip_id);
-        let mut position_read = OwnedRead::new(self.position_source.clone());
-        position_read.advance(offset_num_bytes as usize);
-        let mut skip_read = OwnedRead::new(self.skip_source.clone());
-        skip_read.advance(long_skip_id * LONG_SKIP_IN_BLOCKS);
-        PositionReader {
+        let position_read = self
+            .position_file
+            .slice_from(offset_num_bytes as usize)
+            .read_bytes()?;
+        let skip_read = self
+            .skip_file
+            .slice_from(long_skip_id * LONG_SKIP_IN_BLOCKS)
+            .read_bytes()?;
+        Ok(PositionReader {
             bit_packer: self.bit_packer,
             skip_read,
             position_read,
@@ -74,14 +83,14 @@ impl Positions {
             block_offset: std::i64::MAX as u64,
             anchor_offset: (long_skip_id as u64) * LONG_SKIP_INTERVAL,
             abs_offset: offset,
-        }
+        })
     }
 }
 
 #[derive(Clone)]
 pub struct PositionReader {
-    skip_read: OwnedRead,
-    position_read: OwnedRead,
+    skip_read: OwnedBytes,
+    position_read: OwnedBytes,
     bit_packer: BitPacker4x,
     buffer: Box<[u32; COMPRESSION_BLOCK_SIZE]>,
 
@@ -93,11 +102,12 @@ pub struct PositionReader {
 
 impl PositionReader {
     pub fn new(
-        position_source: ReadOnlySource,
-        skip_source: ReadOnlySource,
+        position_file: FileSlice,
+        skip_file: FileSlice,
         offset: u64,
-    ) -> PositionReader {
-        Positions::new(position_source, skip_source).reader(offset)
+    ) -> io::Result<PositionReader> {
+        let positions = Positions::new(position_file, skip_file)?;
+        positions.reader(offset)
     }
 
     fn advance_num_blocks(&mut self, num_blocks: usize) {
@@ -131,7 +141,7 @@ impl PositionReader {
             self.advance_num_blocks(num_blocks_to_skip);
             self.anchor_offset = offset - (offset % COMPRESSION_BLOCK_SIZE as u64);
             self.block_offset = self.anchor_offset;
-            let num_bits = self.skip_read.get(0);
+            let num_bits = self.skip_read.as_slice()[0];
             self.bit_packer
                 .decompress(self.position_read.as_ref(), self.buffer.as_mut(), num_bits);
         } else {
@@ -141,7 +151,7 @@ impl PositionReader {
             self.anchor_offset = self.block_offset;
         }
 
-        let mut num_bits = self.skip_read.get(0);
+        let mut num_bits = self.skip_read.as_slice()[0];
         let mut position_data = self.position_read.as_ref();
 
         for i in 1.. {
@@ -155,7 +165,7 @@ impl PositionReader {
             output = &mut output[remaining_in_block..];
             offset += remaining_in_block as u64;
             position_data = &position_data[(num_bits as usize * COMPRESSION_BLOCK_SIZE / 8)..];
-            num_bits = self.skip_read.get(i);
+            num_bits = self.skip_read.as_slice()[i];
             self.bit_packer
                 .decompress(position_data, self.buffer.as_mut(), num_bits);
             self.block_offset += COMPRESSION_BLOCK_SIZE as u64;
diff --git a/src/postings/block_segment_postings.rs b/src/postings/block_segment_postings.rs
index 87d1714f5..849453af5 100644
--- a/src/postings/block_segment_postings.rs
+++ b/src/postings/block_segment_postings.rs
@@ -1,5 +1,8 @@
+use std::io;
+
 use crate::common::{BinarySerializable, VInt};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::fieldnorm::FieldNormReader;
 use crate::postings::compression::{
     AlignedBuffer, BlockDecoder, VIntDecoder, COMPRESSION_BLOCK_SIZE,
@@ -34,7 +37,7 @@ pub struct BlockSegmentPostings {
 
     doc_freq: u32,
 
-    data: ReadOnlySource,
+    data: OwnedBytes,
     pub(crate) skip_reader: SkipReader,
 }
 
@@ -72,37 +75,34 @@ fn decode_vint_block(
 
 fn split_into_skips_and_postings(
     doc_freq: u32,
-    data: ReadOnlySource,
-) -> (Option<ReadOnlySource>, ReadOnlySource) {
+    mut bytes: OwnedBytes,
+) -> (Option<OwnedBytes>, OwnedBytes) {
     if doc_freq < COMPRESSION_BLOCK_SIZE as u32 {
-        return (None, data);
+        return (None, bytes);
     }
-    let mut data_byte_arr = data.as_slice();
-    let skip_len = VInt::deserialize(&mut data_byte_arr)
-        .expect("Data corrupted")
-        .0 as usize;
-    let vint_len = data.len() - data_byte_arr.len();
-    let (skip_data, postings_data) = data.slice_from(vint_len).split(skip_len);
+    let skip_len = VInt::deserialize(&mut bytes).expect("Data corrupted").0 as usize;
+    let (skip_data, postings_data) = bytes.split(skip_len);
     (Some(skip_data), postings_data)
 }
 
 impl BlockSegmentPostings {
-    pub(crate) fn from_data(
+    pub(crate) fn open(
         doc_freq: u32,
-        data: ReadOnlySource,
+        data: FileSlice,
         record_option: IndexRecordOption,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
+    ) -> io::Result<BlockSegmentPostings> {
         let freq_reading_option = match (record_option, requested_option) {
             (IndexRecordOption::Basic, _) => FreqReadingOption::NoFreq,
             (_, IndexRecordOption::Basic) => FreqReadingOption::SkipFreq,
             (_, _) => FreqReadingOption::ReadFreq,
         };
 
-        let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, data);
+        let (skip_data_opt, postings_data) =
+            split_into_skips_and_postings(doc_freq, data.read_bytes()?);
         let skip_reader = match skip_data_opt {
             Some(skip_data) => SkipReader::new(skip_data, doc_freq, record_option),
-            None => SkipReader::new(ReadOnlySource::empty(), doc_freq, record_option),
+            None => SkipReader::new(OwnedBytes::empty(), doc_freq, record_option),
         };
 
         let mut block_segment_postings = BlockSegmentPostings {
@@ -116,7 +116,7 @@ impl BlockSegmentPostings {
             skip_reader,
         };
         block_segment_postings.load_block();
-        block_segment_postings
+        Ok(block_segment_postings)
     }
 
     /// Returns the block_max_score for the current block.
@@ -172,15 +172,15 @@ impl BlockSegmentPostings {
     // # Warning
     //
     // This does not reset the positions list.
-    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: ReadOnlySource) {
+    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: OwnedBytes) {
         let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, postings_data);
-        self.data = ReadOnlySource::new(postings_data);
+        self.data = postings_data;
         self.block_max_score_cache = None;
         self.loaded_offset = std::usize::MAX;
         if let Some(skip_data) = skip_data_opt {
             self.skip_reader.reset(skip_data, doc_freq);
         } else {
-            self.skip_reader.reset(ReadOnlySource::empty(), doc_freq);
+            self.skip_reader.reset(OwnedBytes::empty(), doc_freq);
         }
         self.doc_freq = doc_freq;
         self.load_block();
@@ -344,8 +344,8 @@ impl BlockSegmentPostings {
             freq_reading_option: FreqReadingOption::NoFreq,
             block_max_score_cache: None,
             doc_freq: 0,
-            data: ReadOnlySource::new(vec![]),
-            skip_reader: SkipReader::new(ReadOnlySource::new(vec![]), 0, IndexRecordOption::Basic),
+            data: OwnedBytes::empty(),
+            skip_reader: SkipReader::new(OwnedBytes::empty(), 0, IndexRecordOption::Basic),
         }
     }
 }
@@ -467,10 +467,12 @@ mod tests {
         index_writer.commit().unwrap();
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
-        let inverted_index = segment_reader.inverted_index(int_field);
+        let inverted_index = segment_reader.inverted_index(int_field).unwrap();
         let term = Term::from_field_u64(int_field, 0u64);
         let term_info = inverted_index.get_term_info(&term).unwrap();
-        inverted_index.read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+        inverted_index
+            .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+            .unwrap()
     }
 
