summaryrefslogtreecommitdiff
path: root/src/pkg/archive/tar/writer.go
blob: 6eff6f6f84d8eaa903b87c135ec4f5f6684b4667 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
// 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 (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"path"
	"strconv"
	"strings"
	"time"
)

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")
	errNameTooLong     = errors.New("archive/tar: name too long")
	errInvalidHeader   = errors.New("archive/tar: header field too long or contains invalid values")
)

// 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.
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
	preferPax  bool // use pax header instead of binary numeric header
}

// 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.
// If the value is too long for the field and allowPax is true add a paxheader record instead
func (tw *Writer) cString(b []byte, s string, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
	needsPaxHeader := allowPax && len(s) > len(b) || !isASCII(s)
	if needsPaxHeader {
		paxHeaders[paxKeyword] = s
		return
	}
	if len(s) > len(b) {
		if tw.err == nil {
			tw.err = ErrFieldTooLong
		}
		return
	}
	ascii := toASCII(s)
	copy(b, ascii)
	if len(ascii) < len(b) {
		b[len(ascii)] = 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, false, paxNone, nil)
}

// Write x into b, either as octal or as binary (GNUtar/star extension).
// If the value is too long for the field and writingPax is enabled both for the field and the add a paxheader record instead
func (tw *Writer) numeric(b []byte, x int64, allowPax bool, paxKeyword string, paxHeaders map[string]string) {
	// Try octal first.
	s := strconv.FormatInt(x, 8)
	if len(s) < len(b) {
		tw.octal(b, x)
		return
	}

	// If it is too long for octal, and pax is preferred, use a pax header
	if allowPax && tw.preferPax {
		tw.octal(b, 0)
		s := strconv.FormatInt(x, 10)
		paxHeaders[paxKeyword] = s
		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
}

var (
	minTime = time.Unix(0, 0)
	// There is room for 11 octal digits (33 bits) of mtime.
	maxTime = minTime.Add((1<<33 - 1) * time.Second)
)

// 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 {
	return tw.writeHeader(hdr, true)
}

// 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.
// As this method is called internally by writePax header to allow it to
// suppress writing the pax header.
func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
	if tw.closed {
		return ErrWriteAfterClose
	}
	if tw.err == nil {
		tw.Flush()
	}
	if tw.err != nil {
		return tw.err
	}

	// a map to hold pax header records, if any are needed
	paxHeaders := make(map[string]string)

	// TODO(shanemhansen): we might want to use PAX headers for
	// subsecond time resolution, but for now let's just capture
	// too long fields or non ascii characters

	header := make([]byte, blockSize)
	s := slicer(header)

	// keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
	pathHeaderBytes := s.next(fileNameSize)

	tw.cString(pathHeaderBytes, hdr.Name, true, paxPath, paxHeaders)

	// Handle out of range ModTime carefully.
	var modTime int64
	if !hdr.ModTime.Before(minTime) && !hdr.ModTime.After(maxTime) {
		modTime = hdr.ModTime.Unix()
	}

	tw.octal(s.next(8), hdr.Mode)                                   // 100:108
	tw.numeric(s.next(8), int64(hdr.Uid), true, paxUid, paxHeaders) // 108:116
	tw.numeric(s.next(8), int64(hdr.Gid), true, paxGid, paxHeaders) // 116:124
	tw.numeric(s.next(12), hdr.Size, true, paxSize, paxHeaders)     // 124:136
	tw.numeric(s.next(12), modTime, false, paxNone, nil)            // 136:148 --- consider using pax for finer granularity
	s.next(8)                                                       // chksum (148:156)
	s.next(1)[0] = hdr.Typeflag                                     // 156:157

	tw.cString(s.next(100), hdr.Linkname, true, paxLinkpath, paxHeaders)

	copy(s.next(8), []byte("ustar\x0000"))                        // 257:265
	tw.cString(s.next(32), hdr.Uname, true, paxUname, paxHeaders) // 265:297
	tw.cString(s.next(32), hdr.Gname, true, paxGname, paxHeaders) // 297:329
	tw.numeric(s.next(8), hdr.Devmajor, false, paxNone, nil)      // 329:337
	tw.numeric(s.next(8), hdr.Devminor, false, paxNone, nil)      // 337:345

