vendor/flate2/src/gz/mod.rs - toolchain/rustc - Git at Google

 use std::ffi::CString;
 use std::io::{BufRead, Error, ErrorKind, Read, Result, Write};
 use std::time;

 use crate::bufreader::BufReader;
 use crate::{Compression, Crc};

 pub static FHCRC: u8 = 1 << 1;
 pub static FEXTRA: u8 = 1 << 2;
 pub static FNAME: u8 = 1 << 3;
 pub static FCOMMENT: u8 = 1 << 4;
 pub static FRESERVED: u8 = 1 << 5 | 1 << 6 | 1 << 7;

 pub mod bufread;
 pub mod read;
 pub mod write;

 // The maximum length of the header filename and comment fields. More than
 // enough for these fields in reasonable use, but prevents possible attacks.
 const MAX_HEADER_BUF: usize = 65535;

 /// A structure representing the header of a gzip stream.
 ///
 /// The header can contain metadata about the file that was compressed, if
 /// present.
 #[derive(PartialEq, Clone, Debug, Default)]
 pub struct GzHeader {
     extra: Option<Vec<u8>>,
     filename: Option<Vec<u8>>,
     comment: Option<Vec<u8>>,
     operating_system: u8,
     mtime: u32,
 }

 impl GzHeader {
     /// Returns the `filename` field of this gzip stream's header, if present.
     pub fn filename(&self) -> Option<&[u8]> {
         self.filename.as_ref().map(|s| &s[..])
     }

     /// Returns the `extra` field of this gzip stream's header, if present.
     pub fn extra(&self) -> Option<&[u8]> {
         self.extra.as_ref().map(|s| &s[..])
     }

     /// Returns the `comment` field of this gzip stream's header, if present.
     pub fn comment(&self) -> Option<&[u8]> {
         self.comment.as_ref().map(|s| &s[..])
     }

     /// Returns the `operating_system` field of this gzip stream's header.
     ///
     /// There are predefined values for various operating systems.
     /// 255 means that the value is unknown.
     pub fn operating_system(&self) -> u8 {
         self.operating_system
     }

     /// This gives the most recent modification time of the original file being compressed.
     ///
     /// The time is in Unix format, i.e., seconds since 00:00:00 GMT, Jan. 1, 1970.
     /// (Note that this may cause problems for MS-DOS and other systems that use local
     /// rather than Universal time.) If the compressed data did not come from a file,
     /// `mtime` is set to the time at which compression started.
     /// `mtime` = 0 means no time stamp is available.
     ///
     /// The usage of `mtime` is discouraged because of Year 2038 problem.
     pub fn mtime(&self) -> u32 {
         self.mtime
     }

     /// Returns the most recent modification time represented by a date-time type.
     /// Returns `None` if the value of the underlying counter is 0,
     /// indicating no time stamp is available.
     ///
     ///
     /// The time is measured as seconds since 00:00:00 GMT, Jan. 1 1970.
     /// See [`mtime`](#method.mtime) for more detail.
     pub fn mtime_as_datetime(&self) -> Option<time::SystemTime> {
         if self.mtime == 0 {
             None
         } else {
             let duration = time::Duration::new(u64::from(self.mtime), 0);
             let datetime = time::UNIX_EPOCH + duration;
             Some(datetime)
         }
     }
 }

 #[derive(Debug)]
 pub enum GzHeaderState {
     Start(u8, [u8; 10]),
     Xlen(Option<Box<Crc>>, u8, [u8; 2]),
     Extra(Option<Box<Crc>>, u16),
     Filename(Option<Box<Crc>>),
     Comment(Option<Box<Crc>>),
     Crc(Option<Box<Crc>>, u8, [u8; 2]),
     Complete,
 }

 impl Default for GzHeaderState {
     fn default() -> Self {
         Self::Complete
     }
 }

 #[derive(Debug, Default)]
 pub struct GzHeaderParser {
     state: GzHeaderState,
     flags: u8,
     header: GzHeader,
 }

 impl GzHeaderParser {
     fn new() -> Self {
         GzHeaderParser {
             state: GzHeaderState::Start(0, [0; 10]),
             flags: 0,
             header: GzHeader::default(),
         }
     }