     #[test]
@@ -491,37 +493,38 @@ mod tests {
     }
 
     #[test]
-    fn test_reset_block_segment_postings() {
+    fn test_reset_block_segment_postings() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let int_field = schema_builder.add_u64_field("id", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_for_tests().unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         // create two postings list, one containg even number,
         // the other containing odd numbers.
         for i in 0..6 {
             let doc = doc!(int_field=> (i % 2) as u64);
             index_writer.add_document(doc);
         }
-        index_writer.commit().unwrap();
-        let searcher = index.reader().unwrap().searcher();
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         let mut block_segments;
         {
             let term = Term::from_field_u64(int_field, 0u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
+            let inverted_index = segment_reader.inverted_index(int_field)?;
             let term_info = inverted_index.get_term_info(&term).unwrap();
             block_segments = inverted_index
-                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)?;
         }
         assert_eq!(block_segments.docs(), &[0, 2, 4]);
         {
             let term = Term::from_field_u64(int_field, 1u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
+            let inverted_index = segment_reader.inverted_index(int_field)?;
             let term_info = inverted_index.get_term_info(&term).unwrap();
-            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments);
+            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments)?;
         }
         assert_eq!(block_segments.docs(), &[1, 3, 5]);
+        Ok(())
     }
 }
diff --git a/src/postings/mod.rs b/src/postings/mod.rs
index 3f9cce259..d4c97962d 100644
--- a/src/postings/mod.rs
+++ b/src/postings/mod.rs
@@ -101,12 +101,12 @@ pub mod tests {
         index_writer.commit()?;
 
         let searcher = index.reader()?.searcher();
-        let inverted_index = searcher.segment_reader(0u32).inverted_index(title);
+        let inverted_index = searcher.segment_reader(0u32).inverted_index(title)?;
         let term = Term::from_field_text(title, "abc");
         let mut positions = Vec::new();
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             postings.positions(&mut positions);
@@ -120,7 +120,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.advance(), 1);
@@ -129,7 +129,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1), 1);
             assert_eq!(postings.doc(), 1);
@@ -138,7 +138,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1002), 1002);
             assert_eq!(postings.doc(), 1002);
@@ -147,7 +147,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(100), 100);
             assert_eq!(postings.seek(1002), 1002);
@@ -159,7 +159,7 @@ pub mod tests {
     }
 
     #[test]
-    pub fn test_drop_token_that_are_too_long() {
+    pub fn test_drop_token_that_are_too_long() -> crate::Result<()> {
         let ok_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN).collect();
         let mut exceeding_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN + 1).collect();
         exceeding_token_text.push_str(" hello");
@@ -184,7 +184,7 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
             assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
@@ -196,12 +196,13 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(1u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
             assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
             assert_eq!(&bytes[..], ok_token_text.as_bytes());
         }
+        Ok(())
     }
 
     #[test]
@@ -261,15 +262,15 @@ pub mod tests {
             {
                 let term_a = Term::from_field_text(text_field, "abcdef");
                 assert!(segment_reader
-                    .inverted_index(term_a.field())
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_a.field())?
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .is_none());
             }
             {
                 let term_a = Term::from_field_text(text_field, "a");
                 let mut postings_a = segment_reader
-                    .inverted_index(term_a.field())
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_a.field())?
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_a.len(), 1000);
                 assert_eq!(postings_a.doc(), 0);
@@ -291,8 +292,8 @@ pub mod tests {
             {
                 let term_e = Term::from_field_text(text_field, "e");
                 let mut postings_e = segment_reader
-                    .inverted_index(term_e.field())
-                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_e.field())?
+                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_e.len(), 1000 - 2);
                 for i in 2u32..1000u32 {
@@ -312,7 +313,7 @@ pub mod tests {
     }
 
     #[test]
-    pub fn test_position_and_fieldnorm2() {
+    pub fn test_position_and_fieldnorm2() -> crate::Result<()> {
         let mut positions: Vec<u32> = Vec::new();
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
@@ -328,16 +329,17 @@ pub mod tests {
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
         let mut postings = segment_reader
-            .inverted_index(text_field)
-            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+            .inverted_index(text_field)?
+            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
             .unwrap();
         assert_eq!(postings.doc(), 1u32);
         postings.positions(&mut positions);
         assert_eq!(&positions[..], &[1u32, 4]);
+        Ok(())
     }
 
     #[test]
-    fn test_skip_next() {
+    fn test_skip_next() -> crate::Result<()> {
         let term_0 = Term::from_field_u64(Field::from_field_id(0), 0);
         let term_1 = Term::from_field_u64(Field::from_field_id(0), 1);
         let term_2 = Term::from_field_u64(Field::from_field_id(0), 2);
@@ -348,10 +350,9 @@ pub mod tests {
             let mut schema_builder = Schema::builder();
             let value_field = schema_builder.add_u64_field("value", INDEXED);
             let schema = schema_builder.build();
-
             let index = Index::create_in_ram(schema);
             {
-                let mut index_writer = index.writer_for_tests().unwrap();
+                let mut index_writer = index.writer_for_tests()?;
                 for i in 0u64..num_docs as u64 {
                     let doc = doc!(value_field => 2u64, value_field => i % 2u64);
                     index_writer.add_document(doc);
@@ -360,15 +361,15 @@ pub mod tests {
             }
             index
         };
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         // check that the basic usage works
         for i in 0..num_docs - 1 {
             for j in i + 1..num_docs {
                 let mut segment_postings = segment_reader
-                    .inverted_index(term_2.field())
-                    .read_postings(&term_2, IndexRecordOption::Basic)
+                    .inverted_index(term_2.field())?
+                    .read_postings(&term_2, IndexRecordOption::Basic)?
                     .unwrap();
                 assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
@@ -380,8 +381,8 @@ pub mod tests {
 
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             // check that `skip_next` advances the iterator
@@ -400,8 +401,8 @@ pub mod tests {
         // check that filtering works
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .inverted_index(term_0.field())?
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 {
@@ -410,8 +411,8 @@ pub mod tests {
             }
 
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .inverted_index(term_0.field())?
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 - 1 {
@@ -422,19 +423,19 @@ pub mod tests {
 
         // delete some of the documents
         {
-            let mut index_writer = index.writer_for_tests().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_0);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         assert_eq!(searcher.segment_readers().len(), 1);
         let segment_reader = searcher.segment_reader(0);
 
         // make sure seeking still works
         for i in 0..num_docs {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             if i % 2 == 0 {
@@ -450,8 +451,8 @@ pub mod tests {
         // now try with a longer sequence
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             let mut last = 2; // start from 5 to avoid seeking to 3 twice
@@ -476,20 +477,19 @@ pub mod tests {
 
         // delete everything else
         {
-            let mut index_writer = index.writer_for_tests().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_1);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
 
         // finally, check that it's empty
         {
-            let searchable_segment_ids = index
-                .searchable_segment_ids()
-                .expect("could not get index segment ids");
+            let searchable_segment_ids = index.searchable_segment_ids()?;
             assert!(searchable_segment_ids.is_empty());
             assert_eq!(searcher.num_docs(), 0);
         }
+        Ok(())
     }
 
     pub static TERM_A: Lazy<Term> = Lazy::new(|| {
@@ -621,7 +621,7 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
-                .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .read_postings(&*TERM_A, IndexRecordOption::Basic)?
                 .unwrap();
             while segment_postings.advance() != TERMINATED {}
         });
@@ -636,18 +636,22 @@ mod bench {
             let segment_postings_a = segment_reader
                 .inverted_index(TERM_A.field())
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_b = segment_reader
                 .inverted_index(TERM_B.field())
                 .read_postings(&*TERM_B, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_c = segment_reader
                 .inverted_index(TERM_C.field())
                 .read_postings(&*TERM_C, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_d = segment_reader
                 .inverted_index(TERM_D.field())
                 .read_postings(&*TERM_D, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let mut intersection = Intersection::new(vec![
                 segment_postings_a,
@@ -668,6 +672,7 @@ mod bench {
         let mut segment_postings = segment_reader
             .inverted_index(TERM_A.field())
             .read_postings(&*TERM_A, IndexRecordOption::Basic)
+            .unwrap()
             .unwrap();
 
         let mut existing_docs = Vec::new();
diff --git a/src/postings/postings_writer.rs b/src/postings/postings_writer.rs
index 401ba0df1..36e46a0c5 100644
--- a/src/postings/postings_writer.rs
+++ b/src/postings/postings_writer.rs
@@ -161,7 +161,7 @@ impl MultiFieldPostingsWriter {
             }
 
             let postings_writer = &self.per_field_postings_writers[field.field_id() as usize];
-            let fieldnorm_reader = fieldnorm_readers.get_field(field);
+            let fieldnorm_reader = fieldnorm_readers.get_field(field)?;
             let mut field_serializer = serializer.new_field(
                 field,
                 postings_writer.total_num_tokens(),
diff --git a/src/postings/segment_postings.rs b/src/postings/segment_postings.rs
index 25c7a5ff4..89aa04bb6 100644
--- a/src/postings/segment_postings.rs
+++ b/src/postings/segment_postings.rs
@@ -12,7 +12,7 @@ use crate::postings::Postings;
 use crate::schema::IndexRecordOption;
 use crate::{DocId, TERMINATED};
 
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::fastfield::DeleteBitSet;
 use crate::postings::BlockSegmentPostings;
 
@@ -86,12 +86,13 @@ impl SegmentPostings {
                 .close_term(docs.len() as u32)
                 .expect("In memory Serialization should never fail.");
         }
-        let block_segment_postings = BlockSegmentPostings::from_data(
+        let block_segment_postings = BlockSegmentPostings::open(
             docs.len() as u32,
-            ReadOnlySource::from(buffer),
+            FileSlice::new(buffer),
             IndexRecordOption::Basic,
             IndexRecordOption::Basic,
-        );
+        )
+        .unwrap();
         SegmentPostings::from_block_postings(block_segment_postings, None)
     }
 
