232 lines
5.4 KiB
Go
232 lines
5.4 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package gzip implements reading and writing of gzip format compressed files,
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// as specified in RFC 1952.
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package gzip
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import (
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"bufio"
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"compress/flate"
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"errors"
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"hash"
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"hash/crc32"
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"io"
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"time"
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)
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// BUG(nigeltao): Comments and Names don't properly map UTF-8 character codes outside of
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// the 0x00-0x7f range to ISO 8859-1 (Latin-1).
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const (
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gzipID1 = 0x1f
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gzipID2 = 0x8b
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gzipDeflate = 8
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flagText = 1 << 0
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flagHdrCrc = 1 << 1
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flagExtra = 1 << 2
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flagName = 1 << 3
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flagComment = 1 << 4
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)
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func makeReader(r io.Reader) flate.Reader {
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if rr, ok := r.(flate.Reader); ok {
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return rr
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}
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return bufio.NewReader(r)
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}
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var HeaderError = errors.New("invalid gzip header")
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var ChecksumError = errors.New("gzip checksum error")
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// The gzip file stores a header giving metadata about the compressed file.
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// That header is exposed as the fields of the Compressor and Decompressor structs.
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type Header struct {
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Comment string // comment
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Extra []byte // "extra data"
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ModTime time.Time // modification time
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Name string // file name
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OS byte // operating system type
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}
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// An Decompressor is an io.Reader that can be read to retrieve
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// uncompressed data from a gzip-format compressed file.
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//
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// In general, a gzip file can be a concatenation of gzip files,
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// each with its own header. Reads from the Decompressor
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// return the concatenation of the uncompressed data of each.
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// Only the first header is recorded in the Decompressor fields.
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//
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// Gzip files store a length and checksum of the uncompressed data.
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// The Decompressor will return a ChecksumError when Read
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// reaches the end of the uncompressed data if it does not
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// have the expected length or checksum. Clients should treat data
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// returned by Read as tentative until they receive the successful
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// (zero length, nil error) Read marking the end of the data.
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type Decompressor struct {
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Header
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r flate.Reader
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decompressor io.ReadCloser
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digest hash.Hash32
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size uint32
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flg byte
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buf [512]byte
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err error
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}
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// NewReader creates a new Decompressor reading the given reader.
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// The implementation buffers input and may read more data than necessary from r.
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// It is the caller's responsibility to call Close on the Decompressor when done.
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func NewReader(r io.Reader) (*Decompressor, error) {
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z := new(Decompressor)
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z.r = makeReader(r)
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z.digest = crc32.NewIEEE()
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if err := z.readHeader(true); err != nil {
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z.err = err
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return nil, err
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}
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return z, nil
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}
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// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
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func get4(p []byte) uint32 {
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return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
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}
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func (z *Decompressor) readString() (string, error) {
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var err error
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for i := 0; ; i++ {
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if i >= len(z.buf) {
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return "", HeaderError
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}
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z.buf[i], err = z.r.ReadByte()
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if err != nil {
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return "", err
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}
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if z.buf[i] == 0 {
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// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
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// TODO(nigeltao): Convert from ISO 8859-1 (Latin-1) to UTF-8.
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return string(z.buf[0:i]), nil
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}
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}
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panic("not reached")
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}
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func (z *Decompressor) read2() (uint32, error) {
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_, err := io.ReadFull(z.r, z.buf[0:2])
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if err != nil {
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return 0, err
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}
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return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil
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}
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func (z *Decompressor) readHeader(save bool) error {
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_, err := io.ReadFull(z.r, z.buf[0:10])
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if err != nil {
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return err
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}
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if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
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return HeaderError
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}
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z.flg = z.buf[3]
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if save {
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z.ModTime = time.Unix(int64(get4(z.buf[4:8])), 0)
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// z.buf[8] is xfl, ignored
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z.OS = z.buf[9]
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}
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z.digest.Reset()
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z.digest.Write(z.buf[0:10])
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if z.flg&flagExtra != 0 {
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n, err := z.read2()
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if err != nil {
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return err
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}
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data := make([]byte, n)
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if _, err = io.ReadFull(z.r, data); err != nil {
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return err
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}
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if save {
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z.Extra = data
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}
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}
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var s string
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if z.flg&flagName != 0 {
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if s, err = z.readString(); err != nil {
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return err
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}
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if save {
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z.Name = s
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}
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}
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if z.flg&flagComment != 0 {
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if s, err = z.readString(); err != nil {
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return err
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}
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if save {
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z.Comment = s
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}
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}
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if z.flg&flagHdrCrc != 0 {
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n, err := z.read2()
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if err != nil {
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return err
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}
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sum := z.digest.Sum32() & 0xFFFF
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if n != sum {
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return HeaderError
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}
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}
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z.digest.Reset()
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z.decompressor = flate.NewReader(z.r)
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return nil
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}
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func (z *Decompressor) Read(p []byte) (n int, err error) {
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if z.err != nil {
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return 0, z.err
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}
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if len(p) == 0 {
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return 0, nil
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}
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n, err = z.decompressor.Read(p)
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z.digest.Write(p[0:n])
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z.size += uint32(n)
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if n != 0 || err != io.EOF {
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z.err = err
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return
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}
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// Finished file; check checksum + size.
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if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil {
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z.err = err
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return 0, err
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}
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crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8])
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sum := z.digest.Sum32()
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if sum != crc32 || isize != z.size {
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z.err = ChecksumError
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return 0, z.err
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}
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// File is ok; is there another?
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if err = z.readHeader(false); err != nil {
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z.err = err
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return
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}
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// Yes. Reset and read from it.
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z.digest.Reset()
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z.size = 0
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return z.Read(p)
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}
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// Calling Close does not close the wrapped io.Reader originally passed to NewReader.
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func (z *Decompressor) Close() error { return z.decompressor.Close() }
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