     fn parse<'a, R: Read>(&mut self, r: &'a mut R) -> Result<()> {
         loop {
             match &mut self.state {
                 GzHeaderState::Start(count, buffer) => {
                     while (*count as usize) < buffer.len() {
                         *count += read_into(r, &mut buffer[*count as usize..])? as u8;
                     }
                     // Gzip identification bytes
                     if buffer[0] != 0x1f || buffer[1] != 0x8b {
                         return Err(bad_header());
                     }
                     // Gzip compression method (8 = deflate)
                     if buffer[2] != 8 {
                         return Err(bad_header());
                     }
                     self.flags = buffer[3];
                     // RFC1952: "must give an error indication if any reserved bit is non-zero"
                     if self.flags & FRESERVED != 0 {
                         return Err(bad_header());
                     }
                     self.header.mtime = ((buffer[4] as u32) << 0)
                         | ((buffer[5] as u32) << 8)
                         | ((buffer[6] as u32) << 16)
                         | ((buffer[7] as u32) << 24);
                     let _xfl = buffer[8];
                     self.header.operating_system = buffer[9];
                     let crc = if self.flags & FHCRC != 0 {
                         let mut crc = Box::new(Crc::new());
                         crc.update(buffer);
                         Some(crc)
                     } else {
                         None
                     };
                     self.state = GzHeaderState::Xlen(crc, 0, [0; 2]);
                 }
                 GzHeaderState::Xlen(crc, count, buffer) => {
                     if self.flags & FEXTRA != 0 {
                         while (*count as usize) < buffer.len() {
                             *count += read_into(r, &mut buffer[*count as usize..])? as u8;
                         }
                         if let Some(crc) = crc {
                             crc.update(buffer);
                         }
                         let xlen = parse_le_u16(&buffer);
                         self.header.extra = Some(vec![0; xlen as usize]);
                         self.state = GzHeaderState::Extra(crc.take(), 0);
                     } else {
                         self.state = GzHeaderState::Filename(crc.take());
                     }
                 }
                 GzHeaderState::Extra(crc, count) => {
                     debug_assert!(self.header.extra.is_some());
                     let extra = self.header.extra.as_mut().unwrap();
                     while (*count as usize) < extra.len() {
                         *count += read_into(r, &mut extra[*count as usize..])? as u16;
                     }
                     if let Some(crc) = crc {
                         crc.update(extra);
                     }
                     self.state = GzHeaderState::Filename(crc.take());
                 }
                 GzHeaderState::Filename(crc) => {
                     if self.flags & FNAME != 0 {
                         let filename = self.header.filename.get_or_insert_with(Vec::new);
                         read_to_nul(r, filename)?;
                         if let Some(crc) = crc {
                             crc.update(filename);
                             crc.update(b"\0");
                         }
                     }
                     self.state = GzHeaderState::Comment(crc.take());
                 }
                 GzHeaderState::Comment(crc) => {
                     if self.flags & FCOMMENT != 0 {
                         let comment = self.header.comment.get_or_insert_with(Vec::new);
                         read_to_nul(r, comment)?;
                         if let Some(crc) = crc {
                             crc.update(comment);
                             crc.update(b"\0");
                         }
                     }
                     self.state = GzHeaderState::Crc(crc.take(), 0, [0; 2]);
                 }
                 GzHeaderState::Crc(crc, count, buffer) => {
                     if let Some(crc) = crc {
                         debug_assert!(self.flags & FHCRC != 0);
                         while (*count as usize) < buffer.len() {
                             *count += read_into(r, &mut buffer[*count as usize..])? as u8;
                         }
                         let stored_crc = parse_le_u16(&buffer);
                         let calced_crc = crc.sum() as u16;
                         if stored_crc != calced_crc {
                             return Err(corrupt());
                         }
                     }
                     self.state = GzHeaderState::Complete;
                 }
                 GzHeaderState::Complete => {
                     return Ok(());
                 }
             }
         }
     }

     fn header(&self) -> Option<&GzHeader> {
         match self.state {
             GzHeaderState::Complete => Some(&self.header),
             _ => None,
         }
     }
 }

 impl From<GzHeaderParser> for GzHeader {
     fn from(parser: GzHeaderParser) -> Self {
         debug_assert!(matches!(parser.state, GzHeaderState::Complete));
         parser.header
     }
 }

 // Attempt to fill the `buffer` from `r`. Return the number of bytes read.
 // Return an error if EOF is read before the buffer is full.  This differs
 // from `read` in that Ok(0) means that more data may be available.
 fn read_into<R: Read>(r: &mut R, buffer: &mut [u8]) -> Result<usize> {
     debug_assert!(!buffer.is_empty());
     match r.read(buffer) {
         Ok(0) => Err(ErrorKind::UnexpectedEof.into()),
         Ok(n) => Ok(n),
         Err(ref e) if e.kind() == ErrorKind::Interrupted => Ok(0),
         Err(e) => Err(e),
     }
 }

 // Read `r` up to the first nul byte, pushing non-nul bytes to `buffer`.
 fn read_to_nul<R: Read>(r: &mut R, buffer: &mut Vec<u8>) -> Result<()> {
     let mut bytes = r.bytes();
     loop {
         match bytes.next().transpose()? {
             Some(byte) if byte == 0 => {
                 return Ok(());
             }
             Some(_) if buffer.len() == MAX_HEADER_BUF => {
                 return Err(Error::new(
                     ErrorKind::InvalidInput,
                     "gzip header field too long",
                 ));
             }
             Some(byte) => {
                 buffer.push(byte);
             }
             None => {
                 return Err(ErrorKind::UnexpectedEof.into());
             }
         }
     }
 }

 fn parse_le_u16(buffer: &[u8; 2]) -> u16 {
     (buffer[0] as u16) | ((buffer[1] as u16) << 8)
 }

 fn bad_header() -> Error {
     Error::new(ErrorKind::InvalidInput, "invalid gzip header")
 }

 fn corrupt() -> Error {
     Error::new(
         ErrorKind::InvalidInput,
         "corrupt gzip stream does not have a matching checksum",
     )
 }

