src/frame/decompress.rs - platform/external/rust/crates/lz4_flex - Git at Google

 use std::{
     convert::TryInto,
     fmt,
     hash::Hasher,
     io::{self, BufRead, ErrorKind},
     mem::size_of,
 };
 use twox_hash::XxHash32;

 use super::header::{
     BlockInfo, BlockMode, FrameInfo, LZ4F_LEGACY_MAGIC_NUMBER, MAGIC_NUMBER_SIZE,
     MAX_FRAME_INFO_SIZE, MIN_FRAME_INFO_SIZE,
 };
 use super::Error;
 use crate::{
     block::WINDOW_SIZE,
     sink::{vec_sink_for_decompression, SliceSink},
 };

 /// A reader for decompressing the LZ4 frame format
 ///
 /// This Decoder wraps any other reader that implements `io::Read`.
 /// Bytes read will be decompressed according to the [LZ4 frame format](
 /// https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md).
 ///
 /// # Example 1
 /// Deserializing json values out of a compressed file.
 ///
 /// ```no_run
 /// let compressed_input = std::fs::File::open("datafile").unwrap();
 /// let mut decompressed_input = lz4_flex::frame::FrameDecoder::new(compressed_input);
 /// let json: serde_json::Value = serde_json::from_reader(decompressed_input).unwrap();
 /// ```
 ///
 /// # Example
 /// Deserializing multiple json values out of a compressed file
 ///
 /// ```no_run
 /// let compressed_input = std::fs::File::open("datafile").unwrap();
 /// let mut decompressed_input = lz4_flex::frame::FrameDecoder::new(compressed_input);
 /// loop {
 ///     match serde_json::from_reader::<_, serde_json::Value>(&mut decompressed_input) {
 ///         Ok(json) => { println!("json {:?}", json); }
 ///         Err(e) if e.is_eof() => break,
 ///         Err(e) => panic!("{}", e),
 ///     }
 /// }
 /// ```
 pub struct FrameDecoder<R: io::Read> {
     /// The underlying reader.
     r: R,
     /// The FrameInfo of the frame currently being decoded.
     /// It starts as `None` and is filled with the FrameInfo is read from the input.
     /// It's reset to `None` once the frame EndMarker is read from the input.
     current_frame_info: Option<FrameInfo>,
     /// Xxhash32 used when content checksum is enabled.
     content_hasher: XxHash32,
     /// Total length of decompressed output for the current frame.
     content_len: u64,
     /// 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 and length: starting point of bytes previously output
     /// that are still part of the decompressor window.
     ext_dict_offset: usize,
     ext_dict_len: usize,
     /// Index into dst: starting point of bytes not yet read by caller.
     dst_start: usize,
     /// Index into dst: ending point of bytes not yet read by caller.
     dst_end: usize,
 }

 impl<R: io::Read> FrameDecoder<R> {
     /// Creates a new Decoder for the specified reader.
     pub fn new(rdr: R) -> FrameDecoder<R> {
         FrameDecoder {
             r: rdr,
             src: Default::default(),
             dst: Default::default(),
             ext_dict_offset: 0,
             ext_dict_len: 0,
             dst_start: 0,
             dst_end: 0,
             current_frame_info: None,
             content_hasher: XxHash32::with_seed(0),
             content_len: 0,
         }
     }

     /// 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
     }

     /// Consumes the FrameDecoder and returns the underlying reader.
     pub fn into_inner(self) -> R {
         self.r
     }

     fn read_frame_info(&mut self) -> Result<usize, io::Error> {
         let mut buffer = [0u8; MAX_FRAME_INFO_SIZE];

         match self.r.read(&mut buffer[..MAGIC_NUMBER_SIZE])? {
             0 => return Ok(0),
             MAGIC_NUMBER_SIZE => (),
             read => self.r.read_exact(&mut buffer[read..MAGIC_NUMBER_SIZE])?,
         }

