// 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, err } hdr.Name = s } if flg&flagComment != 0 { if s, err = z.readString(); err != nil { return hdr, 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() }