vendor/snap/src/read.rs - toolchain/rustc - Git at Google

 /*!
 This module provides two `std::io::Read` implementations:

 * [`read::FrameDecoder`](struct.FrameDecoder.html)
   wraps another `std::io::Read` implemenation, and decompresses data encoded
   using the Snappy frame format. Use this if you have a compressed data source
   and wish to read it as uncompressed data.
 * [`read::FrameEncoder`](struct.FrameEncoder.html)
   wraps another `std::io::Read` implemenation, and compresses data encoded
   using the Snappy frame format. Use this if you have uncompressed data source
   and wish to read it as compressed data.

 Typically, `read::FrameDecoder` is the version that you'll want.
 */

 use std::cmp;
 use std::fmt;
 use std::io;

 use crate::bytes;
 use crate::compress::Encoder;
 use crate::crc32::CheckSummer;
 use crate::decompress::{decompress_len, Decoder};
 use crate::error::Error;
 use crate::frame::{
     compress_frame, ChunkType, CHUNK_HEADER_AND_CRC_SIZE,
     MAX_COMPRESS_BLOCK_SIZE, STREAM_BODY, STREAM_IDENTIFIER,
 };
 use crate::MAX_BLOCK_SIZE;

 /// The maximum size of a compressed block, including the header and stream
 /// identifier, that can be emitted by FrameEncoder.
 const MAX_READ_FRAME_ENCODER_BLOCK_SIZE: usize = STREAM_IDENTIFIER.len()
     + CHUNK_HEADER_AND_CRC_SIZE
     + MAX_COMPRESS_BLOCK_SIZE;

 /// A reader for decompressing a Snappy stream.
 ///
 /// This `FrameDecoder` wraps any other reader that implements `std::io::Read`.
 /// Bytes read from this reader are decompressed using the
 /// [Snappy frame format](https://github.com/google/snappy/blob/master/framing_format.txt)
 /// (file extension `sz`, MIME type `application/x-snappy-framed`).
 ///
 /// This reader can potentially make many small reads from the underlying
 /// stream depending on its format, therefore, passing in a buffered reader
 /// may be beneficial.
 pub struct FrameDecoder<R: io::Read> {
     /// The underlying reader.
     r: R,
     /// A Snappy decoder that we reuse that does the actual block based
     /// decompression.
     dec: Decoder,
     /// A CRC32 checksummer that is configured to either use the portable
     /// fallback version or the SSE4.2 accelerated version when the right CPU
     /// features are available.
     checksummer: CheckSummer,
     /// The compressed bytes buffer, taken from the underlying reader.
     src: Vec<u8>,
     /// The decompressed bytes buffer. Bytes are decompressed from src to dst
     /// before being passed back to the caller.
     dst: Vec<u8>,
     /// Index into dst: starting point of bytes not yet given back to caller.
     dsts: usize,
     /// Index into dst: ending point of bytes not yet given back to caller.
     dste: usize,
     /// Whether we've read the special stream header or not.
     read_stream_ident: bool,
 }

 impl<R: io::Read> FrameDecoder<R> {
     /// Create a new reader for streaming Snappy decompression.
     pub fn new(rdr: R) -> FrameDecoder<R> {
         FrameDecoder {
             r: rdr,
             dec: Decoder::new(),
             checksummer: CheckSummer::new(),
             src: vec![0; MAX_COMPRESS_BLOCK_SIZE],
             dst: vec![0; MAX_BLOCK_SIZE],
             dsts: 0,
             dste: 0,
             read_stream_ident: false,
         }
     }

     /// Gets a reference to the underlying reader in this decoder.
     pub fn get_ref(&self) -> &R {
         &self.r
     }

     /// Gets a mutable reference to the underlying reader in this decoder.
     ///
     /// Note that mutation of the stream may result in surprising results if
     /// this decoder is continued to be used.
     pub fn get_mut(&mut self) -> &mut R {
         &mut self.r
     }