         if u32::from_le_bytes(buffer[0..MAGIC_NUMBER_SIZE].try_into().unwrap())
             != LZ4F_LEGACY_MAGIC_NUMBER
         {
             match self
                 .r
                 .read(&mut buffer[MAGIC_NUMBER_SIZE..MIN_FRAME_INFO_SIZE])?
             {
                 0 => return Ok(0),
                 MIN_FRAME_INFO_SIZE => (),
                 read => self
                     .r
                     .read_exact(&mut buffer[MAGIC_NUMBER_SIZE + read..MIN_FRAME_INFO_SIZE])?,
             }
         }
         let required = FrameInfo::read_size(&buffer[..MIN_FRAME_INFO_SIZE])?;
         if required != MIN_FRAME_INFO_SIZE && required != MAGIC_NUMBER_SIZE {
             self.r
                 .read_exact(&mut buffer[MIN_FRAME_INFO_SIZE..required])?;
         }

         let frame_info = FrameInfo::read(&buffer[..required])?;
         if frame_info.dict_id.is_some() {
             // Unsupported right now so it must be None
             return Err(Error::DictionaryNotSupported.into());
         }

         let max_block_size = frame_info.block_size.get_size();
         let dst_size = if frame_info.block_mode == BlockMode::Linked {
             // In linked mode we consume the output (bumping dst_start) but leave the
             // beginning of dst to be used as a prefix in subsequent blocks.
             // That is at least until we have at least `max_block_size + WINDOW_SIZE`
             // bytes in dst, then we setup an ext_dict with the last WINDOW_SIZE bytes
             // and the output goes to the beginning of dst again.
             // Since we always want to be able to write a full block (up to max_block_size)
             // we need a buffer with at least `max_block_size * 2 + WINDOW_SIZE` bytes.
             max_block_size * 2 + WINDOW_SIZE
         } else {
             max_block_size
         };
         self.src.clear();
         self.dst.clear();
         self.src.reserve_exact(max_block_size);
         self.dst.reserve_exact(dst_size);
         self.current_frame_info = Some(frame_info);
         self.content_hasher = XxHash32::with_seed(0);
         self.content_len = 0;
         self.ext_dict_len = 0;
         self.dst_start = 0;
         self.dst_end = 0;
         Ok(required)
     }

     #[inline]
     fn read_checksum(r: &mut R) -> Result<u32, io::Error> {
         let mut checksum_buffer = [0u8; size_of::<u32>()];
         r.read_exact(&mut checksum_buffer[..])?;
         let checksum = u32::from_le_bytes(checksum_buffer);
         Ok(checksum)
     }

     #[inline]
     fn check_block_checksum(data: &[u8], expected_checksum: u32) -> Result<(), io::Error> {
         let mut block_hasher = XxHash32::with_seed(0);
         block_hasher.write(data);
         let calc_checksum = block_hasher.finish() as u32;
         if calc_checksum != expected_checksum {
             return Err(Error::BlockChecksumError.into());
         }
         Ok(())
     }

     fn read_block(&mut self) -> io::Result<usize> {
         debug_assert_eq!(self.dst_start, self.dst_end);
         let frame_info = self.current_frame_info.as_ref().unwrap();