@@ -131,12 +132,13 @@ impl SegmentPostings {
         postings_serializer
             .close_term(doc_and_tfs.len() as u32)
             .unwrap();
-        let block_segment_postings = BlockSegmentPostings::from_data(
+        let block_segment_postings = BlockSegmentPostings::open(
             doc_and_tfs.len() as u32,
-            ReadOnlySource::from(buffer),
+            FileSlice::new(buffer),
             IndexRecordOption::WithFreqs,
             IndexRecordOption::WithFreqs,
-        );
+        )
+        .unwrap();
         SegmentPostings::from_block_postings(block_segment_postings, None)
     }
 
@@ -204,7 +206,7 @@ impl DocSet for SegmentPostings {
     }
 
     /// Return the current document's `DocId`.
-    #[inline]
+    #[inline(always)]
     fn doc(&self) -> DocId {
         self.block_cursor.doc(self.cur)
     }
diff --git a/src/postings/skip.rs b/src/postings/skip.rs
index 8b3263886..0f90beff9 100644
--- a/src/postings/skip.rs
+++ b/src/postings/skip.rs
@@ -1,10 +1,9 @@
-use crate::common::{read_u32_vint_no_advance, serialize_vint_u32, BinarySerializable, VInt};
-use crate::directory::ReadOnlySource;
+use crate::common::{read_u32_vint_no_advance, serialize_vint_u32, BinarySerializable};
+use crate::directory::OwnedBytes;
 use crate::postings::compression::{compressed_block_size, COMPRESSION_BLOCK_SIZE};
 use crate::query::BM25Weight;
 use crate::schema::IndexRecordOption;
 use crate::{DocId, Score, TERMINATED};
-use owned_read::OwnedRead;
 
 pub struct SkipSerializer {
     buffer: Vec<u8>,
@@ -62,7 +61,7 @@ impl SkipSerializer {
 pub(crate) struct SkipReader {
     last_doc_in_block: DocId,
     pub(crate) last_doc_in_previous_block: DocId,
-    owned_read: OwnedRead,
+    owned_read: OwnedBytes,
     skip_info: IndexRecordOption,
     byte_offset: usize,
     remaining_docs: u32, // number of docs remaining, including the
@@ -93,7 +92,7 @@ impl Default for BlockInfo {
 }
 
 impl SkipReader {
-    pub fn new(data: ReadOnlySource, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
+    pub fn new(data: OwnedBytes, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
         let mut skip_reader = SkipReader {
             last_doc_in_block: if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
                 0
@@ -101,7 +100,7 @@ impl SkipReader {
                 TERMINATED
             },
             last_doc_in_previous_block: 0u32,
-            owned_read: OwnedRead::new(data),
+            owned_read: data,
             skip_info,
             block_info: BlockInfo::VInt { num_docs: doc_freq },
             byte_offset: 0,
@@ -114,14 +113,14 @@ impl SkipReader {
         skip_reader
     }
 
-    pub fn reset(&mut self, data: ReadOnlySource, doc_freq: u32) {
+    pub fn reset(&mut self, data: OwnedBytes, doc_freq: u32) {
         self.last_doc_in_block = if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
             0
         } else {
             TERMINATED
         };
         self.last_doc_in_previous_block = 0u32;
-        self.owned_read = OwnedRead::new(data);
+        self.owned_read = data;
         self.block_info = BlockInfo::VInt { num_docs: doc_freq };
         self.byte_offset = 0;
         self.remaining_docs = doc_freq;
@@ -154,17 +153,24 @@ impl SkipReader {
         self.position_offset
     }
 
+    #[inline(always)]
     pub fn byte_offset(&self) -> usize {
         self.byte_offset
     }
 
     fn read_block_info(&mut self) {
-        let doc_delta = u32::deserialize(&mut self.owned_read).expect("Skip data corrupted");
+        let doc_delta = {
+            let bytes = self.owned_read.as_slice();
+            let mut buf = [0; 4];
+            buf.copy_from_slice(&bytes[..4]);
+            u32::from_le_bytes(buf)
+        };
         self.last_doc_in_block += doc_delta as DocId;
-        let doc_num_bits = self.owned_read.get(0);
+        let doc_num_bits = self.owned_read.as_slice()[4];
+
         match self.skip_info {
             IndexRecordOption::Basic => {
-                self.owned_read.advance(1);
+                self.owned_read.advance(5);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits: 0,
@@ -174,11 +180,11 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqs => {
-                let tf_num_bits = self.owned_read.get(1);
-                let block_wand_fieldnorm_id = self.owned_read.get(2);
-                let data = &self.owned_read.as_ref()[3..];
-                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(data);
-                self.owned_read.advance(3 + num_bytes);
+                let bytes = self.owned_read.as_slice();
+                let tf_num_bits = bytes[5];
+                let block_wand_fieldnorm_id = bytes[6];
+                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(&bytes[7..]);
+                self.owned_read.advance(7 + num_bytes);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -188,13 +194,16 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqsAndPositions => {
-                let tf_num_bits = self.owned_read.get(1);
-                self.owned_read.advance(2);
-                let tf_sum = u32::deserialize(&mut self.owned_read).expect("Failed reading tf_sum");
-                let block_wand_fieldnorm_id = self.owned_read.get(0);
-                self.owned_read.advance(1);
-                let block_wand_term_freq =
-                    VInt::deserialize_u64(&mut self.owned_read).unwrap() as u32;
+                let bytes = self.owned_read.as_slice();
+                let tf_num_bits = bytes[5];
+                let tf_sum = {
+                    let mut buf = [0; 4];
+                    buf.copy_from_slice(&bytes[6..10]);
+                    u32::from_le_bytes(buf)
+                };
+                let block_wand_fieldnorm_id = bytes[10];
+                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(&bytes[11..]);
+                self.owned_read.advance(11 + num_bytes);
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -262,7 +271,7 @@ mod tests {
     use super::BlockInfo;
     use super::IndexRecordOption;
     use super::{SkipReader, SkipSerializer};
-    use crate::directory::ReadOnlySource;
+    use crate::directory::OwnedBytes;
     use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
 
     #[test]
@@ -278,11 +287,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::new(buf),
-            doc_freq,
-            IndexRecordOption::WithFreqs,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::WithFreqs);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info,
@@ -323,11 +329,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::from(buf),
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),
@@ -367,11 +370,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = COMPRESSION_BLOCK_SIZE as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::from(buf),
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),
diff --git a/src/postings/stacker/expull.rs b/src/postings/stacker/expull.rs
index ba44505a2..0510eac64 100644
--- a/src/postings/stacker/expull.rs
+++ b/src/postings/stacker/expull.rs
@@ -206,8 +206,8 @@ mod tests {
     fn test_stack_long() {
         let mut heap = MemoryArena::new();
         let mut stack = ExpUnrolledLinkedList::new();
-        let source: Vec<u32> = (0..100).collect();
-        for &el in &source {
+        let data: Vec<u32> = (0..100).collect();
+        for &el in &data {
             assert!(stack
                 .writer(&mut heap)
                 .write_u32::<LittleEndian>(el)
@@ -221,7 +221,7 @@ mod tests {
             result.push(LittleEndian::read_u32(&remaining[..4]));
             remaining = &remaining[4..];
         }
-        assert_eq!(&result[..], &source[..]);
+        assert_eq!(&result[..], &data[..]);
     }
 
     #[test]
diff --git a/src/query/automaton_weight.rs b/src/query/automaton_weight.rs
index f25375384..83ee9c88e 100644
--- a/src/query/automaton_weight.rs
+++ b/src/query/automaton_weight.rs
@@ -42,13 +42,13 @@ where
     fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         let max_doc = reader.max_doc();
         let mut doc_bitset = BitSet::with_max_value(max_doc);
-        let inverted_index = reader.inverted_index(self.field);
+        let inverted_index = reader.inverted_index(self.field)?;
         let term_dict = inverted_index.terms();
         let mut term_stream = self.automaton_stream(term_dict);
         while term_stream.advance() {
             let term_info = term_stream.value();
             let mut block_segment_postings = inverted_index
-                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic)?;
             loop {
                 let docs = block_segment_postings.docs();
                 if docs.is_empty() {
diff --git a/src/query/bm25.rs b/src/query/bm25.rs
index 131115bbc..0bb1b4f08 100644
--- a/src/query/bm25.rs
+++ b/src/query/bm25.rs
@@ -52,7 +52,7 @@ impl BM25Weight {
         }
     }
 
