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// 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 tar implements access to tar archives.

// It aims to cover most of the variations, including those produced

// by GNU and BSD tars.

//

// References:

//   http://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5

//   http://www.gnu.org/software/tar/manual/html_node/Standard.html

package tar

import "time"

const (

        blockSize = 512

        // Types

        TypeReg           = '0'    // regular file

        TypeRegA          = '\x00' // regular file

        TypeLink          = '1'    // hard link

        TypeSymlink       = '2'    // symbolic link

        TypeChar          = '3'    // character device node

        TypeBlock         = '4'    // block device node

        TypeDir           = '5'    // directory

        TypeFifo          = '6'    // fifo node

        TypeCont          = '7'    // reserved

        TypeXHeader       = 'x'    // extended header

        TypeXGlobalHeader = 'g'    // global extended header

)

// A Header represents a single header in a tar archive.

// Some fields may not be populated.

type Header struct {

        Name       string    // name of header file entry

        Mode       int64     // permission and mode bits

        Uid        int       // user id of owner

        Gid        int       // group id of owner

        Size       int64     // length in bytes

        ModTime    time.Time // modified time

        Typeflag   byte      // type of header entry

        Linkname   string    // target name of link

        Uname      string    // user name of owner

        Gname      string    // group name of owner

        Devmajor   int64     // major number of character or block device

        Devminor   int64     // minor number of character or block device

        AccessTime time.Time // access time

        ChangeTime time.Time // status change time

}

var zeroBlock = make([]byte, blockSize)

// POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.

// We compute and return both.

func checksum(header []byte) (unsigned int64, signed int64) {

        for i := 0; i < len(header); i++ {

                if i == 148 {

                        // The chksum field (header[148:156]) is special: it should be treated as space bytes.

                        unsigned += ' ' * 8

                        signed += ' ' * 8

                        i += 7

                        continue

                }

                unsigned += int64(header[i])

                signed += int64(int8(header[i]))

        }

        return

}

type slicer []byte

func (sp *slicer) next(n int) (b []byte) {

        s := *sp

        b, *sp = s[0:n], s[n:]

        return

}