381 lines
10 KiB
Go
381 lines
10 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/gzip"
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"encoding/binary"
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"hash/crc32"
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"io"
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"time"
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"github.com/klauspost/compress/flate"
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)
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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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var (
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// ErrChecksum is returned when reading GZIP data that has an invalid checksum.
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ErrChecksum = gzip.ErrChecksum
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// ErrHeader is returned when reading GZIP data that has an invalid header.
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ErrHeader = gzip.ErrHeader
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)
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var le = binary.LittleEndian
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// noEOF converts io.EOF to io.ErrUnexpectedEOF.
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func noEOF(err error) error {
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if err == io.EOF {
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return io.ErrUnexpectedEOF
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}
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return err
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}
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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 Writer and Reader structs.
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//
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// Strings must be UTF-8 encoded and may only contain Unicode code points
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// U+0001 through U+00FF, due to limitations of the GZIP file format.
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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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// A Reader 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 Reader
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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 Reader 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 Reader will return a ErrChecksum 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 io.EOF
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// marking the end of the data.
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type Reader struct {
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Header // valid after NewReader or Reader.Reset
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r flate.Reader
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br *bufio.Reader
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decompressor io.ReadCloser
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digest uint32 // CRC-32, IEEE polynomial (section 8)
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size uint32 // Uncompressed size (section 2.3.1)
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buf [512]byte
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err error
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multistream bool
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}
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// NewReader creates a new Reader reading the given reader.
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// If r does not also implement io.ByteReader,
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// the decompressor may read more data than necessary from r.
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//
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// It is the caller's responsibility to call Close on the Reader when done.
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//
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// The Reader.Header fields will be valid in the Reader returned.
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func NewReader(r io.Reader) (*Reader, error) {
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z := new(Reader)
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if err := z.Reset(r); err != nil {
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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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// Reset discards the Reader z's state and makes it equivalent to the
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// result of its original state from NewReader, but reading from r instead.
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// This permits reusing a Reader rather than allocating a new one.
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func (z *Reader) Reset(r io.Reader) error {
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*z = Reader{
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decompressor: z.decompressor,
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multistream: true,
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br: z.br,
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}
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if rr, ok := r.(flate.Reader); ok {
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z.r = rr
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} else {
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// Reuse if we can.
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if z.br != nil {
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z.br.Reset(r)
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} else {
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z.br = bufio.NewReader(r)
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}
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z.r = z.br
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}
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z.Header, z.err = z.readHeader()
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return z.err
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}
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// Multistream controls whether the reader supports multistream files.
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//
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// If enabled (the default), the Reader expects the input to be a sequence
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// of individually gzipped data streams, each with its own header and
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// trailer, ending at EOF. The effect is that the concatenation of a sequence
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// of gzipped files is treated as equivalent to the gzip of the concatenation
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// of the sequence. This is standard behavior for gzip readers.
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//
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// Calling Multistream(false) disables this behavior; disabling the behavior
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// can be useful when reading file formats that distinguish individual gzip
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// data streams or mix gzip data streams with other data streams.
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// In this mode, when the Reader reaches the end of the data stream,
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// Read returns io.EOF. If the underlying reader implements io.ByteReader,
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// it will be left positioned just after the gzip stream.
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// To start the next stream, call z.Reset(r) followed by z.Multistream(false).
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// If there is no next stream, z.Reset(r) will return io.EOF.
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func (z *Reader) Multistream(ok bool) {
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z.multistream = ok
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}
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// readString reads a NUL-terminated string from z.r.
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// It treats the bytes read as being encoded as ISO 8859-1 (Latin-1) and
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// will output a string encoded using UTF-8.
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// This method always updates z.digest with the data read.
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func (z *Reader) readString() (string, error) {
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var err error
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needConv := false
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for i := 0; ; i++ {
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if i >= len(z.buf) {
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return "", ErrHeader
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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] > 0x7f {
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needConv = true
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}
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if z.buf[i] == 0 {
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// Digest covers the NUL terminator.
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z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:i+1])
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// Strings are ISO 8859-1, Latin-1 (RFC 1952, section 2.3.1).
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if needConv {
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s := make([]rune, 0, i)
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for _, v := range z.buf[:i] {
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s = append(s, rune(v))
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}
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return string(s), nil
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}
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return string(z.buf[:i]), nil
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}
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}
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}
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// readHeader reads the GZIP header according to section 2.3.1.
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// This method does not set z.err.
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func (z *Reader) readHeader() (hdr Header, err error) {
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if _, err = io.ReadFull(z.r, z.buf[:10]); err != nil {
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// RFC 1952, section 2.2, says the following:
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// A gzip file consists of a series of "members" (compressed data sets).
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//
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// Other than this, the specification does not clarify whether a
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// "series" is defined as "one or more" or "zero or more". To err on the
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// side of caution, Go interprets this to mean "zero or more".