	// keep a reference to the prefix to allow to overwrite it later if we detect that we can use ustar longnames instead of pax
	prefixHeaderBytes := s.next(155)
	tw.cString(prefixHeaderBytes, "", false, paxNone, nil) // 345:500  prefix

	// Use the GNU magic instead of POSIX magic if we used any GNU extensions.
	if tw.usedBinary {
		copy(header[257:265], []byte("ustar  \x00"))
	}

	_, paxPathUsed := paxHeaders[paxPath]
	// try to use a ustar header when only the name is too long
	if !tw.preferPax && len(paxHeaders) == 1 && paxPathUsed {
		suffix := hdr.Name
		prefix := ""
		if len(hdr.Name) > fileNameSize && isASCII(hdr.Name) {
			var err error
			prefix, suffix, err = tw.splitUSTARLongName(hdr.Name)
			if err == nil {
				// ok we can use a ustar long name instead of pax, now correct the fields

				// remove the path field from the pax header. this will suppress the pax header
				delete(paxHeaders, paxPath)

				// update the path fields
				tw.cString(pathHeaderBytes, suffix, false, paxNone, nil)
				tw.cString(prefixHeaderBytes, prefix, false, paxNone, nil)

				// Use the ustar magic if we used ustar long names.
				if len(prefix) > 0 && !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
	}

	if allowPax {
		for k, v := range hdr.Xattrs {
			paxHeaders[paxXattr+k] = v
		}
	}

	if len(paxHeaders) > 0 {
		if !allowPax {
			return errInvalidHeader
		}
		if err := tw.writePAXHeader(hdr, paxHeaders); err != nil {
			return err
		}
	}
	tw.nb = int64(hdr.Size)
	tw.pad = (blockSize - (tw.nb % blockSize)) % blockSize

	_, tw.err = tw.w.Write(header)
	return tw.err
}

// writeUSTARLongName splits a USTAR long name hdr.Name.
// name must be < 256 characters. errNameTooLong is returned
// if hdr.Name can't be split. The splitting heuristic
// is compatible with gnu tar.
func (tw *Writer) splitUSTARLongName(name string) (prefix, suffix string, err error) {
	length := len(name)
	if length > fileNamePrefixSize+1 {
		length = fileNamePrefixSize + 1
	} else if name[length-1] == '/' {
		length--
	}
	i := strings.LastIndex(name[:length], "/")
	// nlen contains the resulting length in the name field.
	// plen contains the resulting length in the prefix field.
	nlen := len(name) - i - 1
	plen := i
	if i <= 0 || nlen > fileNameSize || nlen == 0 || plen > fileNamePrefixSize {
		err = errNameTooLong
		return
	}
	prefix, suffix = name[:i], name[i+1:]
	return
}

// writePaxHeader writes an extended pax header to the
// archive.
func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) error {
	// Prepare extended header
	ext := new(Header)
	ext.Typeflag = TypeXHeader
	// Setting ModTime is required for reader parsing to
	// succeed, and seems harmless enough.
	ext.ModTime = hdr.ModTime
	// The spec asks that we namespace our pseudo files
	// with the current pid.
	pid := os.Getpid()
	dir, file := path.Split(hdr.Name)
	fullName := path.Join(dir,
		fmt.Sprintf("PaxHeaders.%d", pid), file)

	ascii := toASCII(fullName)
	if len(ascii) > 100 {
		ascii = ascii[:100]
	}
	ext.Name = ascii
	// Construct the body
	var buf bytes.Buffer

	for k, v := range paxHeaders {
		fmt.Fprint(&buf, paxHeader(k+"="+v))
	}

	ext.Size = int64(len(buf.Bytes()))
	if err := tw.writeHeader(ext, false); err != nil {
		return err
	}
	if _, err := tw.Write(buf.Bytes()); err != nil {
		return err
	}
	if err := tw.Flush(); err != nil {
		return err
	}
	return nil
}

// paxHeader formats a single pax record, prefixing it with the appropriate length
func paxHeader(msg string) string {
	const padding = 2 // Extra padding for space and newline
	size := len(msg) + padding
	size += len(strconv.Itoa(size))
	record := fmt.Sprintf("%d %s\n", size, msg)
	if len(record) != size {
		// Final adjustment if adding size increased
		// the number of digits in size
		size = len(record)
		record = fmt.Sprintf("%d %s\n", size, msg)
	}
	return record
}

// 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
}