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"
 	"encoding/binary"
 	"errors"
 	"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
 )

 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")
 )

 var le = binary.LittleEndian

 // noEOF converts io.EOF to io.ErrUnexpectedEOF.
 func noEOF(err error) error {
 	if err == io.EOF {
 		return io.ErrUnexpectedEOF
 	}
 	return err
 }

 // 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 an [ErrChecksum] when [Reader.Read]
 // reaches the end of the uncompressed data if it does not
 // have the expected length or checksum. Clients should treat data
 // returned by [Reader.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       uint32 // CRC-32, IEEE polynomial (section 8)
 	size         uint32 // Uncompressed size (section 2.3.1)
 	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)
 	if err := z.Reset(r); 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 = Reader{
 		decompressor: z.decompressor,
 		multistream:  true,
 	}
 	if rr, ok := r.(flate.Reader); ok {
 		z.r = rr
 	} else {
 		z.r = bufio.NewReader(r)
 	}
 	z.Header, z.err = z.readHeader()
 	return z.err
 }

 // 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,
 // [Reader.Read] returns [io.EOF]. The underlying reader must implement [io.ByteReader]
 // in order to 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
 }

 // readString reads a NUL-terminated string from z.r.
 // It treats the bytes read as being encoded as ISO 8859-1 (Latin-1) and
 // will output a string encoded using UTF-8.
 // This method always updates z.digest with the data read.
 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 {
 			// Digest covers the NUL terminator.
 			z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:i+1])

 			// Strings are ISO 8859-1, Latin-1 (RFC 1952, section 2.3.1).
 			if needConv {
 				s := make([]rune, 0, i)
 				for _, v := range z.buf[:i] {
 					s = append(s, rune(v))
 				}
 				return string(s), nil
 			}
 			return string(z.buf[:i]), nil
 		}
 	}
 }

 // readHeader reads the GZIP header according to section 2.3.1.
 // This method does not set z.err.
 func (z *Reader) readHeader() (hdr Header, err error) {
 	if _, err = io.ReadFull(z.r, z.buf[:10]); err != nil {
 		// RFC 1952, 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 hdr, err
 	}
 	if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
 		return hdr, ErrHeader
 	}
 	flg := z.buf[3]
 	if t := int64(le.Uint32(z.buf[4:8])); t > 0 {
 		// Section 2.3.1, the zero value for MTIME means that the
 		// modified time is not set.
 		hdr.ModTime = time.Unix(t, 0)
 	}
 	// z.buf[8] is XFL and is currently ignored.
 	hdr.OS = z.buf[9]
 	z.digest = crc32.ChecksumIEEE(z.buf[:10])

 	if flg&flagExtra != 0 {
 		if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
 			return hdr, noEOF(err)
 		}
 		z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:2])
 		data := make([]byte, le.Uint16(z.buf[:2]))
 		if _, err = io.ReadFull(z.r, data); err != nil {
 			return hdr, noEOF(err)
 		}
 		z.digest = crc32.Update(z.digest, crc32.IEEETable, data)
 		hdr.Extra = data
 	}

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

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

 	if flg&flagHdrCrc != 0 {
 		if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
 			return hdr, noEOF(err)
 		}
 		digest := le.Uint16(z.buf[:2])
 		if digest != uint16(z.digest) {
 			return hdr, ErrHeader
 		}
 	}

 	z.digest = 0
 	if z.decompressor == nil {
 		z.decompressor = flate.NewReader(z.r)
 	} else {
 		z.decompressor.(flate.Resetter).Reset(z.r, nil)
 	}
 	return hdr, nil
 }

 // Read implements [io.Reader], reading uncompressed bytes from its underlying [Reader].
 func (z *Reader) Read(p []byte) (n int, err error) {
 	if z.err != nil {
 		return 0, z.err
 	}

 	for n == 0 {
 		n, z.err = z.decompressor.Read(p)
 		z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n])
 		z.size += uint32(n)
 		if z.err != io.EOF {
 			// In the normal case we return here.
 			return n, z.err
 		}

 		// Finished file; check checksum and size.
 		if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil {
 			z.err = noEOF(err)
 			return n, z.err
 		}
 		digest := le.Uint32(z.buf[:4])
 		size := le.Uint32(z.buf[4:8])
 		if digest != z.digest || size != z.size {
 			z.err = ErrChecksum
 			return n, z.err
 		}
 		z.digest, z.size = 0, 0

 		// File is ok; check if there is another.
 		if !z.multistream {
 			return n, io.EOF
 		}
 		z.err = nil // Remove io.EOF

 		if _, z.err = z.readHeader(); z.err != nil {
 			return n, z.err
 		}
 	}

 	return n, nil
 }

 // Close closes the [Reader]. It does not close the underlying [io.Reader].
 // In order for the GZIP checksum to be verified, the reader must be
 // fully consumed until the [io.EOF].
 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"
	"encoding/binary"
	"errors"
	"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
	)