 /// A builder structure to create a new gzip Encoder.
 ///
 /// This structure controls header configuration options such as the filename.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::io::prelude::*;
 /// # use std::io;
 /// use std::fs::File;
 /// use flate2::GzBuilder;
 /// use flate2::Compression;
 ///
 /// // GzBuilder opens a file and writes a sample string using GzBuilder pattern
 ///
 /// # fn sample_builder() -> Result<(), io::Error> {
 /// let f = File::create("examples/hello_world.gz")?;
 /// let mut gz = GzBuilder::new()
 ///                 .filename("hello_world.txt")
 ///                 .comment("test file, please delete")
 ///                 .write(f, Compression::default());
 /// gz.write_all(b"hello world")?;
 /// gz.finish()?;
 /// # Ok(())
 /// # }
 /// ```
 #[derive(Debug)]
 pub struct GzBuilder {
     extra: Option<Vec<u8>>,
     filename: Option<CString>,
     comment: Option<CString>,
     operating_system: Option<u8>,
     mtime: u32,
 }

 impl Default for GzBuilder {
     fn default() -> Self {
         Self::new()
     }
 }

 impl GzBuilder {
     /// Create a new blank builder with no header by default.
     pub fn new() -> GzBuilder {
         GzBuilder {
             extra: None,
             filename: None,
             comment: None,
             operating_system: None,
             mtime: 0,
         }
     }

     /// Configure the `mtime` field in the gzip header.
     pub fn mtime(mut self, mtime: u32) -> GzBuilder {
         self.mtime = mtime;
         self
     }

     /// Configure the `operating_system` field in the gzip header.
     pub fn operating_system(mut self, os: u8) -> GzBuilder {
         self.operating_system = Some(os);
         self
     }

     /// Configure the `extra` field in the gzip header.
     pub fn extra<T: Into<Vec<u8>>>(mut self, extra: T) -> GzBuilder {
         self.extra = Some(extra.into());
         self
     }

     /// Configure the `filename` field in the gzip header.
     ///
     /// # Panics
     ///
     /// Panics if the `filename` slice contains a zero.
     pub fn filename<T: Into<Vec<u8>>>(mut self, filename: T) -> GzBuilder {
         self.filename = Some(CString::new(filename.into()).unwrap());
         self
     }

     /// Configure the `comment` field in the gzip header.
     ///
     /// # Panics
     ///
     /// Panics if the `comment` slice contains a zero.
     pub fn comment<T: Into<Vec<u8>>>(mut self, comment: T) -> GzBuilder {
         self.comment = Some(CString::new(comment.into()).unwrap());
         self
     }

     /// Consume this builder, creating a writer encoder in the process.
     ///
     /// The data written to the returned encoder will be compressed and then
     /// written out to the supplied parameter `w`.
     pub fn write<W: Write>(self, w: W, lvl: Compression) -> write::GzEncoder<W> {
         write::gz_encoder(self.into_header(lvl), w, lvl)
     }

     /// Consume this builder, creating a reader encoder in the process.
     ///
     /// Data read from the returned encoder will be the compressed version of
     /// the data read from the given reader.
     pub fn read<R: Read>(self, r: R, lvl: Compression) -> read::GzEncoder<R> {
         read::gz_encoder(self.buf_read(BufReader::new(r), lvl))
     }

     /// Consume this builder, creating a reader encoder in the process.
     ///
     /// Data read from the returned encoder will be the compressed version of
     /// the data read from the given reader.
     pub fn buf_read<R>(self, r: R, lvl: Compression) -> bufread::GzEncoder<R>
     where
         R: BufRead,
     {
         bufread::gz_encoder(self.into_header(lvl), r, lvl)
     }

     fn into_header(self, lvl: Compression) -> Vec<u8> {
         let GzBuilder {
             extra,
             filename,
             comment,
             operating_system,
             mtime,
         } = self;
         let mut flg = 0;
         let mut header = vec![0u8; 10];
         if let Some(v) = extra {
             flg |= FEXTRA;
             header.push((v.len() >> 0) as u8);
             header.push((v.len() >> 8) as u8);
             header.extend(v);
         }
         if let Some(filename) = filename {
             flg |= FNAME;
             header.extend(filename.as_bytes_with_nul().iter().copied());
         }
         if let Some(comment) = comment {
             flg |= FCOMMENT;
             header.extend(comment.as_bytes_with_nul().iter().copied());
         }
         header[0] = 0x1f;
         header[1] = 0x8b;
         header[2] = 8;
         header[3] = flg;
         header[4] = (mtime >> 0) as u8;
         header[5] = (mtime >> 8) as u8;
         header[6] = (mtime >> 16) as u8;
         header[7] = (mtime >> 24) as u8;
         header[8] = if lvl.0 >= Compression::best().0 {
             2
         } else if lvl.0 <= Compression::fast().0 {
             4
         } else {
             0
         };

         // Typically this byte indicates what OS the gz stream was created on,
         // but in an effort to have cross-platform reproducible streams just
         // default this value to 255. I'm not sure that if we "correctly" set
         // this it'd do anything anyway...
         header[9] = operating_system.unwrap_or(255);
         header
     }
 }

 #[cfg(test)]
 mod tests {
     use std::io::prelude::*;

     use super::{read, write, GzBuilder, GzHeaderParser};
     use crate::{Compression, GzHeader};
     use rand::{thread_rng, Rng};

     #[test]
     fn roundtrip() {
         let mut e = write::GzEncoder::new(Vec::new(), Compression::default());
         e.write_all(b"foo bar baz").unwrap();
         let inner = e.finish().unwrap();
         let mut d = read::GzDecoder::new(&inner[..]);
         let mut s = String::new();
         d.read_to_string(&mut s).unwrap();
         assert_eq!(s, "foo bar baz");
     }

