Added memmap version.

Cargo.toml

@@ -7,5 +7,6 @@ edition = "2018"
 [dependencies]
 bzip2 = "0.4"
 flate2 = "1.0"
+memmap = "0.7"
 mime = "0.3"
 mime_guess = "2.0"

src/lib.rs

@@ -150,3 +150,76 @@ pub mod bufread {
         }
     }
 }
+
+pub mod memmap {
+    use std::fs::File;
+    use std::io::{Cursor, Read, Seek, SeekFrom};
+    use std::path::Path;
+
+    use bzip2::read::BzDecoder;
+    use flate2::read::GzDecoder;
+    use memmap::{Mmap, MmapOptions};
+
+    pub enum MmapDecoder {
+        Raw(Cursor<Mmap>),
+        Gz(GzDecoder<Cursor<Mmap>>),
+        Bz(BzDecoder<Cursor<Mmap>>),
+    }
+
+    impl MmapDecoder {
+        pub fn open<P>(path: P) -> Result<MmapDecoder, std::io::Error>
+        where
+            P: AsRef<Path>,
+        {
+            let file = File::open(&path)?;
+            let mmap = unsafe { MmapOptions::new().map(&file)? };
+            let cursor = Cursor::new(mmap);
+
+            Ok(match mime_guess::from_path(path).first_raw() {
+                Some("application/x-gzip") => MmapDecoder::Gz(GzDecoder::new(cursor)),
+                Some("application/x-bzip2") => MmapDecoder::Bz(BzDecoder::new(cursor)),
+                _ => MmapDecoder::Raw(cursor),
+            })
+        }
+
+        #[inline]
+        pub fn stream_len(&mut self) -> std::io::Result<u64> {
+            let file = match self {
+                MmapDecoder::Raw(file) => file,
+                MmapDecoder::Gz(file) => file.get_mut(),
+                MmapDecoder::Bz(file) => file.get_mut(),
+            };
+
+            let old_pos = file.seek(SeekFrom::Current(0))?;
+            let len = file.seek(SeekFrom::End(0))?;
+
+            if old_pos != len {
+                file.seek(SeekFrom::Start(old_pos))?;
+            }
+
+            Ok(len)
+        }
+
+        #[inline]
+        pub fn stream_position(&mut self) -> std::io::Result<u64> {
+            let file = match self {
+                MmapDecoder::Raw(file) => file,
+                MmapDecoder::Gz(file) => file.get_mut(),
+                MmapDecoder::Bz(file) => file.get_mut(),
+            };
+
+            file.seek(SeekFrom::Current(0))
+        }
+    }
+
+    impl Read for MmapDecoder {
+        #[inline]
+        fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+            match self {
+                MmapDecoder::Raw(file) => file.read(buf),
+                MmapDecoder::Gz(file) => file.read(buf),
+                MmapDecoder::Bz(file) => file.read(buf),
+            }
+        }
+    }
+}