         // Adjust dst buffer offsets to decompress the next block
         let max_block_size = frame_info.block_size.get_size();
         if frame_info.block_mode == BlockMode::Linked {
             // In linked mode we consume the output (bumping dst_start) but leave the
             // beginning of dst to be used as a prefix in subsequent blocks.
             // That is at least until we have at least `max_block_size + WINDOW_SIZE`
             // bytes in dst, then we setup an ext_dict with the last WINDOW_SIZE bytes
             // and the output goes to the beginning of dst again.
             debug_assert_eq!(self.dst.capacity(), max_block_size * 2 + WINDOW_SIZE);
             if self.dst_start + max_block_size > self.dst.capacity() {
                 // Output might not fit in the buffer.
                 // The ext_dict will become the last WINDOW_SIZE bytes
                 debug_assert!(self.dst_start >= max_block_size + WINDOW_SIZE);
                 self.ext_dict_offset = self.dst_start - WINDOW_SIZE;
                 self.ext_dict_len = WINDOW_SIZE;
                 // Output goes in the beginning of the buffer again.
                 self.dst_start = 0;
                 self.dst_end = 0;
             } else if self.dst_start + self.ext_dict_len > WINDOW_SIZE {
                 // There's more than WINDOW_SIZE bytes of lookback adding the prefix and ext_dict.
                 // Since we have a limited buffer we must shrink ext_dict in favor of the prefix,
                 // so that we can fit up to max_block_size bytes between dst_start and ext_dict
                 // start.
                 let delta = self
                     .ext_dict_len
                     .min(self.dst_start + self.ext_dict_len - WINDOW_SIZE);
                 self.ext_dict_offset += delta;
                 self.ext_dict_len -= delta;
                 debug_assert!(self.dst_start + self.ext_dict_len >= WINDOW_SIZE)
             }
         } else {
             debug_assert_eq!(self.ext_dict_len, 0);
             debug_assert_eq!(self.dst.capacity(), max_block_size);
             self.dst_start = 0;
             self.dst_end = 0;
         }

         // Read and decompress block
         let block_info = {
             let mut buffer = [0u8; 4];
             if let Err(err) = self.r.read_exact(&mut buffer) {
                 if err.kind() == ErrorKind::UnexpectedEof {
                     return Ok(0);
                 } else {
                     return Err(err);
                 }
             }
             BlockInfo::read(&buffer)?
         };
         match block_info {
             BlockInfo::Uncompressed(len) => {
                 let len = len as usize;
                 if len > max_block_size {
                     return Err(Error::BlockTooBig.into());
                 }
                 // TODO: Attempt to avoid initialization of read buffer when
                 // https://github.com/rust-lang/rust/issues/42788 stabilizes
                 self.r.read_exact(vec_resize_and_get_mut(
                     &mut self.dst,
                     self.dst_start,
                     self.dst_start + len,
                 ))?;
                 if frame_info.block_checksums {
                     let expected_checksum = Self::read_checksum(&mut self.r)?;
                     Self::check_block_checksum(
                         &self.dst[self.dst_start..self.dst_start + len],
                         expected_checksum,
                     )?;
                 }

                 self.dst_end += len;
                 self.content_len += len as u64;
             }
             BlockInfo::Compressed(len) => {
                 let len = len as usize;
                 if len > max_block_size {
                     return Err(Error::BlockTooBig.into());
                 }
                 // TODO: Attempt to avoid initialization of read buffer when
                 // https://github.com/rust-lang/rust/issues/42788 stabilizes
                 self.r
                     .read_exact(vec_resize_and_get_mut(&mut self.src, 0, len))?;
                 if frame_info.block_checksums {
                     let expected_checksum = Self::read_checksum(&mut self.r)?;
                     Self::check_block_checksum(&self.src[..len], expected_checksum)?;
                 }

                 let with_dict_mode =
                     frame_info.block_mode == BlockMode::Linked && self.ext_dict_len != 0;
                 let decomp_size = if with_dict_mode {
                     debug_assert!(self.dst_start + max_block_size <= self.ext_dict_offset);
                     let (head, tail) = self.dst.split_at_mut(self.ext_dict_offset);
                     let ext_dict = &tail[..self.ext_dict_len];

                     debug_assert!(head.len() - self.dst_start >= max_block_size);
                     crate::block::decompress::decompress_internal::<true, _>(
                         &self.src[..len],
                         &mut SliceSink::new(head, self.dst_start),
                         ext_dict,
                     )
                 } else {
                     // Independent blocks OR linked blocks with only prefix data
                     debug_assert!(self.dst.capacity() - self.dst_start >= max_block_size);
                     crate::block::decompress::decompress_internal::<false, _>(
                         &self.src[..len],
                         &mut vec_sink_for_decompression(
                             &mut self.dst,
                             0,
                             self.dst_start,
                             self.dst_start + max_block_size,
                         ),
                         b"",
                     )
                 }
                 .map_err(Error::DecompressionError)?;

                 self.dst_end += decomp_size;
                 self.content_len += decomp_size as u64;
             }

