Source file src/pkg/archive/tar/common.go

// 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.

// The tar package 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

const (
    blockSize = 512

    // Types
    TypeReg           = '0'
    TypeRegA          = '\x00'
    TypeLink          = '1'
    TypeSymlink       = '2'
    TypeChar          = '3'
    TypeBlock         = '4'
    TypeDir           = '5'
    TypeFifo          = '6'
    TypeCont          = '7'
    TypeXHeader       = 'x'
    TypeXGlobalHeader = 'g'
)

// A Header represents a single header in a tar archive.
// Some fields may not be populated.
type Header struct {
    Name     string
    Mode     int64
    Uid      int
    Gid      int
    Size     int64
    Mtime    int64
    Typeflag byte
    Linkname string
    Uname    string
    Gname    string
    Devmajor int64
    Devminor int64
    Atime    int64
    Ctime    int64
}

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
}