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Source file src/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	//
    47	// Strings must be UTF-8 encoded and may only contain Unicode code points
    48	// U+0001 through U+00FF, due to limitations of the GZIP file format.
    49	type Header struct {
    50		Comment string    // comment
    51		Extra   []byte    // "extra data"
    52		ModTime time.Time // modification time
    53		Name    string    // file name
    54		OS      byte      // operating system type
    55	}
    56	
    57	// A Reader is an io.Reader that can be read to retrieve
    58	// uncompressed data from a gzip-format compressed file.
    59	//
    60	// In general, a gzip file can be a concatenation of gzip files,
    61	// each with its own header.  Reads from the Reader
    62	// return the concatenation of the uncompressed data of each.
    63	// Only the first header is recorded in the Reader fields.
    64	//
    65	// Gzip files store a length and checksum of the uncompressed data.
    66	// The Reader will return a ErrChecksum when Read
    67	// reaches the end of the uncompressed data if it does not
    68	// have the expected length or checksum.  Clients should treat data
    69	// returned by Read as tentative until they receive the io.EOF
    70	// marking the end of the data.
    71	type Reader struct {
    72		Header       // valid after NewReader or Reader.Reset
    73		r            flate.Reader
    74		decompressor io.ReadCloser
    75		digest       hash.Hash32
    76		size         uint32
    77		flg          byte
    78		buf          [512]byte
    79		err          error
    80		multistream  bool
    81	}
    82	
    83	// NewReader creates a new Reader reading the given reader.
    84	// If r does not also implement io.ByteReader,
    85	// the decompressor may read more data than necessary from r.
    86	//
    87	// It is the caller's responsibility to call Close on the Reader when done.
    88	//
    89	// The Reader.Header fields will be valid in the Reader returned.
    90	func NewReader(r io.Reader) (*Reader, error) {
    91		z := new(Reader)
    92		z.r = makeReader(r)
    93		z.multistream = true
    94		z.digest = crc32.NewIEEE()
    95		if err := z.readHeader(true); err != nil {
    96			return nil, err
    97		}
    98		return z, nil
    99	}
   100	
   101	// Reset discards the Reader z's state and makes it equivalent to the
   102	// result of its original state from NewReader, but reading from r instead.
   103	// This permits reusing a Reader rather than allocating a new one.
   104	func (z *Reader) Reset(r io.Reader) error {
   105		z.r = makeReader(r)
   106		if z.digest == nil {
   107			z.digest = crc32.NewIEEE()
   108		} else {
   109			z.digest.Reset()
   110		}
   111		z.size = 0
   112		z.err = nil
   113		z.multistream = true
   114		return z.readHeader(true)
   115	}
   116	
   117	// Multistream controls whether the reader supports multistream files.
   118	//
   119	// If enabled (the default), the Reader expects the input to be a sequence
   120	// of individually gzipped data streams, each with its own header and
   121	// trailer, ending at EOF. The effect is that the concatenation of a sequence
   122	// of gzipped files is treated as equivalent to the gzip of the concatenation
   123	// of the sequence. This is standard behavior for gzip readers.
   124	//
   125	// Calling Multistream(false) disables this behavior; disabling the behavior
   126	// can be useful when reading file formats that distinguish individual gzip
   127	// data streams or mix gzip data streams with other data streams.
   128	// In this mode, when the Reader reaches the end of the data stream,
   129	// Read returns io.EOF. If the underlying reader implements io.ByteReader,
   130	// it will be left positioned just after the gzip stream.
   131	// To start the next stream, call z.Reset(r) followed by z.Multistream(false).
   132	// If there is no next stream, z.Reset(r) will return io.EOF.
   133	func (z *Reader) Multistream(ok bool) {
   134		z.multistream = ok
   135	}
   136	
   137	// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
   138	func get4(p []byte) uint32 {
   139		return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
   140	}
   141	
   142	func (z *Reader) readString() (string, error) {
   143		var err error
   144		needconv := false
   145		for i := 0; ; i++ {
   146			if i >= len(z.buf) {
   147				return "", ErrHeader
   148			}
   149			z.buf[i], err = z.r.ReadByte()
   150			if err != nil {
   151				return "", err
   152			}
   153			if z.buf[i] > 0x7f {
   154				needconv = true
   155			}
   156			if z.buf[i] == 0 {
   157				// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
   158				if needconv {
   159					s := make([]rune, 0, i)
   160					for _, v := range z.buf[0:i] {
   161						s = append(s, rune(v))
   162					}
   163					return string(s), nil
   164				}
   165				return string(z.buf[0:i]), nil
   166			}
   167		}
   168	}
   169	
   170	func (z *Reader) read2() (uint32, error) {
   171		_, err := io.ReadFull(z.r, z.buf[0:2])
   172		if err != nil {
   173			if err == io.EOF {
   174				err = io.ErrUnexpectedEOF
   175			}
   176			return 0, err
   177		}
   178		return uint32(z.buf[0]) | uint32(z.buf[1])<<8, nil
   179	}
   180	
   181	func (z *Reader) readHeader(save bool) error {
   182		_, err := io.ReadFull(z.r, z.buf[0:10])
   183		if err != nil {
   184			// RFC1952 section 2.2 says the following:
   185			//	A gzip file consists of a series of "members" (compressed data sets).
