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/crc32"
 	"io"
 	"time"
 )

 // 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
 	HuffmanOnly        = flate.HuffmanOnly
 )

 // A Writer is an io.WriteCloser.
 // Writes to a Writer are compressed and written to w.
 type Writer struct {
 	Header      // written at first call to Write, Flush, or Close
 	w           io.Writer
 	level       int
 	wroteHeader bool
 	compressor  *flate.Writer
 	digest      uint32 // CRC-32, IEEE polynomial (section 8)
 	size        uint32 // Uncompressed size (section 2.3.1)
 	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 [Writer] 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, Flush, or Close.
 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], [HuffmanOnly]
 // 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 < HuffmanOnly || 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) {
 	compressor := z.compressor
 	if compressor != nil {
 		compressor.Reset(w)
 	}
 	*z = Writer{
 		Header: Header{
 			OS: 255, // unknown
 		},
 		w:          w,
 		level:      level,
 		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)
 }

 // 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")
 	}
 	le.PutUint16(z.buf[:2], uint16(len(b)))
 	_, err := z.w.Write(z.buf[: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[: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 = [10]byte{0: gzipID1, 1: gzipID2, 2: gzipDeflate}
 		if z.Extra != nil {
 			z.buf[3] |= 0x04
 		}
 		if z.Name != "" {
 			z.buf[3] |= 0x08
 		}
 		if z.Comment != "" {
 			z.buf[3] |= 0x10
 		}
 		if z.ModTime.After(time.Unix(0, 0)) {
 			// Section 2.3.1, the zero value for MTIME means that the
 			// modified time is not set.
 			le.PutUint32(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
 		}
 		z.buf[9] = z.OS
 		_, z.err = z.w.Write(z.buf[:10])
 		if z.err != nil {
 			return 0, z.err
 		}
 		if z.Extra != nil {
 			z.err = z.writeBytes(z.Extra)
 			if z.err != nil {
 				return 0, z.err
 			}
 		}
 		if z.Name != "" {
 			z.err = z.writeString(z.Name)
 			if z.err != nil {
 				return 0, z.err
 			}
 		}
 		if z.Comment != "" {
 			z.err = z.writeString(z.Comment)
 			if z.err != nil {
 				return 0, z.err
 			}
 		}
 		if z.compressor == nil {
 			z.compressor, _ = flate.NewWriter(z.w, z.level)
 		}
 	}
 	z.size += uint32(len(p))
 	z.digest = crc32.Update(z.digest, crc32.IEEETable, 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] by flushing any unwritten data to the underlying
 // [io.Writer] and writing the GZIP footer.
 // It 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
 	}
 	le.PutUint32(z.buf[:4], z.digest)
 	le.PutUint32(z.buf[4:8], z.size)
 	_, z.err = z.w.Write(z.buf[: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/crc32"
	"io"
	"time"
	)

	// 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
	HuffmanOnly = flate.HuffmanOnly
	)

	// A Writer is an io.WriteCloser.
	// Writes to a Writer are compressed and written to w.
	type Writer struct {
	Header // written at first call to Write, Flush, or Close
	w io.Writer
	level int
	wroteHeader bool
	compressor *flate.Writer
	digest uint32 // CRC-32, IEEE polynomial (section 8)
	size uint32 // Uncompressed size (section 2.3.1)
	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 [Writer] 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, Flush, or Close.
	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], [HuffmanOnly]
	// 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 < HuffmanOnly \|\| 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) {
	compressor := z.compressor
	if compressor != nil {
	compressor.Reset(w)
	}
	*z = Writer{
	Header: Header{
	OS: 255, // unknown
	},
	w: w,
	level: level,
	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)
	}

	// 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")
	}
	le.PutUint16(z.buf[:2], uint16(len(b)))
	_, err := z.w.Write(z.buf[: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[: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 = [10]byte{0: gzipID1, 1: gzipID2, 2: gzipDeflate}
	if z.Extra != nil {
	z.buf[3] \|= 0x04
	}
	if z.Name != "" {
	z.buf[3] \|= 0x08
	}
	if z.Comment != "" {
	z.buf[3] \|= 0x10
	}
	if z.ModTime.After(time.Unix(0, 0)) {
	// Section 2.3.1, the zero value for MTIME means that the
	// modified time is not set.
	le.PutUint32(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
	}
	z.buf[9] = z.OS
	_, z.err = z.w.Write(z.buf[:10])
	if z.err != nil {
	return 0, z.err
	}
	if z.Extra != nil {
	z.err = z.writeBytes(z.Extra)
	if z.err != nil {
	return 0, z.err
	}
	}
	if z.Name != "" {
	z.err = z.writeString(z.Name)
	if z.err != nil {
	return 0, z.err
	}
	}
	if z.Comment != "" {
	z.err = z.writeString(z.Comment)
	if z.err != nil {
	return 0, z.err
	}
	}
	if z.compressor == nil {
	z.compressor, _ = flate.NewWriter(z.w, z.level)
	}
	}
	z.size += uint32(len(p))
	z.digest = crc32.Update(z.digest, crc32.IEEETable, 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] by flushing any unwritten data to the underlying
	// [io.Writer] and writing the GZIP footer.
	// It 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
	}
	le.PutUint32(z.buf[:4], z.digest)
	le.PutUint32(z.buf[4:8], z.size)
	_, z.err = z.w.Write(z.buf[:8])
	return z.err
	}