     /// Gets the underlying reader of this decoder.
     pub fn into_inner(self) -> R {
         self.r
     }
 }

 impl<R: io::Read> io::Read for FrameDecoder<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         macro_rules! fail {
             ($err:expr) => {
                 return Err(io::Error::from($err))
             };
         }
         loop {
             if self.dsts < self.dste {
                 let len = cmp::min(self.dste - self.dsts, buf.len());
                 let dste = self.dsts.checked_add(len).unwrap();
                 buf[0..len].copy_from_slice(&self.dst[self.dsts..dste]);
                 self.dsts = dste;
                 return Ok(len);
             }
             if !read_exact_eof(&mut self.r, &mut self.src[0..4])? {
                 return Ok(0);
             }
             let ty = ChunkType::from_u8(self.src[0]);
             if !self.read_stream_ident {
                 if ty != Ok(ChunkType::Stream) {
                     fail!(Error::StreamHeader { byte: self.src[0] });
                 }
                 self.read_stream_ident = true;
             }
             let len64 = bytes::read_u24_le(&self.src[1..]) as u64;
             if len64 > self.src.len() as u64 {
                 fail!(Error::UnsupportedChunkLength {
                     len: len64,
                     header: false,
                 });
             }
             let len = len64 as usize;
             match ty {
                 Err(b) if 0x02 <= b && b <= 0x7F => {
                     // Spec says that chunk types 0x02-0x7F are reserved and
                     // conformant decoders must return an error.
                     fail!(Error::UnsupportedChunkType { byte: b });
                 }
                 Err(b) if 0x80 <= b && b <= 0xFD => {
                     // Spec says that chunk types 0x80-0xFD are reserved but
                     // skippable.
                     self.r.read_exact(&mut self.src[0..len])?;
                 }
                 Err(b) => {
                     // Can never happen. 0x02-0x7F and 0x80-0xFD are handled
                     // above in the error case. That leaves 0x00, 0x01, 0xFE
                     // and 0xFF, each of which correspond to one of the four
                     // defined chunk types.
                     unreachable!("BUG: unhandled chunk type: {}", b);
                 }
                 Ok(ChunkType::Padding) => {
                     // Just read and move on.
                     self.r.read_exact(&mut self.src[0..len])?;
                 }
                 Ok(ChunkType::Stream) => {
                     if len != STREAM_BODY.len() {
                         fail!(Error::UnsupportedChunkLength {
                             len: len64,
                             header: true,
                         })
                     }
                     self.r.read_exact(&mut self.src[0..len])?;
                     if &self.src[0..len] != STREAM_BODY {
                         fail!(Error::StreamHeaderMismatch {
                             bytes: self.src[0..len].to_vec(),
                         });
                     }
                 }
                 Ok(ChunkType::Uncompressed) => {
                     if len < 4 {
                         fail!(Error::UnsupportedChunkLength {
                             len: len as u64,
                             header: false,
                         });
                     }
                     let expected_sum = bytes::io_read_u32_le(&mut self.r)?;
                     let n = len - 4;
                     if n > self.dst.len() {
                         fail!(Error::UnsupportedChunkLength {
                             len: n as u64,
                             header: false,
                         });
                     }
                     self.r.read_exact(&mut self.dst[0..n])?;
                     let got_sum =
                         self.checksummer.crc32c_masked(&self.dst[0..n]);
                     if expected_sum != got_sum {
                         fail!(Error::Checksum {
                             expected: expected_sum,
                             got: got_sum,
                         });
                     }
                     self.dsts = 0;
                     self.dste = n;
                 }
                 Ok(ChunkType::Compressed) => {
                     if len < 4 {
                         fail!(Error::UnsupportedChunkLength {
                             len: len as u64,
                             header: false,
                         });
                     }
                     let expected_sum = bytes::io_read_u32_le(&mut self.r)?;
                     let sn = len - 4;
                     if sn > self.src.len() {
                         fail!(Error::UnsupportedChunkLength {
                             len: len64,
                             header: false,
                         });
                     }
                     self.r.read_exact(&mut self.src[0..sn])?;
                     let dn = decompress_len(&self.src)?;
                     if dn > self.dst.len() {
                         fail!(Error::UnsupportedChunkLength {
                             len: dn as u64,
                             header: false,
                         });
                     }
                     self.dec
                         .decompress(&self.src[0..sn], &mut self.dst[0..dn])?;
                     let got_sum =
                         self.checksummer.crc32c_masked(&self.dst[0..dn]);
                     if expected_sum != got_sum {
                         fail!(Error::Checksum {
                             expected: expected_sum,
                             got: got_sum,
                         });
                     }
                     self.dsts = 0;
                     self.dste = dn;
                 }
             }
         }
     }
 }

