| // 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 gzip implements reading and writing of gzip format compressed files, |
| // as specified in RFC 1952. |
| package gzip |
| |
| import ( |
| "bufio" |
| "compress/flate" |
| "encoding/binary" |
| "errors" |
| "hash/crc32" |
| "io" |
| "time" |
| ) |
| |
| const ( |
| gzipID1 = 0x1f |
| gzipID2 = 0x8b |
| gzipDeflate = 8 |
| flagText = 1 << 0 |
| flagHdrCrc = 1 << 1 |
| flagExtra = 1 << 2 |
| flagName = 1 << 3 |
| flagComment = 1 << 4 |
| ) |
| |
| var ( |
| // ErrChecksum is returned when reading GZIP data that has an invalid checksum. |
| ErrChecksum = errors.New("gzip: invalid checksum") |
| // ErrHeader is returned when reading GZIP data that has an invalid header. |
| ErrHeader = errors.New("gzip: invalid header") |
| ) |
| |
| var le = binary.LittleEndian |
| |
| // noEOF converts io.EOF to io.ErrUnexpectedEOF. |
| func noEOF(err error) error { |
| if err == io.EOF { |
| return io.ErrUnexpectedEOF |
| } |
| return err |
| } |
| |
| // The gzip file stores a header giving metadata about the compressed file. |
| // That header is exposed as the fields of the Writer and Reader structs. |
| // |
| // Strings must be UTF-8 encoded and may only contain Unicode code points |
| // U+0001 through U+00FF, due to limitations of the GZIP file format. |
| type Header struct { |
| Comment string // comment |
| Extra []byte // "extra data" |
| ModTime time.Time // modification time |
| Name string // file name |
| OS byte // operating system type |
| } |
| |
| // A Reader is an io.Reader that can be read to retrieve |
| // uncompressed data from a gzip-format compressed file. |
| // |
| // In general, a gzip file can be a concatenation of gzip files, |
| // each with its own header. Reads from the Reader |
| // return the concatenation of the uncompressed data of each. |
| // Only the first header is recorded in the Reader fields. |
| // |
| // Gzip files store a length and checksum of the uncompressed data. |
| // The Reader will return an ErrChecksum when Read |
| // reaches the end of the uncompressed data if it does not |
| // have the expected length or checksum. Clients should treat data |
| // returned by Read as tentative until they receive the io.EOF |
| // marking the end of the data. |
| type Reader struct { |
| Header // valid after NewReader or Reader.Reset |
| r flate.Reader |
| decompressor io.ReadCloser |
| digest uint32 // CRC-32, IEEE polynomial (section 8) |
| size uint32 // Uncompressed size (section 2.3.1) |
| buf [512]byte |
| err error |
| multistream bool |
| } |
| |
| // NewReader creates a new Reader reading the given reader. |
| // If r does not also implement io.ByteReader, |
| // the decompressor may read more data than necessary from r. |
| // |
| // It is the caller's responsibility to call Close on the Reader when done. |
| // |
| // The Reader.Header fields will be valid in the Reader returned. |
| func NewReader(r io.Reader) (*Reader, error) { |
| z := new(Reader) |
| if err := z.Reset(r); err != nil { |
| return nil, err |
| } |
| return z, nil |
| } |
| |
| // Reset discards the Reader z's state and makes it equivalent to the |
| // result of its original state from NewReader, but reading from r instead. |
| // This permits reusing a Reader rather than allocating a new one. |
| func (z *Reader) Reset(r io.Reader) error { |
| *z = Reader{ |
| decompressor: z.decompressor, |
| multistream: true, |
| } |
| if rr, ok := r.(flate.Reader); ok { |
| z.r = rr |
| } else { |
| z.r = bufio.NewReader(r) |
| } |
| z.Header, z.err = z.readHeader() |
| return z.err |
| } |
| |
| // Multistream controls whether the reader supports multistream files. |
| // |
| // If enabled (the default), the Reader expects the input to be a sequence |
| // of individually gzipped data streams, each with its own header and |
| // trailer, ending at EOF. The effect is that the concatenation of a sequence |
| // of gzipped files is treated as equivalent to the gzip of the concatenation |
| // of the sequence. This is standard behavior for gzip readers. |
| // |
| // Calling Multistream(false) disables this behavior; disabling the behavior |
| // can be useful when reading file formats that distinguish individual gzip |
| // data streams or mix gzip data streams with other data streams. |
| // In this mode, when the Reader reaches the end of the data stream, |
| // Read returns io.EOF. The underlying reader must implement io.ByteReader |
| // in order to be left positioned just after the gzip stream. |
| // To start the next stream, call z.Reset(r) followed by z.Multistream(false). |
