Eliminate dependency from pageserver_api to postgres_ffi (#12273)

Introduce a separate `postgres_ffi_types` crate which contains a few
types and functions that were used in the API. `postgres_ffi_types` is a
much small crate than `postgres_ffi`, and it doesn't depend on bindgen
or the Postgres C headers.

Move NeonWalRecord and Value types to wal_decoder crate. They are only
used in the pageserver-safekeeper "ingest" API. The rest of the ingest
API types are defined in wal_decoder, so move these there as well.

libs/wal_decoder/src/models/value.rs

@@ -0,0 +1,257 @@
+//! This module defines the value type used by the storage engine.
+//!
+//! A [`Value`] represents either a completely new value for one Key ([`Value::Image`]),
+//! or a "delta" of how to get from previous version of the value to the new one
+//! ([`Value::WalRecord`]])
+//!
+//! Note that the [`Value`] type is used for the permananent storage format, so any
+//! changes to it must be backwards compatible.
+
+use bytes::Bytes;
+use serde::{Deserialize, Serialize};
+
+use crate::models::record::NeonWalRecord;
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+pub enum Value {
+    /// An Image value contains a full copy of the value
+    Image(Bytes),
+    /// A WalRecord value contains a WAL record that needs to be
+    /// replayed get the full value. Replaying the WAL record
+    /// might need a previous version of the value (if will_init()
+    /// returns false), or it may be replayed stand-alone (true).
+    WalRecord(NeonWalRecord),
+}
+
+impl Value {
+    #[inline(always)]
+    pub fn is_image(&self) -> bool {
+        matches!(self, Value::Image(_))
+    }
+
+    #[inline(always)]
+    pub fn will_init(&self) -> bool {
+        match self {
+            Value::Image(_) => true,
+            Value::WalRecord(rec) => rec.will_init(),
+        }
+    }
+
+    #[inline(always)]
+    pub fn estimated_size(&self) -> usize {
+        match self {
+            Value::Image(image) => image.len(),
+            Value::WalRecord(NeonWalRecord::AuxFile {
+                content: Some(content),
+                ..
+            }) => content.len(),
+            Value::WalRecord(NeonWalRecord::Postgres { rec, .. }) => rec.len(),
+            Value::WalRecord(NeonWalRecord::ClogSetAborted { xids }) => xids.len() * 4,
+            Value::WalRecord(NeonWalRecord::ClogSetCommitted { xids, .. }) => xids.len() * 4,
+            Value::WalRecord(NeonWalRecord::MultixactMembersCreate { members, .. }) => {
+                members.len() * 8
+            }
+            _ => 8192, /* use image size as the estimation */
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum InvalidInput {
+    TooShortValue,
+    TooShortPostgresRecord,
+}
+
+/// We could have a ValueRef where everything is `serde(borrow)`. Before implementing that, lets
+/// use this type for querying if a slice looks some particular way.
+pub struct ValueBytes;
+
+impl ValueBytes {
+    #[inline(always)]
+    pub fn will_init(raw: &[u8]) -> Result<bool, InvalidInput> {
+        if raw.len() < 12 {
+            return Err(InvalidInput::TooShortValue);
+        }
+
+        let value_discriminator = &raw[0..4];
+
+        if value_discriminator == [0, 0, 0, 0] {
+            // Value::Image always initializes
+            return Ok(true);
+        }
+
+        if value_discriminator != [0, 0, 0, 1] {
+            // not a Value::WalRecord(..)
+            return Ok(false);
+        }
+
+        let walrecord_discriminator = &raw[4..8];
+
+        if walrecord_discriminator != [0, 0, 0, 0] {
+            // only NeonWalRecord::Postgres can have will_init
+            return Ok(false);
+        }
+
+        if raw.len() < 17 {
+            return Err(InvalidInput::TooShortPostgresRecord);
+        }
+
+        Ok(raw[8] == 1)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use bytes::Bytes;
+    use utils::bin_ser::BeSer;
+
+    use super::*;
+
+    macro_rules! roundtrip {
+        ($orig:expr, $expected:expr) => {{
+            let orig: Value = $orig;
+
+            let actual = Value::ser(&orig).unwrap();