   186			//
   187			// Other than this, the specification does not clarify whether a
   188			// "series" is defined as "one or more" or "zero or more". To err on the
   189			// side of caution, Go interprets this to mean "zero or more".
   190			// Thus, it is okay to return io.EOF here.
   191			return err
   192		}
   193		if z.buf[0] != gzipID1 || z.buf[1] != gzipID2 || z.buf[2] != gzipDeflate {
   194			return ErrHeader
   195		}
   196		z.flg = z.buf[3]
   197		if save {
   198			z.ModTime = time.Unix(int64(get4(z.buf[4:8])), 0)
   199			// z.buf[8] is xfl, ignored
   200			z.OS = z.buf[9]
   201		}
   202		z.digest.Reset()
   203		z.digest.Write(z.buf[0:10])
   204	
   205		if z.flg&flagExtra != 0 {
   206			n, err := z.read2()
   207			if err != nil {
   208				return err
   209			}
   210			data := make([]byte, n)
   211			if _, err = io.ReadFull(z.r, data); err != nil {
   212				if err == io.EOF {
   213					err = io.ErrUnexpectedEOF
   214				}
   215				return err
   216			}
   217			if save {
   218				z.Extra = data
   219			}
   220		}
   221	
   222		var s string
   223		if z.flg&flagName != 0 {
   224			if s, err = z.readString(); err != nil {
   225				return err
   226			}
   227			if save {
   228				z.Name = s
   229			}
   230		}
   231	
   232		if z.flg&flagComment != 0 {
   233			if s, err = z.readString(); err != nil {
   234				return err
   235			}
   236			if save {
   237				z.Comment = s
   238			}
   239		}
   240	
   241		if z.flg&flagHdrCrc != 0 {
   242			n, err := z.read2()
   243			if err != nil {
   244				return err
   245			}
   246			sum := z.digest.Sum32() & 0xFFFF
   247			if n != sum {
   248				return ErrHeader
   249			}
   250		}
   251	
   252		z.digest.Reset()
   253		if z.decompressor == nil {
   254			z.decompressor = flate.NewReader(z.r)
   255		} else {
   256			z.decompressor.(flate.Resetter).Reset(z.r, nil)
   257		}
   258		return nil
   259	}
   260	
   261	func (z *Reader) Read(p []byte) (n int, err error) {
   262		if z.err != nil {
   263			return 0, z.err
   264		}
   265		if len(p) == 0 {
   266			return 0, nil
   267		}
   268	
   269		n, err = z.decompressor.Read(p)
   270		z.digest.Write(p[0:n])
   271		z.size += uint32(n)
   272		if n != 0 || err != io.EOF {
   273			z.err = err
   274			return
   275		}
   276	
   277		// Finished file; check checksum + size.
   278		if _, err := io.ReadFull(z.r, z.buf[0:8]); err != nil {
   279			if err == io.EOF {
   280				err = io.ErrUnexpectedEOF
   281			}
   282			z.err = err
   283			return 0, err
   284		}
   285		crc32, isize := get4(z.buf[0:4]), get4(z.buf[4:8])
   286		sum := z.digest.Sum32()
   287		if sum != crc32 || isize != z.size {
   288			z.err = ErrChecksum
   289			return 0, z.err
   290		}
   291	
   292		// File is ok; is there another?
   293		if !z.multistream {
   294			return 0, io.EOF
   295		}
   296	
   297		if err = z.readHeader(false); err != nil {
   298			z.err = err
   299			return
   300		}
   301	
   302		// Yes.  Reset and read from it.
   303		z.digest.Reset()
   304		z.size = 0
   305		return z.Read(p)
   306	}
   307	
   308	// Close closes the Reader. It does not close the underlying io.Reader.
   309	func (z *Reader) Close() error { return z.decompressor.Close() }
   310	

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