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// Copyright 2016 The Gorilla WebSocket 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 websocket
import (
"compress/flate"
"errors"
"io"
"strings"
)
func decompressNoContextTakeover(r io.Reader) io.Reader {
const tail =
// Add four bytes as specified in RFC
"\x00\x00\xff\xff" +
// Add final block to squelch unexpected EOF error from flate reader.
"\x01\x00\x00\xff\xff"
return flate.NewReader(io.MultiReader(r, strings.NewReader(tail)))
}
func compressNoContextTakeover(w io.WriteCloser) (io.WriteCloser, error) {
tw := &truncWriter{w: w}
fw, err := flate.NewWriter(tw, 3)
return &flateWrapper{fw: fw, tw: tw}, err
}
// truncWriter is an io.Writer that writes all but the last four bytes of the
// stream to another io.Writer.
type truncWriter struct {
w io.WriteCloser
n int
p [4]byte
}
func (w *truncWriter) Write(p []byte) (int, error) {
n := 0
// fill buffer first for simplicity.
if w.n < len(w.p) {
n = copy(w.p[w.n:], p)
p = p[n:]
w.n += n
if len(p) == 0 {
return n, nil
}
}
m := len(p)
if m > len(w.p) {
m = len(w.p)
}
if nn, err := w.w.Write(w.p[:m]); err != nil {
return n + nn, err
}
copy(w.p[:], w.p[m:])
copy(w.p[len(w.p)-m:], p[len(p)-m:])
nn, err := w.w.Write(p[:len(p)-m])
return n + nn, err
}
type flateWrapper struct {
fw *flate.Writer
tw *truncWriter
}
func (w *flateWrapper) Write(p []byte) (int, error) {
return w.fw.Write(p)
}
func (w *flateWrapper) Close() error {
err1 := w.fw.Flush()
if w.tw.p != [4]byte{0, 0, 0xff, 0xff} {
return errors.New("websocket: internal error, unexpected bytes at end of flate stream")
}
err2 := w.tw.w.Close()
if err1 != nil {
return err1
}
return err2
}
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