 impl<R: fmt::Debug + io::Read> fmt::Debug for FrameDecoder<R> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("FrameDecoder")
             .field("r", &self.r)
             .field("dec", &self.dec)
             .field("checksummer", &self.checksummer)
             .field("src", &"[...]")
             .field("dst", &"[...]")
             .field("dsts", &self.dsts)
             .field("dste", &self.dste)
             .field("read_stream_ident", &self.read_stream_ident)
             .finish()
     }
 }

 /// A reader for compressing data using snappy as it is read.
 ///
 /// This `FrameEncoder` wraps any other reader that implements `std::io::Read`.
 /// Bytes read from this reader are compressed using the
 /// [Snappy frame format](https://github.com/google/snappy/blob/master/framing_format.txt)
 /// (file extension `sz`, MIME type `application/x-snappy-framed`).
 ///
 /// Usually you'll want
 /// [`read::FrameDecoder`](struct.FrameDecoder.html)
 /// (for decompressing while reading) or
 /// [`write::FrameEncoder`](../write/struct.FrameEncoder.html)
 /// (for compressing while writing) instead.
 ///
 /// Unlike `FrameDecoder`, this will attempt to make large reads roughly
 /// equivalent to the size of a single Snappy block. Therefore, callers may not
 /// benefit from using a buffered reader.
 pub struct FrameEncoder<R: io::Read> {
     /// Internally, we split `FrameEncoder` in two to keep the borrow checker
     /// happy. The `inner` member contains everything that `read_frame` needs
     /// to fetch a frame's worth of data and compress it.
     inner: Inner<R>,
     /// Data that we've encoded and are ready to return to our caller.
     dst: Vec<u8>,
     /// Starting point of bytes in `dst` not yet given back to the caller.
     dsts: usize,
     /// Ending point of bytes in `dst` that we want to give to our caller.
     dste: usize,
 }

 struct Inner<R: io::Read> {
     /// The underlying data source.
     r: R,
     /// An encoder that we reuse that does the actual block based compression.
     enc: Encoder,
     /// A CRC32 checksummer that is configured to either use the portable
     /// fallback version or the SSE4.2 accelerated version when the right CPU
     /// features are available.
     checksummer: CheckSummer,
     /// Data taken from the underlying `r`, and not yet compressed.
     src: Vec<u8>,
     /// Have we written the standard snappy header to `dst` yet?
     wrote_stream_ident: bool,
 }

 impl<R: io::Read> FrameEncoder<R> {
     /// Create a new reader for streaming Snappy compression.
     pub fn new(rdr: R) -> FrameEncoder<R> {
         FrameEncoder {
             inner: Inner {
                 r: rdr,
                 enc: Encoder::new(),
                 checksummer: CheckSummer::new(),
                 src: vec![0; MAX_BLOCK_SIZE],
                 wrote_stream_ident: false,
             },
             dst: vec![0; MAX_READ_FRAME_ENCODER_BLOCK_SIZE],
             dsts: 0,
             dste: 0,
         }
     }

     /// Gets a reference to the underlying reader in this decoder.
     pub fn get_ref(&self) -> &R {
         &self.inner.r
     }

     /// Gets a mutable reference to the underlying reader in this decoder.
     ///
     /// Note that mutation of the stream may result in surprising results if
     /// this encoder is continued to be used.
     pub fn get_mut(&mut self) -> &mut R {
         &mut self.inner.r
     }

