-
Notifications
You must be signed in to change notification settings - Fork 309
/
encode.go
784 lines (712 loc) · 20.8 KB
/
encode.go
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
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
// Copyright 2011 The Snappy-Go Authors. All rights reserved.
// Copyright (c) 2019 Klaus Post. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package s2
import (
"crypto/rand"
"encoding/binary"
"errors"
"fmt"
"io"
"math"
"math/bits"
"runtime"
"sync"
)
// Encode returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func Encode(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if len(dst) < n {
dst = make([]byte, n)
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlock(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// EncodeBetter returns the encoded form of src. The returned slice may be a sub-
// slice of dst if dst was large enough to hold the entire encoded block.
// Otherwise, a newly allocated slice will be returned.
//
// EncodeBetter compresses better than Encode but typically with a
// 10-40% speed decrease on both compression and decompression.
//
// The dst and src must not overlap. It is valid to pass a nil dst.
//
// The blocks will require the same amount of memory to decode as encoding,
// and does not make for concurrent decoding.
// Also note that blocks do not contain CRC information, so corruption may be undetected.
//
// If you need to encode larger amounts of data, consider using
// the streaming interface which gives all of these features.
func EncodeBetter(dst, src []byte) []byte {
if n := MaxEncodedLen(len(src)); n < 0 {
panic(ErrTooLarge)
} else if len(dst) < n {
dst = make([]byte, n)
}
// The block starts with the varint-encoded length of the decompressed bytes.
d := binary.PutUvarint(dst, uint64(len(src)))
if len(src) == 0 {
return dst[:d]
}
if len(src) < minNonLiteralBlockSize {
d += emitLiteral(dst[d:], src)
return dst[:d]
}
n := encodeBlockBetter(dst[d:], src)
if n > 0 {
d += n
return dst[:d]
}
// Not compressible
d += emitLiteral(dst[d:], src)
return dst[:d]
}
// ConcatBlocks will concatenate the supplied blocks and append them to the supplied destination.
// If the destination is nil or too small, a new will be allocated.
// The blocks are not validated, so garbage in = garbage out.
// dst may not overlap block data.
// Any data in dst is preserved as is, so it will not be considered a block.
func ConcatBlocks(dst []byte, blocks ...[]byte) ([]byte, error) {
totalSize := uint64(0)
compSize := 0
for _, b := range blocks {
l, hdr, err := decodedLen(b)
if err != nil {
return nil, err
}
totalSize += uint64(l)
compSize += len(b) - hdr
}
if totalSize == 0 {
dst = append(dst, 0)
return dst, nil
}
if totalSize > math.MaxUint32 {
return nil, ErrTooLarge
}
var tmp [binary.MaxVarintLen32]byte
hdrSize := binary.PutUvarint(tmp[:], totalSize)
wantSize := hdrSize + compSize
if cap(dst)-len(dst) < wantSize {
dst = append(make([]byte, 0, wantSize+len(dst)), dst...)
}
dst = append(dst, tmp[:hdrSize]...)
for _, b := range blocks {
_, hdr, err := decodedLen(b)
if err != nil {
return nil, err
}
dst = append(dst, b[hdr:]...)
}
return dst, nil
}
// inputMargin is the minimum number of extra input bytes to keep, inside
// encodeBlock's inner loop. On some architectures, this margin lets us
// implement a fast path for emitLiteral, where the copy of short (<= 16 byte)
// literals can be implemented as a single load to and store from a 16-byte
// register. That literal's actual length can be as short as 1 byte, so this
// can copy up to 15 bytes too much, but that's OK as subsequent iterations of
// the encoding loop will fix up the copy overrun, and this inputMargin ensures
// that we don't overrun the dst and src buffers.
const inputMargin = 8
// minNonLiteralBlockSize is the minimum size of the input to encodeBlock that
// will be accepted by the encoder.
const minNonLiteralBlockSize = 32
// MaxBlockSize is the maximum value where MaxEncodedLen will return a valid block size.