     #[test]
     fn roundtrip_zero() {
         let e = write::GzEncoder::new(Vec::new(), Compression::default());
         let inner = e.finish().unwrap();
         let mut d = read::GzDecoder::new(&inner[..]);
         let mut s = String::new();
         d.read_to_string(&mut s).unwrap();
         assert_eq!(s, "");
     }

     #[test]
     fn roundtrip_big() {
         let mut real = Vec::new();
         let mut w = write::GzEncoder::new(Vec::new(), Compression::default());
         let v = crate::random_bytes().take(1024).collect::<Vec<_>>();
         for _ in 0..200 {
             let to_write = &v[..thread_rng().gen_range(0..v.len())];
             real.extend(to_write.iter().copied());
             w.write_all(to_write).unwrap();
         }
         let result = w.finish().unwrap();
         let mut r = read::GzDecoder::new(&result[..]);
         let mut v = Vec::new();
         r.read_to_end(&mut v).unwrap();
         assert_eq!(v, real);
     }

     #[test]
     fn roundtrip_big2() {
         let v = crate::random_bytes().take(1024 * 1024).collect::<Vec<_>>();
         let mut r = read::GzDecoder::new(read::GzEncoder::new(&v[..], Compression::default()));
         let mut res = Vec::new();
         r.read_to_end(&mut res).unwrap();
         assert_eq!(res, v);
     }

     // A Rust implementation of CRC that closely matches the C code in RFC1952.
     // Only use this to create CRCs for tests.
     struct Rfc1952Crc {
         /* Table of CRCs of all 8-bit messages. */
         crc_table: [u32; 256],
     }

     impl Rfc1952Crc {
         fn new() -> Self {
             let mut crc = Rfc1952Crc {
                 crc_table: [0; 256],
             };
             /* Make the table for a fast CRC. */
             for n in 0usize..256 {
                 let mut c = n as u32;
                 for _k in 0..8 {
                     if c & 1 != 0 {
                         c = 0xedb88320 ^ (c >> 1);
                     } else {
                         c = c >> 1;
                     }
                 }
                 crc.crc_table[n] = c;
             }
             crc
         }

         /*
          Update a running crc with the bytes buf and return
          the updated crc. The crc should be initialized to zero. Pre- and
          post-conditioning (one's complement) is performed within this
          function so it shouldn't be done by the caller.
         */
         fn update_crc(&self, crc: u32, buf: &[u8]) -> u32 {
             let mut c = crc ^ 0xffffffff;

             for b in buf {
                 c = self.crc_table[(c as u8 ^ *b) as usize] ^ (c >> 8);
             }
             c ^ 0xffffffff
         }

         /* Return the CRC of the bytes buf. */
         fn crc(&self, buf: &[u8]) -> u32 {
             self.update_crc(0, buf)
         }
     }

     #[test]
     fn roundtrip_header() {
         let mut header = GzBuilder::new()
             .mtime(1234)
             .operating_system(57)
             .filename("filename")
             .comment("comment")
             .into_header(Compression::fast());

         // Add a CRC to the header
         header[3] = header[3] ^ super::FHCRC;
         let rfc1952_crc = Rfc1952Crc::new();
         let crc32 = rfc1952_crc.crc(&header);
         let crc16 = crc32 as u16;
         header.extend(&crc16.to_le_bytes());

         let mut parser = GzHeaderParser::new();
         parser.parse(&mut header.as_slice()).unwrap();
         let actual = parser.header().unwrap();
         assert_eq!(
             actual,
             &GzHeader {
                 extra: None,
                 filename: Some("filename".as_bytes().to_vec()),
                 comment: Some("comment".as_bytes().to_vec()),
                 operating_system: 57,
                 mtime: 1234
             }
         )
     }

     #[test]
     fn fields() {
         let r = vec![0, 2, 4, 6];
         let e = GzBuilder::new()
             .filename("foo.rs")
             .comment("bar")
             .extra(vec![0, 1, 2, 3])
             .read(&r[..], Compression::default());
         let mut d = read::GzDecoder::new(e);
         assert_eq!(d.header().unwrap().filename(), Some(&b"foo.rs"[..]));
         assert_eq!(d.header().unwrap().comment(), Some(&b"bar"[..]));
         assert_eq!(d.header().unwrap().extra(), Some(&b"\x00\x01\x02\x03"[..]));
         let mut res = Vec::new();
         d.read_to_end(&mut res).unwrap();
         assert_eq!(res, vec![0, 2, 4, 6]);
     }

     #[test]
     fn keep_reading_after_end() {
         let mut e = write::GzEncoder::new(Vec::new(), Compression::default());
         e.write_all(b"foo bar baz").unwrap();
         let inner = e.finish().unwrap();
         let mut d = read::GzDecoder::new(&inner[..]);
         let mut s = String::new();
         d.read_to_string(&mut s).unwrap();
         assert_eq!(s, "foo bar baz");
         d.read_to_string(&mut s).unwrap();
         assert_eq!(s, "foo bar baz");
     }

     #[test]
     fn qc_reader() {
         ::quickcheck::quickcheck(test as fn(_) -> _);

         fn test(v: Vec<u8>) -> bool {
             let r = read::GzEncoder::new(&v[..], Compression::default());
             let mut r = read::GzDecoder::new(r);
             let mut v2 = Vec::new();
             r.read_to_end(&mut v2).unwrap();
             v == v2
         }
     }