     /// Read previously compressed data from `self.dst`, returning the number of
     /// bytes read. If `self.dst` is empty, returns 0.
     fn read_from_dst(&mut self, buf: &mut [u8]) -> usize {
         let available_bytes = self.dste - self.dsts;
         let count = cmp::min(available_bytes, buf.len());
         buf[..count].copy_from_slice(&self.dst[self.dsts..self.dsts + count]);
         self.dsts += count;
         count
     }
 }

 impl<R: io::Read> io::Read for FrameEncoder<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         // Try reading previously compressed bytes from our `dst` buffer, if
         // any.
         let count = self.read_from_dst(buf);

         if count > 0 {
             // We had some bytes in our `dst` buffer that we used.
             Ok(count)
         } else if buf.len() >= MAX_READ_FRAME_ENCODER_BLOCK_SIZE {
             // Our output `buf` is big enough that we can directly write into
             // it, so bypass `dst` entirely.
             self.inner.read_frame(buf)
         } else {
             // We need to refill `self.dst`, and then return some bytes from
             // that.
             let count = self.inner.read_frame(&mut self.dst)?;
             self.dsts = 0;
             self.dste = count;
             Ok(self.read_from_dst(buf))
         }
     }
 }

 impl<R: io::Read> Inner<R> {
     /// Read from `self.r`, and create a new frame, writing it to `dst`, which
     /// must be at least `MAX_READ_FRAME_ENCODER_BLOCK_SIZE` bytes in size.
     fn read_frame(&mut self, dst: &mut [u8]) -> io::Result<usize> {
         debug_assert!(dst.len() >= MAX_READ_FRAME_ENCODER_BLOCK_SIZE);

         // We make one read to the underlying reader. If the underlying reader
         // doesn't fill the buffer but there are still bytes to be read, then
         // compression won't be optimal. The alternative would be to block
         // until our buffer is maximally full (or we see EOF), but this seems
         // more surprising. In general, io::Read implementations should try to
         // fill the caller's buffer as much as they can, so this seems like the
         // better choice.
         let nread = self.r.read(&mut self.src)?;
         if nread == 0 {
             return Ok(0);
         }

         // If we haven't yet written the stream header to `dst`, write it.
         let mut dst_write_start = 0;
         if !self.wrote_stream_ident {
             dst[0..STREAM_IDENTIFIER.len()].copy_from_slice(STREAM_IDENTIFIER);
             dst_write_start += STREAM_IDENTIFIER.len();
             self.wrote_stream_ident = true;
         }

         // Reserve space for our chunk header. We need to use `split_at_mut` so
         // that we can get two mutable slices pointing at non-overlapping parts
         // of `dst`.
         let (chunk_header, remaining_dst) =
             dst[dst_write_start..].split_at_mut(CHUNK_HEADER_AND_CRC_SIZE);
         dst_write_start += CHUNK_HEADER_AND_CRC_SIZE;

         // Compress our frame if possible, telling `compress_frame` to always
         // put the output in `dst`.
         let frame_data = compress_frame(
             &mut self.enc,
             self.checksummer,
             &self.src[..nread],
             chunk_header,
             remaining_dst,
             true,
         )?;
         Ok(dst_write_start + frame_data.len())
     }
 }

 impl<R: fmt::Debug + io::Read> fmt::Debug for FrameEncoder<R> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("FrameEncoder")
             .field("inner", &self.inner)
             .field("dst", &"[...]")
             .field("dsts", &self.dsts)
             .field("dste", &self.dste)
             .finish()
     }
 }

 impl<R: fmt::Debug + io::Read> fmt::Debug for Inner<R> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Inner")
             .field("r", &self.r)
             .field("enc", &self.enc)
             .field("checksummer", &self.checksummer)
             .field("src", &"[...]")
             .field("wrote_stream_ident", &self.wrote_stream_ident)
             .finish()
     }
 }

 // read_exact_eof is like Read::read_exact, except it detects EOF
 // and returns Ok(false) instead of an error.
 //
 // If buf was read successfully, it returns Ok(true).
 fn read_exact_eof<R: io::Read>(
     rdr: &mut R,
     buf: &mut [u8],
 ) -> io::Result<bool> {
     match rdr.read(buf) {
         // EOF
         Ok(0) => Ok(false),
         // Read everything w/ the read call
         Ok(i) if i == buf.len() => Ok(true),
         // There's some bytes left to fill, which can be deferred to read_exact
         Ok(i) => {
             rdr.read_exact(&mut buf[i..])?;
             Ok(true)
         }
         Err(e) => Err(e),
     }
 }
	/*!
	This module provides two `std::io::Read` implementations:

	* [`read::FrameDecoder`](struct.FrameDecoder.html)
	wraps another `std::io::Read` implemenation, and decompresses data encoded
	using the Snappy frame format. Use this if you have a compressed data source
	and wish to read it as uncompressed data.
	* [`read::FrameEncoder`](struct.FrameEncoder.html)
	wraps another `std::io::Read` implemenation, and compresses data encoded
	using the Snappy frame format. Use this if you have uncompressed data source
	and wish to read it as compressed data.

	Typically, `read::FrameDecoder` is the version that you'll want.
	*/

	use std::cmp;
	use std::fmt;
	use std::io;

	use crate::bytes;
	use crate::compress::Encoder;
	use crate::crc32::CheckSummer;
	use crate::decompress::{decompress_len, Decoder};
	use crate::error::Error;
	use crate::frame::{
	compress_frame, ChunkType, CHUNK_HEADER_AND_CRC_SIZE,
	MAX_COMPRESS_BLOCK_SIZE, STREAM_BODY, STREAM_IDENTIFIER,
	};
	use crate::MAX_BLOCK_SIZE;

	/// The maximum size of a compressed block, including the header and stream
	/// identifier, that can be emitted by FrameEncoder.
	const MAX_READ_FRAME_ENCODER_BLOCK_SIZE: usize = STREAM_IDENTIFIER.len()
	+ CHUNK_HEADER_AND_CRC_SIZE
	+ MAX_COMPRESS_BLOCK_SIZE;

	/// A reader for decompressing a Snappy stream.
	///
	/// This `FrameDecoder` wraps any other reader that implements `std::io::Read`.
	/// Bytes read from this reader are decompressed using the
	/// [Snappy frame format](https://github.com/google/snappy/blob/master/framing_format.txt)
	/// (file extension `sz`, MIME type `application/x-snappy-framed`).
	///
	/// This reader can potentially make many small reads from the underlying
	/// stream depending on its format, therefore, passing in a buffered reader
	/// may be beneficial.
	pub struct FrameDecoder<R: io::Read> {
	/// The underlying reader.
	r: R,
	/// A Snappy decoder that we reuse that does the actual block based
	/// decompression.
	dec: Decoder,
	/// A CRC32 checksummer that is configured to either use the portable
	/// fallback version or the SSE4.2 accelerated version when the right CPU
	/// features are available.
	checksummer: CheckSummer,
	/// The compressed bytes buffer, taken from the underlying reader.
	src: Vec<u8>,
	/// The decompressed bytes buffer. Bytes are decompressed from src to dst
	/// before being passed back to the caller.
	dst: Vec<u8>,
	/// Index into dst: starting point of bytes not yet given back to caller.
	dsts: usize,
	/// Index into dst: ending point of bytes not yet given back to caller.
	dste: usize,
	/// Whether we've read the special stream header or not.
	read_stream_ident: bool,
	}

	impl<R: io::Read> FrameDecoder<R> {
	/// Create a new reader for streaming Snappy decompression.
	pub fn new(rdr: R) -> FrameDecoder<R> {
	FrameDecoder {
	r: rdr,
	dec: Decoder::new(),
	checksummer: CheckSummer::new(),
	src: vec![0; MAX_COMPRESS_BLOCK_SIZE],
	dst: vec![0; MAX_BLOCK_SIZE],
	dsts: 0,
	dste: 0,
	read_stream_ident: false,
	}
	}

	/// Gets a reference to the underlying reader in this decoder.
	pub fn get_ref(&self) -> &R {
	&self.r
	}

	/// Gets a mutable reference to the underlying reader in this decoder.
	///
	/// Note that mutation of the stream may result in surprising results if
	/// this decoder is continued to be used.
	pub fn get_mut(&mut self) -> &mut R {
	&mut self.r
	}

