summaryrefslogtreecommitdiff
path: root/vendor/github.com/klauspost/compress/zstd/decoder.go
blob: 286c8f9d71f962c4672c06de5fc70ea1ffc71e75 (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
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
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
// Copyright 2019+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.
// Based on work by Yann Collet, released under BSD License.

package zstd

import (
	"bytes"
	"context"
	"encoding/binary"
	"io"
	"sync"

	"github.com/klauspost/compress/zstd/internal/xxhash"
)

// Decoder provides decoding of zstandard streams.
// The decoder has been designed to operate without allocations after a warmup.
// This means that you should store the decoder for best performance.
// To re-use a stream decoder, use the Reset(r io.Reader) error to switch to another stream.
// A decoder can safely be re-used even if the previous stream failed.
// To release the resources, you must call the Close() function on a decoder.
type Decoder struct {
	o decoderOptions

	// Unreferenced decoders, ready for use.
	decoders chan *blockDec

	// Current read position used for Reader functionality.
	current decoderState

	// sync stream decoding
	syncStream struct {
		decodedFrame uint64
		br           readerWrapper
		enabled      bool
		inFrame      bool
	}

	frame *frameDec

	// Custom dictionaries.
	// Always uses copies.
	dicts map[uint32]dict

	// streamWg is the waitgroup for all streams
	streamWg sync.WaitGroup
}

// decoderState is used for maintaining state when the decoder
// is used for streaming.
type decoderState struct {
	// current block being written to stream.
	decodeOutput

	// output in order to be written to stream.
	output chan decodeOutput

	// cancel remaining output.
	cancel context.CancelFunc

	// crc of current frame
	crc *xxhash.Digest

	flushed bool
}

var (
	// Check the interfaces we want to support.
	_ = io.WriterTo(&Decoder{})
	_ = io.Reader(&Decoder{})
)

// NewReader creates a new decoder.
// A nil Reader can be provided in which case Reset can be used to start a decode.
//
// A Decoder can be used in two modes:
//
// 1) As a stream, or
// 2) For stateless decoding using DecodeAll.
//
// Only a single stream can be decoded concurrently, but the same decoder
// can run multiple concurrent stateless decodes. It is even possible to
// use stateless decodes while a stream is being decoded.
//
// The Reset function can be used to initiate a new stream, which is will considerably
// reduce the allocations normally caused by NewReader.
func NewReader(r io.Reader, opts ...DOption) (*Decoder, error) {
	initPredefined()
	var d Decoder
	d.o.setDefault()
	for _, o := range opts {
		err := o(&d.o)
		if err != nil {
			return nil, err
		}
	}
	d.current.crc = xxhash.New()
	d.current.flushed = true

	if r == nil {
		d.current.err = ErrDecoderNilInput
	}

	// Transfer option dicts.
	d.dicts = make(map[uint32]dict, len(d.o.dicts))
	for _, dc := range d.o.dicts {
		d.dicts[dc.id] = dc
	}
	d.o.dicts = nil

	// Create decoders
	d.decoders = make(chan *blockDec, d.o.concurrent)
	for i := 0; i < d.o.concurrent; i++ {
		dec := newBlockDec(d.o.lowMem)
		dec.localFrame = newFrameDec(d.o)
		d.decoders <- dec
	}

	if r == nil {
		return &d, nil
	}
	return &d, d.Reset(r)
}

// Read bytes from the decompressed stream into p.
// Returns the number of bytes written and any error that occurred.
// When the stream is done, io.EOF will be returned.
func (d *Decoder) Read(p []byte) (int, error) {
	var n int
	for {
		if len(d.current.b) > 0 {
			filled := copy(p, d.current.b)
			p = p[filled:]
			d.current.b = d.current.b[filled:]
			n += filled
		}
		if len(p) == 0 {
			break
		}
		if len(d.current.b) == 0 {
			// We have an error and no more data
			if d.current.err != nil {
				break
			}
			if !d.nextBlock(n == 0) {
				return n, d.current.err
			}
		}
	}
	if len(d.current.b) > 0 {
		if debugDecoder {
			println("returning", n, "still bytes left:", len(d.current.b))
		}
		// Only return error at end of block
		return n, nil
	}
	if d.current.err != nil {
		d.drainOutput()
	}
	if debugDecoder {
		println("returning", n, d.current.err, len(d.decoders))
	}
	return n, d.current.err
}

