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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 gzip package implements reading and writing of
// gzip format compressed files, as specified in RFC 1952.
package gzip
import (
"bufio"
"compress/flate"
"hash"
"hash/crc32"
"io"
"os"
)
// BUG(nigeltao): Comments and Names don't properly map UTF-8 character codes outside of
// the 0x00-0x7f range to ISO 8859-1 (Latin-1).
const (
gzipID1 = 0x1f
gzipID2 = 0x8b
gzipDeflate = 8
flagText = 1 << 0
flagHdrCrc = 1 << 1
flagExtra = 1 << 2
flagName = 1 << 3
flagComment = 1 << 4
)
func makeReader(r io.Reader) flate.Reader {
if rr, ok := r.(flate.Reader); ok {
return rr
}
return bufio.NewReader(r)
}
var HeaderError os.Error = os.ErrorString("invalid gzip header")
var ChecksumError os.Error = os.ErrorString("gzip checksum error")
// The gzip file stores a header giving metadata about the compressed file.
// That header is exposed as the fields of the Compressor and Decompressor structs.
type Header struct {
Comment string // comment
Extra []byte // "extra data"
Mtime uint32 // modification time (seconds since January 1, 1970)
Name string // file name
OS byte // operating system type
}
// An Decompressor is an io.Reader that can be read to retrieve
// uncompressed data from a gzip-format compressed file.
//
// In general, a gzip file can be a concatenation of gzip files,
// each with its own header. Reads from the Decompressor
// return the concatenation of the uncompressed data of each.
// Only the first header is recorded in the Decompressor fields.
//
// Gzip files store a length and checksum of the uncompressed data.
// The Decompressor will return a ChecksumError when Read
// reaches the end of the uncompressed data if it does not
// have the expected length or checksum. Clients should treat data
// returned by Read as tentative until they receive the successful
// (zero length, nil error) Read marking the end of the data.
type Decompressor struct {
Header
r flate.Reader
decompressor io.ReadCloser
digest hash.Hash32
size uint32
flg byte
buf [512]byte
err os.Error
}
// NewReader creates a new Decompressor reading the given reader.
// The implementation buffers input and may read more data than necessary from r.
// It is the caller's responsibility to call Close on the Decompressor when done.
func NewReader(r io.Reader) (*Decompressor, os.Error) {
z := new(Decompressor)
z.r = makeReader(r)
z.digest = crc32.NewIEEE()
if err := z.readHeader(true); err != nil {
z.err = err
return nil, err
}
return z, nil
}
// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
func get4(p []byte) uint32 {
return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
}
func (z *Decompressor) readString() (string, os.Error) {
var err os.Error
for i := 0; ; i++ {
if i >= len(z.buf) {
return "", HeaderError
}
z.buf[i], err = z.r.ReadByte()
if err != nil {
return "", err
}
if z.buf[i] == 0 {
// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
// TODO(nigeltao): Convert from ISO 8859-1 (Latin-1) to UTF-8.
return string(z.buf[0:i]), nil
}
}
panic("not reached")
}
func (z *Decompressor) read2() (uint32, os.Error) {
_, err := io.ReadFull(z.r, z.buf[0:2])
if err != nil {
return 0, err
}
return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil
}
func (z *Decompressor) readHeader(save bool) os.Error {
_, err := io.ReadFull(z.r, z.buf[0:10])
if err != nil {
return err
}
if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
return HeaderError
}
z.flg = z.buf[3]
if save {
z.Mtime = get4(z.buf[4:8])
// z.buf[8] is xfl, ignored
z.OS = z.buf[9]
}
z.digest.Reset()
z.digest.Write(z.buf[0:10])
if z.flg&flagExtra != 0 {
n, err := z.read2()
if err != nil {
return err
}
data := make([]byte, n)
if _, err = io.ReadFull(z.r, data); err != nil {
return err
}
if save {
z.Extra = data
}
}
var s string
if z.flg&flagName != 0 {
if s, err = z.readString(); err != nil {
return err
}
if save {
z.Name = s
}
}
if z.flg&flagComment != 0 {
if s, err = z.readString(); err != nil {
return err
}
if save {
z.Comment = s
}
}
if z.flg&flagHdrCrc != 0 {
n, err := z.read2()
if err != nil {
return err
}
sum := z.digest.Sum32() & 0xFFFF
if n != sum {
return HeaderError
}
}
z.digest.Reset()
z.decompressor = flate.NewReader(z.r)
return nil
}
func (z *Decompressor) 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.decompressor.Read(p)
z.digest.Write(p[0:n])
z.size += uint32(n)
if n != 0 || err != os.EOF {
z.err = err
return
}
// Finished file; check checksum + size.
if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil {
z.err = err
return 0, err
}
crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8])
sum := z.digest.Sum32()
if sum != crc32 || isize != z.size {
z.err = ChecksumError
return 0, z.err
}
// File is ok; is there another?
if err = z.readHeader(false); err != nil {
z.err = err
return
}
// Yes. Reset and read from it.
z.digest.Reset()
z.size = 0
return z.Read(p)
}
// Calling Close does not close the wrapped io.Reader originally passed to NewReader.
func (z *Decompressor) Close() os.Error { return z.decompressor.Close() }
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