	/// Gets the underlying reader of this decoder.
	pub fn into_inner(self) -> R {
	self.r
	}
	}

	impl<R: io::Read> io::Read for FrameDecoder<R> {
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	macro_rules! fail {
	($err:expr) => {
	return Err(io::Error::from($err))
	};
	}
	loop {
	if self.dsts < self.dste {
	let len = cmp::min(self.dste - self.dsts, buf.len());
	let dste = self.dsts.checked_add(len).unwrap();
	buf[0..len].copy_from_slice(&self.dst[self.dsts..dste]);
	self.dsts = dste;
	return Ok(len);
	}
	if !read_exact_eof(&mut self.r, &mut self.src[0..4])? {
	return Ok(0);
	}
	let ty = ChunkType::from_u8(self.src[0]);
	if !self.read_stream_ident {
	if ty != Ok(ChunkType::Stream) {
	fail!(Error::StreamHeader { byte: self.src[0] });
	}
	self.read_stream_ident = true;
	}
	let len64 = bytes::read_u24_le(&self.src[1..]) as u64;
	if len64 > self.src.len() as u64 {
	fail!(Error::UnsupportedChunkLength {
	len: len64,
	header: false,
	});
	}
	let len = len64 as usize;
	match ty {
	Err(b) if 0x02 <= b && b <= 0x7F => {
	// Spec says that chunk types 0x02-0x7F are reserved and
	// conformant decoders must return an error.
	fail!(Error::UnsupportedChunkType { byte: b });
	}
	Err(b) if 0x80 <= b && b <= 0xFD => {
	// Spec says that chunk types 0x80-0xFD are reserved but
	// skippable.
	self.r.read_exact(&mut self.src[0..len])?;
	}
	Err(b) => {
	// Can never happen. 0x02-0x7F and 0x80-0xFD are handled
	// above in the error case. That leaves 0x00, 0x01, 0xFE
	// and 0xFF, each of which correspond to one of the four
	// defined chunk types.
	unreachable!("BUG: unhandled chunk type: {}", b);
	}
	Ok(ChunkType::Padding) => {
	// Just read and move on.
	self.r.read_exact(&mut self.src[0..len])?;
	}
	Ok(ChunkType::Stream) => {
	if len != STREAM_BODY.len() {
	fail!(Error::UnsupportedChunkLength {
	len: len64,
	header: true,
	})
	}
	self.r.read_exact(&mut self.src[0..len])?;
	if &self.src[0..len] != STREAM_BODY {
	fail!(Error::StreamHeaderMismatch {
	bytes: self.src[0..len].to_vec(),
	});
	}
	}
	Ok(ChunkType::Uncompressed) => {
	if len < 4 {
	fail!(Error::UnsupportedChunkLength {
	len: len as u64,
	header: false,
	});
	}
	let expected_sum = bytes::io_read_u32_le(&mut self.r)?;
	let n = len - 4;
	if n > self.dst.len() {
	fail!(Error::UnsupportedChunkLength {
	len: n as u64,
	header: false,
	});
	}
	self.r.read_exact(&mut self.dst[0..n])?;
	let got_sum =
	self.checksummer.crc32c_masked(&self.dst[0..n]);
	if expected_sum != got_sum {
	fail!(Error::Checksum {
	expected: expected_sum,
	got: got_sum,
	});
	}
	self.dsts = 0;
	self.dste = n;
	}
	Ok(ChunkType::Compressed) => {
	if len < 4 {
	fail!(Error::UnsupportedChunkLength {
	len: len as u64,
	header: false,
	});
	}
	let expected_sum = bytes::io_read_u32_le(&mut self.r)?;
	let sn = len - 4;
	if sn > self.src.len() {
	fail!(Error::UnsupportedChunkLength {
	len: len64,
	header: false,
	});
	}
	self.r.read_exact(&mut self.src[0..sn])?;
	let dn = decompress_len(&self.src)?;
	if dn > self.dst.len() {
	fail!(Error::UnsupportedChunkLength {
	len: dn as u64,
	header: false,
	});
	}
	self.dec
	.decompress(&self.src[0..sn], &mut self.dst[0..dn])?;
	let got_sum =
	self.checksummer.crc32c_masked(&self.dst[0..dn]);
	if expected_sum != got_sum {
	fail!(Error::Checksum {
	expected: expected_sum,
	got: got_sum,
	});
	}
	self.dsts = 0;
	self.dste = dn;
	}
	}
	}
	}
	}