     #[test]
     fn flush_after_write() {
         let mut f = write::GzEncoder::new(Vec::new(), Compression::default());
         write!(f, "Hello world").unwrap();
         f.flush().unwrap();
     }
 }
	use std::ffi::CString;
	use std::io::{BufRead, Error, ErrorKind, Read, Result, Write};
	use std::time;

	use crate::bufreader::BufReader;
	use crate::{Compression, Crc};

	pub static FHCRC: u8 = 1 << 1;
	pub static FEXTRA: u8 = 1 << 2;
	pub static FNAME: u8 = 1 << 3;
	pub static FCOMMENT: u8 = 1 << 4;
	pub static FRESERVED: u8 = 1 << 5 \| 1 << 6 \| 1 << 7;

	pub mod bufread;
	pub mod read;
	pub mod write;

	// The maximum length of the header filename and comment fields. More than
	// enough for these fields in reasonable use, but prevents possible attacks.
	const MAX_HEADER_BUF: usize = 65535;

	/// A structure representing the header of a gzip stream.
	///
	/// The header can contain metadata about the file that was compressed, if
	/// present.
	#[derive(PartialEq, Clone, Debug, Default)]
	pub struct GzHeader {
	extra: Option<Vec<u8>>,
	filename: Option<Vec<u8>>,
	comment: Option<Vec<u8>>,
	operating_system: u8,
	mtime: u32,
	}

	impl GzHeader {
	/// Returns the `filename` field of this gzip stream's header, if present.
	pub fn filename(&self) -> Option<&[u8]> {
	self.filename.as_ref().map(\|s\| &s[..])
	}

	/// Returns the `extra` field of this gzip stream's header, if present.
	pub fn extra(&self) -> Option<&[u8]> {
	self.extra.as_ref().map(\|s\| &s[..])
	}

	/// Returns the `comment` field of this gzip stream's header, if present.
	pub fn comment(&self) -> Option<&[u8]> {
	self.comment.as_ref().map(\|s\| &s[..])
	}

	/// Returns the `operating_system` field of this gzip stream's header.
	///
	/// There are predefined values for various operating systems.
	/// 255 means that the value is unknown.
	pub fn operating_system(&self) -> u8 {
	self.operating_system
	}

	/// This gives the most recent modification time of the original file being compressed.
	///
	/// The time is in Unix format, i.e., seconds since 00:00:00 GMT, Jan. 1, 1970.
	/// (Note that this may cause problems for MS-DOS and other systems that use local
	/// rather than Universal time.) If the compressed data did not come from a file,
	/// `mtime` is set to the time at which compression started.
	/// `mtime` = 0 means no time stamp is available.
	///
	/// The usage of `mtime` is discouraged because of Year 2038 problem.
	pub fn mtime(&self) -> u32 {
	self.mtime
	}

	/// Returns the most recent modification time represented by a date-time type.
	/// Returns `None` if the value of the underlying counter is 0,
	/// indicating no time stamp is available.
	///
	///
	/// The time is measured as seconds since 00:00:00 GMT, Jan. 1 1970.
	/// See [`mtime`](#method.mtime) for more detail.
	pub fn mtime_as_datetime(&self) -> Option<time::SystemTime> {
	if self.mtime == 0 {
	None
	} else {
	let duration = time::Duration::new(u64::from(self.mtime), 0);
	let datetime = time::UNIX_EPOCH + duration;
	Some(datetime)
	}
	}
	}

	#[derive(Debug)]
	pub enum GzHeaderState {
	Start(u8, [u8; 10]),
	Xlen(Option<Box<Crc>>, u8, [u8; 2]),
	Extra(Option<Box<Crc>>, u16),
	Filename(Option<Box<Crc>>),
	Comment(Option<Box<Crc>>),
	Crc(Option<Box<Crc>>, u8, [u8; 2]),
	Complete,
	}

	impl Default for GzHeaderState {
	fn default() -> Self {
	Self::Complete
	}
	}

	#[derive(Debug, Default)]
	pub struct GzHeaderParser {
	state: GzHeaderState,
	flags: u8,
	header: GzHeader,
	}

	impl GzHeaderParser {
	fn new() -> Self {
	GzHeaderParser {
	state: GzHeaderState::Start(0, [0; 10]),
	flags: 0,
	header: GzHeader::default(),
	}
	}

