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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 zip
import (
// A Compressor returns a compressing writer, writing to the
// provided writer. On Close, any pending data should be flushed.
type Compressor func(io.Writer) (io.WriteCloser, error)
// Decompressor is a function that wraps a Reader with a decompressing Reader.
// The decompressed ReadCloser is returned to callers who open files from
// within the archive. These callers are responsible for closing this reader
// when they're finished reading.
type Decompressor func(io.Reader) io.ReadCloser
var flateWriterPool sync.Pool
func newFlateWriter(w io.Writer) io.WriteCloser {
fw, ok := flateWriterPool.Get().(*flate.Writer)
if ok {
} else {
fw, _ = flate.NewWriter(w, 5)
return &pooledFlateWriter{fw: fw}
type pooledFlateWriter struct {
mu sync.Mutex // guards Close and Write
fw *flate.Writer
func (w *pooledFlateWriter) Write(p []byte) (n int, err error) {
if w.fw == nil {
return 0, errors.New("Write after Close")
return w.fw.Write(p)
func (w *pooledFlateWriter) Close() error {
var err error
if w.fw != nil {
err = w.fw.Close()
w.fw = nil
return err
var (
mu sync.RWMutex // guards compressor and decompressor maps
compressors = map[uint16]Compressor{
Store: func(w io.Writer) (io.WriteCloser, error) { return &nopCloser{w}, nil },
Deflate: func(w io.Writer) (io.WriteCloser, error) { return newFlateWriter(w), nil },
decompressors = map[uint16]Decompressor{
Store: ioutil.NopCloser,
Deflate: flate.NewReader,
// RegisterDecompressor allows custom decompressors for a specified method ID.
func RegisterDecompressor(method uint16, d Decompressor) {
defer mu.Unlock()
if _, ok := decompressors[method]; ok {
panic("decompressor already registered")
decompressors[method] = d
// RegisterCompressor registers custom compressors for a specified method ID.
// The common methods Store and Deflate are built in.
func RegisterCompressor(method uint16, comp Compressor) {
defer mu.Unlock()
if _, ok := compressors[method]; ok {
panic("compressor already registered")
compressors[method] = comp
func compressor(method uint16) Compressor {
defer mu.RUnlock()
return compressors[method]
func decompressor(method uint16) Decompressor {
defer mu.RUnlock()
return decompressors[method]