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jeremybenn |
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tar
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// TODO(dsymonds):
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// - catch more errors (no first header, write after close, etc.)
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import (
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"errors"
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"io"
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"strconv"
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)
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var (
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ErrWriteTooLong = errors.New("write too long")
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ErrFieldTooLong = errors.New("header field too long")
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ErrWriteAfterClose = errors.New("write after close")
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)
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// A Writer provides sequential writing of a tar archive in POSIX.1 format.
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// A tar archive consists of a sequence of files.
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// Call WriteHeader to begin a new file, and then call Write to supply that file's data,
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// writing at most hdr.Size bytes in total.
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//
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// Example:
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// tw := tar.NewWriter(w)
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// hdr := new(Header)
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// hdr.Size = length of data in bytes
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// // populate other hdr fields as desired
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// if err := tw.WriteHeader(hdr); err != nil {
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// // handle error
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// }
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// io.Copy(tw, data)
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// tw.Close()
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type Writer struct {
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w io.Writer
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err error
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nb int64 // number of unwritten bytes for current file entry
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pad int64 // amount of padding to write after current file entry
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closed bool
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usedBinary bool // whether the binary numeric field extension was used
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}
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// NewWriter creates a new Writer writing to w.
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func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
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// Flush finishes writing the current file (optional).
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func (tw *Writer) Flush() error {
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n := tw.nb + tw.pad
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for n > 0 && tw.err == nil {
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nr := n
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if nr > blockSize {
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nr = blockSize
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}
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var nw int
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nw, tw.err = tw.w.Write(zeroBlock[0:nr])
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n -= int64(nw)
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}
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tw.nb = 0
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tw.pad = 0
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return tw.err
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}
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// Write s into b, terminating it with a NUL if there is room.
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func (tw *Writer) cString(b []byte, s string) {
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if len(s) > len(b) {
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if tw.err == nil {
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tw.err = ErrFieldTooLong
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}
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return
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}
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copy(b, s)
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if len(s) < len(b) {
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b[len(s)] = 0
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}
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}
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// Encode x as an octal ASCII string and write it into b with leading zeros.
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func (tw *Writer) octal(b []byte, x int64) {
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s := strconv.FormatInt(x, 8)
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// leading zeros, but leave room for a NUL.
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for len(s)+1 < len(b) {
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s = "0" + s
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}
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tw.cString(b, s)
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}
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// Write x into b, either as octal or as binary (GNUtar/star extension).
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func (tw *Writer) numeric(b []byte, x int64) {
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// Try octal first.
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s := strconv.FormatInt(x, 8)
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if len(s) < len(b) {
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tw.octal(b, x)
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return
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}
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// Too big: use binary (big-endian).
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tw.usedBinary = true
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for i := len(b) - 1; x > 0 && i >= 0; i-- {
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b[i] = byte(x)
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x >>= 8
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}
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b[0] |= 0x80 // highest bit indicates binary format
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}
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// WriteHeader writes hdr and prepares to accept the file's contents.
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// WriteHeader calls Flush if it is not the first header.
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// Calling after a Close will return ErrWriteAfterClose.
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func (tw *Writer) WriteHeader(hdr *Header) error {
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if tw.closed {
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return ErrWriteAfterClose
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}
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if tw.err == nil {
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tw.Flush()
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}
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if tw.err != nil {
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return tw.err
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}
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tw.nb = int64(hdr.Size)
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tw.pad = -tw.nb & (blockSize - 1) // blockSize is a power of two
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header := make([]byte, blockSize)
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s := slicer(header)
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// TODO(dsymonds): handle names longer than 100 chars
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copy(s.next(100), []byte(hdr.Name))
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tw.octal(s.next(8), hdr.Mode) // 100:108
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tw.numeric(s.next(8), int64(hdr.Uid)) // 108:116
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tw.numeric(s.next(8), int64(hdr.Gid)) // 116:124
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tw.numeric(s.next(12), hdr.Size) // 124:136
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tw.numeric(s.next(12), hdr.ModTime.Unix()) // 136:148
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s.next(8) // chksum (148:156)
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s.next(1)[0] = hdr.Typeflag // 156:157
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tw.cString(s.next(100), hdr.Linkname) // linkname (157:257)
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copy(s.next(8), []byte("ustar\x0000")) // 257:265
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tw.cString(s.next(32), hdr.Uname) // 265:297
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tw.cString(s.next(32), hdr.Gname) // 297:329
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tw.numeric(s.next(8), hdr.Devmajor) // 329:337
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tw.numeric(s.next(8), hdr.Devminor) // 337:345
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// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
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if tw.usedBinary {
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copy(header[257:265], []byte("ustar \x00"))
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}
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// The chksum field is terminated by a NUL and a space.
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// This is different from the other octal fields.
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chksum, _ := checksum(header)
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tw.octal(header[148:155], chksum)
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header[155] = ' '
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if tw.err != nil {
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// problem with header; probably integer too big for a field.
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return tw.err
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}
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_, tw.err = tw.w.Write(header)
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return tw.err
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}
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// Write writes to the current entry in the tar archive.
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// Write returns the error ErrWriteTooLong if more than
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// hdr.Size bytes are written after WriteHeader.
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func (tw *Writer) Write(b []byte) (n int, err error) {
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if tw.closed {
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err = ErrWriteTooLong
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return
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}
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overwrite := false
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if int64(len(b)) > tw.nb {
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b = b[0:tw.nb]
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overwrite = true
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}
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n, err = tw.w.Write(b)
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tw.nb -= int64(n)
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if err == nil && overwrite {
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err = ErrWriteTooLong
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return
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}
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tw.err = err
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return
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}
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// Close closes the tar archive, flushing any unwritten
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// data to the underlying writer.
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func (tw *Writer) Close() error {
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if tw.err != nil || tw.closed {
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return tw.err
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}
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tw.Flush()
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tw.closed = true
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// trailer: two zero blocks
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for i := 0; i < 2; i++ {
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_, tw.err = tw.w.Write(zeroBlock)
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if tw.err != nil {
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break
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}
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}
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return tw.err
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}
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