src/compress/gzip/gunzip.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package gzip implements reading and writing of gzip format compressed files,
 // as specified in RFC 1952.
 package gzip

 import (
 	"bufio"
 	"compress/flate"
 	"errors"
 	"hash"
 	"hash/crc32"
 	"io"
 	"time"
 )

 const (
 	gzipID1     = 0x1f
 	gzipID2     = 0x8b
 	gzipDeflate = 8
 	flagText    = 1 << 0
 	flagHdrCrc  = 1 << 1
 	flagExtra   = 1 << 2
 	flagName    = 1 << 3
 	flagComment = 1 << 4
 )

 func makeReader(r io.Reader) flate.Reader {
 	if rr, ok := r.(flate.Reader); ok {
 		return rr
 	}
 	return bufio.NewReader(r)
 }

 var (
 	// ErrChecksum is returned when reading GZIP data that has an invalid checksum.
 	ErrChecksum = errors.New("gzip: invalid checksum")
 	// ErrHeader is returned when reading GZIP data that has an invalid header.
 	ErrHeader = errors.New("gzip: invalid header")
 )

 // The gzip file stores a header giving metadata about the compressed file.
 // That header is exposed as the fields of the Writer and Reader structs.
 //
 // Strings must be UTF-8 encoded and may only contain Unicode code points
 // U+0001 through U+00FF, due to limitations of the GZIP file format.
 type Header struct {
 	Comment string    // comment
 	Extra   []byte    // "extra data"
 	ModTime time.Time // modification time
 	Name    string    // file name
 	OS      byte      // operating system type
 }

 // A Reader is an io.Reader that can be read to retrieve
 // uncompressed data from a gzip-format compressed file.
 //
 // In general, a gzip file can be a concatenation of gzip files,
 // each with its own header.  Reads from the Reader
 // return the concatenation of the uncompressed data of each.
 // Only the first header is recorded in the Reader fields.
 //
 // Gzip files store a length and checksum of the uncompressed data.
 // The Reader will return a ErrChecksum when Read
 // reaches the end of the uncompressed data if it does not
 // have the expected length or checksum.  Clients should treat data
 // returned by Read as tentative until they receive the io.EOF
 // marking the end of the data.
 type Reader struct {
 	Header       // valid after NewReader or Reader.Reset
 	r            flate.Reader
 	decompressor io.ReadCloser
 	digest       hash.Hash32
 	size         uint32
 	flg          byte
 	buf          [512]byte
 	err          error
 	multistream  bool
 }

 // NewReader creates a new Reader reading the given reader.
 // If r does not also implement io.ByteReader,
 // the decompressor may read more data than necessary from r.
 //
 // It is the caller's responsibility to call Close on the Reader when done.
 //
 // The Reader.Header fields will be valid in the Reader returned.
 func NewReader(r io.Reader) (*Reader, error) {
 	z := new(Reader)
 	z.r = makeReader(r)
 	z.multistream = true
 	z.digest = crc32.NewIEEE()
 	if err := z.readHeader(true); err != nil {
 		return nil, err
 	}
 	return z, nil
 }

 // Reset discards the Reader z's state and makes it equivalent to the
 // result of its original state from NewReader, but reading from r instead.
 // This permits reusing a Reader rather than allocating a new one.
 func (z *Reader) Reset(r io.Reader) error {
 	z.r = makeReader(r)
 	if z.digest == nil {
 		z.digest = crc32.NewIEEE()
 	} else {
 		z.digest.Reset()
 	}
 	z.size = 0
 	z.err = nil
 	z.multistream = true
 	return z.readHeader(true)
 }

 // Multistream controls whether the reader supports multistream files.
 //
 // If enabled (the default), the Reader expects the input to be a sequence
 // of individually gzipped data streams, each with its own header and
 // trailer, ending at EOF. The effect is that the concatenation of a sequence
 // of gzipped files is treated as equivalent to the gzip of the concatenation
 // of the sequence. This is standard behavior for gzip readers.
 //
 // Calling Multistream(false) disables this behavior; disabling the behavior
 // can be useful when reading file formats that distinguish individual gzip
 // data streams or mix gzip data streams with other data streams.
 // In this mode, when the Reader reaches the end of the data stream,
 // Read returns io.EOF. If the underlying reader implements io.ByteReader,
 // it will be left positioned just after the gzip stream.
 // To start the next stream, call z.Reset(r) followed by z.Multistream(false).
 // If there is no next stream, z.Reset(r) will return io.EOF.
 func (z *Reader) Multistream(ok bool) {
 	z.multistream = ok
 }

 // GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
 func get4(p []byte) uint32 {
 	return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
 }

 func (z *Reader) readString() (string, error) {
 	var err error
 	needconv := false
 	for i := 0; ; i++ {
 		if i >= len(z.buf) {
 			return "", ErrHeader
 		}
 		z.buf[i], err = z.r.ReadByte()
 		if err != nil {
 			return "", err
 		}
 		if z.buf[i] > 0x7f {
 			needconv = true
 		}
 		if z.buf[i] == 0 {
 			// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
 			if needconv {
 				s := make([]rune, 0, i)
 				for _, v := range z.buf[0:i] {
 					s = append(s, rune(v))
 				}
 				return string(s), nil
 			}
 			return string(z.buf[0:i]), nil
 		}
 	}
 }

 func (z *Reader) read2() (uint32, error) {
 	_, err := io.ReadFull(z.r, z.buf[0:2])
 	if err != nil {
 		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
 		}
 		return 0, err
 	}
 	return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil
 }

 func (z *Reader) readHeader(save bool) error {
 	_, err := io.ReadFull(z.r, z.buf[0:10])
 	if err != nil {
 		// RFC1952 section 2.2 says the following:
 		//	A gzip file consists of a series of "members" (compressed data sets).
 		//
 		// Other than this, the specification does not clarify whether a
 		// "series" is defined as "one or more" or "zero or more". To err on the
 		// side of caution, Go interprets this to mean "zero or more".
 		// Thus, it is okay to return io.EOF here.
 		return err
 	}
 	if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
 		return ErrHeader
 	}
 	z.flg = z.buf[3]
 	if save {
 		z.ModTime = time.Unix(int64(get4(z.buf[4:8])), 0)
 		// z.buf[8] is xfl, ignored
 		z.OS = z.buf[9]
 	}
 	z.digest.Reset()
 	z.digest.Write(z.buf[0:10])

 	if z.flg&flagExtra != 0 {
 		n, err := z.read2()
 		if err != nil {
 			return err
 		}
 		data := make([]byte, n)
 		if _, err = io.ReadFull(z.r, data); err != nil {
 			if err == io.EOF {
 				err = io.ErrUnexpectedEOF
 			}
 			return err
 		}
 		if save {
 			z.Extra = data
 		}
 	}

 	var s string
 	if z.flg&flagName != 0 {
 		if s, err = z.readString(); err != nil {
 			return err
 		}
 		if save {
 			z.Name = s
 		}
 	}

 	if z.flg&flagComment != 0 {
 		if s, err = z.readString(); err != nil {
 			return err
 		}
 		if save {
 			z.Comment = s
 		}
 	}

 	if z.flg&flagHdrCrc != 0 {
 		n, err := z.read2()
 		if err != nil {
 			return err
 		}
 		sum := z.digest.Sum32() & 0xFFFF
 		if n != sum {
 			return ErrHeader
 		}
 	}

 	z.digest.Reset()
 	if z.decompressor == nil {
 		z.decompressor = flate.NewReader(z.r)
 	} else {
 		z.decompressor.(flate.Resetter).Reset(z.r, nil)
 	}
 	return nil
 }

 func (z *Reader) Read(p []byte) (n int, err error) {
 	if z.err != nil {
 		return 0, z.err
 	}
 	if len(p) == 0 {
 		return 0, nil
 	}

 	n, err = z.decompressor.Read(p)
 	z.digest.Write(p[0:n])
 	z.size += uint32(n)
 	if n != 0 || err != io.EOF {
 		z.err = err
 		return
 	}

 	// Finished file; check checksum + size.
 	if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil {
 		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
 		}
 		z.err = err
 		return 0, err
 	}
 	crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8])
 	sum := z.digest.Sum32()
 	if sum != crc32 || isize != z.size {
 		z.err = ErrChecksum
 		return 0, z.err
 	}

 	// File is ok; is there another?
 	if !z.multistream {
 		return 0, io.EOF
 	}

 	if err = z.readHeader(false); err != nil {
 		z.err = err
 		return
 	}

 	// Yes.  Reset and read from it.
 	z.digest.Reset()
 	z.size = 0
 	return z.Read(p)
 }

