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 /* 6 Package zlib implements reading and writing of zlib format compressed data, 7 as specified in RFC 1950. 8 9 The implementation provides filters that uncompress during reading 10 and compress during writing. For example, to write compressed data 11 to a buffer: 12 13 var b bytes.Buffer 14 w := zlib.NewWriter(&b) 15 w.Write([]byte("hello, world\n")) 16 w.Close() 17 18 and to read that data back: 19 20 r, err := zlib.NewReader(&b) 21 io.Copy(os.Stdout, r) 22 r.Close() 23 */ 24 package zlib 25 26 import ( 27 "bufio" 28 "compress/flate" 29 "errors" 30 "hash" 31 "hash/adler32" 32 "io" 33 ) 34 35 const zlibDeflate = 8 36 37 var ( 38 // ErrChecksum is returned when reading ZLIB data that has an invalid checksum. 39 ErrChecksum = errors.New("zlib: invalid checksum") 40 // ErrDictionary is returned when reading ZLIB data that has an invalid dictionary. 41 ErrDictionary = errors.New("zlib: invalid dictionary") 42 // ErrHeader is returned when reading ZLIB data that has an invalid header. 43 ErrHeader = errors.New("zlib: invalid header") 44 ) 45 46 type reader struct { 47 r flate.Reader 48 decompressor io.ReadCloser 49 digest hash.Hash32 50 err error 51 scratch [4]byte 52 } 53 54 // Resetter resets a ReadCloser returned by NewReader or NewReaderDict to 55 // to switch to a new underlying Reader. This permits reusing a ReadCloser 56 // instead of allocating a new one. 57 type Resetter interface { 58 // Reset discards any buffered data and resets the Resetter as if it was 59 // newly initialized with the given reader. 60 Reset(r io.Reader, dict []byte) error 61 } 62 63 // NewReader creates a new ReadCloser. 64 // Reads from the returned ReadCloser read and decompress data from r. 65 // If r does not implement io.ByteReader, the decompressor may read more 66 // data than necessary from r. 67 // It is the caller's responsibility to call Close on the ReadCloser when done. 68 // 69 // The ReadCloser returned by NewReader also implements Resetter. 70 func NewReader(r io.Reader) (io.ReadCloser, error) { 71 return NewReaderDict(r, nil) 72 } 73 74 // NewReaderDict is like NewReader but uses a preset dictionary. 75 // NewReaderDict ignores the dictionary if the compressed data does not refer to it. 76 // If the compressed data refers to a different dictionary, NewReaderDict returns ErrDictionary. 77 // 78 // The ReadCloser returned by NewReaderDict also implements Resetter. 79 func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error) { 80 z := new(reader) 81 err := z.Reset(r, dict) 82 if err != nil { 83 return nil, err 84 } 85 return z, nil 86 } 87 88 func (z *reader) Read(p []byte) (int, error) { 89 if z.err != nil { 90 return 0, z.err 91 } 92 93 var n int 94 n, z.err = z.decompressor.Read(p) 95 z.digest.Write(p[0:n]) 96 if z.err != io.EOF { 97 // In the normal case we return here. 98 return n, z.err 99 } 100 101 // Finished file; check checksum. 102 if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil { 103 if err == io.EOF { 104 err = io.ErrUnexpectedEOF 105 } 106 z.err = err 107 return n, z.err 108 } 109 // ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952). 110 checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3]) 111 if checksum != z.digest.Sum32() { 112 z.err = ErrChecksum 113 return n, z.err 114 } 115 return n, io.EOF 116 } 117 118 // Calling Close does not close the wrapped io.Reader originally passed to NewReader. 119 // In order for the ZLIB checksum to be verified, the reader must be 120 // fully consumed until the io.EOF. 121 func (z *reader) Close() error { 122 if z.err != nil && z.err != io.EOF { 123 return z.err 124 } 125 z.err = z.decompressor.Close() 126 return z.err 127 } 128 129 func (z *reader) Reset(r io.Reader, dict []byte) error { 130 *z = reader{decompressor: z.decompressor} 131 if fr, ok := r.(flate.Reader); ok { 132 z.r = fr 133 } else { 134 z.r = bufio.NewReader(r) 135 } 136 137 // Read the header (RFC 1950 section 2.2.). 138 _, z.err = io.ReadFull(z.r, z.scratch[0:2]) 139 if z.err != nil { 140 if z.err == io.EOF { 141 z.err = io.ErrUnexpectedEOF 142 } 143 return z.err 144 } 145 h := uint(z.scratch[0])<<8 | uint(z.scratch[1]) 146 if (z.scratch[0]&0x0f != zlibDeflate) || (h%31 != 0) { 147 z.err = ErrHeader 148 return z.err 149 } 150 haveDict := z.scratch[1]&0x20 != 0 151 if haveDict { 152 _, z.err = io.ReadFull(z.r, z.scratch[0:4]) 153 if z.err != nil { 154 if z.err == io.EOF { 155 z.err = io.ErrUnexpectedEOF 156 } 157 return z.err 158 } 159 checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3]) 160 if checksum != adler32.Checksum(dict) { 161 z.err = ErrDictionary 162 return z.err 163 } 164 } 165 166 if z.decompressor == nil { 167 if haveDict { 168 z.decompressor = flate.NewReaderDict(z.r, dict) 169 } else { 170 z.decompressor = flate.NewReader(z.r) 171 } 172 } else { 173 z.decompressor.(flate.Resetter).Reset(z.r, dict) 174 } 175 z.digest = adler32.New() 176 return nil 177 } 178