+            let expected: &[u8] = &$expected;
+
+            assert_eq!(utils::Hex(&actual), utils::Hex(expected));
+
+            let deser = Value::des(&actual).unwrap();
+
+            assert_eq!(orig, deser);
+        }};
+    }
+
+    #[test]
+    fn image_roundtrip() {
+        let image = Bytes::from_static(b"foobar");
+        let image = Value::Image(image);
+
+        #[rustfmt::skip]
+        let expected = [
+            // top level discriminator of 4 bytes
+            0x00, 0x00, 0x00, 0x00,
+            // 8 byte length
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x06,
+            // foobar
+            0x66, 0x6f, 0x6f, 0x62, 0x61, 0x72
+        ];
+
+        roundtrip!(image, expected);
+
+        assert!(ValueBytes::will_init(&expected).unwrap());
+    }
+
+    #[test]
+    fn walrecord_postgres_roundtrip() {
+        let rec = NeonWalRecord::Postgres {
+            will_init: true,
+            rec: Bytes::from_static(b"foobar"),
+        };
+        let rec = Value::WalRecord(rec);
+
+        #[rustfmt::skip]
+        let expected = [
+            // flattened discriminator of total 8 bytes
+            0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+            // will_init
+            0x01,
+            // 8 byte length
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x06,
+            // foobar
+            0x66, 0x6f, 0x6f, 0x62, 0x61, 0x72
+        ];
+
+        roundtrip!(rec, expected);
+
+        assert!(ValueBytes::will_init(&expected).unwrap());
+    }
+
+    #[test]
+    fn bytes_inspection_too_short_image() {
+        let rec = Value::Image(Bytes::from_static(b""));
+
+        #[rustfmt::skip]
+        let expected = [
+            // top level discriminator of 4 bytes
+            0x00, 0x00, 0x00, 0x00,
+            // 8 byte length
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        ];
+
+        roundtrip!(rec, expected);
+
+        assert!(ValueBytes::will_init(&expected).unwrap());
+        assert_eq!(expected.len(), 12);
+        for len in 0..12 {
+            assert_eq!(
+                ValueBytes::will_init(&expected[..len]).unwrap_err(),
+                InvalidInput::TooShortValue
+            );
+        }
+    }
+
+    #[test]
+    fn bytes_inspection_too_short_postgres_record() {
+        let rec = NeonWalRecord::Postgres {
+            will_init: false,
+            rec: Bytes::from_static(b""),
+        };
+        let rec = Value::WalRecord(rec);
+
+        #[rustfmt::skip]
+        let expected = [
+            // flattened discriminator of total 8 bytes
+            0x00, 0x00, 0x00, 0x01,
+            0x00, 0x00, 0x00, 0x00,
+            // will_init
+            0x00,
+            // 8 byte length
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        ];
+
+        roundtrip!(rec, expected);
+
+        assert!(!ValueBytes::will_init(&expected).unwrap());
+        assert_eq!(expected.len(), 17);
+        for len in 12..17 {
+            assert_eq!(
+                ValueBytes::will_init(&expected[..len]).unwrap_err(),
+                InvalidInput::TooShortPostgresRecord
+            )
+        }
+        for len in 0..12 {
+            assert_eq!(
+                ValueBytes::will_init(&expected[..len]).unwrap_err(),
+                InvalidInput::TooShortValue
+            )
+        }
+    }
+
+    #[test]
+    fn clear_visibility_map_flags_example() {
+        let rec = NeonWalRecord::ClearVisibilityMapFlags {
+            new_heap_blkno: Some(0x11),
+            old_heap_blkno: None,
+            flags: 0x03,
+        };
+        let rec = Value::WalRecord(rec);
+
+        #[rustfmt::skip]
+        let expected = [
+            // discriminators
+            0x00, 0x00, 0x00, 0x01,
+            0x00, 0x00, 0x00, 0x01,
+            // Some == 1 followed by 4 bytes
+            0x01, 0x00, 0x00, 0x00, 0x11,
+            // None == 0
+            0x00,
+            // flags
+            0x03
+        ];
+
+        roundtrip!(rec, expected);
+
+        assert!(!ValueBytes::will_init(&expected).unwrap());
+    }
+}