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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 eventually writing) of
// gzip format compressed files, as specified in RFC 1952.
package gzip
import (
"bufio";
"compress/flate";
"hash";
"hash/crc32";
"io";
"os";
)
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")
// A GzipInflater is an io.Reader that can be read to retrieve
// uncompressed data from a gzip-format compressed file.
// The gzip file stores a header giving metadata about the compressed file.
// That header is exposed as the fields of the GzipInflater struct.
//
// In general, a gzip file can be a concatenation of gzip files,
// each with its own header. Reads from the GzipInflater
// return the concatenation of the uncompressed data of each.
// Only the first header is recorded in the GzipInflater fields.
//
// Gzip files store a length and checksum of the uncompressed data.
// The GzipInflater 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 GzipInflater 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
r flate.Reader;
inflater io.Reader;
digest hash.Hash32;
size uint32;
flg byte;
buf [512]byte;
err os.Error;
eof bool;
}
// NewGzipInflater creates a new GzipInflater reading the given reader.
// The implementation buffers input and may read more data than necessary from r.
func NewGzipInflater(r io.Reader) (*GzipInflater, os.Error) {
z := new(GzipInflater);
z.r = makeReader(r);
z.digest = crc32.NewIEEE();
if err := z.readHeader(true); err != nil {
z.err = err;
return nil, err;
}
return z, nil;
}
func get4(p []byte) uint32 {
return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24;
}
func (z *GzipInflater) 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 {
return string(z.buf[0:i]), nil;
}
}
panic("not reached");
}
func (z *GzipInflater) read2() (uint32, os.Error) {
_, err := z.r.Read(z.buf[0:2]);
if err != nil {
return 0, err;
}
return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil;
}
func (z *GzipInflater) readHeader(save bool) os.Error {
n, 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);
var nn int;
if nn, 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.inflater = flate.NewInflater(z.r);
return nil;
}
func (z *GzipInflater) Read(p []byte) (n int, err os.Error) {
if z.err != nil {
return 0, z.err;
}
if z.eof || len(p) == 0 {
return 0, nil;
}
n, err = z.inflater.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);
}
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