// Blocks this big are highly discouraged, though.
const MaxBlockSize = math.MaxUint32 - binary.MaxVarintLen32 - 5
// MaxEncodedLen returns the maximum length of a snappy block, given its
// uncompressed length.
//
// It will return a negative value if srcLen is too large to encode.
// 32 bit platforms will have lower thresholds for rejecting big content.
func MaxEncodedLen(srcLen int) int {
n := uint64(srcLen)
if n > 0xffffffff {
// Also includes negative.
return -1
}
// Size of the varint encoded block size.
n = n + uint64((bits.Len64(n)+7)/7)
// Add maximum size of encoding block as literals.
n += uint64(literalExtraSize(int64(srcLen)))
if n > 0xffffffff {
return -1
}
return int(n)
}
var errClosed = errors.New("s2: Writer is closed")
// NewWriter returns a new Writer that compresses to w, using the
// framing format described at
// https://github.com/google/snappy/blob/master/framing_format.txt
//
// Users must call Close to guarantee all data has been forwarded to
// the underlying io.Writer and that resources are released.
// They may also call Flush zero or more times before calling Close.
func NewWriter(w io.Writer, opts ...WriterOption) *Writer {
w2 := Writer{
blockSize: defaultBlockSize,
concurrency: runtime.GOMAXPROCS(0),
}
for _, opt := range opts {
if err := opt(&w2); err != nil {
w2.errState = err
return &w2
}
}
w2.obufLen = obufHeaderLen + MaxEncodedLen(w2.blockSize)
w2.paramsOK = true
w2.ibuf = make([]byte, 0, w2.blockSize)
w2.buffers.New = func() interface{} {
return make([]byte, w2.obufLen)
}
w2.Reset(w)
return &w2
}
// Writer is an io.Writer that can write Snappy-compressed bytes.
type Writer struct {
errMu sync.Mutex
errState error
// ibuf is a buffer for the incoming (uncompressed) bytes.
ibuf []byte
// wroteStreamHeader is whether we have written the stream header.
wroteStreamHeader bool
paramsOK bool
better bool
blockSize int
obufLen int
concurrency int
written int64
output chan chan result
buffers sync.Pool
writerWg sync.WaitGroup
writer io.Writer
pad int
}
type result []byte
// err returns the previously set error.
// If no error has been set it is set to err if not nil.
func (w *Writer) err(err error) error {
w.errMu.Lock()
errSet := w.errState
if errSet == nil && err != nil {
w.errState = err
errSet = err
}
w.errMu.Unlock()
return errSet
}
// Reset discards the writer's state and switches the Snappy writer to write to w.
// This permits reusing a Writer rather than allocating a new one.
func (w *Writer) Reset(writer io.Writer) {
if !w.paramsOK {
return
}
// Close previous writer, if any.
if w.output != nil {
close(w.output)
w.writerWg.Wait()
w.output = nil
}
w.errState = nil
w.ibuf = w.ibuf[:0]
w.wroteStreamHeader = false
w.written = 0
w.writer = writer
// If we didn't get a writer, stop here.
if writer == nil {
return
}
// If no concurrency requested, don't spin up writer goroutine.
if w.concurrency == 1 {
return
}
toWrite := make(chan chan result, w.concurrency)
w.output = toWrite
w.writerWg.Add(1)
// Start a writer goroutine that will write all output in order.
go func() {
defer w.writerWg.Done()
// Get a queued write.
for write := range toWrite {
// Wait for the data to be available.
in := <-write
if len(in) > 0 {
if w.err(nil) == nil {
// Don't expose data from previous buffers.
in = in[:len(in):len(in)]
// Write to output.
n, err := writer.Write(in)
if err == nil && n != len(in) {
err = io.ErrShortBuffer
}
_ = w.err(err)
w.written += int64(n)
}
if cap(in) >= w.obufLen {
w.buffers.Put([]byte(in))
}
}
// close the incoming write request.
