Source file src/pkg/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 "errors" 13 "hash" 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 func makeReader(r io.Reader) flate.Reader { 31 if rr, ok := r.(flate.Reader); ok { 32 return rr 33 } 34 return bufio.NewReader(r) 35 } 36 37 var ( 38 // ErrChecksum is returned when reading GZIP data that has an invalid checksum. 39 ErrChecksum = errors.New("gzip: invalid checksum") 40 // ErrHeader is returned when reading GZIP data that has an invalid header. 41 ErrHeader = errors.New("gzip: invalid header") 42 ) 43 44 // The gzip file stores a header giving metadata about the compressed file. 45 // That header is exposed as the fields of the Writer and Reader structs. 46 type Header struct { 47 Comment string // comment 48 Extra []byte // "extra data" 49 ModTime time.Time // modification time 50 Name string // file name 51 OS byte // operating system type 52 } 53 54 // A Reader is an io.Reader that can be read to retrieve 55 // uncompressed data from a gzip-format compressed file. 56 // 57 // In general, a gzip file can be a concatenation of gzip files, 58 // each with its own header. Reads from the Reader 59 // return the concatenation of the uncompressed data of each. 60 // Only the first header is recorded in the Reader fields. 61 // 62 // Gzip files store a length and checksum of the uncompressed data. 63 // The Reader will return a ErrChecksum when Read 64 // reaches the end of the uncompressed data if it does not 65 // have the expected length or checksum. Clients should treat data 66 // returned by Read as tentative until they receive the io.EOF 67 // marking the end of the data. 68 type Reader struct { 69 Header 70 r flate.Reader 71 decompressor io.ReadCloser 72 digest hash.Hash32 73 size uint32 74 flg byte 75 buf [512]byte 76 err error 77 } 78 79 // NewReader creates a new Reader reading the given reader. 80 // The implementation buffers input and may read more data than necessary from r. 81 // It is the caller's responsibility to call Close on the Reader when done. 82 func NewReader(r io.Reader) (*Reader, error) { 83 z := new(Reader) 84 z.r = makeReader(r) 85 z.digest = crc32.NewIEEE() 86 if err := z.readHeader(true); err != nil { 87 return nil, err 88 } 89 return z, nil 90 } 91 92 // GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950). 93 func get4(p []byte) uint32 { 94 return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24 95 } 96 97 func (z *Reader) readString() (string, error) { 98 var err error 99 needconv := false 100 for i := 0; ; i++ { 101 if i >= len(z.buf) { 102 return "", ErrHeader 103 } 104 z.buf[i], err = z.r.ReadByte() 105 if err != nil { 106 return "", err 107 } 108 if z.buf[i] > 0x7f { 109 needconv = true 110 } 111 if z.buf[i] == 0 { 112 // GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1). 113 if needconv { 114 s := make([]rune, 0, i) 115 for _, v := range z.buf[0:i] { 116 s = append(s, rune(v)) 117 } 118 return string(s), nil 119 } 120 return string(z.buf[0:i]), nil 121 } 122 } 123 panic("not reached") 124 } 125 126 func (z *Reader) read2() (uint32, error) { 127 _, err := io.ReadFull(z.r, z.buf[0:2]) 128 if err != nil { 129 return 0, err 130 } 131 return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil 132 } 133 134 func (z *Reader) readHeader(save bool) error { 135 _, err := io.ReadFull(z.r, z.buf[0:10]) 136 if err != nil { 137 return err 138 } 139 if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate { 140 return ErrHeader 141 } 142 z.flg = z.buf[3] 143 if save { 144 z.ModTime = time.Unix(int64(get4(z.buf[4:8])), 0) 145 // z.buf[8] is xfl, ignored 146 z.OS = z.buf[9] 147 } 148 z.digest.Reset() 149 z.digest.Write(z.buf[0:10]) 150 151 if z.flg&flagExtra != 0 { 152 n, err := z.read2() 153 if err != nil { 154 return err 155 } 156 data := make([]byte, n) 157 if _, err = io.ReadFull(z.r, data); err != nil { 158 return err 159 } 160 if save { 161 z.Extra = data 162 } 163 } 164 165 var s string 166 if z.flg&flagName != 0 { 167 if s, err = z.readString(); err != nil { 168 return err 169 } 170 if save { 171 z.Name = s 172 } 173 } 174 175 if z.flg&flagComment != 0 { 176 if s, err = z.readString(); err != nil { 177 return err 178 } 179 if save { 180 z.Comment = s 181 } 182 } 183 184 if z.flg&flagHdrCrc != 0 { 185 n, err := z.read2() 186 if err != nil { 187 return err 188 } 189 sum := z.digest.Sum32() & 0xFFFF 190 if n != sum { 191 return ErrHeader 192 } 193 } 194 195 z.digest.Reset() 196 z.decompressor = flate.NewReader(z.r) 197 return nil 198 } 199 200 func (z *Reader) Read(p []byte) (n int, err error) { 201 if z.err != nil { 202 return 0, z.err 203 } 204 if len(p) == 0 { 205 return 0, nil 206 } 207 208 n, err = z.decompressor.Read(p) 209 z.digest.Write(p[0:n]) 210 z.size += uint32(n) 211 if n != 0 || err != io.EOF { 212 z.err = err 213 return 214 } 215 216 // Finished file; check checksum + size. 217 if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil { 218 z.err = err 219 return 0, err 220 } 221 crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8]) 222 sum := z.digest.Sum32() 223 if sum != crc32 || isize != z.size { 224 z.err = ErrChecksum 225 return 0, z.err 226 } 227 228 // File is ok; is there another? 229 if err = z.readHeader(false); err != nil { 230 z.err = err 231 return 232 } 233 234 // Yes. Reset and read from it. 235 z.digest.Reset() 236 z.size = 0 237 return z.Read(p) 238 } 239 240 // Close closes the Reader. It does not close the underlying io.Reader. 241 func (z *Reader) Close() error { return z.decompressor.Close() }