-    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> BM25Weight {
+    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> crate::Result<BM25Weight> {
         assert!(!terms.is_empty(), "BM25 requires at least one term");
         let field = terms[0].field();
         for term in &terms[1..] {
@@ -66,25 +66,27 @@ impl BM25Weight {
         let mut total_num_tokens = 0u64;
         let mut total_num_docs = 0u64;
         for segment_reader in searcher.segment_readers() {
-            let inverted_index = segment_reader.inverted_index(field);
+            let inverted_index = segment_reader.inverted_index(field)?;
             total_num_tokens += inverted_index.total_num_tokens();
             total_num_docs += u64::from(segment_reader.max_doc());
         }
         let average_fieldnorm = total_num_tokens as Score / total_num_docs as Score;
 
         if terms.len() == 1 {
-            let term_doc_freq = searcher.doc_freq(&terms[0]);
-            BM25Weight::for_one_term(term_doc_freq, total_num_docs, average_fieldnorm)
+            let term_doc_freq = searcher.doc_freq(&terms[0])?;
+            Ok(BM25Weight::for_one_term(
+                term_doc_freq,
+                total_num_docs,
+                average_fieldnorm,
+            ))
         } else {
-            let idf = terms
-                .iter()
-                .map(|term| {
-                    let term_doc_freq = searcher.doc_freq(term);
-                    idf(term_doc_freq, total_num_docs)
-                })
-                .sum::<Score>();
-            let idf_explain = Explanation::new("idf", idf);
-            BM25Weight::new(idf_explain, average_fieldnorm)
+            let mut idf_sum: Score = 0.0;
+            for term in terms {
+                let term_doc_freq = searcher.doc_freq(term)?;
+                idf_sum += idf(term_doc_freq, total_num_docs);
+            }
+            let idf_explain = Explanation::new("idf", idf_sum);
+            Ok(BM25Weight::new(idf_explain, average_fieldnorm))
         }
     }
 
diff --git a/src/query/phrase_query/phrase_query.rs b/src/query/phrase_query/phrase_query.rs
index 1032337d4..601b662d7 100644
--- a/src/query/phrase_query/phrase_query.rs
+++ b/src/query/phrase_query/phrase_query.rs
@@ -95,7 +95,7 @@ impl PhraseQuery {
             )));
         }
         let terms = self.phrase_terms();
-        let bm25_weight = BM25Weight::for_terms(searcher, &terms);
+        let bm25_weight = BM25Weight::for_terms(searcher, &terms)?;
         Ok(PhraseWeight::new(
             self.phrase_terms.clone(),
             bm25_weight,
diff --git a/src/query/phrase_query/phrase_weight.rs b/src/query/phrase_query/phrase_weight.rs
index 063ad763b..1f60275ea 100644
--- a/src/query/phrase_query/phrase_weight.rs
+++ b/src/query/phrase_query/phrase_weight.rs
@@ -48,8 +48,8 @@ impl PhraseWeight {
             let mut term_postings_list = Vec::new();
             for &(offset, ref term) in &self.phrase_terms {
                 if let Some(postings) = reader
-                    .inverted_index(term.field())
-                    .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term.field())?
+                    .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 {
                     term_postings_list.push((offset, postings));
                 } else {
@@ -66,8 +66,8 @@ impl PhraseWeight {
             let mut term_postings_list = Vec::new();
             for &(offset, ref term) in &self.phrase_terms {
                 if let Some(postings) = reader
-                    .inverted_index(term.field())
-                    .read_postings_no_deletes(&term, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term.field())?
+                    .read_postings_no_deletes(&term, IndexRecordOption::WithFreqsAndPositions)?
                 {
                     term_postings_list.push((offset, postings));
                 } else {
diff --git a/src/query/range_query.rs b/src/query/range_query.rs
index 936ea33e9..7d78bf4f2 100644
--- a/src/query/range_query.rs
+++ b/src/query/range_query.rs
@@ -296,13 +296,13 @@ impl Weight for RangeWeight {
         let max_doc = reader.max_doc();
         let mut doc_bitset = BitSet::with_max_value(max_doc);
 
-        let inverted_index = reader.inverted_index(self.field);
+        let inverted_index = reader.inverted_index(self.field)?;
         let term_dict = inverted_index.terms();
         let mut term_range = self.term_range(term_dict);
         while term_range.advance() {
             let term_info = term_range.value();
             let mut block_segment_postings = inverted_index
-                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic)?;
             loop {
                 let docs = block_segment_postings.docs();
                 if docs.is_empty() {
diff --git a/src/query/term_query/term_query.rs b/src/query/term_query/term_query.rs
index 0fb8c596f..a653be561 100644
--- a/src/query/term_query/term_query.rs
+++ b/src/query/term_query/term_query.rs
@@ -87,21 +87,31 @@ impl TermQuery {
     /// While `.weight(...)` returns a boxed trait object,
     /// this method return a specific implementation.
     /// This is useful for optimization purpose.
-    pub fn specialized_weight(&self, searcher: &Searcher, scoring_enabled: bool) -> TermWeight {
+    pub fn specialized_weight(
+        &self,
+        searcher: &Searcher,
+        scoring_enabled: bool,
+    ) -> crate::Result<TermWeight> {
         let term = self.term.clone();
-        let bm25_weight = BM25Weight::for_terms(searcher, &[term]);
+        let bm25_weight = BM25Weight::for_terms(searcher, &[term])?;
         let index_record_option = if scoring_enabled {
             self.index_record_option
         } else {
             IndexRecordOption::Basic
         };
-        TermWeight::new(self.term.clone(), index_record_option, bm25_weight)
+        Ok(TermWeight::new(
+            self.term.clone(),
+            index_record_option,
+            bm25_weight,
+        ))
     }
 }
 
 impl Query for TermQuery {
     fn weight(&self, searcher: &Searcher, scoring_enabled: bool) -> crate::Result<Box<dyn Weight>> {
-        Ok(Box::new(self.specialized_weight(searcher, scoring_enabled)))
+        Ok(Box::new(
+            self.specialized_weight(searcher, scoring_enabled)?,
+        ))
     }
     fn query_terms(&self, term_set: &mut BTreeSet<Term>) {
         term_set.insert(self.term.clone());
diff --git a/src/query/term_query/term_scorer.rs b/src/query/term_query/term_scorer.rs
index 583b518fc..86552026e 100644
--- a/src/query/term_query/term_scorer.rs
+++ b/src/query/term_query/term_scorer.rs
@@ -253,7 +253,7 @@ mod tests {
     }
 
     fn test_block_wand_aux(term_query: &TermQuery, searcher: &Searcher) -> crate::Result<()> {
-        let term_weight = term_query.specialized_weight(&searcher, true);
+        let term_weight = term_query.specialized_weight(&searcher, true)?;
         for reader in searcher.segment_readers() {
             let mut block_max_scores = vec![];
             let mut block_max_scores_b = vec![];
diff --git a/src/query/term_query/term_weight.rs b/src/query/term_query/term_weight.rs
index adaf38a62..339cf2033 100644
--- a/src/query/term_query/term_weight.rs
+++ b/src/query/term_query/term_weight.rs
@@ -36,11 +36,9 @@ impl Weight for TermWeight {
             Ok(self.scorer(reader, 1.0)?.count(delete_bitset))
         } else {
             let field = self.term.field();
-            Ok(reader
-                .inverted_index(field)
-                .get_term_info(&self.term)
-                .map(|term_info| term_info.doc_freq)
-                .unwrap_or(0))
+            let inv_index = reader.inverted_index(field)?;
+            let term_info = inv_index.get_term_info(&self.term);
+            Ok(term_info.map(|term_info| term_info.doc_freq).unwrap_or(0))
         }
     }
 
@@ -97,11 +95,11 @@ impl TermWeight {
         boost: Score,
     ) -> crate::Result<TermScorer> {
         let field = self.term.field();
-        let inverted_index = reader.inverted_index(field);
+        let inverted_index = reader.inverted_index(field)?;
         let fieldnorm_reader = reader.get_fieldnorms_reader(field)?;
         let similarity_weight = self.similarity_weight.boost_by(boost);
         let postings_opt: Option<SegmentPostings> =
-            inverted_index.read_postings(&self.term, self.index_record_option);
+            inverted_index.read_postings(&self.term, self.index_record_option)?;
         if let Some(segment_postings) = postings_opt {
             Ok(TermScorer::new(
                 segment_postings,
diff --git a/src/reader/mod.rs b/src/reader/mod.rs
index ff993de83..0a38c8cbb 100644
--- a/src/reader/mod.rs
+++ b/src/reader/mod.rs
@@ -9,8 +9,8 @@ use crate::directory::META_LOCK;
 use crate::Index;
 use crate::Searcher;
 use crate::SegmentReader;
-use std::convert::TryInto;
 use std::sync::Arc;
+use std::{convert::TryInto, io};
 
