libgo/go/compress/gzip/gunzip.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package gzip implements reading and writing of gzip format compressed files,
   6 // as specified in RFC 1952.
   7 package gzip
   8
   9 import (
  10         "bufio"
  11         "compress/flate"
  12         "encoding/binary"
  13         "errors"
  14         "hash/crc32"
  15         "io"
  16         "time"
  17 )
  18
  19 const (
  20         gzipID1     = 0x1f
  21         gzipID2     = 0x8b
  22         gzipDeflate = 8
  23         flagText    = 1 << 0
  24         flagHdrCrc  = 1 << 1
  25         flagExtra   = 1 << 2
  26         flagName    = 1 << 3
  27         flagComment = 1 << 4
  28 )
  29
  30 var (
  31         // ErrChecksum is returned when reading GZIP data that has an invalid checksum.
  32         ErrChecksum = errors.New("gzip: invalid checksum")
  33         // ErrHeader is returned when reading GZIP data that has an invalid header.
  34         ErrHeader = errors.New("gzip: invalid header")
  35 )
  36
  37 var le = binary.LittleEndian
  38
  39 // noEOF converts io.EOF to io.ErrUnexpectedEOF.
  40 func noEOF(err error) error {
  41         if err == io.EOF {
  42                 return io.ErrUnexpectedEOF
  43         }
  44         return err
  45 }
  46
  47 // The gzip file stores a header giving metadata about the compressed file.
  48 // That header is exposed as the fields of the Writer and Reader structs.
  49 //
  50 // Strings must be UTF-8 encoded and may only contain Unicode code points
  51 // U+0001 through U+00FF, due to limitations of the GZIP file format.
  52 type Header struct {
  53         Comment string    // comment
  54         Extra   []byte    // "extra data"
  55         ModTime time.Time // modification time
  56         Name    string    // file name
  57         OS      byte      // operating system type
  58 }
  59
  60 // A Reader is an io.Reader that can be read to retrieve
  61 // uncompressed data from a gzip-format compressed file.
  62 //
  63 // In general, a gzip file can be a concatenation of gzip files,
  64 // each with its own header. Reads from the Reader
  65 // return the concatenation of the uncompressed data of each.
  66 // Only the first header is recorded in the Reader fields.
  67 //
  68 // Gzip files store a length and checksum of the uncompressed data.
  69 // The Reader will return a ErrChecksum when Read
  70 // reaches the end of the uncompressed data if it does not
  71 // have the expected length or checksum. Clients should treat data
  72 // returned by Read as tentative until they receive the io.EOF
  73 // marking the end of the data.
  74 type Reader struct {
  75         Header       // valid after NewReader or Reader.Reset
  76         r            flate.Reader
  77         decompressor io.ReadCloser
  78         digest       uint32 // CRC-32, IEEE polynomial (section 8)
  79         size         uint32 // Uncompressed size (section 2.3.1)
  80         buf          [512]byte
  81         err          error
  82         multistream  bool
  83 }
  84
  85 // NewReader creates a new Reader reading the given reader.
  86 // If r does not also implement io.ByteReader,
  87 // the decompressor may read more data than necessary from r.
  88 //
  89 // It is the caller's responsibility to call Close on the Reader when done.
  90 //
  91 // The Reader.Header fields will be valid in the Reader returned.
  92 func NewReader(r io.Reader) (*Reader, error) {
  93         z := new(Reader)
  94         if err := z.Reset(r); err != nil {
  95                 return nil, err
  96         }
  97         return z, nil
  98 }
  99
 100 // Reset discards the Reader z's state and makes it equivalent to the
 101 // result of its original state from NewReader, but reading from r instead.
 102 // This permits reusing a Reader rather than allocating a new one.
 103 func (z *Reader) Reset(r io.Reader) error {
 104         *z = Reader{
 105                 decompressor: z.decompressor,
 106                 multistream:  true,
 107         }
 108         if rr, ok := r.(flate.Reader); ok {
 109                 z.r = rr
 110         } else {
 111                 z.r = bufio.NewReader(r)
 112         }
 113         z.Header, z.err = z.readHeader()
 114         return z.err
 115 }
 116
 117 // Multistream controls whether the reader supports multistream files.
 118 //
 119 // If enabled (the default), the Reader expects the input to be a sequence
 120 // of individually gzipped data streams, each with its own header and
 121 // trailer, ending at EOF. The effect is that the concatenation of a sequence
 122 // of gzipped files is treated as equivalent to the gzip of the concatenation
 123 // of the sequence. This is standard behavior for gzip readers.
 124 //
 125 // Calling Multistream(false) disables this behavior; disabling the behavior
 126 // can be useful when reading file formats that distinguish individual gzip
 127 // data streams or mix gzip data streams with other data streams.
 128 // In this mode, when the Reader reaches the end of the data stream,
 129 // Read returns io.EOF. If the underlying reader implements io.ByteReader,
 130 // it will be left positioned just after the gzip stream.
 131 // To start the next stream, call z.Reset(r) followed by z.Multistream(false).
 132 // If there is no next stream, z.Reset(r) will return io.EOF.
 133 func (z *Reader) Multistream(ok bool) {
 134         z.multistream = ok
 135 }
 136
 137 // readString reads a NUL-terminated string from z.r.
 138 // It treats the bytes read as being encoded as ISO 8859-1 (Latin-1) and
 139 // will output a string encoded using UTF-8.