| // If there is no next stream, z.Reset(r) will return io.EOF. |
| func (z *Reader) Multistream(ok bool) { |
| z.multistream = ok |
| } |
| |
| // readString reads a NUL-terminated string from z.r. |
| // It treats the bytes read as being encoded as ISO 8859-1 (Latin-1) and |
| // will output a string encoded using UTF-8. |
| // This method always updates z.digest with the data read. |
| func (z *Reader) readString() (string, error) { |
| var err error |
| needConv := false |
| for i := 0; ; i++ { |
| if i >= len(z.buf) { |
| return "", ErrHeader |
| } |
| z.buf[i], err = z.r.ReadByte() |
| if err != nil { |
| return "", err |
| } |
| if z.buf[i] > 0x7f { |
| needConv = true |
| } |
| if z.buf[i] == 0 { |
| // Digest covers the NUL terminator. |
| z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:i+1]) |
| |
| // Strings are ISO 8859-1, Latin-1 (RFC 1952, section 2.3.1). |
| if needConv { |
| s := make([]rune, 0, i) |
| for _, v := range z.buf[:i] { |
| s = append(s, rune(v)) |
| } |
| return string(s), nil |
| } |
| return string(z.buf[:i]), nil |
| } |
| } |
| } |
| |
| // readHeader reads the GZIP header according to section 2.3.1. |
| // This method does not set z.err. |
| func (z *Reader) readHeader() (hdr Header, err error) { |
| if _, err = io.ReadFull(z.r, z.buf[:10]); err != nil { |
| // RFC 1952, section 2.2, says the following: |
| // A gzip file consists of a series of "members" (compressed data sets). |
| // |
| // Other than this, the specification does not clarify whether a |
| // "series" is defined as "one or more" or "zero or more". To err on the |
| // side of caution, Go interprets this to mean "zero or more". |
| // Thus, it is okay to return io.EOF here. |
| return hdr, err |
| } |
| if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate { |
| return hdr, ErrHeader |
| } |
| flg := z.buf[3] |
| if t := int64(le.Uint32(z.buf[4:8])); t > 0 { |
| // Section 2.3.1, the zero value for MTIME means that the |
| // modified time is not set. |
| hdr.ModTime = time.Unix(t, 0) |
| } |
| // z.buf[8] is XFL and is currently ignored. |
| hdr.OS = z.buf[9] |
| z.digest = crc32.ChecksumIEEE(z.buf[:10]) |
| |
| if flg&flagExtra != 0 { |
| if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil { |
| return hdr, noEOF(err) |
| } |
| z.digest = crc32.Update(z.digest, crc32.IEEETable, z.buf[:2]) |
| data := make([]byte, le.Uint16(z.buf[:2])) |
| if _, err = io.ReadFull(z.r, data); err != nil { |
| return hdr, noEOF(err) |
| } |
| z.digest = crc32.Update(z.digest, crc32.IEEETable, data) |
| hdr.Extra = data |
| } |
| |
| var s string |
| if flg&flagName != 0 { |
| if s, err = z.readString(); err != nil { |
| return hdr, noEOF(err) |
| } |
| hdr.Name = s |
| } |
| |
| if flg&flagComment != 0 { |
| if s, err = z.readString(); err != nil { |
| return hdr, noEOF(err) |
| } |
| hdr.Comment = s |
| } |
| |
| if flg&flagHdrCrc != 0 { |
| if _, err = io.ReadFull(z.r, z.buf[:2]); err != nil { |
| return hdr, noEOF(err) |
| } |
| digest := le.Uint16(z.buf[:2]) |
| if digest != uint16(z.digest) { |
| return hdr, ErrHeader |
| } |
| } |
| |
| z.digest = 0 |
| if z.decompressor == nil { |
| z.decompressor = flate.NewReader(z.r) |
| } else { |
| z.decompressor.(flate.Resetter).Reset(z.r, nil) |
| } |
| return hdr, nil |
| } |
| |
| // Read implements io.Reader, reading uncompressed bytes from its underlying Reader. |
| func (z *Reader) Read(p []byte) (n int, err error) { |
| if z.err != nil { |
| return 0, z.err |
| } |
| |
| n, z.err = z.decompressor.Read(p) |
| z.digest = crc32.Update(z.digest, crc32.IEEETable, p[:n]) |
| z.size += uint32(n) |
| if z.err != io.EOF { |
| // In the normal case we return here. |
| return n, z.err |
| } |
| |
| // Finished file; check checksum and size. |
| if _, err := io.ReadFull(z.r, z.buf[:8]); err != nil { |
| z.err = noEOF(err) |
| return n, z.err |
| } |
| digest := le.Uint32(z.buf[:4]) |
| size := le.Uint32(z.buf[4:8]) |
| if digest != z.digest || size != z.size { |
| z.err = ErrChecksum |
| return n, z.err |
| } |
| z.digest, z.size = 0, 0 |
| |
| // File is ok; check if there is another. |
| if !z.multistream { |
| return n, io.EOF |
| } |
| z.err = nil // Remove io.EOF |
| |
| if _, z.err = z.readHeader(); z.err != nil { |
| return n, z.err |
| } |
| |
| // Read from next file, if necessary. |
| if n > 0 { |
| return n, nil |
| } |
| return z.Read(p) |
| } |
| |
| // Close closes the Reader. It does not close the underlying io.Reader. |
| // In order for the GZIP checksum to be verified, the reader must be |
| // fully consumed until the io.EOF. |
| func (z *Reader) Close() error { return z.decompressor.Close() } |