 /// Defines when a new version of the index should be reloaded.
 ///
@@ -138,11 +138,11 @@ impl InnerIndexReader {
                 .collect::<crate::Result<_>>()?
         };
         let schema = self.index.schema();
-        let searchers = std::iter::repeat_with(|| {
+        let searchers: Vec<Searcher> = std::iter::repeat_with(|| {
             Searcher::new(schema.clone(), self.index.clone(), segment_readers.clone())
         })
         .take(self.num_searchers)
-        .collect();
+        .collect::<io::Result<_>>()?;
         self.searcher_pool.publish_new_generation(searchers);
         Ok(())
     }
diff --git a/src/schema/term.rs b/src/schema/term.rs
index 266c7b9fb..2d182caa5 100644
--- a/src/schema/term.rs
+++ b/src/schema/term.rs
@@ -152,7 +152,7 @@ impl<B> Term<B>
 where
     B: AsRef<[u8]>,
 {
-    /// Wraps a source of data
+    /// Wraps a object holding bytes
     pub fn wrap(data: B) -> Term<B> {
         Term(data)
     }
diff --git a/src/snippet/mod.rs b/src/snippet/mod.rs
index 59485ef8b..f71de1d9d 100644
--- a/src/snippet/mod.rs
+++ b/src/snippet/mod.rs
@@ -263,19 +263,17 @@ impl SnippetGenerator {
     ) -> crate::Result<SnippetGenerator> {
         let mut terms = BTreeSet::new();
         query.query_terms(&mut terms);
-        let terms_text: BTreeMap<String, Score> = terms
-            .into_iter()
-            .filter(|term| term.field() == field)
-            .flat_map(|term| {
-                let doc_freq = searcher.doc_freq(&term);
+        let mut terms_text: BTreeMap<String, Score> = Default::default();
+        for term in terms {
+            if term.field() != field {
+                continue;
+            }
+            let doc_freq = searcher.doc_freq(&term)?;
+            if doc_freq > 0 {
                 let score = 1.0 / (1.0 + doc_freq as Score);
-                if doc_freq > 0 {
-                    Some((term.text().to_string(), score))
-                } else {
-                    None
-                }
-            })
-            .collect();
+                terms_text.insert(term.text().to_string(), score);
+            }
+        }
         let tokenizer = searcher.index().tokenizer_for_field(field)?;
         Ok(SnippetGenerator {
             terms_text,
diff --git a/src/space_usage/mod.rs b/src/space_usage/mod.rs
index b09e5ed0a..3bad8f8b0 100644
--- a/src/space_usage/mod.rs
+++ b/src/space_usage/mod.rs
@@ -307,7 +307,7 @@ mod test {
         let index = Index::create_in_ram(schema.clone());
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
-        let searcher_space_usage = searcher.space_usage();
+        let searcher_space_usage = searcher.space_usage().unwrap();
         assert_eq!(0, searcher_space_usage.total());
     }
 
@@ -346,7 +346,7 @@ mod test {
 
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
-        let searcher_space_usage = searcher.space_usage();
+        let searcher_space_usage = searcher.space_usage().unwrap();
         assert!(searcher_space_usage.total() > 0);
         assert_eq!(1, searcher_space_usage.segments().len());
 
@@ -386,7 +386,7 @@ mod test {
 
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
-        let searcher_space_usage = searcher.space_usage();
+        let searcher_space_usage = searcher.space_usage().unwrap();
         assert!(searcher_space_usage.total() > 0);
         assert_eq!(1, searcher_space_usage.segments().len());
 
@@ -425,7 +425,7 @@ mod test {
         }
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
-        let searcher_space_usage = searcher.space_usage();
+        let searcher_space_usage = searcher.space_usage().unwrap();
         assert!(searcher_space_usage.total() > 0);
         assert_eq!(1, searcher_space_usage.segments().len());
 
@@ -446,49 +446,47 @@ mod test {
     }
 
     #[test]
-    fn test_deletes() {
+    fn test_deletes() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let name = schema_builder.add_u64_field("name", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema.clone());
 
         {
-            let mut index_writer = index.writer_for_tests().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(name => 1u64));
             index_writer.add_document(doc!(name => 2u64));
             index_writer.add_document(doc!(name => 3u64));
             index_writer.add_document(doc!(name => 4u64));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
 
         {
-            let mut index_writer2 = index.writer(50_000_000).unwrap();
+            let mut index_writer2 = index.writer(50_000_000)?;
             index_writer2.delete_term(Term::from_field_u64(name, 2u64));
             index_writer2.delete_term(Term::from_field_u64(name, 3u64));
-
             // ok, now we should have a deleted doc
-            index_writer2.commit().unwrap();
+            index_writer2.commit()?;
         }
 
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
-        let searcher_space_usage = searcher.space_usage();
+        let searcher_space_usage = searcher.space_usage()?;
         assert!(searcher_space_usage.total() > 0);
         assert_eq!(1, searcher_space_usage.segments().len());
 
-        let segment = &searcher_space_usage.segments()[0];
-        assert!(segment.total() > 0);
+        let segment_space_usage = &searcher_space_usage.segments()[0];
+        assert!(segment_space_usage.total() > 0);
 
-        assert_eq!(2, segment.num_docs());
+        assert_eq!(2, segment_space_usage.num_docs());
 
-        expect_single_field(segment.termdict(), &name, 1, 512);
-        expect_single_field(segment.postings(), &name, 1, 512);
-        assert_eq!(0, segment.positions().total());
-        assert_eq!(0, segment.positions_skip_idx().total());
-        assert_eq!(0, segment.fast_fields().total());
-        expect_single_field(segment.fieldnorms(), &name, 1, 512);
-        // TODO: understand why the following fails
-        //        assert_eq!(0, segment.store().total());
-        assert!(segment.deletes() > 0);
+        expect_single_field(segment_space_usage.termdict(), &name, 1, 512);
+        expect_single_field(segment_space_usage.postings(), &name, 1, 512);
+        assert_eq!(0, segment_space_usage.positions().total());
+        assert_eq!(0, segment_space_usage.positions_skip_idx().total());
+        assert_eq!(0, segment_space_usage.fast_fields().total());
+        expect_single_field(segment_space_usage.fieldnorms(), &name, 1, 512);
+        assert!(segment_space_usage.deletes() > 0);
+        Ok(())
     }
 }
diff --git a/src/store/mod.rs b/src/store/mod.rs
index bb15301b7..ada5a76cd 100644
--- a/src/store/mod.rs
+++ b/src/store/mod.rs
@@ -103,19 +103,18 @@ pub mod tests {
     }
 
     #[test]
-    fn test_store() {
+    fn test_store() -> crate::Result<()> {
         let path = Path::new("store");
         let mut directory = RAMDirectory::create();
-        let store_file = directory.open_write(path).unwrap();
-        let schema = write_lorem_ipsum_store(store_file, 1_000);
+        let store_wrt = directory.open_write(path)?;
+        let schema = write_lorem_ipsum_store(store_wrt, 1_000);
         let field_title = schema.get_field("title").unwrap();
-        let store_source = directory.open_read(path).unwrap();
-        let store = StoreReader::from_source(store_source);
+        let store_file = directory.open_read(path)?;
+        let store = StoreReader::open(store_file)?;
         for i in 0..1_000 {
             assert_eq!(
                 *store
-                    .get(i)
-                    .unwrap()
+                    .get(i)?
                     .get_first(field_title)
                     .unwrap()
                     .text()
@@ -123,6 +122,7 @@ pub mod tests {
                 format!("Doc {}", i)
             );
         }
+        Ok(())
     }
 }
 
@@ -152,8 +152,8 @@ mod bench {
         let mut directory = RAMDirectory::create();
         let path = Path::new("store");
         write_lorem_ipsum_store(directory.open_write(path).unwrap(), 1_000);
-        let store_source = directory.open_read(path).unwrap();
-        let store = StoreReader::from_source(store_source);
+        let store_file = directory.open_read(path).unwrap();
+        let store = StoreReader::open(store_file).unwrap();
         b.iter(|| {
             store.get(12).unwrap();
         });
diff --git a/src/store/reader.rs b/src/store/reader.rs
index c6d0dc000..cedcfd28a 100644
--- a/src/store/reader.rs
+++ b/src/store/reader.rs
@@ -1,8 +1,8 @@
 use super::decompress;
 use super::skiplist::SkipList;
-use crate::common::BinarySerializable;
 use crate::common::VInt;
-use crate::directory::ReadOnlySource;
+use crate::common::{BinarySerializable, HasLen};
+use crate::directory::{FileSlice, OwnedBytes};
 use crate::schema::Document;
 use crate::space_usage::StoreSpaceUsage;
 use crate::DocId;
@@ -13,8 +13,8 @@ use std::mem::size_of;
 /// Reads document off tantivy's [`Store`](./index.html)
 #[derive(Clone)]
 pub struct StoreReader {
-    data: ReadOnlySource,
-    offset_index_source: ReadOnlySource,
+    data: FileSlice,
+    offset_index_file: OwnedBytes,
     current_block_offset: RefCell<usize>,
     current_block: RefCell<Vec<u8>>,
     max_doc: DocId,
@@ -22,19 +22,20 @@ pub struct StoreReader {
 
 impl StoreReader {
     /// Opens a store reader
-    pub fn from_source(data: ReadOnlySource) -> StoreReader {
-        let (data_source, offset_index_source, max_doc) = split_source(data);
-        StoreReader {
-            data: data_source,
-            offset_index_source,
+    // TODO rename open
+    pub fn open(store_file: FileSlice) -> io::Result<StoreReader> {
+        let (data_file, offset_index_file, max_doc) = split_file(store_file)?;
+        Ok(StoreReader {
+            data: data_file,
+            offset_index_file: offset_index_file.read_bytes()?,
             current_block_offset: RefCell::new(usize::max_value()),
             current_block: RefCell::new(Vec::new()),
             max_doc,
-        }
+        })
     }
 
     pub(crate) fn block_index(&self) -> SkipList<'_, u64> {
-        SkipList::from(self.offset_index_source.as_slice())
+        SkipList::from(self.offset_index_file.as_slice())
     }
 
     fn block_offset(&self, doc_id: DocId) -> (DocId, u64) {
@@ -44,23 +45,22 @@ impl StoreReader {
             .unwrap_or((0u32, 0u64))
     }
 
