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

 // Copyright 2010 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

 import (
 	"compress/flate"
 	"errors"
 	"fmt"
 	"hash"
 	"hash/crc32"
 	"io"
 )

 // These constants are copied from the flate package, so that code that imports
 // "compress/gzip" does not also have to import "compress/flate".
 const (
 	NoCompression      = flate.NoCompression
 	BestSpeed          = flate.BestSpeed
 	BestCompression    = flate.BestCompression
 	DefaultCompression = flate.DefaultCompression
 )

 // A Writer is an io.WriteCloser.
 // Writes to a Writer are compressed and written to w.
 type Writer struct {
 	Header
 	w           io.Writer
 	level       int
 	wroteHeader bool
 	compressor  *flate.Writer
 	digest      hash.Hash32
 	size        uint32
 	closed      bool
 	buf         [10]byte
 	err         error
 }

 // NewWriter returns a new Writer.
 // Writes to the returned writer are compressed and written to w.
 //
 // It is the caller's responsibility to call Close on the WriteCloser when done.
 // Writes may be buffered and not flushed until Close.
 //
 // Callers that wish to set the fields in Writer.Header must do so before
 // the first call to Write or Close. The Comment and Name header fields are
 // UTF-8 strings in Go, but the underlying format requires NUL-terminated ISO
 // 8859-1 (Latin-1). NUL or non-Latin-1 runes in those strings will lead to an
 // error on Write.
 func NewWriter(w io.Writer) *Writer {
 	z, _ := NewWriterLevel(w, DefaultCompression)
 	return z
 }

 // NewWriterLevel is like NewWriter but specifies the compression level instead
 // of assuming DefaultCompression.
 //
 // The compression level can be DefaultCompression, NoCompression, or any
 // integer value between BestSpeed and BestCompression inclusive. The error
 // returned will be nil if the level is valid.
 func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
 	if level < DefaultCompression || level > BestCompression {
 		return nil, fmt.Errorf("gzip: invalid compression level: %d", level)
 	}
 	z := new(Writer)
 	z.init(w, level)
 	return z, nil
 }

 func (z *Writer) init(w io.Writer, level int) {
 	digest := z.digest
 	if digest != nil {
 		digest.Reset()
 	} else {
 		digest = crc32.NewIEEE()
 	}
 	compressor := z.compressor
 	if compressor != nil {
 		compressor.Reset(w)
 	}
 	*z = Writer{
 		Header: Header{
 			OS: 255, // unknown
 		},
 		w:          w,
 		level:      level,
 		digest:     digest,
 		compressor: compressor,
 	}
 }

 // Reset discards the Writer z's state and makes it equivalent to the
 // result of its original state from NewWriter or NewWriterLevel, but
 // writing to w instead. This permits reusing a Writer rather than
 // allocating a new one.
 func (z *Writer) Reset(w io.Writer) {
 	z.init(w, z.level)
 }

 // GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
 func put2(p []byte, v uint16) {
 	p[0] = uint8(v >> 0)
 	p[1] = uint8(v >> 8)
 }

 func put4(p []byte, v uint32) {
 	p[0] = uint8(v >> 0)
 	p[1] = uint8(v >> 8)
 	p[2] = uint8(v >> 16)
 	p[3] = uint8(v >> 24)
 }

 // writeBytes writes a length-prefixed byte slice to z.w.
 func (z *Writer) writeBytes(b []byte) error {
 	if len(b) > 0xffff {
 		return errors.New("gzip.Write: Extra data is too large")
 	}
 	put2(z.buf[0:2], uint16(len(b)))
 	_, err := z.w.Write(z.buf[0:2])
 	if err != nil {
 		return err
 	}
 	_, err = z.w.Write(b)
 	return err
 }

 // writeString writes a UTF-8 string s in GZIP's format to z.w.
 // GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
 func (z *Writer) writeString(s string) (err error) {
 	// GZIP stores Latin-1 strings; error if non-Latin-1; convert if non-ASCII.
 	needconv := false
 	for _, v := range s {
 		if v == 0 || v > 0xff {
 			return errors.New("gzip.Write: non-Latin-1 header string")
 		}
 		if v > 0x7f {
 			needconv = true
 		}
 	}
 	if needconv {
 		b := make([]byte, 0, len(s))
 		for _, v := range s {
 			b = append(b, byte(v))
 		}
 		_, err = z.w.Write(b)
 	} else {
 		_, err = io.WriteString(z.w, s)
 	}
 	if err != nil {
 		return err
 	}
 	// GZIP strings are NUL-terminated.
 	z.buf[0] = 0
 	_, err = z.w.Write(z.buf[0:1])
 	return err
 }