             BlockInfo::EndMark => {
                 if let Some(expected) = frame_info.content_size {
                     if self.content_len != expected {
                         return Err(Error::ContentLengthError {
                             expected,
                             actual: self.content_len,
                         }
                         .into());
                     }
                 }
                 if frame_info.content_checksum {
                     let expected_checksum = Self::read_checksum(&mut self.r)?;
                     let calc_checksum = self.content_hasher.finish() as u32;
                     if calc_checksum != expected_checksum {
                         return Err(Error::ContentChecksumError.into());
                     }
                 }
                 self.current_frame_info = None;
                 return Ok(0);
             }
         }

         // Content checksum, if applicable
         if frame_info.content_checksum {
             self.content_hasher
                 .write(&self.dst[self.dst_start..self.dst_end]);
         }

         Ok(self.dst_end - self.dst_start)
     }

     fn read_more(&mut self) -> io::Result<usize> {
         if self.current_frame_info.is_none() && self.read_frame_info()? == 0 {
             return Ok(0);
         }
         self.read_block()
     }
 }

 impl<R: io::Read> io::Read for FrameDecoder<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         loop {
             // Fill read buffer if there's uncompressed data left
             if self.dst_start < self.dst_end {
                 let read_len = std::cmp::min(self.dst_end - self.dst_start, buf.len());
                 let dst_read_end = self.dst_start + read_len;
                 buf[..read_len].copy_from_slice(&self.dst[self.dst_start..dst_read_end]);
                 self.dst_start = dst_read_end;
                 return Ok(read_len);
             }
             if self.read_more()? == 0 {
                 return Ok(0);
             }
         }
     }

     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         let mut written = 0;
         loop {
             match self.fill_buf() {
                 Ok(b) if b.is_empty() => return Ok(written),
                 Ok(b) => {
                     let s = std::str::from_utf8(b).map_err(|_| {
                         io::Error::new(
                             io::ErrorKind::InvalidData,
                             "stream did not contain valid UTF-8",
                         )
                     })?;
                     buf.push_str(s);
                     let len = s.len();
                     self.consume(len);
                     written += len;
                 }
                 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
                 Err(e) => return Err(e),
             }
         }
     }

     fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
         let mut written = 0;
         loop {
             match self.fill_buf() {
                 Ok(b) if b.is_empty() => return Ok(written),
                 Ok(b) => {
                     buf.extend_from_slice(b);
                     let len = b.len();
                     self.consume(len);
                     written += len;
                 }
                 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
                 Err(e) => return Err(e),
             }
         }
     }
 }

 impl<R: io::Read> io::BufRead for FrameDecoder<R> {
     fn fill_buf(&mut self) -> io::Result<&[u8]> {
         if self.dst_start == self.dst_end {
             self.read_more()?;
         }
         Ok(&self.dst[self.dst_start..self.dst_end])
     }

     fn consume(&mut self, amt: usize) {
         assert!(amt <= self.dst_end - self.dst_start);
         self.dst_start += amt;
     }
 }

 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("content_hasher", &self.content_hasher)
             .field("content_len", &self.content_len)
             .field("src", &"[...]")
             .field("dst", &"[...]")
             .field("dst_start", &self.dst_start)
             .field("dst_end", &self.dst_end)
             .field("ext_dict_offset", &self.ext_dict_offset)
             .field("ext_dict_len", &self.ext_dict_len)
             .field("current_frame_info", &self.current_frame_info)
             .finish()
     }
 }