	fn parse<'a, R: Read>(&mut self, r: &'a mut R) -> Result<()> {
	loop {
	match &mut self.state {
	GzHeaderState::Start(count, buffer) => {
	while (*count as usize) < buffer.len() {
	count += read_into(r, &mut buffer[count as usize..])? as u8;
	}
	// Gzip identification bytes
	if buffer[0] != 0x1f \|\| buffer[1] != 0x8b {
	return Err(bad_header());
	}
	// Gzip compression method (8 = deflate)
	if buffer[2] != 8 {
	return Err(bad_header());
	}
	self.flags = buffer[3];
	// RFC1952: "must give an error indication if any reserved bit is non-zero"
	if self.flags & FRESERVED != 0 {
	return Err(bad_header());
	}
	self.header.mtime = ((buffer[4] as u32) << 0)
	\| ((buffer[5] as u32) << 8)
	\| ((buffer[6] as u32) << 16)
	\| ((buffer[7] as u32) << 24);
	let _xfl = buffer[8];
	self.header.operating_system = buffer[9];
	let crc = if self.flags & FHCRC != 0 {
	let mut crc = Box::new(Crc::new());
	crc.update(buffer);
	Some(crc)
	} else {
	None
	};
	self.state = GzHeaderState::Xlen(crc, 0, [0; 2]);
	}
	GzHeaderState::Xlen(crc, count, buffer) => {
	if self.flags & FEXTRA != 0 {
	while (*count as usize) < buffer.len() {
	count += read_into(r, &mut buffer[count as usize..])? as u8;
	}
	if let Some(crc) = crc {
	crc.update(buffer);
	}
	let xlen = parse_le_u16(&buffer);
	self.header.extra = Some(vec![0; xlen as usize]);
	self.state = GzHeaderState::Extra(crc.take(), 0);
	} else {
	self.state = GzHeaderState::Filename(crc.take());
	}
	}
	GzHeaderState::Extra(crc, count) => {
	debug_assert!(self.header.extra.is_some());
	let extra = self.header.extra.as_mut().unwrap();
	while (*count as usize) < extra.len() {
	count += read_into(r, &mut extra[count as usize..])? as u16;
	}
	if let Some(crc) = crc {
	crc.update(extra);
	}
	self.state = GzHeaderState::Filename(crc.take());
	}
	GzHeaderState::Filename(crc) => {
	if self.flags & FNAME != 0 {
	let filename = self.header.filename.get_or_insert_with(Vec::new);
	read_to_nul(r, filename)?;
	if let Some(crc) = crc {
	crc.update(filename);
	crc.update(b"\0");
	}
	}
	self.state = GzHeaderState::Comment(crc.take());
	}
	GzHeaderState::Comment(crc) => {
	if self.flags & FCOMMENT != 0 {
	let comment = self.header.comment.get_or_insert_with(Vec::new);
	read_to_nul(r, comment)?;
	if let Some(crc) = crc {
	crc.update(comment);
	crc.update(b"\0");
	}
	}
	self.state = GzHeaderState::Crc(crc.take(), 0, [0; 2]);
	}
	GzHeaderState::Crc(crc, count, buffer) => {
	if let Some(crc) = crc {
	debug_assert!(self.flags & FHCRC != 0);
	while (*count as usize) < buffer.len() {
	count += read_into(r, &mut buffer[count as usize..])? as u8;
	}
	let stored_crc = parse_le_u16(&buffer);
	let calced_crc = crc.sum() as u16;
	if stored_crc != calced_crc {
	return Err(corrupt());
	}
	}
	self.state = GzHeaderState::Complete;
	}
	GzHeaderState::Complete => {
	return Ok(());
	}
	}
	}
	}

	fn header(&self) -> Option<&GzHeader> {
	match self.state {
	GzHeaderState::Complete => Some(&self.header),
	_ => None,
	}
	}
	}

	impl From<GzHeaderParser> for GzHeader {
	fn from(parser: GzHeaderParser) -> Self {
	debug_assert!(matches!(parser.state, GzHeaderState::Complete));
	parser.header
	}
	}

	// Attempt to fill the `buffer` from `r`. Return the number of bytes read.
	// Return an error if EOF is read before the buffer is full. This differs
	// from `read` in that Ok(0) means that more data may be available.
	fn read_into<R: Read>(r: &mut R, buffer: &mut [u8]) -> Result<usize> {
	debug_assert!(!buffer.is_empty());
	match r.read(buffer) {
	Ok(0) => Err(ErrorKind::UnexpectedEof.into()),
	Ok(n) => Ok(n),
	Err(ref e) if e.kind() == ErrorKind::Interrupted => Ok(0),
	Err(e) => Err(e),
	}
	}

	// Read `r` up to the first nul byte, pushing non-nul bytes to `buffer`.
	fn read_to_nul<R: Read>(r: &mut R, buffer: &mut Vec<u8>) -> Result<()> {
	let mut bytes = r.bytes();
	loop {
	match bytes.next().transpose()? {
	Some(byte) if byte == 0 => {
	return Ok(());
	}
	Some(_) if buffer.len() == MAX_HEADER_BUF => {
	return Err(Error::new(
	ErrorKind::InvalidInput,
	"gzip header field too long",
	));
	}
	Some(byte) => {
	buffer.push(byte);
	}
	None => {
	return Err(ErrorKind::UnexpectedEof.into());
	}
	}
	}
	}

	fn parse_le_u16(buffer: &[u8; 2]) -> u16 {
	(buffer[0] as u16) \| ((buffer[1] as u16) << 8)
	}

	fn bad_header() -> Error {
	Error::new(ErrorKind::InvalidInput, "invalid gzip header")
	}

	fn corrupt() -> Error {
	Error::new(
	ErrorKind::InvalidInput,
	"corrupt gzip stream does not have a matching checksum",
	)
	}

