Source file src/pkg/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	// Package tar 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	import "time"
    15	
    16	const (
    17		blockSize = 512
    18	
    19		// Types
    20		TypeReg           = '0'    // regular file
    21		TypeRegA          = '\x00' // regular file
    22		TypeLink          = '1'    // hard link
    23		TypeSymlink       = '2'    // symbolic link
    24		TypeChar          = '3'    // character device node
    25		TypeBlock         = '4'    // block device node
    26		TypeDir           = '5'    // directory
    27		TypeFifo          = '6'    // fifo node
    28		TypeCont          = '7'    // reserved
    29		TypeXHeader       = 'x'    // extended header
    30		TypeXGlobalHeader = 'g'    // global extended header
    31	)
    32	
    33	// A Header represents a single header in a tar archive.
    34	// Some fields may not be populated.
    35	type Header struct {
    36		Name       string    // name of header file entry
    37		Mode       int64     // permission and mode bits
    38		Uid        int       // user id of owner
    39		Gid        int       // group id of owner
    40		Size       int64     // length in bytes
    41		ModTime    time.Time // modified time
    42		Typeflag   byte      // type of header entry
    43		Linkname   string    // target name of link
    44		Uname      string    // user name of owner
    45		Gname      string    // group name of owner
    46		Devmajor   int64     // major number of character or block device
    47		Devminor   int64     // minor number of character or block device
    48		AccessTime time.Time // access time
    49		ChangeTime time.Time // status change time
    50	}
    51	
    52	var zeroBlock = make([]byte, blockSize)
    53	
    54	// POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.
    55	// We compute and return both.
    56	func checksum(header []byte) (unsigned int64, signed int64) {
    57		for i := 0; i < len(header); i++ {
    58			if i == 148 {
    59				// The chksum field (header[148:156]) is special: it should be treated as space bytes.
    60				unsigned += ' ' * 8
    61				signed += ' ' * 8
    62				i += 7
    63				continue
    64			}
    65			unsigned += int64(header[i])
    66			signed += int64(int8(header[i]))
    67		}
    68		return
    69	}
    70	
    71	type slicer []byte
    72	
    73	func (sp *slicer) next(n int) (b []byte) {
    74		s := *sp
    75		b, *sp = s[0:n], s[n:]
    76		return
    77	}