-    pub(crate) fn block_data(&self) -> &[u8] {
-        self.data.as_slice()
+    pub(crate) fn block_data(&self) -> io::Result<OwnedBytes> {
+        self.data.read_bytes()
     }
 
-    fn compressed_block(&self, addr: usize) -> &[u8] {
-        let total_buffer = self.data.as_slice();
-        let mut buffer = &total_buffer[addr..];
-        let block_len = u32::deserialize(&mut buffer).expect("") as usize;
-        &buffer[..block_len]
+    fn compressed_block(&self, addr: usize) -> io::Result<OwnedBytes> {
+        let (block_len_bytes, block_body) = self.data.slice_from(addr).split(4);
+        let block_len = u32::deserialize(&mut block_len_bytes.read_bytes()?)?;
+        block_body.slice_to(block_len as usize).read_bytes()
     }
 
     fn read_block(&self, block_offset: usize) -> io::Result<()> {
         if block_offset != *self.current_block_offset.borrow() {
             let mut current_block_mut = self.current_block.borrow_mut();
             current_block_mut.clear();
-            let compressed_block = self.compressed_block(block_offset);
-            decompress(compressed_block, &mut current_block_mut)?;
+            let compressed_block = self.compressed_block(block_offset)?;
+            decompress(compressed_block.as_slice(), &mut current_block_mut)?;
             *self.current_block_offset.borrow_mut() = block_offset;
         }
         Ok(())
@@ -89,21 +89,21 @@ impl StoreReader {
 
     /// Summarize total space usage of this store reader.
     pub fn space_usage(&self) -> StoreSpaceUsage {
-        StoreSpaceUsage::new(self.data.len(), self.offset_index_source.len())
+        StoreSpaceUsage::new(self.data.len(), self.offset_index_file.len())
     }
 }
 
-fn split_source(data: ReadOnlySource) -> (ReadOnlySource, ReadOnlySource, DocId) {
+fn split_file(data: FileSlice) -> io::Result<(FileSlice, FileSlice, DocId)> {
     let data_len = data.len();
     let footer_offset = data_len - size_of::<u64>() - size_of::<u32>();
-    let serialized_offset: ReadOnlySource = data.slice(footer_offset, data_len);
+    let serialized_offset: OwnedBytes = data.slice(footer_offset, data_len).read_bytes()?;
     let mut serialized_offset_buf = serialized_offset.as_slice();
-    let offset = u64::deserialize(&mut serialized_offset_buf).unwrap();
+    let offset = u64::deserialize(&mut serialized_offset_buf)?;
     let offset = offset as usize;
-    let max_doc = u32::deserialize(&mut serialized_offset_buf).unwrap();
-    (
+    let max_doc = u32::deserialize(&mut serialized_offset_buf)?;
+    Ok((
         data.slice(0, offset),
         data.slice(offset, footer_offset),
         max_doc,
-    )
+    ))
 }
diff --git a/src/store/writer.rs b/src/store/writer.rs
index 5ddda2c7f..ea1b69835 100644
--- a/src/store/writer.rs
+++ b/src/store/writer.rs
@@ -75,7 +75,8 @@ impl StoreWriter {
         let start_offset = self.writer.written_bytes() as u64;
 
         // just bulk write all of the block of the given reader.
-        self.writer.write_all(store_reader.block_data())?;
+        self.writer
+            .write_all(store_reader.block_data()?.as_slice())?;
 
         // concatenate the index of the `store_reader`, after translating
         // its start doc id and its start file offset.
diff --git a/src/termdict/mod.rs b/src/termdict/mod.rs
index fd1c4fa19..70136f4d2 100644
--- a/src/termdict/mod.rs
+++ b/src/termdict/mod.rs
@@ -36,9 +36,9 @@ pub use self::termdict::{TermDictionary, TermDictionaryBuilder};
 mod tests {
     use super::{TermDictionary, TermDictionaryBuilder, TermStreamer};
     use crate::core::Index;
-    use crate::directory::{Directory, RAMDirectory, ReadOnlySource};
+    use crate::directory::{Directory, FileSlice, RAMDirectory};
     use crate::postings::TermInfo;
-    use crate::schema::{Document, Schema, TEXT};
+    use crate::schema::{Schema, TEXT};
     use std::path::PathBuf;
     use std::str;
 
@@ -59,7 +59,7 @@ mod tests {
     }
 
     #[test]
-    fn test_term_ordinals() {
+    fn test_term_ordinals() -> crate::Result<()> {
         const COUNTRIES: [&'static str; 7] = [
             "San Marino",
             "Serbia",
@@ -72,42 +72,37 @@ mod tests {
         let mut directory = RAMDirectory::create();
         let path = PathBuf::from("TermDictionary");
         {
-            let write = directory.open_write(&path).unwrap();
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write).unwrap();
+            let write = directory.open_write(&path)?;
+            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
             for term in COUNTRIES.iter() {
-                term_dictionary_builder
-                    .insert(term.as_bytes(), &make_term_info(0u64))
-                    .unwrap();
+                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
             }
-            term_dictionary_builder.finish().unwrap();
+            term_dictionary_builder.finish()?;
         }
-        let source = directory.open_read(&path).unwrap();
-        let term_dict: TermDictionary = TermDictionary::from_source(&source);
+        let term_file = directory.open_read(&path)?;
+        let term_dict: TermDictionary = TermDictionary::open(term_file)?;
         for (term_ord, term) in COUNTRIES.iter().enumerate() {
             assert_eq!(term_dict.term_ord(term).unwrap(), term_ord as u64);
             let mut bytes = vec![];
             assert!(term_dict.ord_to_term(term_ord as u64, &mut bytes));
             assert_eq!(bytes, term.as_bytes());
         }
+        Ok(())
     }
 
     #[test]
-    fn test_term_dictionary_simple() {
+    fn test_term_dictionary_simple() -> crate::Result<()> {
         let mut directory = RAMDirectory::create();
         let path = PathBuf::from("TermDictionary");
         {
-            let write = directory.open_write(&path).unwrap();
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write).unwrap();
-            term_dictionary_builder
-                .insert("abc".as_bytes(), &make_term_info(34u64))
-                .unwrap();
-            term_dictionary_builder
-                .insert("abcd".as_bytes(), &make_term_info(346u64))
-                .unwrap();
-            term_dictionary_builder.finish().unwrap();
+            let write = directory.open_write(&path)?;
+            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
+            term_dictionary_builder.insert("abc".as_bytes(), &make_term_info(34u64))?;
+            term_dictionary_builder.insert("abcd".as_bytes(), &make_term_info(346u64))?;
+            term_dictionary_builder.finish()?;
         }
-        let source = directory.open_read(&path).unwrap();
-        let term_dict: TermDictionary = TermDictionary::from_source(&source);
+        let file = directory.open_read(&path)?;
+        let term_dict: TermDictionary = TermDictionary::open(file)?;
         assert_eq!(term_dict.get("abc").unwrap().doc_freq, 34u32);
         assert_eq!(term_dict.get("abcd").unwrap().doc_freq, 346u32);
         let mut stream = term_dict.stream();
@@ -130,43 +125,26 @@ mod tests {
             assert_eq!(stream.value().doc_freq, 346u32);
         }
         assert!(!stream.advance());
+        Ok(())
     }
 
     #[test]
-    fn test_term_iterator() {
+    fn test_term_iterator() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
         {
-            let mut index_writer = index.writer_for_tests().unwrap();
-            {
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "a b d f");
-                    index_writer.add_document(doc);
-                }
-                index_writer.commit().unwrap();
-            }
-            {
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "a b c d f");
-                    index_writer.add_document(doc);
-                }
-                index_writer.commit().unwrap();
-            }
-            {
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "e f");
-                    index_writer.add_document(doc);
-                }
-                index_writer.commit().unwrap();
-            }
+            let mut index_writer = index.writer_for_tests()?;
+            index_writer.add_document(doc!(text_field=>"a b d f"));
+            index_writer.commit()?;
+            index_writer.add_document(doc!(text_field=>"a b c d f"));
+            index_writer.commit()?;
+            index_writer.add_document(doc!(text_field => "e f"));
+            index_writer.commit()?;
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
 
-        let field_searcher = searcher.field(text_field);
+        let field_searcher = searcher.field(text_field)?;
         let mut term_it = field_searcher.terms();
         let mut term_string = String::new();
         while term_it.advance() {
@@ -174,10 +152,11 @@ mod tests {
             term_string.push_str(str::from_utf8(term_it.key()).expect("test"));
         }
         assert_eq!(&*term_string, "abcdef");
+        Ok(())
     }
 
