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// Copyright 2009 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.
// The zlib package implements reading and writing of zlib
// format compressed files, as specified in RFC 1950.
package zlib
import (
"bufio"
"compress/flate"
"hash"
"hash/adler32"
"io"
"os"
)
const zlibDeflate = 8
var ChecksumError os.Error = os.ErrorString("zlib checksum error")
var HeaderError os.Error = os.ErrorString("invalid zlib header")
var UnsupportedError os.Error = os.ErrorString("unsupported zlib format")
type reader struct {
r flate.Reader
inflater io.ReadCloser
digest hash.Hash32
err os.Error
scratch [4]byte
}
// NewInflater creates a new io.ReadCloser that satisfies reads by decompressing data read from r.
// The implementation buffers input and may read more data than necessary from r.
// It is the caller's responsibility to call Close on the ReadCloser when done.
func NewInflater(r io.Reader) (io.ReadCloser, os.Error) {
z := new(reader)
if fr, ok := r.(flate.Reader); ok {
z.r = fr
} else {
z.r = bufio.NewReader(r)
}
_, err := io.ReadFull(z.r, z.scratch[0:2])
if err != nil {
return nil, err
}
h := uint(z.scratch[0])<<8 | uint(z.scratch[1])
if (z.scratch[0]&0x0f != zlibDeflate) || (h%31 != 0) {
return nil, HeaderError
}
if z.scratch[1]&0x20 != 0 {
// BUG(nigeltao): The zlib package does not implement the FDICT flag.
return nil, UnsupportedError
}
z.digest = adler32.New()
z.inflater = flate.NewInflater(z.r)
return z, nil
}
func (z *reader) Read(p []byte) (n int, err os.Error) {
if z.err != nil {
return 0, z.err
}
if len(p) == 0 {
return 0, nil
}
n, err = z.inflater.Read(p)
z.digest.Write(p[0:n])
if n != 0 || err != os.EOF {
z.err = err
return
}
// Finished file; check checksum.
if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil {
z.err = err
return 0, err
}
// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])
if checksum != z.digest.Sum32() {
z.err = ChecksumError
return 0, z.err
}
return
}
// Calling Close does not close the wrapped io.Reader originally passed to NewInflater.
func (z *reader) Close() os.Error {
if z.err != nil {
return z.err
}
z.err = z.inflater.Close()
return z.err
}
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