	impl<R: fmt::Debug + io::Read> fmt::Debug for FrameDecoder<R> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	f.debug_struct("FrameDecoder")
	.field("r", &self.r)
	.field("dec", &self.dec)
	.field("checksummer", &self.checksummer)
	.field("src", &"[...]")
	.field("dst", &"[...]")
	.field("dsts", &self.dsts)
	.field("dste", &self.dste)
	.field("read_stream_ident", &self.read_stream_ident)
	.finish()
	}
	}

	/// A reader for compressing data using snappy as it is read.
	///
	/// This `FrameEncoder` wraps any other reader that implements `std::io::Read`.
	/// Bytes read from this reader are compressed using the
	/// [Snappy frame format](https://github.com/google/snappy/blob/master/framing_format.txt)
	/// (file extension `sz`, MIME type `application/x-snappy-framed`).
	///
	/// Usually you'll want
	/// [`read::FrameDecoder`](struct.FrameDecoder.html)
	/// (for decompressing while reading) or
	/// [`write::FrameEncoder`](../write/struct.FrameEncoder.html)
	/// (for compressing while writing) instead.
	///
	/// Unlike `FrameDecoder`, this will attempt to make large reads roughly
	/// equivalent to the size of a single Snappy block. Therefore, callers may not
	/// benefit from using a buffered reader.
	pub struct FrameEncoder<R: io::Read> {
	/// Internally, we split `FrameEncoder` in two to keep the borrow checker
	/// happy. The `inner` member contains everything that `read_frame` needs
	/// to fetch a frame's worth of data and compress it.
	inner: Inner<R>,
	/// Data that we've encoded and are ready to return to our caller.
	dst: Vec<u8>,
	/// Starting point of bytes in `dst` not yet given back to the caller.
	dsts: usize,
	/// Ending point of bytes in `dst` that we want to give to our caller.
	dste: usize,
	}

	struct Inner<R: io::Read> {
	/// The underlying data source.
	r: R,
	/// An encoder that we reuse that does the actual block based compression.
	enc: Encoder,
	/// A CRC32 checksummer that is configured to either use the portable
	/// fallback version or the SSE4.2 accelerated version when the right CPU
	/// features are available.
	checksummer: CheckSummer,
	/// Data taken from the underlying `r`, and not yet compressed.
	src: Vec<u8>,
	/// Have we written the standard snappy header to `dst` yet?
	wrote_stream_ident: bool,
	}

	impl<R: io::Read> FrameEncoder<R> {
	/// Create a new reader for streaming Snappy compression.
	pub fn new(rdr: R) -> FrameEncoder<R> {
	FrameEncoder {
	inner: Inner {
	r: rdr,
	enc: Encoder::new(),
	checksummer: CheckSummer::new(),
	src: vec![0; MAX_BLOCK_SIZE],
	wrote_stream_ident: false,
	},
	dst: vec![0; MAX_READ_FRAME_ENCODER_BLOCK_SIZE],
	dsts: 0,
	dste: 0,
	}
	}

	/// Gets a reference to the underlying reader in this decoder.
	pub fn get_ref(&self) -> &R {
	&self.inner.r
	}

	/// Gets a mutable reference to the underlying reader in this decoder.
	///
	/// Note that mutation of the stream may result in surprising results if
	/// this encoder is continued to be used.
	pub fn get_mut(&mut self) -> &mut R {
	&mut self.inner.r
	}