 140 // This method always updates z.digest with the data read.
 141 func (z *Reader) readString() (string, error) {
 142         var err error
 143         needConv := false
 144         for i := 0; ; i++ {
 145                 if i >= len(z.buf) {
 146                         return "", ErrHeader
 147                 }
 148                 z.buf[i], err = z.r.ReadByte()
 149                 if err != nil {
 150                         return "", err
 151                 }
 152                 if z.buf[i] > 0x7f {
 153                         needConv = true
 154                 }
 155                 if z.buf[i] == 0 {
 156                         // Digest covers the NUL terminator.
 157                         z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:i+1])
 158
 159                         // Strings are ISO 8859-1, Latin-1 (RFC 1952, section 2.3.1).
 160                         if needConv {
 161                                 s := make([]rune, 0, i)
 162                                 for _, v := range z.buf[:i] {
 163                                         s = append(s, rune(v))
 164                                 }
 165                                 return string(s), nil
 166                         }
 167                         return string(z.buf[:i]), nil
 168                 }
 169         }
 170 }
 171
 172 // readHeader reads the GZIP header according to section 2.3.1.
 173 // This method does not set z.err.
 174 func (z *Reader) readHeader() (hdr Header, err error) {
 175         if _, err = io.ReadFull(z.r, z.buf[:10]); err != nil {
 176                 // RFC 1952, section 2.2, says the following:
 177                 //      A gzip file consists of a series of "members" (compressed data sets).
 178                 //
 179                 // Other than this, the specification does not clarify whether a
 180                 // "series" is defined as "one or more" or "zero or more". To err on the
 181                 // side of caution, Go interprets this to mean "zero or more".
 182                 // Thus, it is okay to return io.EOF here.
 183                 return hdr, err
 184         }
 185         if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
 186                 return hdr, ErrHeader
 187         }
 188         flg := z.buf[3]
 189         if t := int64(le.Uint32(z.buf[4:8])); t > 0 {
 190                 // Section 2.3.1, the zero value for MTIME means that the
 191                 // modified time is not set.
 192                 hdr.ModTime = time.Unix(t, 0)
 193         }
 194         // z.buf[8] is XFL and is currently ignored.
 195         hdr.OS = z.buf[9]
 196         z.digest = crc32.ChecksumIEEE(z.buf[:10])
 197
 198         if flg&flagExtra != 0 {
 199                 if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
 200                         return hdr, noEOF(err)
 201                 }
 202                 z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:2])
 203                 data := make([]byte, le.Uint16(z.buf[:2]))
 204                 if _, err = io.ReadFull(z.r, data); err != nil {
 205                         return hdr, noEOF(err)
 206                 }
 207                 z.digest = crc32.Update(z.digest, crc32.IEEETable, data)
 208                 hdr.Extra = data
 209         }
 210
 211         var s string
 212         if flg&flagName != 0 {
 213                 if s, err = z.readString(); err != nil {
 214                         return hdr, err
 215                 }
 216                 hdr.Name = s
 217         }
 218
 219         if flg&flagComment != 0 {
 220                 if s, err = z.readString(); err != nil {
 221                         return hdr, err
 222                 }
 223                 hdr.Comment = s
 224         }
 225
 226         if flg&flagHdrCrc != 0 {
 227                 if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil {
 228                         return hdr, noEOF(err)
 229                 }
 230                 digest := le.Uint16(z.buf[:2])
 231                 if digest != uint16(z.digest) {
 232                         return hdr, ErrHeader
 233                 }
 234         }
 235
 236         z.digest = 0
 237         if z.decompressor == nil {
 238                 z.decompressor = flate.NewReader(z.r)
 239         } else {
 240                 z.decompressor.(flate.Resetter).Reset(z.r, nil)
 241         }
 242         return hdr, nil
 243 }
 244
 245 // Read implements io.Reader, reading uncompressed bytes from its underlying Reader.
 246 func (z *Reader) Read(p []byte) (n int, err error) {
 247         if z.err != nil {
 248                 return 0, z.err
 249         }
 250
 251         n, z.err = z.decompressor.Read(p)
 252         z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n])
 253         z.size += uint32(n)
 254         if z.err != io.EOF {
 255                 // In the normal case we return here.
 256                 return n, z.err
 257         }
 258
 259         // Finished file; check checksum and size.
 260         if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil {
 261                 z.err = noEOF(err)
 262                 return n, z.err
 263         }
 264         digest := le.Uint32(z.buf[:4])
 265         size := le.Uint32(z.buf[4:8])
 266         if digest != z.digest || size != z.size {
 267                 z.err = ErrChecksum
 268                 return n, z.err
 269         }
 270         z.digest, z.size = 0, 0
 271
 272         // File is ok; check if there is another.
 273         if !z.multistream {
 274                 return n, io.EOF
 275         }
 276         z.err = nil // Remove io.EOF
 277
 278         if _, z.err = z.readHeader(); z.err != nil {
 279                 return n, z.err
 280         }
 281
 282         // Read from next file, if necessary.
 283         if n > 0 {
 284                 return n, nil
 285         }
 286         return z.Read(p)
 287 }
 288
 289 // Close closes the Reader. It does not close the underlying io.Reader.
 290 // In order for the GZIP checksum to be verified, the reader must be
 291 // fully consumed until the io.EOF.
 292 func (z *Reader) Close() error { return z.decompressor.Close() }