// Reset will reset the decoder the supplied stream after the current has finished processing.
// Note that this functionality cannot be used after Close has been called.
// Reset can be called with a nil reader to release references to the previous reader.
// After being called with a nil reader, no other operations than Reset or DecodeAll or Close
// should be used.
func (d *Decoder) Reset(r io.Reader) error {
	if d.current.err == ErrDecoderClosed {
		return d.current.err
	}

	d.drainOutput()

	d.syncStream.br.r = nil
	if r == nil {
		d.current.err = ErrDecoderNilInput
		if len(d.current.b) > 0 {
			d.current.b = d.current.b[:0]
		}
		d.current.flushed = true
		return nil
	}

	// If bytes buffer and < 5MB, do sync decoding anyway.
	if bb, ok := r.(byter); ok && bb.Len() < 5<<20 {
		bb2 := bb
		if debugDecoder {
			println("*bytes.Buffer detected, doing sync decode, len:", bb.Len())
		}
		b := bb2.Bytes()
		var dst []byte
		if cap(d.current.b) > 0 {
			dst = d.current.b
		}

		dst, err := d.DecodeAll(b, dst[:0])
		if err == nil {
			err = io.EOF
		}
		d.current.b = dst
		d.current.err = err
		d.current.flushed = true
		if debugDecoder {
			println("sync decode to", len(dst), "bytes, err:", err)
		}
		return nil
	}
	// Remove current block.
	d.stashDecoder()
	d.current.decodeOutput = decodeOutput{}
	d.current.err = nil
	d.current.flushed = false
	d.current.d = nil

	// Ensure no-one else is still running...
	d.streamWg.Wait()
	if d.frame == nil {
		d.frame = newFrameDec(d.o)
	}

	if d.o.concurrent == 1 {
		return d.startSyncDecoder(r)
	}

	d.current.output = make(chan decodeOutput, d.o.concurrent)
	ctx, cancel := context.WithCancel(context.Background())
	d.current.cancel = cancel
	d.streamWg.Add(1)
	go d.startStreamDecoder(ctx, r, d.current.output)

	return nil
}

// drainOutput will drain the output until errEndOfStream is sent.
func (d *Decoder) drainOutput() {
	if d.current.cancel != nil {
		if debugDecoder {
			println("cancelling current")
		}
		d.current.cancel()
		d.current.cancel = nil
	}
	if d.current.d != nil {
		if debugDecoder {
			printf("re-adding current decoder %p, decoders: %d", d.current.d, len(d.decoders))
		}
		d.decoders <- d.current.d
		d.current.d = nil
		d.current.b = nil
	}
	if d.current.output == nil || d.current.flushed {
		println("current already flushed")
		return
	}
	for v := range d.current.output {
		if v.d != nil {
			if debugDecoder {
				printf("re-adding decoder %p", v.d)
			}
			d.decoders <- v.d
		}
	}
	d.current.output = nil
	d.current.flushed = true
}

// WriteTo writes data to w until there's no more data to write or when an error occurs.
// The return value n is the number of bytes written.
// Any error encountered during the write is also returned.
func (d *Decoder) WriteTo(w io.Writer) (int64, error) {
	var n int64
	for {
		if len(d.current.b) > 0 {
			n2, err2 := w.Write(d.current.b)
			n += int64(n2)
			if err2 != nil && (d.current.err == nil || d.current.err == io.EOF) {
				d.current.err = err2
			} else if n2 != len(d.current.b) {
				d.current.err = io.ErrShortWrite
			}
		}
		if d.current.err != nil {
			break
		}
		d.nextBlock(true)
	}
	err := d.current.err
	if err != nil {
		d.drainOutput()
	}
	if err == io.EOF {
		err = nil
	}
	return n, err
}

// DecodeAll allows stateless decoding of a blob of bytes.
// Output will be appended to dst, so if the destination size is known
// you can pre-allocate the destination slice to avoid allocations.
// DecodeAll can be used concurrently.
// The Decoder concurrency limits will be respected.
func (d *Decoder) DecodeAll(input, dst []byte) ([]byte, error) {
	if d.decoders == nil {
		return dst, ErrDecoderClosed
	}

