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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
// TODO(dsymonds):
// - catch more errors (no first header, etc.)
import (
"errors"
"fmt"
"io"
"strconv"
)
var (
ErrWriteTooLong = errors.New("archive/tar: write too long")
ErrFieldTooLong = errors.New("archive/tar: header field too long")
ErrWriteAfterClose = errors.New("archive/tar: write after close")
)
// A Writer provides sequential writing of a tar archive in POSIX.1 format.
// A tar archive consists of a sequence of files.
// Call WriteHeader to begin a new file, and then call Write to supply that file's data,
// writing at most hdr.Size bytes in total.
//
// Example:
// tw := tar.NewWriter(w)
// hdr := new(Header)
// hdr.Size = length of data in bytes
// // populate other hdr fields as desired
// if err := tw.WriteHeader(hdr); err != nil {
// // handle error
// }
// io.Copy(tw, data)
// tw.Close()
type Writer struct {
w io.Writer
err error
nb int64 // number of unwritten bytes for current file entry
pad int64 // amount of padding to write after current file entry
closed bool
usedBinary bool // whether the binary numeric field extension was used
}
// NewWriter creates a new Writer writing to w.
func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
// Flush finishes writing the current file (optional).
func (tw *Writer) Flush() error {
if tw.nb > 0 {
tw.err = fmt.Errorf("archive/tar: missed writing %d bytes", tw.nb)
return tw.err
}
n := tw.nb + tw.pad
for n > 0 && tw.err == nil {
nr := n
if nr > blockSize {
nr = blockSize
}
var nw int
nw, tw.err = tw.w.Write(zeroBlock[0:nr])
n -= int64(nw)
}
tw.nb = 0
tw.pad = 0
return tw.err
}
// Write s into b, terminating it with a NUL if there is room.
func (tw *Writer) cString(b []byte, s string) {
if len(s) > len(b) {
if tw.err == nil {
tw.err = ErrFieldTooLong
}
return
}
copy(b, s)
if len(s) < len(b) {
b[len(s)] = 0
}
}
// Encode x as an octal ASCII string and write it into b with leading zeros.
func (tw *Writer) octal(b []byte, x int64) {
s := strconv.FormatInt(x, 8)
// leading zeros, but leave room for a NUL.
for len(s)+1 < len(b) {
s = "0" + s
}
tw.cString(b, s)
}
// Write x into b, either as octal or as binary (GNUtar/star extension).
func (tw *Writer) numeric(b []byte, x int64) {
// Try octal first.
s := strconv.FormatInt(x, 8)
if len(s) < len(b) {
tw.octal(b, x)
return
}
// Too big: use binary (big-endian).
tw.usedBinary = true
for i := len(b) - 1; x > 0 && i >= 0; i-- {
b[i] = byte(x)
x >>= 8
}
b[0] |= 0x80 // highest bit indicates binary format
}
// WriteHeader writes hdr and prepares to accept the file's contents.
// WriteHeader calls Flush if it is not the first header.
// Calling after a Close will return ErrWriteAfterClose.
func (tw *Writer) WriteHeader(hdr *Header) error {
if tw.closed {
return ErrWriteAfterClose
}
if tw.err == nil {
tw.Flush()
}
if tw.err != nil {
return tw.err
}
tw.nb = int64(hdr.Size)
tw.pad = -tw.nb & (blockSize - 1) // blockSize is a power of two
header := make([]byte, blockSize)
s := slicer(header)
// TODO(dsymonds): handle names longer than 100 chars
copy(s.next(100), []byte(hdr.Name))
tw.octal(s.next(8), hdr.Mode) // 100:108
tw.numeric(s.next(8), int64(hdr.Uid)) // 108:116
tw.numeric(s.next(8), int64(hdr.Gid)) // 116:124
tw.numeric(s.next(12), hdr.Size) // 124:136
tw.numeric(s.next(12), hdr.ModTime.Unix()) // 136:148
s.next(8) // chksum (148:156)
s.next(1)[0] = hdr.Typeflag // 156:157
tw.cString(s.next(100), hdr.Linkname) // linkname (157:257)
copy(s.next(8), []byte("ustar\x0000")) // 257:265
tw.cString(s.next(32), hdr.Uname) // 265:297
tw.cString(s.next(32), hdr.Gname) // 297:329
tw.numeric(s.next(8), hdr.Devmajor) // 329:337
tw.numeric(s.next(8), hdr.Devminor) // 337:345
// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
if tw.usedBinary {
copy(header[257:265], []byte("ustar \x00"))
}
// The chksum field is terminated by a NUL and a space.
// This is different from the other octal fields.
chksum, _ := checksum(header)
tw.octal(header[148:155], chksum)
header[155] = ' '
if tw.err != nil {
// problem with header; probably integer too big for a field.
return tw.err
}
_, tw.err = tw.w.Write(header)
return tw.err
}
// Write writes to the current entry in the tar archive.
// Write returns the error ErrWriteTooLong if more than
// hdr.Size bytes are written after WriteHeader.
func (tw *Writer) Write(b []byte) (n int, err error) {
if tw.closed {
err = ErrWriteTooLong
return
}
overwrite := false
if int64(len(b)) > tw.nb {
b = b[0:tw.nb]
overwrite = true
}
n, err = tw.w.Write(b)
tw.nb -= int64(n)
if err == nil && overwrite {
err = ErrWriteTooLong
return
}
tw.err = err
return
}
// Close closes the tar archive, flushing any unwritten
// data to the underlying writer.
func (tw *Writer) Close() error {
if tw.err != nil || tw.closed {
return tw.err
}
tw.Flush()
tw.closed = true
if tw.err != nil {
return tw.err
}
// trailer: two zero blocks
for i := 0; i < 2; i++ {
_, tw.err = tw.w.Write(zeroBlock)
if tw.err != nil {
break
}
}
return tw.err
}
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