218 lines
5.1 KiB
Go
218 lines
5.1 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package gzip
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import (
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"compress/flate"
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"errors"
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"fmt"
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"hash"
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"hash/crc32"
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"io"
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)
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// These constants are copied from the flate package, so that code that imports
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// "compress/gzip" does not also have to import "compress/flate".
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const (
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NoCompression = flate.NoCompression
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BestSpeed = flate.BestSpeed
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BestCompression = flate.BestCompression
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DefaultCompression = flate.DefaultCompression
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)
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// A Writer is an io.WriteCloser that satisfies writes by compressing data written
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// to its wrapped io.Writer.
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type Writer struct {
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Header
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w io.Writer
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level int
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compressor io.WriteCloser
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digest hash.Hash32
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size uint32
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closed bool
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buf [10]byte
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err error
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}
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// NewWriter creates a new Writer that satisfies writes by compressing data
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// written to w.
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//
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// It is the caller's responsibility to call Close on the WriteCloser when done.
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// Writes may be buffered and not flushed until Close.
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//
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// Callers that wish to set the fields in Writer.Header must do so before
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// the first call to Write or Close. The Comment and Name header fields are
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// UTF-8 strings in Go, but the underlying format requires NUL-terminated ISO
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// 8859-1 (Latin-1). NUL or non-Latin-1 runes in those strings will lead to an
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// error on Write.
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func NewWriter(w io.Writer) *Writer {
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z, _ := NewWriterLevel(w, DefaultCompression)
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return z
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}
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// NewWriterLevel is like NewWriter but specifies the compression level instead
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// of assuming DefaultCompression.
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//
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// The compression level can be DefaultCompression, NoCompression, or any
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// integer value between BestSpeed and BestCompression inclusive. The error
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// returned will be nil if the level is valid.
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func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
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if level < DefaultCompression || level > BestCompression {
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return nil, fmt.Errorf("gzip: invalid compression level: %d", level)
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}
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return &Writer{
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Header: Header{
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OS: 255, // unknown
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},
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w: w,
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level: level,
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digest: crc32.NewIEEE(),
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}, nil
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}
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// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
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func put2(p []byte, v uint16) {
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p[0] = uint8(v >> 0)
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p[1] = uint8(v >> 8)
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}
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func put4(p []byte, v uint32) {
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p[0] = uint8(v >> 0)
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p[1] = uint8(v >> 8)
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p[2] = uint8(v >> 16)
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p[3] = uint8(v >> 24)
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}
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// writeBytes writes a length-prefixed byte slice to z.w.
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func (z *Writer) writeBytes(b []byte) error {
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if len(b) > 0xffff {
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return errors.New("gzip.Write: Extra data is too large")
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}
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put2(z.buf[0:2], uint16(len(b)))
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_, err := z.w.Write(z.buf[0:2])
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if err != nil {
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return err
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}
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_, err = z.w.Write(b)
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return err
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}
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// writeString writes a UTF-8 string s in GZIP's format to z.w.
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// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
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func (z *Writer) writeString(s string) (err error) {
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// GZIP stores Latin-1 strings; error if non-Latin-1; convert if non-ASCII.
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needconv := false
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for _, v := range s {
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if v == 0 || v > 0xff {
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return errors.New("gzip.Write: non-Latin-1 header string")
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}
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if v > 0x7f {
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needconv = true
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}
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}
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if needconv {
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b := make([]byte, 0, len(s))
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for _, v := range s {
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b = append(b, byte(v))
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}
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_, err = z.w.Write(b)
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} else {
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_, err = io.WriteString(z.w, s)
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}
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if err != nil {
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return err
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}
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// GZIP strings are NUL-terminated.
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z.buf[0] = 0
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_, err = z.w.Write(z.buf[0:1])
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return err
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}
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// Write writes a compressed form of p to the underlying io.Writer. The
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// compressed bytes are not necessarily flushed until the Writer is closed.
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func (z *Writer) Write(p []byte) (int, error) {
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if z.err != nil {
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return 0, z.err
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}
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var n int
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// Write the GZIP header lazily.
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if z.compressor == nil {
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z.buf[0] = gzipID1
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z.buf[1] = gzipID2
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z.buf[2] = gzipDeflate
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z.buf[3] = 0
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if z.Extra != nil {
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z.buf[3] |= 0x04
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}
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if z.Name != "" {
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z.buf[3] |= 0x08
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}
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if z.Comment != "" {
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z.buf[3] |= 0x10
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}
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put4(z.buf[4:8], uint32(z.ModTime.Unix()))
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if z.level == BestCompression {
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z.buf[8] = 2
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} else if z.level == BestSpeed {
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z.buf[8] = 4
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} else {
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z.buf[8] = 0
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}
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z.buf[9] = z.OS
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n, z.err = z.w.Write(z.buf[0:10])
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if z.err != nil {
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return n, z.err
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}
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if z.Extra != nil {
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z.err = z.writeBytes(z.Extra)
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if z.err != nil {
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return n, z.err
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}
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}
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if z.Name != "" {
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z.err = z.writeString(z.Name)
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if z.err != nil {
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return n, z.err
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}
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}
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if z.Comment != "" {
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z.err = z.writeString(z.Comment)
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if z.err != nil {
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return n, z.err
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}
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}
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z.compressor, _ = flate.NewWriter(z.w, z.level)
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}
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z.size += uint32(len(p))
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z.digest.Write(p)
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n, z.err = z.compressor.Write(p)
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return n, z.err
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}
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// Close closes the Writer. It does not close the underlying io.Writer.
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func (z *Writer) Close() error {
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if z.err != nil {
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return z.err
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}
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if z.closed {
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return nil
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}
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z.closed = true
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if z.compressor == nil {
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z.Write(nil)
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if z.err != nil {
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return z.err
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}
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}
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z.err = z.compressor.Close()
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if z.err != nil {
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return z.err
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}
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put4(z.buf[0:4], z.digest.Sum32())
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put4(z.buf[4:8], z.size)
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_, z.err = z.w.Write(z.buf[0:8])
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return z.err
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}
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