	// Grab a block decoder and frame decoder.
	block := <-d.decoders
	frame := block.localFrame
	defer func() {
		if debugDecoder {
			printf("re-adding decoder: %p", block)
		}
		frame.rawInput = nil
		frame.bBuf = nil
		if frame.history.decoders.br != nil {
			frame.history.decoders.br.in = nil
		}
		d.decoders <- block
	}()
	frame.bBuf = input

	for {
		frame.history.reset()
		err := frame.reset(&frame.bBuf)
		if err != nil {
			if err == io.EOF {
				if debugDecoder {
					println("frame reset return EOF")
				}
				return dst, nil
			}
			return dst, err
		}
		if frame.DictionaryID != nil {
			dict, ok := d.dicts[*frame.DictionaryID]
			if !ok {
				return nil, ErrUnknownDictionary
			}
			if debugDecoder {
				println("setting dict", frame.DictionaryID)
			}
			frame.history.setDict(&dict)
		}
		if frame.WindowSize > d.o.maxWindowSize {
			return dst, ErrWindowSizeExceeded
		}
		if frame.FrameContentSize != fcsUnknown {
			if frame.FrameContentSize > d.o.maxDecodedSize-uint64(len(dst)) {
				return dst, ErrDecoderSizeExceeded
			}
			if cap(dst)-len(dst) < int(frame.FrameContentSize) {
				dst2 := make([]byte, len(dst), len(dst)+int(frame.FrameContentSize)+compressedBlockOverAlloc)
				copy(dst2, dst)
				dst = dst2
			}
		}

		if cap(dst) == 0 {
			// Allocate len(input) * 2 by default if nothing is provided
			// and we didn't get frame content size.
			size := len(input) * 2
			// Cap to 1 MB.
			if size > 1<<20 {
				size = 1 << 20
			}
			if uint64(size) > d.o.maxDecodedSize {
				size = int(d.o.maxDecodedSize)
			}
			dst = make([]byte, 0, size)
		}

		dst, err = frame.runDecoder(dst, block)
		if err != nil {
			return dst, err
		}
		if len(frame.bBuf) == 0 {
			if debugDecoder {
				println("frame dbuf empty")
			}
			break
		}
	}
	return dst, nil
}

// nextBlock returns the next block.
// If an error occurs d.err will be set.
// Optionally the function can block for new output.
// If non-blocking mode is used the returned boolean will be false
// if no data was available without blocking.
func (d *Decoder) nextBlock(blocking bool) (ok bool) {
	if d.current.err != nil {
		// Keep error state.
		return false
	}
	d.current.b = d.current.b[:0]

	// SYNC:
	if d.syncStream.enabled {
		if !blocking {
			return false
		}
		ok = d.nextBlockSync()
		if !ok {
			d.stashDecoder()
		}
		return ok
	}

	//ASYNC:
	d.stashDecoder()
	if blocking {
		d.current.decodeOutput, ok = <-d.current.output
	} else {
		select {
		case d.current.decodeOutput, ok = <-d.current.output:
		default:
			return false
		}
	}
	if !ok {
		// This should not happen, so signal error state...
		d.current.err = io.ErrUnexpectedEOF
		return false
	}
	next := d.current.decodeOutput
	if next.d != nil && next.d.async.newHist != nil {
		d.current.crc.Reset()
	}
	if debugDecoder {
		var tmp [4]byte
		binary.LittleEndian.PutUint32(tmp[:], uint32(xxhash.Sum64(next.b)))
		println("got", len(d.current.b), "bytes, error:", d.current.err, "data crc:", tmp)
	}

	if !d.o.ignoreChecksum && len(next.b) > 0 {
		n, err := d.current.crc.Write(next.b)
		if err == nil {
			if n != len(next.b) {
				d.current.err = io.ErrShortWrite
			}
		}
	}
	if next.err == nil && next.d != nil && len(next.d.checkCRC) != 0 {
		got := d.current.crc.Sum64()
		var tmp [4]byte
		binary.LittleEndian.PutUint32(tmp[:], uint32(got))
		if !d.o.ignoreChecksum && !bytes.Equal(tmp[:], next.d.checkCRC) {
			if debugDecoder {
				println("CRC Check Failed:", tmp[:], " (got) !=", next.d.checkCRC, "(on stream)")
			}
			d.current.err = ErrCRCMismatch
		} else {
			if debugDecoder {
				println("CRC ok", tmp[:])
			}
		}
	}