 /// Similar to `v.get_mut(start..end) but will adjust the len if needed.
 #[inline]
 fn vec_resize_and_get_mut(v: &mut Vec<u8>, start: usize, end: usize) -> &mut [u8] {
     if end > v.len() {
         v.resize(end, 0)
     }
     &mut v[start..end]
 }
	use std::{
	convert::TryInto,
	fmt,
	hash::Hasher,
	io::{self, BufRead, ErrorKind},
	mem::size_of,
	};
	use twox_hash::XxHash32;

	use super::header::{
	BlockInfo, BlockMode, FrameInfo, LZ4F_LEGACY_MAGIC_NUMBER, MAGIC_NUMBER_SIZE,
	MAX_FRAME_INFO_SIZE, MIN_FRAME_INFO_SIZE,
	};
	use super::Error;
	use crate::{
	block::WINDOW_SIZE,
	sink::{vec_sink_for_decompression, SliceSink},
	};

	/// A reader for decompressing the LZ4 frame format
	///
	/// This Decoder wraps any other reader that implements `io::Read`.
	/// Bytes read will be decompressed according to the [LZ4 frame format](
	/// https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md).
	///
	/// # Example 1
	/// Deserializing json values out of a compressed file.
	///
	/// ```no_run
	/// let compressed_input = std::fs::File::open("datafile").unwrap();
	/// let mut decompressed_input = lz4_flex::frame::FrameDecoder::new(compressed_input);
	/// let json: serde_json::Value = serde_json::from_reader(decompressed_input).unwrap();
	/// ```
	///
	/// # Example
	/// Deserializing multiple json values out of a compressed file
	///
	/// ```no_run
	/// let compressed_input = std::fs::File::open("datafile").unwrap();
	/// let mut decompressed_input = lz4_flex::frame::FrameDecoder::new(compressed_input);
	/// loop {
	/// match serde_json::from_reader::<_, serde_json::Value>(&mut decompressed_input) {
	/// Ok(json) => { println!("json {:?}", json); }
	/// Err(e) if e.is_eof() => break,
	/// Err(e) => panic!("{}", e),
	/// }
	/// }
	/// ```
	pub struct FrameDecoder<R: io::Read> {
	/// The underlying reader.
	r: R,
	/// The FrameInfo of the frame currently being decoded.
	/// It starts as `None` and is filled with the FrameInfo is read from the input.
	/// It's reset to `None` once the frame EndMarker is read from the input.
	current_frame_info: Option<FrameInfo>,
	/// Xxhash32 used when content checksum is enabled.
	content_hasher: XxHash32,
	/// Total length of decompressed output for the current frame.
	content_len: u64,
	/// 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 and length: starting point of bytes previously output
	/// that are still part of the decompressor window.
	ext_dict_offset: usize,
	ext_dict_len: usize,
	/// Index into dst: starting point of bytes not yet read by caller.
	dst_start: usize,
	/// Index into dst: ending point of bytes not yet read by caller.
	dst_end: usize,
	}

	impl<R: io::Read> FrameDecoder<R> {
	/// Creates a new Decoder for the specified reader.
	pub fn new(rdr: R) -> FrameDecoder<R> {
	FrameDecoder {
	r: rdr,
	src: Default::default(),
	dst: Default::default(),
	ext_dict_offset: 0,
	ext_dict_len: 0,
	dst_start: 0,
	dst_end: 0,
	current_frame_info: None,
	content_hasher: XxHash32::with_seed(0),
	content_len: 0,
	}
	}