	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")
	)

	var le = binary.LittleEndian

	// noEOF converts io.EOF to io.ErrUnexpectedEOF.
	func noEOF(err error) error {
	if err == io.EOF {
	return io.ErrUnexpectedEOF
	}
	return err
	}

	// 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 an [ErrChecksum] when [Reader.Read]
	// reaches the end of the uncompressed data if it does not
	// have the expected length or checksum. Clients should treat data
	// returned by [Reader.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 uint32 // CRC-32, IEEE polynomial (section 8)
	size uint32 // Uncompressed size (section 2.3.1)
	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)
	if err := z.Reset(r); 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 = Reader{
	decompressor: z.decompressor,
	multistream: true,
	}
	if rr, ok := r.(flate.Reader); ok {
	z.r = rr
	} else {
	z.r = bufio.NewReader(r)
	}
	z.Header, z.err = z.readHeader()
	return z.err
	}

	// 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,
	// [Reader.Read] returns [io.EOF]. The underlying reader must implement [io.ByteReader]
	// in order to 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
	}

	// readString reads a NUL-terminated string from z.r.
	// It treats the bytes read as being encoded as ISO 8859-1 (Latin-1) and
	// will output a string encoded using UTF-8.
	// This method always updates z.digest with the data read.
	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 {
	// Digest covers the NUL terminator.
	z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:i+1])

	// Strings are ISO 8859-1, Latin-1 (RFC 1952, section 2.3.1).
	if needConv {
	s := make([]rune, 0, i)
	for _, v := range z.buf[:i] {
	s = append(s, rune(v))
	}
	return string(s), nil
	}
	return string(z.buf[:i]), nil
	}
	}
	}

	// readHeader reads the GZIP header according to section 2.3.1.
	// This method does not set z.err.
	func (z *Reader) readHeader() (hdr Header, err error) {
	if _, err = io.ReadFull(z.r, z.buf[:10]); err != nil {
	// RFC 1952, 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 hdr, err
	}
	if z.buf[0] != gzipID1 \|\| z.buf[1] != gzipID2 \|\| z.buf[2] != gzipDeflate {
	return hdr, ErrHeader
	}
	flg := z.buf[3]
	if t := int64(le.Uint32(z.buf[4:8])); t > 0 {
	// Section 2.3.1, the zero value for MTIME means that the
	// modified time is not set.
	hdr.ModTime = time.Unix(t, 0)
	}
	// z.buf[8] is XFL and is currently ignored.
	hdr.OS = z.buf[9]
	z.digest = crc32.ChecksumIEEE(z.buf[:10])

	if flg&flagExtra != 0 {
	if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
	return hdr, noEOF(err)
	}
	z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:2])
	data := make([]byte, le.Uint16(z.buf[:2]))
	if _, err = io.ReadFull(z.r, data); err != nil {
	return hdr, noEOF(err)
	}
	z.digest = crc32.Update(z.digest, crc32.IEEETable, data)
	hdr.Extra = data
	}

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

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

	if flg&flagHdrCrc != 0 {
	if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
	return hdr, noEOF(err)
	}
	digest := le.Uint16(z.buf[:2])
	if digest != uint16(z.digest) {
	return hdr, ErrHeader
	}
	}

	z.digest = 0
	if z.decompressor == nil {
	z.decompressor = flate.NewReader(z.r)
	} else {
	z.decompressor.(flate.Resetter).Reset(z.r, nil)
	}
	return hdr, nil
	}

	// Read implements [io.Reader], reading uncompressed bytes from its underlying [Reader].
	func (z *Reader) Read(p []byte) (n int, err error) {
	if z.err != nil {
	return 0, z.err
	}

	for n == 0 {
	n, z.err = z.decompressor.Read(p)
	z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n])
	z.size += uint32(n)
	if z.err != io.EOF {
	// In the normal case we return here.
	return n, z.err
	}

	// Finished file; check checksum and size.
	if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil {
	z.err = noEOF(err)
	return n, z.err
	}
	digest := le.Uint32(z.buf[:4])
	size := le.Uint32(z.buf[4:8])
	if digest != z.digest \|\| size != z.size {
	z.err = ErrChecksum
	return n, z.err
	}
	z.digest, z.size = 0, 0

	// File is ok; check if there is another.
	if !z.multistream {
	return n, io.EOF
	}
	z.err = nil // Remove io.EOF

	if _, z.err = z.readHeader(); z.err != nil {
	return n, z.err
	}
	}

	return n, nil
	}

	// Close closes the [Reader]. It does not close the underlying [io.Reader].
	// In order for the GZIP checksum to be verified, the reader must be
	// fully consumed until the [io.EOF].
	func (z *Reader) Close() error { return z.decompressor.Close() }