	return true
}

func (d *Decoder) nextBlockSync() (ok bool) {
	if d.current.d == nil {
		d.current.d = <-d.decoders
	}
	for len(d.current.b) == 0 {
		if !d.syncStream.inFrame {
			d.frame.history.reset()
			d.current.err = d.frame.reset(&d.syncStream.br)
			if d.current.err != nil {
				return false
			}
			if d.frame.DictionaryID != nil {
				dict, ok := d.dicts[*d.frame.DictionaryID]
				if !ok {
					d.current.err = ErrUnknownDictionary
					return false
				} else {
					d.frame.history.setDict(&dict)
				}
			}
			if d.frame.WindowSize > d.o.maxDecodedSize || d.frame.WindowSize > d.o.maxWindowSize {
				d.current.err = ErrDecoderSizeExceeded
				return false
			}

			d.syncStream.decodedFrame = 0
			d.syncStream.inFrame = true
		}
		d.current.err = d.frame.next(d.current.d)
		if d.current.err != nil {
			return false
		}
		d.frame.history.ensureBlock()
		if debugDecoder {
			println("History trimmed:", len(d.frame.history.b), "decoded already:", d.syncStream.decodedFrame)
		}
		histBefore := len(d.frame.history.b)
		d.current.err = d.current.d.decodeBuf(&d.frame.history)

		if d.current.err != nil {
			println("error after:", d.current.err)
			return false
		}
		d.current.b = d.frame.history.b[histBefore:]
		if debugDecoder {
			println("history after:", len(d.frame.history.b))
		}

		// Check frame size (before CRC)
		d.syncStream.decodedFrame += uint64(len(d.current.b))
		if d.syncStream.decodedFrame > d.frame.FrameContentSize {
			if debugDecoder {
				printf("DecodedFrame (%d) > FrameContentSize (%d)\n", d.syncStream.decodedFrame, d.frame.FrameContentSize)
			}
			d.current.err = ErrFrameSizeExceeded
			return false
		}

		// Check FCS
		if d.current.d.Last && d.frame.FrameContentSize != fcsUnknown && d.syncStream.decodedFrame != d.frame.FrameContentSize {
			if debugDecoder {
				printf("DecodedFrame (%d) != FrameContentSize (%d)\n", d.syncStream.decodedFrame, d.frame.FrameContentSize)
			}
			d.current.err = ErrFrameSizeMismatch
			return false
		}

		// Update/Check CRC
		if d.frame.HasCheckSum {
			if !d.o.ignoreChecksum {
				d.frame.crc.Write(d.current.b)
			}
			if d.current.d.Last {
				if !d.o.ignoreChecksum {
					d.current.err = d.frame.checkCRC()
				} else {
					d.current.err = d.frame.consumeCRC()
				}
				if d.current.err != nil {
					println("CRC error:", d.current.err)
					return false
				}
			}
		}
		d.syncStream.inFrame = !d.current.d.Last
	}
	return true
}

func (d *Decoder) stashDecoder() {
	if d.current.d != nil {
		if debugDecoder {
			printf("re-adding current decoder %p", d.current.d)
		}
		d.decoders <- d.current.d
		d.current.d = nil
	}
}

// Close will release all resources.
// It is NOT possible to reuse the decoder after this.
func (d *Decoder) Close() {
	if d.current.err == ErrDecoderClosed {
		return
	}
	d.drainOutput()
	if d.current.cancel != nil {
		d.current.cancel()
		d.streamWg.Wait()
		d.current.cancel = nil
	}
	if d.decoders != nil {
		close(d.decoders)
		for dec := range d.decoders {
			dec.Close()
		}
		d.decoders = nil
	}
	if d.current.d != nil {
		d.current.d.Close()
		d.current.d = nil
	}
	d.current.err = ErrDecoderClosed
}

// IOReadCloser returns the decoder as an io.ReadCloser for convenience.
// Any changes to the decoder will be reflected, so the returned ReadCloser
// can be reused along with the decoder.
// io.WriterTo is also supported by the returned ReadCloser.
func (d *Decoder) IOReadCloser() io.ReadCloser {
	return closeWrapper{d: d}
}

// closeWrapper wraps a function call as a closer.
type closeWrapper struct {
	d *Decoder
}

