maildir: remove mmap feature

we're not using it and it simplifies the code a little to
remove it.

refs: https://github.com/KumoCorp/kumomta/issues/109

Cargo.lock

@@ -3566,7 +3566,6 @@ dependencies = [
  "chrono",
  "gethostname 0.5.0",
  "mailparsing",
- "memmap2",
  "percent-encoding",
  "tempfile",
  "walkdir",
@@ -3649,15 +3648,6 @@ version = "2.7.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
 
-[[package]]
-name = "memmap2"
-version = "0.9.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fd3f7eed9d3848f8b98834af67102b720745c4ec028fcd0aa0239277e7de374f"
-dependencies = [
- "libc",
-]
-
 [[package]]
 name = "memmem"
 version = "0.1.1"

Cargo.toml

@@ -113,7 +113,6 @@ mailparse = "0.14"
 maplit = "1.0"
 map_vec = "0.6"
 memchr = "2.5"
-memmap2 = "0.9"
 metrics = "0.24"
 metrics-prometheus = "0.8"
 metrics-tracing-context = "0.17"

crates/maildir/Cargo.toml

@@ -18,10 +18,6 @@ maintenance = { status = "passively-maintained" }
 chrono = {workspace=true, default-features=false}
 gethostname = {workspace=true}
 mailparsing = { path="../mailparsing" }
-memmap2 = { workspace = true, optional = true }
-
-[features]
-mmap = ["memmap2"]
 
 [dev-dependencies]
 percent-encoding = {workspace=true}

crates/maildir/src/lib.rs

@@ -74,10 +74,7 @@ impl From<&'static str> for MailEntryError {
 
 enum MailData {
     None,
-    #[cfg(not(feature = "mmap"))]
     Bytes(Vec<u8>),
-    #[cfg(feature = "mmap")]
-    File(memmap2::Mmap),
 }
 
 impl MailData {
@@ -91,10 +88,7 @@ impl MailData {
     fn data(&self) -> Option<&[u8]> {
         match self {
             Self::None => None,
-            #[cfg(not(feature = "mmap"))]
             MailData::Bytes(ref b) => Some(b),
-            #[cfg(feature = "mmap")]
-            MailData::File(ref m) => Some(m),
         }
     }
 }
@@ -118,20 +112,10 @@ impl MailEntry {
 
     fn read_data(&mut self) -> std::io::Result<()> {
         if self.data.is_none() {
-            #[cfg(feature = "mmap")]
-            {
-                let f = fs::File::open(&self.path)?;
-                let mmap = unsafe { memmap2::MmapOptions::new().map(&f)? };
-                self.data = MailData::File(mmap);
-            }
-
-            #[cfg(not(feature = "mmap"))]
-            {
-                let mut f = fs::File::open(&self.path)?;
-                let mut d = Vec::<u8>::new();
-                f.read_to_end(&mut d)?;
-                self.data = MailData::Bytes(d);
-            }
+            let mut f = fs::File::open(&self.path)?;
+            let mut d = Vec::<u8>::new();
+            f.read_to_end(&mut d)?;
+            self.data = MailData::Bytes(d);
         }
         Ok(())
     }