// This can be used for synchronizing flushes.
close(write)
}
}()
}
// Write satisfies the io.Writer interface.
func (w *Writer) Write(p []byte) (nRet int, errRet error) {
// If we exceed the input buffer size, start writing
for len(p) > (cap(w.ibuf)-len(w.ibuf)) && w.err(nil) == nil {
var n int
if len(w.ibuf) == 0 {
// Large write, empty buffer.
// Write directly from p to avoid copy.
n, _ = w.write(p)
} else {
n = copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
w.ibuf = w.ibuf[:len(w.ibuf)+n]
w.write(w.ibuf)
w.ibuf = w.ibuf[:0]
}
nRet += n
p = p[n:]
}
if err := w.err(nil); err != nil {
return nRet, err
}
// p should always be able to fit into w.ibuf now.
n := copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
w.ibuf = w.ibuf[:len(w.ibuf)+n]
nRet += n
return nRet, nil
}
// ReadFrom implements the io.ReaderFrom interface.
// Using this is typically more efficient since it avoids a memory copy.
// ReadFrom reads data from r until EOF or error.
// The return value n is the number of bytes read.
// Any error except io.EOF encountered during the read is also returned.
func (w *Writer) ReadFrom(r io.Reader) (n int64, err error) {
if len(w.ibuf) > 0 {
err := w.Flush()
if err != nil {
return 0, err
}
}
for {
inbuf := w.buffers.Get().([]byte)[:w.blockSize+obufHeaderLen]
n2, err := io.ReadFull(r, inbuf[obufHeaderLen:])
if err != nil {
if err == io.ErrUnexpectedEOF {
err = io.EOF
}
if err != io.EOF {
return n, w.err(err)
}
}
if n2 == 0 {
break
}
n += int64(n2)
err2 := w.writeFull(inbuf[:n2+obufHeaderLen])
if w.err(err2) != nil {
break
}
if err != nil {
// We got EOF and wrote everything
break
}
}
return n, w.err(nil)
}
func (w *Writer) write(p []byte) (nRet int, errRet error) {
if err := w.err(nil); err != nil {
return 0, err
}
if w.concurrency == 1 {
return w.writeSync(p)
}
// Spawn goroutine and write block to output channel.
for len(p) > 0 {
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
hWriter <- []byte(magicChunk)
}
var uncompressed []byte
if len(p) > w.blockSize {
uncompressed, p = p[:w.blockSize], p[w.blockSize:]
} else {
uncompressed, p = p, nil
}
// Copy input.
// If the block is incompressible, this is used for the result.
inbuf := w.buffers.Get().([]byte)[:len(uncompressed)+obufHeaderLen]
obuf := w.buffers.Get().([]byte)[:w.obufLen]
copy(inbuf[obufHeaderLen:], uncompressed)
uncompressed = inbuf[obufHeaderLen:]
output := make(chan result)
// Queue output now, so we keep order.
w.output <- output
go func() {
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
var n2 int
if w.better {
n2 = encodeBlockBetter(obuf[obufHeaderLen+n:], uncompressed)
} else {
n2 = encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
}
// Check if we should use this, or store as uncompressed instead.
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
// Use input as output.
obuf, inbuf = inbuf, obuf
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
// Queue final output.
output <- obuf
// Put unused buffer back in pool.
w.buffers.Put(inbuf)
}()
nRet += len(uncompressed)
}
return nRet, nil
}
// writeFull is a special version of write that will always write the full buffer.
// Data to be compressed should start at offset obufHeaderLen and fill the remainder of the buffer.
// The data will be written as a single block.
// The caller is not allowed to use inbuf after this function has been called.
func (w *Writer) writeFull(inbuf []byte) (errRet error) {
if err := w.err(nil); err != nil {
return err
}
// Spawn goroutine and write block to output channel.
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
hWriter := make(chan result)
w.output <- hWriter
hWriter <- []byte(magicChunk)
}
// Get an output buffer.
obuf := w.buffers.Get().([]byte)[:w.obufLen]
uncompressed := inbuf[obufHeaderLen:]
output := make(chan result)
// Queue output now, so we keep order.
w.output <- output
go func() {
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
var n2 int
if w.better {
n2 = encodeBlockBetter(obuf[obufHeaderLen+n:], uncompressed)
} else {
n2 = encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
}
// Check if we should use this, or store as uncompressed instead.
