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// 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 that satisfies writes by compressing data written
// to its wrapped io.Writer.
type Writer struct {
Header
w io.Writer
level int
compressor io.WriteCloser
digest hash.Hash32
size uint32
closed bool
buf [10]byte
err error
}
// NewWriter creates a new Writer that satisfies writes by compressing data
// 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)
}
return &Writer{
Header: Header{
OS: 255, // unknown
},
w: w,
level: level,
digest: crc32.NewIEEE(),
}, nil
}
// 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.compressor == nil {
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
}
}
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
}
// Close closes the Writer. 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.compressor == nil {
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
}
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