	/// 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
	}

	/// Consumes the FrameDecoder and returns the underlying reader.
	pub fn into_inner(self) -> R {
	self.r
	}

	fn read_frame_info(&mut self) -> Result<usize, io::Error> {
	let mut buffer = [0u8; MAX_FRAME_INFO_SIZE];

	match self.r.read(&mut buffer[..MAGIC_NUMBER_SIZE])? {
	0 => return Ok(0),
	MAGIC_NUMBER_SIZE => (),
	read => self.r.read_exact(&mut buffer[read..MAGIC_NUMBER_SIZE])?,
	}

	if u32::from_le_bytes(buffer[0..MAGIC_NUMBER_SIZE].try_into().unwrap())
	!= LZ4F_LEGACY_MAGIC_NUMBER
	{
	match self
	.r
	.read(&mut buffer[MAGIC_NUMBER_SIZE..MIN_FRAME_INFO_SIZE])?
	{
	0 => return Ok(0),
	MIN_FRAME_INFO_SIZE => (),
	read => self
	.r
	.read_exact(&mut buffer[MAGIC_NUMBER_SIZE + read..MIN_FRAME_INFO_SIZE])?,
	}
	}
	let required = FrameInfo::read_size(&buffer[..MIN_FRAME_INFO_SIZE])?;
	if required != MIN_FRAME_INFO_SIZE && required != MAGIC_NUMBER_SIZE {
	self.r
	.read_exact(&mut buffer[MIN_FRAME_INFO_SIZE..required])?;
	}

	let frame_info = FrameInfo::read(&buffer[..required])?;
	if frame_info.dict_id.is_some() {
	// Unsupported right now so it must be None
	return Err(Error::DictionaryNotSupported.into());
	}

	let max_block_size = frame_info.block_size.get_size();
	let dst_size = if frame_info.block_mode == BlockMode::Linked {
	// In linked mode we consume the output (bumping dst_start) but leave the
	// beginning of dst to be used as a prefix in subsequent blocks.
	// That is at least until we have at least `max_block_size + WINDOW_SIZE`
	// bytes in dst, then we setup an ext_dict with the last WINDOW_SIZE bytes
	// and the output goes to the beginning of dst again.
	// Since we always want to be able to write a full block (up to max_block_size)
	// we need a buffer with at least `max_block_size * 2 + WINDOW_SIZE` bytes.
	max_block_size * 2 + WINDOW_SIZE
	} else {
	max_block_size
	};
	self.src.clear();
	self.dst.clear();
	self.src.reserve_exact(max_block_size);
	self.dst.reserve_exact(dst_size);
	self.current_frame_info = Some(frame_info);
	self.content_hasher = XxHash32::with_seed(0);
	self.content_len = 0;
	self.ext_dict_len = 0;
	self.dst_start = 0;
	self.dst_end = 0;
	Ok(required)
	}

	#[inline]
	fn read_checksum(r: &mut R) -> Result<u32, io::Error> {
	let mut checksum_buffer = [0u8; size_of::<u32>()];
	r.read_exact(&mut checksum_buffer[..])?;
	let checksum = u32::from_le_bytes(checksum_buffer);
	Ok(checksum)
	}

	#[inline]
	fn check_block_checksum(data: &[u8], expected_checksum: u32) -> Result<(), io::Error> {
	let mut block_hasher = XxHash32::with_seed(0);
	block_hasher.write(data);
	let calc_checksum = block_hasher.finish() as u32;
	if calc_checksum != expected_checksum {
	return Err(Error::BlockChecksumError.into());
	}
	Ok(())
	}

	fn read_block(&mut self) -> io::Result<usize> {
	debug_assert_eq!(self.dst_start, self.dst_end);
	let frame_info = self.current_frame_info.as_ref().unwrap();