 // Close closes the Reader. It does not close the underlying io.Reader.
 func (z *Reader) Close() error { return z.decompressor.Close() }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package gzip implements reading and writing of gzip format compressed files,
	// as specified in RFC 1952.
	package gzip

	import (
	"bufio"
	"compress/flate"
	"errors"
	"hash"
	"hash/crc32"
	"io"
	"time"
	)

	const (
	gzipID1 = 0x1f
	gzipID2 = 0x8b
	gzipDeflate = 8
	flagText = 1 << 0
	flagHdrCrc = 1 << 1
	flagExtra = 1 << 2
	flagName = 1 << 3
	flagComment = 1 << 4
	)

	func makeReader(r io.Reader) flate.Reader {
	if rr, ok := r.(flate.Reader); ok {
	return rr
	}
	return bufio.NewReader(r)
	}

	var (
	// ErrChecksum is returned when reading GZIP data that has an invalid checksum.
	ErrChecksum = errors.New("gzip: invalid checksum")
	// ErrHeader is returned when reading GZIP data that has an invalid header.
	ErrHeader = errors.New("gzip: invalid header")
	)

	// The gzip file stores a header giving metadata about the compressed file.
	// That header is exposed as the fields of the Writer and Reader structs.
	//
	// Strings must be UTF-8 encoded and may only contain Unicode code points
	// U+0001 through U+00FF, due to limitations of the GZIP file format.
	type Header struct {
	Comment string // comment
	Extra []byte // "extra data"
	ModTime time.Time // modification time
	Name string // file name
	OS byte // operating system type
	}

	// A Reader is an io.Reader that can be read to retrieve
	// uncompressed data from a gzip-format compressed file.
	//
	// In general, a gzip file can be a concatenation of gzip files,
	// each with its own header. Reads from the Reader
	// return the concatenation of the uncompressed data of each.
	// Only the first header is recorded in the Reader fields.
	//
	// Gzip files store a length and checksum of the uncompressed data.
	// The Reader will return a ErrChecksum when Read
	// reaches the end of the uncompressed data if it does not
	// have the expected length or checksum. Clients should treat data
	// returned by Read as tentative until they receive the io.EOF
	// marking the end of the data.
	type Reader struct {
	Header // valid after NewReader or Reader.Reset
	r flate.Reader
	decompressor io.ReadCloser
	digest hash.Hash32
	size uint32
	flg byte
	buf [512]byte
	err error
	multistream bool
	}

	// NewReader creates a new Reader reading the given reader.
	// If r does not also implement io.ByteReader,
	// the decompressor may read more data than necessary from r.
	//
	// It is the caller's responsibility to call Close on the Reader when done.
	//
	// The Reader.Header fields will be valid in the Reader returned.
	func NewReader(r io.Reader) (*Reader, error) {
	z := new(Reader)
	z.r = makeReader(r)
	z.multistream = true
	z.digest = crc32.NewIEEE()
	if err := z.readHeader(true); err != nil {
	return nil, err
	}
	return z, nil
	}

	// Reset discards the Reader z's state and makes it equivalent to the
	// result of its original state from NewReader, but reading from r instead.
	// This permits reusing a Reader rather than allocating a new one.
	func (z *Reader) Reset(r io.Reader) error {
	z.r = makeReader(r)
	if z.digest == nil {
	z.digest = crc32.NewIEEE()
	} else {
	z.digest.Reset()
	}
	z.size = 0
	z.err = nil
	z.multistream = true
	return z.readHeader(true)
	}

	// Multistream controls whether the reader supports multistream files.
	//
	// If enabled (the default), the Reader expects the input to be a sequence
	// of individually gzipped data streams, each with its own header and
	// trailer, ending at EOF. The effect is that the concatenation of a sequence
	// of gzipped files is treated as equivalent to the gzip of the concatenation
	// of the sequence. This is standard behavior for gzip readers.
	//
	// Calling Multistream(false) disables this behavior; disabling the behavior
	// can be useful when reading file formats that distinguish individual gzip
	// data streams or mix gzip data streams with other data streams.
	// In this mode, when the Reader reaches the end of the data stream,
	// Read returns io.EOF. If the underlying reader implements io.ByteReader,
	// it will be left positioned just after the gzip stream.
	// To start the next stream, call z.Reset(r) followed by z.Multistream(false).
	// If there is no next stream, z.Reset(r) will return io.EOF.
	func (z *Reader) Multistream(ok bool) {
	z.multistream = ok
	}

	// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
	func get4(p []byte) uint32 {
	return uint32(p[0]) \| uint32(p[1])<<8 \| uint32(p[2])<<16 \| uint32(p[3])<<24
	}

	func (z *Reader) readString() (string, error) {
	var err error
	needconv := false
	for i := 0; ; i++ {
	if i >= len(z.buf) {
	return "", ErrHeader
	}
	z.buf[i], err = z.r.ReadByte()
	if err != nil {
	return "", err
	}
	if z.buf[i] > 0x7f {
	needconv = true
	}
	if z.buf[i] == 0 {
	// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
	if needconv {
	s := make([]rune, 0, i)
	for _, v := range z.buf[0:i] {
	s = append(s, rune(v))
	}
	return string(s), nil
	}
	return string(z.buf[0:i]), nil
	}
	}
	}

	func (z *Reader) read2() (uint32, error) {
	_, err := io.ReadFull(z.r, z.buf[0:2])
	if err != nil {
	if err == io.EOF {
	err = io.ErrUnexpectedEOF
	}
	return 0, err
	}
	return uint32(z.buf[0]) \| uint32(z.buf[1])<<8, nil
	}

	func (z *Reader) readHeader(save bool) error {
	_, err := io.ReadFull(z.r, z.buf[0:10])
	if err != nil {
	// RFC1952 section 2.2 says the following:
	// A gzip file consists of a series of "members" (compressed data sets).
	//
	// Other than this, the specification does not clarify whether a
	// "series" is defined as "one or more" or "zero or more". To err on the
	// side of caution, Go interprets this to mean "zero or more".
	// Thus, it is okay to return io.EOF here.
	return err
	}
	if z.buf[0] != gzipID1 \|\| z.buf[1] != gzipID2 \|\| z.buf[2] != gzipDeflate {
	return ErrHeader
	}
	z.flg = z.buf[3]
	if save {
	z.ModTime = time.Unix(int64(get4(z.buf[4:8])), 0)
	// z.buf[8] is xfl, ignored
	z.OS = z.buf[9]
	}
	z.digest.Reset()
	z.digest.Write(z.buf[0:10])

	if z.flg&flagExtra != 0 {
	n, err := z.read2()
	if err != nil {
	return err
	}
	data := make([]byte, n)
	if _, err = io.ReadFull(z.r, data); err != nil {
	if err == io.EOF {
	err = io.ErrUnexpectedEOF
	}
	return err
	}
	if save {
	z.Extra = data
	}
	}

	var s string
	if z.flg&flagName != 0 {
	if s, err = z.readString(); err != nil {
	return err
	}
	if save {
	z.Name = s
	}
	}

	if z.flg&flagComment != 0 {
	if s, err = z.readString(); err != nil {
	return err
	}
	if save {
	z.Comment = s
	}
	}

	if z.flg&flagHdrCrc != 0 {
	n, err := z.read2()
	if err != nil {
	return err
	}
	sum := z.digest.Sum32() & 0xFFFF
	if n != sum {
	return ErrHeader
	}
	}

	z.digest.Reset()
	if z.decompressor == nil {
	z.decompressor = flate.NewReader(z.r)
	} else {
	z.decompressor.(flate.Resetter).Reset(z.r, nil)
	}
	return nil
	}

	func (z *Reader) Read(p []byte) (n int, err error) {
	if z.err != nil {
	return 0, z.err
	}
	if len(p) == 0 {
	return 0, nil
	}

	n, err = z.decompressor.Read(p)
	z.digest.Write(p[0:n])
	z.size += uint32(n)
	if n != 0 \|\| err != io.EOF {
	z.err = err
	return
	}

	// Finished file; check checksum + size.
	if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil {
	if err == io.EOF {
	err = io.ErrUnexpectedEOF
	}
	z.err = err
	return 0, err
	}
	crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8])
	sum := z.digest.Sum32()
	if sum != crc32 \|\| isize != z.size {
	z.err = ErrChecksum
	return 0, z.err
	}

	// File is ok; is there another?
	if !z.multistream {
	return 0, io.EOF
	}

	if err = z.readHeader(false); err != nil {
	z.err = err
	return
	}

	// Yes. Reset and read from it.
	z.digest.Reset()
	z.size = 0
	return z.Read(p)
	}

	// Close closes the Reader. It does not close the underlying io.Reader.
	func (z *Reader) Close() error { return z.decompressor.Close() }