// WriteTo forwards WriteTo calls to the decoder.
func (c closeWrapper) WriteTo(w io.Writer) (n int64, err error) {
	return c.d.WriteTo(w)
}

// Read forwards read calls to the decoder.
func (c closeWrapper) Read(p []byte) (n int, err error) {
	return c.d.Read(p)
}

// Close closes the decoder.
func (c closeWrapper) Close() error {
	c.d.Close()
	return nil
}

type decodeOutput struct {
	d   *blockDec
	b   []byte
	err error
}

func (d *Decoder) startSyncDecoder(r io.Reader) error {
	d.frame.history.reset()
	d.syncStream.br = readerWrapper{r: r}
	d.syncStream.inFrame = false
	d.syncStream.enabled = true
	d.syncStream.decodedFrame = 0
	return nil
}

// Create Decoder:
// ASYNC:
// Spawn 3 go routines.
// 0: Read frames and decode block literals.
// 1: Decode sequences.
// 2: Execute sequences, send to output.
func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output chan decodeOutput) {
	defer d.streamWg.Done()
	br := readerWrapper{r: r}

	var seqDecode = make(chan *blockDec, d.o.concurrent)
	var seqExecute = make(chan *blockDec, d.o.concurrent)

	// Async 1: Decode sequences...
	go func() {
		var hist history
		var hasErr bool

		for block := range seqDecode {
			if hasErr {
				if block != nil {
					seqExecute <- block
				}
				continue
			}
			if block.async.newHist != nil {
				if debugDecoder {
					println("Async 1: new history, recent:", block.async.newHist.recentOffsets)
				}
				hist.decoders = block.async.newHist.decoders
				hist.recentOffsets = block.async.newHist.recentOffsets
				hist.windowSize = block.async.newHist.windowSize
				if block.async.newHist.dict != nil {
					hist.setDict(block.async.newHist.dict)
				}
			}
			if block.err != nil || block.Type != blockTypeCompressed {
				hasErr = block.err != nil
				seqExecute <- block
				continue
			}

			hist.decoders.literals = block.async.literals
			block.err = block.prepareSequences(block.async.seqData, &hist)
			if debugDecoder && block.err != nil {
				println("prepareSequences returned:", block.err)
			}
			hasErr = block.err != nil
			if block.err == nil {
				block.err = block.decodeSequences(&hist)
				if debugDecoder && block.err != nil {
					println("decodeSequences returned:", block.err)
				}
				hasErr = block.err != nil
				//				block.async.sequence = hist.decoders.seq[:hist.decoders.nSeqs]
				block.async.seqSize = hist.decoders.seqSize
			}
			seqExecute <- block
		}
		close(seqExecute)
	}()

	var wg sync.WaitGroup
	wg.Add(1)

	// Async 3: Execute sequences...
	frameHistCache := d.frame.history.b
	go func() {
		var hist history
		var decodedFrame uint64
		var fcs uint64
		var hasErr bool
		for block := range seqExecute {
			out := decodeOutput{err: block.err, d: block}
			if block.err != nil || hasErr {
				hasErr = true
				output <- out
				continue
			}
			if block.async.newHist != nil {
				if debugDecoder {
					println("Async 2: new history")
				}
				hist.windowSize = block.async.newHist.windowSize
				hist.allocFrameBuffer = block.async.newHist.allocFrameBuffer
				if block.async.newHist.dict != nil {
					hist.setDict(block.async.newHist.dict)
				}

				if cap(hist.b) < hist.allocFrameBuffer {
					if cap(frameHistCache) >= hist.allocFrameBuffer {
						hist.b = frameHistCache
					} else {
						hist.b = make([]byte, 0, hist.allocFrameBuffer)
						println("Alloc history sized", hist.allocFrameBuffer)
					}
				}
				hist.b = hist.b[:0]
				fcs = block.async.fcs
				decodedFrame = 0
			}
			do := decodeOutput{err: block.err, d: block}
			switch block.Type {
			case blockTypeRLE:
				if debugDecoder {
					println("add rle block length:", block.RLESize)
				}