	/// Read previously compressed data from `self.dst`, returning the number of
	/// bytes read. If `self.dst` is empty, returns 0.
	fn read_from_dst(&mut self, buf: &mut [u8]) -> usize {
	let available_bytes = self.dste - self.dsts;
	let count = cmp::min(available_bytes, buf.len());
	buf[..count].copy_from_slice(&self.dst[self.dsts..self.dsts + count]);
	self.dsts += count;
	count
	}
	}

	impl<R: io::Read> io::Read for FrameEncoder<R> {
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	// Try reading previously compressed bytes from our `dst` buffer, if
	// any.
	let count = self.read_from_dst(buf);

	if count > 0 {
	// We had some bytes in our `dst` buffer that we used.
	Ok(count)
	} else if buf.len() >= MAX_READ_FRAME_ENCODER_BLOCK_SIZE {
	// Our output `buf` is big enough that we can directly write into
	// it, so bypass `dst` entirely.
	self.inner.read_frame(buf)
	} else {
	// We need to refill `self.dst`, and then return some bytes from
	// that.
	let count = self.inner.read_frame(&mut self.dst)?;
	self.dsts = 0;
	self.dste = count;
	Ok(self.read_from_dst(buf))
	}
	}
	}

	impl<R: io::Read> Inner<R> {
	/// Read from `self.r`, and create a new frame, writing it to `dst`, which
	/// must be at least `MAX_READ_FRAME_ENCODER_BLOCK_SIZE` bytes in size.
	fn read_frame(&mut self, dst: &mut [u8]) -> io::Result<usize> {
	debug_assert!(dst.len() >= MAX_READ_FRAME_ENCODER_BLOCK_SIZE);

	// We make one read to the underlying reader. If the underlying reader
	// doesn't fill the buffer but there are still bytes to be read, then
	// compression won't be optimal. The alternative would be to block
	// until our buffer is maximally full (or we see EOF), but this seems
	// more surprising. In general, io::Read implementations should try to
	// fill the caller's buffer as much as they can, so this seems like the
	// better choice.
	let nread = self.r.read(&mut self.src)?;
	if nread == 0 {
	return Ok(0);
	}

	// If we haven't yet written the stream header to `dst`, write it.
	let mut dst_write_start = 0;
	if !self.wrote_stream_ident {
	dst[0..STREAM_IDENTIFIER.len()].copy_from_slice(STREAM_IDENTIFIER);
	dst_write_start += STREAM_IDENTIFIER.len();
	self.wrote_stream_ident = true;
	}

	// Reserve space for our chunk header. We need to use `split_at_mut` so
	// that we can get two mutable slices pointing at non-overlapping parts
	// of `dst`.
	let (chunk_header, remaining_dst) =
	dst[dst_write_start..].split_at_mut(CHUNK_HEADER_AND_CRC_SIZE);
	dst_write_start += CHUNK_HEADER_AND_CRC_SIZE;

	// Compress our frame if possible, telling `compress_frame` to always
	// put the output in `dst`.
	let frame_data = compress_frame(
	&mut self.enc,
	self.checksummer,
	&self.src[..nread],
	chunk_header,
	remaining_dst,
	true,
	)?;
	Ok(dst_write_start + frame_data.len())
	}
	}

	impl<R: fmt::Debug + io::Read> fmt::Debug for FrameEncoder<R> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	f.debug_struct("FrameEncoder")
	.field("inner", &self.inner)
	.field("dst", &"[...]")
	.field("dsts", &self.dsts)
	.field("dste", &self.dste)
	.finish()
	}
	}

	impl<R: fmt::Debug + io::Read> fmt::Debug for Inner<R> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	f.debug_struct("Inner")
	.field("r", &self.r)
	.field("enc", &self.enc)
	.field("checksummer", &self.checksummer)
	.field("src", &"[...]")
	.field("wrote_stream_ident", &self.wrote_stream_ident)
	.finish()
	}
	}

	// read_exact_eof is like Read::read_exact, except it detects EOF
	// and returns Ok(false) instead of an error.
	//
	// If buf was read successfully, it returns Ok(true).
	fn read_exact_eof<R: io::Read>(
	rdr: &mut R,
	buf: &mut [u8],
	) -> io::Result<bool> {
	match rdr.read(buf) {
	// EOF
	Ok(0) => Ok(false),
	// Read everything w/ the read call
	Ok(i) if i == buf.len() => Ok(true),
	// There's some bytes left to fill, which can be deferred to read_exact
	Ok(i) => {
	rdr.read_exact(&mut buf[i..])?;
	Ok(true)
	}
	Err(e) => Err(e),
	}
	}