     #[test]
-    fn test_term_dictionary_stream() {
+    fn test_term_dictionary_stream() -> crate::Result<()> {
         let ids: Vec<_> = (0u32..10_000u32)
             .map(|i| (format!("doc{:0>6}", i), i))
             .collect();
@@ -190,8 +169,8 @@ mod tests {
             }
             term_dictionary_builder.finish().unwrap()
         };
-        let source = ReadOnlySource::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::from_source(&source);
+        let term_file = FileSlice::new(buffer);
+        let term_dictionary: TermDictionary = TermDictionary::open(term_file)?;
         {
             let mut streamer = term_dictionary.stream();
             let mut i = 0;
@@ -203,28 +182,26 @@ mod tests {
             }
         }
 
-        let &(ref key, ref _v) = &ids[2047];
-        term_dictionary.get(key.as_bytes());
+        let &(ref key, ref val) = &ids[2047];
+        assert_eq!(
+            term_dictionary.get(key.as_bytes()),
+            Some(make_term_info(*val as u64))
+        );
+        Ok(())
     }
 
     #[test]
-    fn test_stream_high_range_prefix_suffix() {
+    fn test_stream_high_range_prefix_suffix() -> crate::Result<()> {
         let buffer: Vec<u8> = {
             let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
             // term requires more than 16bits
-            term_dictionary_builder
-                .insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))
-                .unwrap();
-            term_dictionary_builder
-                .insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))
-                .unwrap();
-            term_dictionary_builder
-                .insert("abr", &make_term_info(2))
-                .unwrap();
-            term_dictionary_builder.finish().unwrap()
+            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxy", &make_term_info(1))?;
+            term_dictionary_builder.insert("abcdefghijklmnopqrstuvwxyz", &make_term_info(2))?;
+            term_dictionary_builder.insert("abr", &make_term_info(2))?;
+            term_dictionary_builder.finish()?
         };
-        let source = ReadOnlySource::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::from_source(&source);
+        let term_dict_file = FileSlice::new(buffer);
+        let term_dictionary: TermDictionary = TermDictionary::open(term_dict_file)?;
         let mut kv_stream = term_dictionary.stream();
         assert!(kv_stream.advance());
         assert_eq!(kv_stream.key(), "abcdefghijklmnopqrstuvwxy".as_bytes());
@@ -235,10 +212,11 @@ mod tests {
         assert!(kv_stream.advance());
         assert_eq!(kv_stream.key(), "abr".as_bytes());
         assert!(!kv_stream.advance());
+        Ok(())
     }
 
     #[test]
-    fn test_stream_range() {
+    fn test_stream_range() -> crate::Result<()> {
         let ids: Vec<_> = (0u32..10_000u32)
             .map(|i| (format!("doc{:0>6}", i), i))
             .collect();
@@ -252,9 +230,9 @@ mod tests {
             term_dictionary_builder.finish().unwrap()
         };
 
-        let source = ReadOnlySource::from(buffer);
+        let file = FileSlice::new(buffer);
 
-        let term_dictionary: TermDictionary = TermDictionary::from_source(&source);
+        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
         {
             for i in (0..20).chain(6000..8_000) {
                 let &(ref target_key, _) = &ids[i];
@@ -305,10 +283,11 @@ mod tests {
                 }
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_empty_string() {
+    fn test_empty_string() -> crate::Result<()> {
         let buffer: Vec<u8> = {
             let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
             term_dictionary_builder
@@ -319,30 +298,29 @@ mod tests {
                 .unwrap();
             term_dictionary_builder.finish().unwrap()
         };
-        let source = ReadOnlySource::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::from_source(&source);
+        let file = FileSlice::new(buffer);
+        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
         let mut stream = term_dictionary.stream();
         assert!(stream.advance());
         assert!(stream.key().is_empty());
         assert!(stream.advance());
         assert_eq!(stream.key(), &[1u8]);
         assert!(!stream.advance());
+        Ok(())
     }
 
     #[test]
-    fn test_stream_range_boundaries() {
+    fn test_stream_range_boundaries() -> crate::Result<()> {
         let buffer: Vec<u8> = {
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(vec![]).unwrap();
+            let mut term_dictionary_builder = TermDictionaryBuilder::create(Vec::new())?;
             for i in 0u8..10u8 {
                 let number_arr = [i; 1];
-                term_dictionary_builder
-                    .insert(&number_arr, &make_term_info(i as u64))
-                    .unwrap();
+                term_dictionary_builder.insert(&number_arr, &make_term_info(i as u64))?;
             }
-            term_dictionary_builder.finish().unwrap()
+            term_dictionary_builder.finish()?
         };
-        let source = ReadOnlySource::from(buffer);
-        let term_dictionary: TermDictionary = TermDictionary::from_source(&source);
+        let file = FileSlice::new(buffer);
+        let term_dictionary: TermDictionary = TermDictionary::open(file)?;
 
         let value_list = |mut streamer: TermStreamer<'_>, backwards: bool| {
             let mut res: Vec<u32> = vec![];
@@ -430,10 +408,11 @@ mod tests {
                 .into_stream();
             assert_eq!(value_list(range, true), vec![0u32, 1u32, 2u32, 3u32, 4u32]);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_automaton_search() {
+    fn test_automaton_search() -> crate::Result<()> {
         use crate::query::DFAWrapper;
         use levenshtein_automata::LevenshteinAutomatonBuilder;
 
@@ -450,17 +429,15 @@ mod tests {
         let mut directory = RAMDirectory::create();
         let path = PathBuf::from("TermDictionary");
         {
-            let write = directory.open_write(&path).unwrap();
-            let mut term_dictionary_builder = TermDictionaryBuilder::create(write).unwrap();
+            let write = directory.open_write(&path)?;
+            let mut term_dictionary_builder = TermDictionaryBuilder::create(write)?;
             for term in COUNTRIES.iter() {
-                term_dictionary_builder
-                    .insert(term.as_bytes(), &make_term_info(0u64))
-                    .unwrap();
+                term_dictionary_builder.insert(term.as_bytes(), &make_term_info(0u64))?;
             }
-            term_dictionary_builder.finish().unwrap();
+            term_dictionary_builder.finish()?;
         }
-        let source = directory.open_read(&path).unwrap();
-        let term_dict: TermDictionary = TermDictionary::from_source(&source);
+        let file = directory.open_read(&path)?;
+        let term_dict: TermDictionary = TermDictionary::open(file)?;
 
         // We can now build an entire dfa.
         let lev_automaton_builder = LevenshteinAutomatonBuilder::new(2, true);
@@ -472,5 +449,6 @@ mod tests {
         assert!(range.advance());
         assert_eq!("Spain".as_bytes(), range.key());
         assert!(!range.advance());
+        Ok(())
     }
 }
diff --git a/src/termdict/term_info_store.rs b/src/termdict/term_info_store.rs
index cba4de2ca..b61c41251 100644
--- a/src/termdict/term_info_store.rs
+++ b/src/termdict/term_info_store.rs
@@ -1,8 +1,6 @@
-use crate::common::bitpacker::BitPacker;
 use crate::common::compute_num_bits;
-use crate::common::Endianness;
-use crate::common::{BinarySerializable, FixedSize};
-use crate::directory::ReadOnlySource;
+use crate::common::{bitpacker::BitPacker, BinarySerializable, FixedSize};
+use crate::directory::{FileSlice, OwnedBytes};
 use crate::postings::TermInfo;
 use crate::termdict::TermOrdinal;
 use byteorder::{ByteOrder, LittleEndian};
@@ -79,8 +77,8 @@ impl TermInfoBlockMeta {
 
 pub struct TermInfoStore {
     num_terms: usize,
-    block_meta_source: ReadOnlySource,
-    term_info_source: ReadOnlySource,
+    block_meta_bytes: OwnedBytes,
+    term_info_bytes: OwnedBytes,
 }
 
 fn extract_bits(data: &[u8], addr_bits: usize, num_bits: u8) -> u64 {
@@ -105,35 +103,35 @@ fn extract_bits(data: &[u8], addr_bits: usize, num_bits: u8) -> u64 {
 }
 
 impl TermInfoStore {
-    pub fn open(data: &ReadOnlySource) -> TermInfoStore {
-        let buffer = data.as_slice();
-        let len = Endianness::read_u64(&buffer[0..8]) as usize;
-        let num_terms = Endianness::read_u64(&buffer[8..16]) as usize;
-        let block_meta_source = data.slice(16, 16 + len);
-        let term_info_source = data.slice_from(16 + len);
-        TermInfoStore {
+    pub fn open(term_info_store_file: FileSlice) -> crate::Result<TermInfoStore> {
+        let (len_slice, main_slice) = term_info_store_file.split(16);
+        let mut bytes = len_slice.read_bytes()?;
+        let len = u64::deserialize(&mut bytes)? as usize;
+        let num_terms = u64::deserialize(&mut bytes)? as usize;
+        let (block_meta_file, term_info_file) = main_slice.split(len);
+        let term_info_bytes = term_info_file.read_bytes()?;
+        Ok(TermInfoStore {
             num_terms,
-            block_meta_source,
-            term_info_source,
-        }
+            block_meta_bytes: block_meta_file.read_bytes()?,
+            term_info_bytes,
+        })
     }
 