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
// Use input as output.
obuf, inbuf = inbuf, obuf
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
// Queue final output.
output <- obuf
// Put unused buffer back in pool.
w.buffers.Put(inbuf)
}()
return nil
}
func (w *Writer) writeSync(p []byte) (nRet int, errRet error) {
if err := w.err(nil); err != nil {
return 0, err
}
for len(p) > 0 {
if !w.wroteStreamHeader {
w.wroteStreamHeader = true
n, err := w.writer.Write([]byte(magicChunk))
if err != nil {
return 0, w.err(err)
}
if n != len(magicChunk) {
return 0, w.err(io.ErrShortWrite)
}
w.written += int64(n)
}
var uncompressed []byte
if len(p) > w.blockSize {
uncompressed, p = p[:w.blockSize], p[w.blockSize:]
} else {
uncompressed, p = p, nil
}
obuf := w.buffers.Get().([]byte)[:w.obufLen]
checksum := crc(uncompressed)
// Set to uncompressed.
chunkType := uint8(chunkTypeUncompressedData)
chunkLen := 4 + len(uncompressed)
// Attempt compressing.
n := binary.PutUvarint(obuf[obufHeaderLen:], uint64(len(uncompressed)))
var n2 int
if w.better {
n2 = encodeBlockBetter(obuf[obufHeaderLen+n:], uncompressed)
} else {
n2 = encodeBlock(obuf[obufHeaderLen+n:], uncompressed)
}
if n2 > 0 {
chunkType = uint8(chunkTypeCompressedData)
chunkLen = 4 + n + n2
obuf = obuf[:obufHeaderLen+n+n2]
} else {
obuf = obuf[:8]
}
// Fill in the per-chunk header that comes before the body.
obuf[0] = chunkType
obuf[1] = uint8(chunkLen >> 0)
obuf[2] = uint8(chunkLen >> 8)
obuf[3] = uint8(chunkLen >> 16)
obuf[4] = uint8(checksum >> 0)
obuf[5] = uint8(checksum >> 8)
obuf[6] = uint8(checksum >> 16)
obuf[7] = uint8(checksum >> 24)
n, err := w.writer.Write(obuf)
if err != nil {
return 0, w.err(err)
}
if n != len(obuf) {
return 0, w.err(io.ErrShortWrite)
}
w.written += int64(n)
if chunkType == chunkTypeUncompressedData {
// Write uncompressed data.
n, err := w.writer.Write(uncompressed)
if err != nil {
return 0, w.err(err)
}
if n != len(uncompressed) {
return 0, w.err(io.ErrShortWrite)
}
w.written += int64(n)
}
w.buffers.Put(obuf)
// Queue final output.
nRet += len(uncompressed)
}
return nRet, nil
}
// Flush flushes the Writer to its underlying io.Writer.
// This does not apply padding.
func (w *Writer) Flush() error {
if err := w.err(nil); err != nil {
return err
}
// Queue any data still in input buffer.
if len(w.ibuf) != 0 {
_, err := w.write(w.ibuf)
w.ibuf = w.ibuf[:0]
err = w.err(err)
if err != nil {
return err
}
}
if w.output == nil {
return w.err(nil)
}
// Send empty buffer
res := make(chan result)
w.output <- res
// Block until this has been picked up.
res <- nil
// When it is closed, we have flushed.
<-res
return w.err(nil)
}
// Close calls Flush and then closes the Writer.