 // Write writes a compressed form of p to the underlying io.Writer. The
 // compressed bytes are not necessarily flushed until the Writer is closed.
 func (z *Writer) Write(p []byte) (int, error) {
 	if z.err != nil {
 		return 0, z.err
 	}
 	var n int
 	// Write the GZIP header lazily.
 	if !z.wroteHeader {
 		z.wroteHeader = true
 		z.buf[0] = gzipID1
 		z.buf[1] = gzipID2
 		z.buf[2] = gzipDeflate
 		z.buf[3] = 0
 		if z.Extra != nil {
 			z.buf[3] |= 0x04
 		}
 		if z.Name != "" {
 			z.buf[3] |= 0x08
 		}
 		if z.Comment != "" {
 			z.buf[3] |= 0x10
 		}
 		put4(z.buf[4:8], uint32(z.ModTime.Unix()))
 		if z.level == BestCompression {
 			z.buf[8] = 2
 		} else if z.level == BestSpeed {
 			z.buf[8] = 4
 		} else {
 			z.buf[8] = 0
 		}
 		z.buf[9] = z.OS
 		n, z.err = z.w.Write(z.buf[0:10])
 		if z.err != nil {
 			return n, z.err
 		}
 		if z.Extra != nil {
 			z.err = z.writeBytes(z.Extra)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 		if z.Name != "" {
 			z.err = z.writeString(z.Name)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 		if z.Comment != "" {
 			z.err = z.writeString(z.Comment)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 		if z.compressor == nil {
 			z.compressor, _ = flate.NewWriter(z.w, z.level)
 		}
 	}
 	z.size += uint32(len(p))
 	z.digest.Write(p)
 	n, z.err = z.compressor.Write(p)
 	return n, z.err
 }

 // Flush flushes any pending compressed data to the underlying writer.
 //
 // It is useful mainly in compressed network protocols, to ensure that
 // a remote reader has enough data to reconstruct a packet. Flush does
 // not return until the data has been written. If the underlying
 // writer returns an error, Flush returns that error.
 //
 // In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
 func (z *Writer) Flush() error {
 	if z.err != nil {
 		return z.err
 	}
 	if z.closed {
 		return nil
 	}
 	if !z.wroteHeader {
 		z.Write(nil)
 		if z.err != nil {
 			return z.err
 		}
 	}
 	z.err = z.compressor.Flush()
 	return z.err
 }

 // Close closes the Writer, flushing any unwritten data to the underlying
 // io.Writer, but does not close the underlying io.Writer.
 func (z *Writer) Close() error {
 	if z.err != nil {
 		return z.err
 	}
 	if z.closed {
 		return nil
 	}
 	z.closed = true
 	if !z.wroteHeader {
 		z.Write(nil)
 		if z.err != nil {
 			return z.err
 		}
 	}
 	z.err = z.compressor.Close()
 	if z.err != nil {
 		return z.err
 	}
 	put4(z.buf[0:4], z.digest.Sum32())
 	put4(z.buf[4:8], z.size)
 	_, z.err = z.w.Write(z.buf[0:8])
 	return z.err
 }
	// Copyright 2010 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

	import (
	"compress/flate"
	"errors"
	"fmt"
	"hash"
	"hash/crc32"
	"io"
	)

	// These constants are copied from the flate package, so that code that imports
	// "compress/gzip" does not also have to import "compress/flate".
	const (
	NoCompression = flate.NoCompression
	BestSpeed = flate.BestSpeed
	BestCompression = flate.BestCompression
	DefaultCompression = flate.DefaultCompression
	)

	// A Writer is an io.WriteCloser.
	// Writes to a Writer are compressed and written to w.
	type Writer struct {
	Header
	w io.Writer
	level int
	wroteHeader bool
	compressor *flate.Writer
	digest hash.Hash32
	size uint32
	closed bool
	buf [10]byte
	err error
	}

	// NewWriter returns a new Writer.
	// Writes to the returned writer are compressed and written to w.
	//
	// It is the caller's responsibility to call Close on the WriteCloser when done.
	// Writes may be buffered and not flushed until Close.
	//
	// Callers that wish to set the fields in Writer.Header must do so before
	// the first call to Write or Close. The Comment and Name header fields are
	// UTF-8 strings in Go, but the underlying format requires NUL-terminated ISO
	// 8859-1 (Latin-1). NUL or non-Latin-1 runes in those strings will lead to an
	// error on Write.
	func NewWriter(w io.Writer) *Writer {
	z, _ := NewWriterLevel(w, DefaultCompression)
	return z
	}

	// NewWriterLevel is like NewWriter but specifies the compression level instead
	// of assuming DefaultCompression.
	//
	// The compression level can be DefaultCompression, NoCompression, or any
	// integer value between BestSpeed and BestCompression inclusive. The error
	// returned will be nil if the level is valid.
	func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
	if level < DefaultCompression \|\| level > BestCompression {
	return nil, fmt.Errorf("gzip: invalid compression level: %d", level)
	}
	z := new(Writer)
	z.init(w, level)
	return z, nil
	}

	func (z *Writer) init(w io.Writer, level int) {
	digest := z.digest
	if digest != nil {
	digest.Reset()
	} else {
	digest = crc32.NewIEEE()
	}
	compressor := z.compressor
	if compressor != nil {
	compressor.Reset(w)
	}
	*z = Writer{
	Header: Header{
	OS: 255, // unknown
	},
	w: w,
	level: level,
	digest: digest,
	compressor: compressor,
	}
	}