     pub fn get(&self, term_ord: TermOrdinal) -> TermInfo {
         let block_id = (term_ord as usize) / BLOCK_LEN;
-        let buffer = self.block_meta_source.as_slice();
+        let buffer = self.block_meta_bytes.as_slice();
         let mut block_data: &[u8] = &buffer[block_id * TermInfoBlockMeta::SIZE_IN_BYTES..];
         let term_info_block_data = TermInfoBlockMeta::deserialize(&mut block_data)
             .expect("Failed to deserialize terminfoblockmeta");
         let inner_offset = (term_ord as usize) % BLOCK_LEN;
         if inner_offset == 0 {
-            term_info_block_data.ref_term_info
-        } else {
-            let term_info_data = self.term_info_source.as_slice();
-            term_info_block_data.deserialize_term_info(
-                &term_info_data[term_info_block_data.offset as usize..],
-                inner_offset - 1,
-            )
+            return term_info_block_data.ref_term_info;
         }
+        let term_info_data = self.term_info_bytes.as_slice();
+        term_info_block_data.deserialize_term_info(
+            &term_info_data[term_info_block_data.offset as usize..],
+            inner_offset - 1,
+        )
     }
 
     pub fn num_terms(&self) -> usize {
@@ -263,7 +261,7 @@ mod tests {
     use crate::common::bitpacker::BitPacker;
     use crate::common::compute_num_bits;
     use crate::common::BinarySerializable;
-    use crate::directory::ReadOnlySource;
+    use crate::directory::FileSlice;
     use crate::postings::TermInfo;
 
     #[test]
@@ -309,7 +307,7 @@ mod tests {
     }
 
     #[test]
-    fn test_pack() {
+    fn test_pack() -> crate::Result<()> {
         let mut store_writer = TermInfoStoreWriter::new();
         let mut term_infos = vec![];
         for i in 0..1000 {
@@ -318,14 +316,15 @@ mod tests {
                 postings_offset: (i / 10) as u64,
                 positions_idx: (i * 7) as u64,
             };
-            store_writer.write_term_info(&term_info).unwrap();
+            store_writer.write_term_info(&term_info)?;
             term_infos.push(term_info);
         }
         let mut buffer = Vec::new();
-        store_writer.serialize(&mut buffer).unwrap();
-        let term_info_store = TermInfoStore::open(&ReadOnlySource::from(buffer));
+        store_writer.serialize(&mut buffer)?;
+        let term_info_store = TermInfoStore::open(FileSlice::new(buffer))?;
         for i in 0..1000 {
             assert_eq!(term_info_store.get(i as u64), term_infos[i]);
         }
+        Ok(())
     }
 }
diff --git a/src/termdict/termdict.rs b/src/termdict/termdict.rs
index 1330a11c3..9da4678d9 100644
--- a/src/termdict/termdict.rs
+++ b/src/termdict/termdict.rs
@@ -1,8 +1,8 @@
 use super::term_info_store::{TermInfoStore, TermInfoStoreWriter};
 use super::{TermStreamer, TermStreamerBuilder};
-use crate::common::BinarySerializable;
-use crate::common::CountingWriter;
-use crate::directory::ReadOnlySource;
+use crate::common::{BinarySerializable, CountingWriter};
+use crate::directory::{FileSlice, OwnedBytes};
+use crate::error::DataCorruption;
 use crate::postings::TermInfo;
 use crate::termdict::TermOrdinal;
 use once_cell::sync::Lazy;
@@ -86,17 +86,19 @@ where
     }
 }
 
-fn open_fst_index(source: ReadOnlySource) -> tantivy_fst::Map<ReadOnlySource> {
-    let fst = Fst::new(source).expect("FST data is corrupted");
-    tantivy_fst::Map::from(fst)
+fn open_fst_index(fst_file: FileSlice) -> crate::Result<tantivy_fst::Map<OwnedBytes>> {
+    let bytes = fst_file.read_bytes()?;
+    let fst = Fst::new(bytes)
+        .map_err(|err| DataCorruption::comment_only(format!("Fst data is corrupted: {:?}", err)))?;
+    Ok(tantivy_fst::Map::from(fst))
 }
 
-static EMPTY_DATA_SOURCE: Lazy<ReadOnlySource> = Lazy::new(|| {
+static EMPTY_TERM_DICT_FILE: Lazy<FileSlice> = Lazy::new(|| {
     let term_dictionary_data: Vec<u8> = TermDictionaryBuilder::create(Vec::<u8>::new())
         .expect("Creating a TermDictionaryBuilder in a Vec<u8> should never fail")
         .finish()
         .expect("Writing in a Vec<u8> should never fail");
-    ReadOnlySource::from(term_dictionary_data)
+    FileSlice::new(term_dictionary_data)
 });
 
 /// The term dictionary contains all of the terms in
@@ -106,31 +108,28 @@ static EMPTY_DATA_SOURCE: Lazy<ReadOnlySource> = Lazy::new(|| {
 /// respective `TermOrdinal`. The `TermInfoStore` then makes it
 /// possible to fetch the associated `TermInfo`.
 pub struct TermDictionary {
-    fst_index: tantivy_fst::Map<ReadOnlySource>,
+    fst_index: tantivy_fst::Map<OwnedBytes>,
     term_info_store: TermInfoStore,
 }
 
 impl TermDictionary {
-    /// Opens a `TermDictionary` given a data source.
-    pub fn from_source(source: &ReadOnlySource) -> Self {
-        let total_len = source.len();
-        let length_offset = total_len - 8;
-        let mut split_len_buffer: &[u8] = &source.as_slice()[length_offset..];
-        let footer_size = u64::deserialize(&mut split_len_buffer)
-            .expect("Deserializing 8 bytes should always work") as usize;
-        let split_len = length_offset - footer_size;
-        let fst_source = source.slice(0, split_len);
-        let values_source = source.slice(split_len, length_offset);
-        let fst_index = open_fst_index(fst_source);
-        TermDictionary {
+    /// Opens a `TermDictionary`.
+    pub fn open(file: FileSlice) -> crate::Result<Self> {
+        let (main_slice, footer_len_slice) = file.split_from_end(8);
+        let mut footer_len_bytes = footer_len_slice.read_bytes()?;
+        let footer_size = u64::deserialize(&mut footer_len_bytes)?;
+        let (fst_file_slice, values_file_slice) = main_slice.split_from_end(footer_size as usize);
+        let fst_index = open_fst_index(fst_file_slice)?;
+        let term_info_store = TermInfoStore::open(values_file_slice)?;
+        Ok(TermDictionary {
             fst_index,
-            term_info_store: TermInfoStore::open(&values_source),
-        }
+            term_info_store,
+        })
     }
 
     /// Creates an empty term dictionary which contains no terms.
     pub fn empty() -> Self {
-        TermDictionary::from_source(&*EMPTY_DATA_SOURCE)
+        TermDictionary::open(EMPTY_TERM_DICT_FILE.clone()).unwrap()
     }
 
     /// Returns the number of terms in the dictionary.
diff --git a/tests/failpoints/mod.rs b/tests/failpoints/mod.rs
index 658fadbc1..f3cfab714 100644
--- a/tests/failpoints/mod.rs
+++ b/tests/failpoints/mod.rs
@@ -40,17 +40,17 @@ fn test_failpoints_managed_directory_gc_if_delete_fails() {
 }
 
 #[test]
-fn test_write_commit_fails() {
+fn test_write_commit_fails() -> tantivy::Result<()> {
     let _fail_scenario_guard = fail::FailScenario::setup();
     let mut schema_builder = Schema::builder();
     let text_field = schema_builder.add_text_field("text", TEXT);
     let index = Index::create_in_ram(schema_builder.build());
 
-    let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+    let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
     for _ in 0..100 {
         index_writer.add_document(doc!(text_field => "a"));
     }
-    index_writer.commit().unwrap();
+    index_writer.commit()?;
     fail::cfg("RAMDirectory::atomic_write", "return(error_write_failed)").unwrap();
     for _ in 0..100 {
         index_writer.add_document(doc!(text_field => "b"));
@@ -59,8 +59,9 @@ fn test_write_commit_fails() {
 
     let num_docs_containing = |s: &str| {
         let term_a = Term::from_field_text(text_field, s);
-        index.reader().unwrap().searcher().doc_freq(&term_a)
+        index.reader()?.searcher().doc_freq(&term_a)
     };
-    assert_eq!(num_docs_containing("a"), 100);
-    assert_eq!(num_docs_containing("b"), 0);
+    assert_eq!(num_docs_containing("a")?, 100);
+    assert_eq!(num_docs_containing("b")?, 0);
+    Ok(())
 }