	/// A builder structure to create a new gzip Encoder.
	///
	/// This structure controls header configuration options such as the filename.
	///
	/// # Examples
	///
	/// ```
	/// use std::io::prelude::*;
	/// # use std::io;
	/// use std::fs::File;
	/// use flate2::GzBuilder;
	/// use flate2::Compression;
	///
	/// // GzBuilder opens a file and writes a sample string using GzBuilder pattern
	///
	/// # fn sample_builder() -> Result<(), io::Error> {
	/// let f = File::create("examples/hello_world.gz")?;
	/// let mut gz = GzBuilder::new()
	/// .filename("hello_world.txt")
	/// .comment("test file, please delete")
	/// .write(f, Compression::default());
	/// gz.write_all(b"hello world")?;
	/// gz.finish()?;
	/// # Ok(())
	/// # }
	/// ```
	#[derive(Debug)]
	pub struct GzBuilder {
	extra: Option<Vec<u8>>,
	filename: Option<CString>,
	comment: Option<CString>,
	operating_system: Option<u8>,
	mtime: u32,
	}

	impl Default for GzBuilder {
	fn default() -> Self {
	Self::new()
	}
	}

	impl GzBuilder {
	/// Create a new blank builder with no header by default.
	pub fn new() -> GzBuilder {
	GzBuilder {
	extra: None,
	filename: None,
	comment: None,
	operating_system: None,
	mtime: 0,
	}
	}

	/// Configure the `mtime` field in the gzip header.
	pub fn mtime(mut self, mtime: u32) -> GzBuilder {
	self.mtime = mtime;
	self
	}

	/// Configure the `operating_system` field in the gzip header.
	pub fn operating_system(mut self, os: u8) -> GzBuilder {
	self.operating_system = Some(os);
	self
	}

	/// Configure the `extra` field in the gzip header.
	pub fn extra<T: Into<Vec<u8>>>(mut self, extra: T) -> GzBuilder {
	self.extra = Some(extra.into());
	self
	}

	/// Configure the `filename` field in the gzip header.
	///
	/// # Panics
	///
	/// Panics if the `filename` slice contains a zero.
	pub fn filename<T: Into<Vec<u8>>>(mut self, filename: T) -> GzBuilder {
	self.filename = Some(CString::new(filename.into()).unwrap());
	self
	}

	/// Configure the `comment` field in the gzip header.
	///
	/// # Panics
	///
	/// Panics if the `comment` slice contains a zero.
	pub fn comment<T: Into<Vec<u8>>>(mut self, comment: T) -> GzBuilder {
	self.comment = Some(CString::new(comment.into()).unwrap());
	self
	}

	/// Consume this builder, creating a writer encoder in the process.
	///
	/// The data written to the returned encoder will be compressed and then
	/// written out to the supplied parameter `w`.
	pub fn write<W: Write>(self, w: W, lvl: Compression) -> write::GzEncoder<W> {
	write::gz_encoder(self.into_header(lvl), w, lvl)
	}

	/// Consume this builder, creating a reader encoder in the process.
	///
	/// Data read from the returned encoder will be the compressed version of
	/// the data read from the given reader.
	pub fn read<R: Read>(self, r: R, lvl: Compression) -> read::GzEncoder<R> {
	read::gz_encoder(self.buf_read(BufReader::new(r), lvl))
	}

	/// Consume this builder, creating a reader encoder in the process.
	///
	/// Data read from the returned encoder will be the compressed version of
	/// the data read from the given reader.
	pub fn buf_read<R>(self, r: R, lvl: Compression) -> bufread::GzEncoder<R>
	where
	R: BufRead,
	{
	bufread::gz_encoder(self.into_header(lvl), r, lvl)
	}

	fn into_header(self, lvl: Compression) -> Vec<u8> {
	let GzBuilder {
	extra,
	filename,
	comment,
	operating_system,
	mtime,
	} = self;
	let mut flg = 0;
	let mut header = vec![0u8; 10];
	if let Some(v) = extra {
	flg \|= FEXTRA;
	header.push((v.len() >> 0) as u8);
	header.push((v.len() >> 8) as u8);
	header.extend(v);
	}
	if let Some(filename) = filename {
	flg \|= FNAME;
	header.extend(filename.as_bytes_with_nul().iter().copied());
	}
	if let Some(comment) = comment {
	flg \|= FCOMMENT;
	header.extend(comment.as_bytes_with_nul().iter().copied());
	}
	header[0] = 0x1f;
	header[1] = 0x8b;
	header[2] = 8;
	header[3] = flg;
	header[4] = (mtime >> 0) as u8;
	header[5] = (mtime >> 8) as u8;
	header[6] = (mtime >> 16) as u8;
	header[7] = (mtime >> 24) as u8;
	header[8] = if lvl.0 >= Compression::best().0 {
	2
	} else if lvl.0 <= Compression::fast().0 {
	4
	} else {
	0
	};

	// Typically this byte indicates what OS the gz stream was created on,
	// but in an effort to have cross-platform reproducible streams just
	// default this value to 255. I'm not sure that if we "correctly" set
	// this it'd do anything anyway...
	header[9] = operating_system.unwrap_or(255);
	header
	}
	}

	#[cfg(test)]
	mod tests {
	use std::io::prelude::*;

	use super::{read, write, GzBuilder, GzHeaderParser};
	use crate::{Compression, GzHeader};
	use rand::{thread_rng, Rng};

	#[test]
	fn roundtrip() {
	let mut e = write::GzEncoder::new(Vec::new(), Compression::default());
	e.write_all(b"foo bar baz").unwrap();
	let inner = e.finish().unwrap();
	let mut d = read::GzDecoder::new(&inner[..]);
	let mut s = String::new();
	d.read_to_string(&mut s).unwrap();
	assert_eq!(s, "foo bar baz");
	}

	#[test]
	fn roundtrip_zero() {
	let e = write::GzEncoder::new(Vec::new(), Compression::default());
	let inner = e.finish().unwrap();
	let mut d = read::GzDecoder::new(&inner[..]);
	let mut s = String::new();
	d.read_to_string(&mut s).unwrap();
	assert_eq!(s, "");
	}