// Calling Close multiple times is ok.
func (w *Writer) Close() error {
err := w.Flush()
if w.output != nil {
close(w.output)
w.writerWg.Wait()
w.output = nil
}
if w.err(nil) == nil && w.writer != nil && w.pad > 0 {
add := calcSkippableFrame(w.written, int64(w.pad))
frame, err := skippableFrame(w.ibuf[:0], add, rand.Reader)
if err = w.err(err); err != nil {
return err
}
_, err2 := w.writer.Write(frame)
_ = w.err(err2)
}
_ = w.err(errClosed)
if err == errClosed {
return nil
}
return err
}
const skippableFrameHeader = 4
// calcSkippableFrame will return a total size to be added for written
// to be divisible by multiple.
// The value will always be > skippableFrameHeader.
// The function will panic if written < 0 or wantMultiple <= 0.
func calcSkippableFrame(written, wantMultiple int64) int {
if wantMultiple <= 0 {
panic("wantMultiple <= 0")
}
if written < 0 {
panic("written < 0")
}
leftOver := written % wantMultiple
if leftOver == 0 {
return 0
}
toAdd := wantMultiple - leftOver
for toAdd < skippableFrameHeader {
toAdd += wantMultiple
}
return int(toAdd)
}
// skippableFrame will add a skippable frame with a total size of bytes.
// total should be >= skippableFrameHeader and < maxBlockSize + skippableFrameHeader
func skippableFrame(dst []byte, total int, r io.Reader) ([]byte, error) {
if total == 0 {
return dst, nil
}
if total < skippableFrameHeader {
return dst, fmt.Errorf("s2: requested skippable frame (%d) < 4", total)
}
if int64(total) >= maxBlockSize+skippableFrameHeader {
return dst, fmt.Errorf("s2: requested skippable frame (%d) >= max 1<<24", total)
}
// Chunk type 0xfe "Section 4.4 Padding (chunk type 0xfe)"
dst = append(dst, chunkTypePadding)
f := uint32(total - skippableFrameHeader)
// Add chunk length.
dst = append(dst, uint8(f), uint8(f>>8), uint8(f>>16))
// Add data
start := len(dst)
dst = append(dst, make([]byte, f)...)
_, err := io.ReadFull(r, dst[start:])
return dst, err
}
// WriterOption is an option for creating a encoder.
type WriterOption func(*Writer) error
// WriterConcurrency will set the concurrency,
// meaning the maximum number of decoders to run concurrently.
// The value supplied must be at least 1.
// By default this will be set to GOMAXPROCS.
func WriterConcurrency(n int) WriterOption {
return func(w *Writer) error {
if n <= 0 {
return errors.New("concurrency must be at least 1")
}
w.concurrency = n
return nil
}
}
// WriterBetterCompression will enable better compression.
// EncodeBetter compresses better than Encode but typically with a
// 10-40% speed decrease on both compression and decompression.
func WriterBetterCompression() WriterOption {
return func(w *Writer) error {
w.better = true
return nil
}
}
// WriterBlockSize allows to override the default block size.
// Blocks will be this size or smaller.
// Minimum size is 4KB and and maximum size is 4MB.
//
// Bigger blocks may give bigger throughput on systems with many cores,
// and will increase compression slightly, but it will limit the possible
// concurrency for smaller payloads for both encoding and decoding.
// Default block size is 1MB.
func WriterBlockSize(n int) WriterOption {
return func(w *Writer) error {
if w.blockSize > maxBlockSize || w.blockSize < minBlockSize {
return errors.New("s2: block size too large. Must be <= 4MB and >=4KB")
}
w.blockSize = n
return nil
}
}
// WriterPadding will add padding to all output so the size will be a multiple of n.
// This can be used to obfuscate the exact output size or make blocks of a certain size.
// The contents will be a skippable frame, so it will be invisible by the decoder.
// n must be > 0 and <= 4MB.
// The padded area will be filled with data from crypto/rand.Reader.
// The padding will be applied whenever Close is called on the writer.
func WriterPadding(n int) WriterOption {
return func(w *Writer) error {
if n <= 0 {
return fmt.Errorf("s2: padding must be at least 1")
}
// No need to waste our time.
if n == 1 {
w.pad = 0
}
if n > maxBlockSize {
return fmt.Errorf("s2: padding must less than 4MB")
}
w.pad = n
return nil
}
}