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// Thus, it is okay to return io.EOF here.
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return hdr, 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 hdr, ErrHeader
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}
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flg := z.buf[3]
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hdr.ModTime = time.Unix(int64(le.Uint32(z.buf[4:8])), 0)
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// z.buf[8] is XFL and is currently ignored.
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hdr.OS = z.buf[9]
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z.digest = crc32.ChecksumIEEE(z.buf[:10])
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if flg&flagExtra != 0 {
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if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
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return hdr, noEOF(err)
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}
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z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:2])
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data := make([]byte, le.Uint16(z.buf[:2]))
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if _, err = io.ReadFull(z.r, data); err != nil {
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return hdr, noEOF(err)
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}
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z.digest = crc32.Update(z.digest, crc32.IEEETable, data)
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hdr.Extra = data
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}
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var s string
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if flg&flagName != 0 {
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if s, err = z.readString(); err != nil {
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return hdr, err
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}
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hdr.Name = s
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}
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if flg&flagComment != 0 {
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if s, err = z.readString(); err != nil {
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return hdr, err
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}
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hdr.Comment = s
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}
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if flg&flagHdrCrc != 0 {
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if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
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return hdr, noEOF(err)
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}
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digest := le.Uint16(z.buf[:2])
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if digest != uint16(z.digest) {
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return hdr, ErrHeader
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}
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}
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// Reserved FLG bits must be zero.
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if flg>>5 != 0 {
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return hdr, ErrHeader
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}
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z.digest = 0
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if z.decompressor == nil {
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z.decompressor = flate.NewReader(z.r)
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} else {
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z.decompressor.(flate.Resetter).Reset(z.r, nil)
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}
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return hdr, nil
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}
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// Read implements io.Reader, reading uncompressed bytes from its underlying Reader.
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func (z *Reader) 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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for n == 0 {
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n, z.err = z.decompressor.Read(p)
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z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n])
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z.size += uint32(n)
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if z.err != io.EOF {
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// In the normal case we return here.
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return n, z.err
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}
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// Finished file; check checksum and size.
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if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil {
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z.err = noEOF(err)
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return n, z.err
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}
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digest := le.Uint32(z.buf[:4])
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size := le.Uint32(z.buf[4:8])
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if digest != z.digest || size != z.size {
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z.err = ErrChecksum
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return n, z.err
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}
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z.digest, z.size = 0, 0
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// File is ok; check if there is another.
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if !z.multistream {
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return n, io.EOF
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}
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z.err = nil // Remove io.EOF
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if _, z.err = z.readHeader(); z.err != nil {
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return n, z.err
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}
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}
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return n, nil
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}
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type crcer interface {
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io.Writer
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Sum32() uint32
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Reset()
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}
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type crcUpdater struct {
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z *Reader
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}
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func (c *crcUpdater) Write(p []byte) (int, error) {
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c.z.digest = crc32.Update(c.z.digest, crc32.IEEETable, p)
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return len(p), nil
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}
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func (c *crcUpdater) Sum32() uint32 {
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return c.z.digest
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}
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func (c *crcUpdater) Reset() {
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c.z.digest = 0
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}
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// WriteTo support the io.WriteTo interface for io.Copy and friends.
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func (z *Reader) WriteTo(w io.Writer) (int64, error) {
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total := int64(0)
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crcWriter := crcer(crc32.NewIEEE())
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if z.digest != 0 {
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crcWriter = &crcUpdater{z: z}
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}
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for {
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if z.err != nil {
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if z.err == io.EOF {
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return total, nil
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}
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return total, z.err
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}
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// We write both to output and digest.
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mw := io.MultiWriter(w, crcWriter)
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n, err := z.decompressor.(io.WriterTo).WriteTo(mw)
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total += n
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z.size += uint32(n)
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if err != nil {
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z.err = err
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return total, z.err
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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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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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z.err = err
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return total, err
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}
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z.digest = crcWriter.Sum32()
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digest := le.Uint32(z.buf[:4])
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size := le.Uint32(z.buf[4:8])
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if digest != z.digest || size != z.size {
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z.err = ErrChecksum
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return total, z.err
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}
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z.digest, z.size = 0, 0
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// File is ok; check if there is another.
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if !z.multistream {
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return total, nil
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}
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crcWriter.Reset()
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z.err = nil // Remove io.EOF
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if _, z.err = z.readHeader(); z.err != nil {
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if z.err == io.EOF {
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return total, nil
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}
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return total, z.err
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}
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}
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}
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// Close closes the Reader. It does not close the underlying io.Reader.
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// In order for the GZIP checksum to be verified, the reader must be
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// fully consumed until the io.EOF.
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func (z *Reader) Close() error { return z.decompressor.Close() }
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