	#[test]
	fn roundtrip_big() {
	let mut real = Vec::new();
	let mut w = write::GzEncoder::new(Vec::new(), Compression::default());
	let v = crate::random_bytes().take(1024).collect::<Vec<_>>();
	for _ in 0..200 {
	let to_write = &v[..thread_rng().gen_range(0..v.len())];
	real.extend(to_write.iter().copied());
	w.write_all(to_write).unwrap();
	}
	let result = w.finish().unwrap();
	let mut r = read::GzDecoder::new(&result[..]);
	let mut v = Vec::new();
	r.read_to_end(&mut v).unwrap();
	assert_eq!(v, real);
	}

	#[test]
	fn roundtrip_big2() {
	let v = crate::random_bytes().take(1024 * 1024).collect::<Vec<_>>();
	let mut r = read::GzDecoder::new(read::GzEncoder::new(&v[..], Compression::default()));
	let mut res = Vec::new();
	r.read_to_end(&mut res).unwrap();
	assert_eq!(res, v);
	}

	// A Rust implementation of CRC that closely matches the C code in RFC1952.
	// Only use this to create CRCs for tests.
	struct Rfc1952Crc {
	/* Table of CRCs of all 8-bit messages. */
	crc_table: [u32; 256],
	}

	impl Rfc1952Crc {
	fn new() -> Self {
	let mut crc = Rfc1952Crc {
	crc_table: [0; 256],
	};
	/* Make the table for a fast CRC. */
	for n in 0usize..256 {
	let mut c = n as u32;
	for _k in 0..8 {
	if c & 1 != 0 {
	c = 0xedb88320 ^ (c >> 1);
	} else {
	c = c >> 1;
	}
	}
	crc.crc_table[n] = c;
	}
	crc
	}

	/*
	Update a running crc with the bytes buf and return
	the updated crc. The crc should be initialized to zero. Pre- and
	post-conditioning (one's complement) is performed within this
	function so it shouldn't be done by the caller.
	*/
	fn update_crc(&self, crc: u32, buf: &[u8]) -> u32 {
	let mut c = crc ^ 0xffffffff;

	for b in buf {
	c = self.crc_table[(c as u8 ^ *b) as usize] ^ (c >> 8);
	}
	c ^ 0xffffffff
	}

	/* Return the CRC of the bytes buf. */
	fn crc(&self, buf: &[u8]) -> u32 {
	self.update_crc(0, buf)
	}
	}

	#[test]
	fn roundtrip_header() {
	let mut header = GzBuilder::new()
	.mtime(1234)
	.operating_system(57)
	.filename("filename")
	.comment("comment")
	.into_header(Compression::fast());

	// Add a CRC to the header
	header[3] = header[3] ^ super::FHCRC;
	let rfc1952_crc = Rfc1952Crc::new();
	let crc32 = rfc1952_crc.crc(&header);
	let crc16 = crc32 as u16;
	header.extend(&crc16.to_le_bytes());

	let mut parser = GzHeaderParser::new();
	parser.parse(&mut header.as_slice()).unwrap();
	let actual = parser.header().unwrap();
	assert_eq!(
	actual,
	&GzHeader {
	extra: None,
	filename: Some("filename".as_bytes().to_vec()),
	comment: Some("comment".as_bytes().to_vec()),
	operating_system: 57,
	mtime: 1234
	}
	)
	}

	#[test]
	fn fields() {
	let r = vec![0, 2, 4, 6];
	let e = GzBuilder::new()
	.filename("foo.rs")
	.comment("bar")
	.extra(vec![0, 1, 2, 3])
	.read(&r[..], Compression::default());
	let mut d = read::GzDecoder::new(e);
	assert_eq!(d.header().unwrap().filename(), Some(&b"foo.rs"[..]));
	assert_eq!(d.header().unwrap().comment(), Some(&b"bar"[..]));
	assert_eq!(d.header().unwrap().extra(), Some(&b"\x00\x01\x02\x03"[..]));
	let mut res = Vec::new();
	d.read_to_end(&mut res).unwrap();
	assert_eq!(res, vec![0, 2, 4, 6]);
	}

	#[test]
	fn keep_reading_after_end() {
	let mut e = write::GzEncoder::new(Vec::new(), Compression::default());
	e.write_all(b"foo bar baz").unwrap();
	let inner = e.finish().unwrap();
	let mut d = read::GzDecoder::new(&inner[..]);
	let mut s = String::new();
	d.read_to_string(&mut s).unwrap();
	assert_eq!(s, "foo bar baz");
	d.read_to_string(&mut s).unwrap();
	assert_eq!(s, "foo bar baz");
	}

	#[test]
	fn qc_reader() {
	::quickcheck::quickcheck(test as fn(_) -> _);

	fn test(v: Vec<u8>) -> bool {
	let r = read::GzEncoder::new(&v[..], Compression::default());
	let mut r = read::GzDecoder::new(r);
	let mut v2 = Vec::new();
	r.read_to_end(&mut v2).unwrap();
	v == v2
	}
	}

	#[test]
	fn flush_after_write() {
	let mut f = write::GzEncoder::new(Vec::new(), Compression::default());
	write!(f, "Hello world").unwrap();
	f.flush().unwrap();
	}
	}