libgo/go/archive/tar/common.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 // The tar package implements access to tar archives.
   6 // It aims to cover most of the variations, including those produced
   7 // by GNU and BSD tars.
   8 //
   9 // References:
  10 //   http://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5
  11 //   http://www.gnu.org/software/tar/manual/html_node/Standard.html
  12 package tar
  13
  14 const (
  15         blockSize = 512
  16
  17         // Types
  18         TypeReg           = '0'
  19         TypeRegA          = '\x00'
  20         TypeLink          = '1'
  21         TypeSymlink       = '2'
  22         TypeChar          = '3'
  23         TypeBlock         = '4'
  24         TypeDir           = '5'
  25         TypeFifo          = '6'
  26         TypeCont          = '7'
  27         TypeXHeader       = 'x'
  28         TypeXGlobalHeader = 'g'
  29 )
  30
  31 // A Header represents a single header in a tar archive.
  32 // Some fields may not be populated.
  33 type Header struct {
  34         Name     string
  35         Mode     int64
  36         Uid      int
  37         Gid      int
  38         Size     int64
  39         Mtime    int64
  40         Typeflag byte
  41         Linkname string
  42         Uname    string
  43         Gname    string
  44         Devmajor int64
  45         Devminor int64
  46         Atime    int64
  47         Ctime    int64
  48 }
  49
  50 var zeroBlock = make([]byte, blockSize)
  51
  52 // POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.
  53 // We compute and return both.
  54 func checksum(header []byte) (unsigned int64, signed int64) {
  55         for i := 0; i < len(header); i++ {
  56                 if i == 148 {
  57                         // The chksum field (header[148:156]) is special: it should be treated as space bytes.
  58                         unsigned += ' ' * 8
  59                         signed += ' ' * 8
  60                         i += 7
  61                         continue
  62                 }
  63                 unsigned += int64(header[i])
  64                 signed += int64(int8(header[i]))
  65         }
  66         return
  67 }
  68
  69 type slicer []byte
  70
  71 func (sp *slicer) next(n int) (b []byte) {
  72         s := *sp
  73         b, *sp = s[0:n], s[n:]
  74         return
  75 }