	// Adjust dst buffer offsets to decompress the next block
	let max_block_size = frame_info.block_size.get_size();
	if frame_info.block_mode == BlockMode::Linked {
	// In linked mode we consume the output (bumping dst_start) but leave the
	// beginning of dst to be used as a prefix in subsequent blocks.
	// That is at least until we have at least `max_block_size + WINDOW_SIZE`
	// bytes in dst, then we setup an ext_dict with the last WINDOW_SIZE bytes
	// and the output goes to the beginning of dst again.
	debug_assert_eq!(self.dst.capacity(), max_block_size * 2 + WINDOW_SIZE);
	if self.dst_start + max_block_size > self.dst.capacity() {
	// Output might not fit in the buffer.
	// The ext_dict will become the last WINDOW_SIZE bytes
	debug_assert!(self.dst_start >= max_block_size + WINDOW_SIZE);
	self.ext_dict_offset = self.dst_start - WINDOW_SIZE;
	self.ext_dict_len = WINDOW_SIZE;
	// Output goes in the beginning of the buffer again.
	self.dst_start = 0;
	self.dst_end = 0;
	} else if self.dst_start + self.ext_dict_len > WINDOW_SIZE {
	// There's more than WINDOW_SIZE bytes of lookback adding the prefix and ext_dict.
	// Since we have a limited buffer we must shrink ext_dict in favor of the prefix,
	// so that we can fit up to max_block_size bytes between dst_start and ext_dict
	// start.
	let delta = self
	.ext_dict_len
	.min(self.dst_start + self.ext_dict_len - WINDOW_SIZE);
	self.ext_dict_offset += delta;
	self.ext_dict_len -= delta;
	debug_assert!(self.dst_start + self.ext_dict_len >= WINDOW_SIZE)
	}
	} else {
	debug_assert_eq!(self.ext_dict_len, 0);
	debug_assert_eq!(self.dst.capacity(), max_block_size);
	self.dst_start = 0;
	self.dst_end = 0;
	}

	// Read and decompress block
	let block_info = {
	let mut buffer = [0u8; 4];
	if let Err(err) = self.r.read_exact(&mut buffer) {
	if err.kind() == ErrorKind::UnexpectedEof {
	return Ok(0);
	} else {
	return Err(err);
	}
	}
	BlockInfo::read(&buffer)?
	};
	match block_info {
	BlockInfo::Uncompressed(len) => {
	let len = len as usize;
	if len > max_block_size {
	return Err(Error::BlockTooBig.into());
	}
	// TODO: Attempt to avoid initialization of read buffer when
	// https://github.com/rust-lang/rust/issues/42788 stabilizes
	self.r.read_exact(vec_resize_and_get_mut(
	&mut self.dst,
	self.dst_start,
	self.dst_start + len,
	))?;
	if frame_info.block_checksums {
	let expected_checksum = Self::read_checksum(&mut self.r)?;
	Self::check_block_checksum(
	&self.dst[self.dst_start..self.dst_start + len],
	expected_checksum,
	)?;
	}

	self.dst_end += len;
	self.content_len += len as u64;
	}
	BlockInfo::Compressed(len) => {
	let len = len as usize;
	if len > max_block_size {
	return Err(Error::BlockTooBig.into());
	}
	// TODO: Attempt to avoid initialization of read buffer when
	// https://github.com/rust-lang/rust/issues/42788 stabilizes
	self.r
	.read_exact(vec_resize_and_get_mut(&mut self.src, 0, len))?;
	if frame_info.block_checksums {
	let expected_checksum = Self::read_checksum(&mut self.r)?;
	Self::check_block_checksum(&self.src[..len], expected_checksum)?;
	}

	let with_dict_mode =
	frame_info.block_mode == BlockMode::Linked && self.ext_dict_len != 0;
	let decomp_size = if with_dict_mode {
	debug_assert!(self.dst_start + max_block_size <= self.ext_dict_offset);
	let (head, tail) = self.dst.split_at_mut(self.ext_dict_offset);
	let ext_dict = &tail[..self.ext_dict_len];

	debug_assert!(head.len() - self.dst_start >= max_block_size);
	crate::block::decompress::decompress_internal::<true, _>(
	&self.src[..len],
	&mut SliceSink::new(head, self.dst_start),
	ext_dict,
	)
	} else {
	// Independent blocks OR linked blocks with only prefix data
	debug_assert!(self.dst.capacity() - self.dst_start >= max_block_size);
	crate::block::decompress::decompress_internal::<false, _>(
	&self.src[..len],
	&mut vec_sink_for_decompression(
	&mut self.dst,
	0,
	self.dst_start,
	self.dst_start + max_block_size,
	),
	b"",
	)
	}
	.map_err(Error::DecompressionError)?;

