| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| /* |
| Package zlib implements reading and writing of zlib format compressed data, |
| as specified in RFC 1950. |
| |
| The implementation provides filters that uncompress during reading |
| and compress during writing. For example, to write compressed data |
| to a buffer: |
| |
| var b bytes.Buffer |
| w, err := zlib.NewWriter(&b) |
| w.Write([]byte("hello, world\n")) |
| w.Close() |
| |
| and to read that data back: |
| |
| r, err := zlib.NewReader(&b) |
| io.Copy(os.Stdout, r) |
| r.Close() |
| */ |
| package zlib |
| |
| import ( |
| "bufio" |
| "compress/flate" |
| "hash" |
| "hash/adler32" |
| "io" |
| "os" |
| ) |
| |
| const zlibDeflate = 8 |
| |
| var ChecksumError = os.NewError("zlib checksum error") |
| var HeaderError = os.NewError("invalid zlib header") |
| var DictionaryError = os.NewError("invalid zlib dictionary") |
| |
| type reader struct { |
| r flate.Reader |
| decompressor io.ReadCloser |
| digest hash.Hash32 |
| err os.Error |
| scratch [4]byte |
| } |
| |
| // NewReader creates a new io.ReadCloser that satisfies reads by decompressing data read from r. |
| // The implementation buffers input and may read more data than necessary from r. |
| // It is the caller's responsibility to call Close on the ReadCloser when done. |
| func NewReader(r io.Reader) (io.ReadCloser, os.Error) { |
| return NewReaderDict(r, nil) |
| } |
| |
| // NewReaderDict is like NewReader but uses a preset dictionary. |
| // NewReaderDict ignores the dictionary if the compressed data does not refer to it. |
| func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, os.Error) { |
| z := new(reader) |
| if fr, ok := r.(flate.Reader); ok { |
| z.r = fr |
| } else { |
| z.r = bufio.NewReader(r) |
| } |
| _, err := io.ReadFull(z.r, z.scratch[0:2]) |
| if err != nil { |
| return nil, err |
| } |
| h := uint(z.scratch[0])<<8 | uint(z.scratch[1]) |
| if (z.scratch[0]&0x0f != zlibDeflate) || (h%31 != 0) { |
| return nil, HeaderError |
| } |
| if z.scratch[1]&0x20 != 0 { |
| _, err = io.ReadFull(z.r, z.scratch[0:4]) |
| if err != nil { |
| return nil, err |
| } |
| checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3]) |
| if checksum != adler32.Checksum(dict) { |
| return nil, DictionaryError |
| } |
| z.decompressor = flate.NewReaderDict(z.r, dict) |
| } else { |
| z.decompressor = flate.NewReader(z.r) |
| } |
| z.digest = adler32.New() |
| return z, nil |
| } |
| |
| func (z *reader) Read(p []byte) (n int, err os.Error) { |
| if z.err != nil { |
| return 0, z.err |
| } |
| if len(p) == 0 { |
| return 0, nil |
| } |
| |
| n, err = z.decompressor.Read(p) |
| z.digest.Write(p[0:n]) |
| if n != 0 || err != os.EOF { |
| z.err = err |
| return |
| } |
| |
| // Finished file; check checksum. |
| if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil { |
| z.err = err |
| return 0, err |
| } |
| // ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952). |
| checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3]) |
| if checksum != z.digest.Sum32() { |
| z.err = ChecksumError |
| return 0, z.err |
| } |
| return |
| } |
| |
| // Calling Close does not close the wrapped io.Reader originally passed to NewReader. |
| func (z *reader) Close() os.Error { |
| if z.err != nil { |
| return z.err |
| } |
| z.err = z.decompressor.Close() |
| return z.err |
| } |