	// Reset discards the Writer z's state and makes it equivalent to the
	// result of its original state from NewWriter or NewWriterLevel, but
	// writing to w instead. This permits reusing a Writer rather than
	// allocating a new one.
	func (z *Writer) Reset(w io.Writer) {
	z.init(w, z.level)
	}

	// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
	func put2(p []byte, v uint16) {
	p[0] = uint8(v >> 0)
	p[1] = uint8(v >> 8)
	}

	func put4(p []byte, v uint32) {
	p[0] = uint8(v >> 0)
	p[1] = uint8(v >> 8)
	p[2] = uint8(v >> 16)
	p[3] = uint8(v >> 24)
	}

	// writeBytes writes a length-prefixed byte slice to z.w.
	func (z *Writer) writeBytes(b []byte) error {
	if len(b) > 0xffff {
	return errors.New("gzip.Write: Extra data is too large")
	}
	put2(z.buf[0:2], uint16(len(b)))
	_, err := z.w.Write(z.buf[0:2])
	if err != nil {
	return err
	}
	_, err = z.w.Write(b)
	return err
	}

	// writeString writes a UTF-8 string s in GZIP's format to z.w.
	// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
	func (z *Writer) writeString(s string) (err error) {
	// GZIP stores Latin-1 strings; error if non-Latin-1; convert if non-ASCII.
	needconv := false
	for _, v := range s {
	if v == 0 \|\| v > 0xff {
	return errors.New("gzip.Write: non-Latin-1 header string")
	}
	if v > 0x7f {
	needconv = true
	}
	}
	if needconv {
	b := make([]byte, 0, len(s))
	for _, v := range s {
	b = append(b, byte(v))
	}
	_, err = z.w.Write(b)
	} else {
	_, err = io.WriteString(z.w, s)
	}
	if err != nil {
	return err
	}
	// GZIP strings are NUL-terminated.
	z.buf[0] = 0
	_, err = z.w.Write(z.buf[0:1])
	return err
	}

	// Write writes a compressed form of p to the underlying io.Writer. The
	// compressed bytes are not necessarily flushed until the Writer is closed.
	func (z *Writer) Write(p []byte) (int, error) {
	if z.err != nil {
	return 0, z.err
	}
	var n int
	// Write the GZIP header lazily.
	if !z.wroteHeader {
	z.wroteHeader = true
	z.buf[0] = gzipID1
	z.buf[1] = gzipID2
	z.buf[2] = gzipDeflate
	z.buf[3] = 0
	if z.Extra != nil {
	z.buf[3] \|= 0x04
	}
	if z.Name != "" {
	z.buf[3] \|= 0x08
	}
	if z.Comment != "" {
	z.buf[3] \|= 0x10
	}
	put4(z.buf[4:8], uint32(z.ModTime.Unix()))
	if z.level == BestCompression {
	z.buf[8] = 2
	} else if z.level == BestSpeed {
	z.buf[8] = 4
	} else {
	z.buf[8] = 0
	}
	z.buf[9] = z.OS
	n, z.err = z.w.Write(z.buf[0:10])
	if z.err != nil {
	return n, z.err
	}
	if z.Extra != nil {
	z.err = z.writeBytes(z.Extra)
	if z.err != nil {
	return n, z.err
	}
	}
	if z.Name != "" {
	z.err = z.writeString(z.Name)
	if z.err != nil {
	return n, z.err
	}
	}
	if z.Comment != "" {
	z.err = z.writeString(z.Comment)
	if z.err != nil {
	return n, z.err
	}
	}
	if z.compressor == nil {
	z.compressor, _ = flate.NewWriter(z.w, z.level)
	}
	}
	z.size += uint32(len(p))
	z.digest.Write(p)
	n, z.err = z.compressor.Write(p)
	return n, z.err
	}

	// Flush flushes any pending compressed data to the underlying writer.
	//
	// It is useful mainly in compressed network protocols, to ensure that
	// a remote reader has enough data to reconstruct a packet. Flush does
	// not return until the data has been written. If the underlying
	// writer returns an error, Flush returns that error.
	//
	// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
	func (z *Writer) Flush() error {
	if z.err != nil {
	return z.err
	}
	if z.closed {
	return nil
	}
	if !z.wroteHeader {
	z.Write(nil)
	if z.err != nil {
	return z.err
	}
	}
	z.err = z.compressor.Flush()
	return z.err
	}

	// Close closes the Writer, flushing any unwritten data to the underlying
	// io.Writer, but does not close the underlying io.Writer.
	func (z *Writer) Close() error {
	if z.err != nil {
	return z.err
	}
	if z.closed {
	return nil
	}
	z.closed = true
	if !z.wroteHeader {
	z.Write(nil)
	if z.err != nil {
	return z.err
	}
	}
	z.err = z.compressor.Close()
	if z.err != nil {
	return z.err
	}
	put4(z.buf[0:4], z.digest.Sum32())
	put4(z.buf[4:8], z.size)
	_, z.err = z.w.Write(z.buf[0:8])
	return z.err
	}