				if cap(block.dst) < int(block.RLESize) {
					if block.lowMem {
						block.dst = make([]byte, block.RLESize)
					} else {
						block.dst = make([]byte, maxBlockSize)
					}
				}
				block.dst = block.dst[:block.RLESize]
				v := block.data[0]
				for i := range block.dst {
					block.dst[i] = v
				}
				hist.append(block.dst)
				do.b = block.dst
			case blockTypeRaw:
				if debugDecoder {
					println("add raw block length:", len(block.data))
				}
				hist.append(block.data)
				do.b = block.data
			case blockTypeCompressed:
				if debugDecoder {
					println("execute with history length:", len(hist.b), "window:", hist.windowSize)
				}
				hist.decoders.seqSize = block.async.seqSize
				hist.decoders.literals = block.async.literals
				do.err = block.executeSequences(&hist)
				hasErr = do.err != nil
				if debugDecoder && hasErr {
					println("executeSequences returned:", do.err)
				}
				do.b = block.dst
			}
			if !hasErr {
				decodedFrame += uint64(len(do.b))
				if decodedFrame > fcs {
					println("fcs exceeded", block.Last, fcs, decodedFrame)
					do.err = ErrFrameSizeExceeded
					hasErr = true
				} else if block.Last && fcs != fcsUnknown && decodedFrame != fcs {
					do.err = ErrFrameSizeMismatch
					hasErr = true
				} else {
					if debugDecoder {
						println("fcs ok", block.Last, fcs, decodedFrame)
					}
				}
			}
			output <- do
		}
		close(output)
		frameHistCache = hist.b
		wg.Done()
		if debugDecoder {
			println("decoder goroutines finished")
		}
	}()

decodeStream:
	for {
		var hist history
		var hasErr bool

		decodeBlock := func(block *blockDec) {
			if hasErr {
				if block != nil {
					seqDecode <- block
				}
				return
			}
			if block.err != nil || block.Type != blockTypeCompressed {
				hasErr = block.err != nil
				seqDecode <- block
				return
			}

			remain, err := block.decodeLiterals(block.data, &hist)
			block.err = err
			hasErr = block.err != nil
			if err == nil {
				block.async.literals = hist.decoders.literals
				block.async.seqData = remain
			} else if debugDecoder {
				println("decodeLiterals error:", err)
			}
			seqDecode <- block
		}
		frame := d.frame
		if debugDecoder {
			println("New frame...")
		}
		var historySent bool
		frame.history.reset()
		err := frame.reset(&br)
		if debugDecoder && err != nil {
			println("Frame decoder returned", err)
		}
		if err == nil && frame.DictionaryID != nil {
			dict, ok := d.dicts[*frame.DictionaryID]
			if !ok {
				err = ErrUnknownDictionary
			} else {
				frame.history.setDict(&dict)
			}
		}
		if err == nil && d.frame.WindowSize > d.o.maxWindowSize {
			err = ErrDecoderSizeExceeded
		}
		if err != nil {
			select {
			case <-ctx.Done():
			case dec := <-d.decoders:
				dec.sendErr(err)
				decodeBlock(dec)
			}
			break decodeStream
		}

		// Go through all blocks of the frame.
		for {
			var dec *blockDec
			select {
			case <-ctx.Done():
				break decodeStream
			case dec = <-d.decoders:
				// Once we have a decoder, we MUST return it.
			}
			err := frame.next(dec)
			if !historySent {
				h := frame.history
				if debugDecoder {
					println("Alloc History:", h.allocFrameBuffer)
				}
				hist.reset()
				if h.dict != nil {
					hist.setDict(h.dict)
				}
				dec.async.newHist = &h
				dec.async.fcs = frame.FrameContentSize
				historySent = true
			} else {
				dec.async.newHist = nil
			}
			if debugDecoder && err != nil {
				println("next block returned error:", err)
			}
			dec.err = err
			dec.checkCRC = nil
			if dec.Last && frame.HasCheckSum && err == nil {
				crc, err := frame.rawInput.readSmall(4)
				if err != nil {
					println("CRC missing?", err)
					dec.err = err
				}
				var tmp [4]byte
				copy(tmp[:], crc)
				dec.checkCRC = tmp[:]
				if debugDecoder {
					println("found crc to check:", dec.checkCRC)
				}
			}
			err = dec.err
			last := dec.Last
			decodeBlock(dec)
			if err != nil {
				break decodeStream
			}
			if last {
				break
			}
		}
	}
	close(seqDecode)
	wg.Wait()
	d.frame.history.b = frameHistCache
}