	self.dst_end += decomp_size;
	self.content_len += decomp_size as u64;
	}

	BlockInfo::EndMark => {
	if let Some(expected) = frame_info.content_size {
	if self.content_len != expected {
	return Err(Error::ContentLengthError {
	expected,
	actual: self.content_len,
	}
	.into());
	}
	}
	if frame_info.content_checksum {
	let expected_checksum = Self::read_checksum(&mut self.r)?;
	let calc_checksum = self.content_hasher.finish() as u32;
	if calc_checksum != expected_checksum {
	return Err(Error::ContentChecksumError.into());
	}
	}
	self.current_frame_info = None;
	return Ok(0);
	}
	}

	// Content checksum, if applicable
	if frame_info.content_checksum {
	self.content_hasher
	.write(&self.dst[self.dst_start..self.dst_end]);
	}

	Ok(self.dst_end - self.dst_start)
	}

	fn read_more(&mut self) -> io::Result<usize> {
	if self.current_frame_info.is_none() && self.read_frame_info()? == 0 {
	return Ok(0);
	}
	self.read_block()
	}
	}

	impl<R: io::Read> io::Read for FrameDecoder<R> {
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
	loop {
	// Fill read buffer if there's uncompressed data left
	if self.dst_start < self.dst_end {
	let read_len = std::cmp::min(self.dst_end - self.dst_start, buf.len());
	let dst_read_end = self.dst_start + read_len;
	buf[..read_len].copy_from_slice(&self.dst[self.dst_start..dst_read_end]);
	self.dst_start = dst_read_end;
	return Ok(read_len);
	}
	if self.read_more()? == 0 {
	return Ok(0);
	}
	}
	}

	fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
	let mut written = 0;
	loop {
	match self.fill_buf() {
	Ok(b) if b.is_empty() => return Ok(written),
	Ok(b) => {
	let s = std::str::from_utf8(b).map_err(\|_\| {
	io::Error::new(
	io::ErrorKind::InvalidData,
	"stream did not contain valid UTF-8",
	)
	})?;
	buf.push_str(s);
	let len = s.len();
	self.consume(len);
	written += len;
	}
	Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
	Err(e) => return Err(e),
	}
	}
	}

	fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
	let mut written = 0;
	loop {
	match self.fill_buf() {
	Ok(b) if b.is_empty() => return Ok(written),
	Ok(b) => {
	buf.extend_from_slice(b);
	let len = b.len();
	self.consume(len);
	written += len;
	}
	Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
	Err(e) => return Err(e),
	}
	}
	}
	}

	impl<R: io::Read> io::BufRead for FrameDecoder<R> {
	fn fill_buf(&mut self) -> io::Result<&[u8]> {
	if self.dst_start == self.dst_end {
	self.read_more()?;
	}
	Ok(&self.dst[self.dst_start..self.dst_end])
	}

	fn consume(&mut self, amt: usize) {
	assert!(amt <= self.dst_end - self.dst_start);
	self.dst_start += amt;
	}
	}

	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("content_hasher", &self.content_hasher)
	.field("content_len", &self.content_len)
	.field("src", &"[...]")
	.field("dst", &"[...]")
	.field("dst_start", &self.dst_start)
	.field("dst_end", &self.dst_end)
	.field("ext_dict_offset", &self.ext_dict_offset)
	.field("ext_dict_len", &self.ext_dict_len)
	.field("current_frame_info", &self.current_frame_info)
	.finish()
	}
	}

	/// Similar to `v.get_mut(start..end) but will adjust the len if needed.
	#[inline]
	fn vec_resize_and_get_mut(v: &mut Vec<u8>, start: usize, end: usize) -> &mut [u8] {
	if end > v.len() {
	v.resize(end, 0)
	}
	&mut v[start..end]
	}