summaryrefslogtreecommitdiffstats
path: root/src/image/png/reader_test.go
blob: ccf30b2c6edd985939b5bc2f4d0a80e36a02b101 (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
// 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 png

import (
	"bufio"
	"bytes"
	"fmt"
	"image"
	"image/color"
	"io"
	"os"
	"reflect"
	"strings"
	"testing"
)

var filenames = []string{
	"basn0g01",
	"basn0g01-30",
	"basn0g02",
	"basn0g02-29",
	"basn0g04",
	"basn0g04-31",
	"basn0g08",
	"basn0g16",
	"basn2c08",
	"basn2c16",
	"basn3p01",
	"basn3p02",
	"basn3p04",
	"basn3p04-31i",
	"basn3p08",
	"basn3p08-trns",
	"basn4a08",
	"basn4a16",
	"basn6a08",
	"basn6a16",
	"ftbbn0g01",
	"ftbbn0g02",
	"ftbbn0g04",
	"ftbbn2c16",
	"ftbbn3p08",
	"ftbgn2c16",
	"ftbgn3p08",
	"ftbrn2c08",
	"ftbwn0g16",
	"ftbwn3p08",
	"ftbyn3p08",
	"ftp0n0g08",
	"ftp0n2c08",
	"ftp0n3p08",
	"ftp1n3p08",
}

var filenamesPaletted = []string{
	"basn3p01",
	"basn3p02",
	"basn3p04",
	"basn3p08",
	"basn3p08-trns",
}

var filenamesShort = []string{
	"basn0g01",
	"basn0g04-31",
	"basn6a16",
}

func readPNG(filename string) (image.Image, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return Decode(f)
}

// fakebKGDs maps from filenames to fake bKGD chunks for our approximation to
// the sng command-line tool. Package png doesn't keep that metadata when
// png.Decode returns an image.Image.
var fakebKGDs = map[string]string{
	"ftbbn0g01": "bKGD {gray: 0;}\n",
	"ftbbn0g02": "bKGD {gray: 0;}\n",
	"ftbbn0g04": "bKGD {gray: 0;}\n",
	"ftbbn2c16": "bKGD {red: 0;  green: 0;  blue: 65535;}\n",
	"ftbbn3p08": "bKGD {index: 245}\n",
	"ftbgn2c16": "bKGD {red: 0;  green: 65535;  blue: 0;}\n",
	"ftbgn3p08": "bKGD {index: 245}\n",
	"ftbrn2c08": "bKGD {red: 255;  green: 0;  blue: 0;}\n",
	"ftbwn0g16": "bKGD {gray: 65535;}\n",
	"ftbwn3p08": "bKGD {index: 0}\n",
	"ftbyn3p08": "bKGD {index: 245}\n",
}

// fakegAMAs maps from filenames to fake gAMA chunks for our approximation to
// the sng command-line tool. Package png doesn't keep that metadata when
// png.Decode returns an image.Image.
var fakegAMAs = map[string]string{
	"ftbbn0g01": "",
	"ftbbn0g02": "gAMA {0.45455}\n",
}

// fakeIHDRUsings maps from filenames to fake IHDR "using" lines for our
// approximation to the sng command-line tool. The PNG model is that
// transparency (in the tRNS chunk) is separate to the color/grayscale/palette
// color model (in the IHDR chunk). The Go model is that the concrete
// image.Image type returned by png.Decode, such as image.RGBA (with all pixels
// having 100% alpha) or image.NRGBA, encapsulates whether or not the image has
// transparency. This map is a hack to work around the fact that the Go model
// can't otherwise discriminate PNG's "IHDR says color (with no alpha) but tRNS
// says alpha" and "IHDR says color with alpha".
var fakeIHDRUsings = map[string]string{
	"ftbbn0g01": "    using grayscale;\n",
	"ftbbn0g02": "    using grayscale;\n",
	"ftbbn0g04": "    using grayscale;\n",
	"ftbbn2c16": "    using color;\n",
	"ftbgn2c16": "    using color;\n",
	"ftbrn2c08": "    using color;\n",
	"ftbwn0g16": "    using grayscale;\n",
}

// An approximation of the sng command-line tool.
func sng(w io.WriteCloser, filename string, png image.Image) {
	defer w.Close()
	bounds := png.Bounds()
	cm := png.ColorModel()
	var bitdepth int
	switch cm {
	case color.RGBAModel, color.NRGBAModel, color.AlphaModel, color.GrayModel:
		bitdepth = 8
	default:
		bitdepth = 16
	}
	cpm, _ := cm.(color.Palette)
	var paletted *image.Paletted
	if cpm != nil {
		switch {
		case len(cpm) <= 2:
			bitdepth = 1
		case len(cpm) <= 4:
			bitdepth = 2
		case len(cpm) <= 16:
			bitdepth = 4
		default:
			bitdepth = 8
		}
		paletted = png.(*image.Paletted)
	}

	// Write the filename and IHDR.
	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", bounds.Dx(), bounds.Dy(), bitdepth)
	if s, ok := fakeIHDRUsings[filename]; ok {
		io.WriteString(w, s)
	} else {
		switch {
		case cm == color.RGBAModel, cm == color.RGBA64Model:
			io.WriteString(w, "    using color;\n")
		case cm == color.NRGBAModel, cm == color.NRGBA64Model:
			io.WriteString(w, "    using color alpha;\n")
		case cm == color.GrayModel, cm == color.Gray16Model:
			io.WriteString(w, "    using grayscale;\n")
		case cpm != nil:
			io.WriteString(w, "    using color palette;\n")
		default:
			io.WriteString(w, "unknown PNG decoder color model\n")
		}
	}
	io.WriteString(w, "}\n")

	// We fake a gAMA chunk. The test files have a gAMA chunk but the go PNG
	// parser ignores it (the PNG spec section 11.3 says "Ancillary chunks may
	// be ignored by a decoder").
	if s, ok := fakegAMAs[filename]; ok {
		io.WriteString(w, s)
	} else {
		io.WriteString(w, "gAMA {1.0000}\n")
	}

	// Write the PLTE and tRNS (if applicable).
	useTransparent := false
	if cpm != nil {
		lastAlpha := -1
		io.WriteString(w, "PLTE {\n")
		for i, c := range cpm {
			var r, g, b, a uint8
			switch c := c.(type) {
			case color.RGBA:
				r, g, b, a = c.R, c.G, c.B, 0xff
			case color.NRGBA:
				r, g, b, a = c.R, c.G, c.B, c.A
			default:
				panic("unknown palette color type")
			}
			if a != 0xff {
				lastAlpha = i
			}
			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
		}
		io.WriteString(w, "}\n")
		if s, ok := fakebKGDs[filename]; ok {
			io.WriteString(w, s)
		}
		if lastAlpha != -1 {
			io.WriteString(w, "tRNS {\n")
			for i := 0; i <= lastAlpha; i++ {
				_, _, _, a := cpm[i].RGBA()
				a >>= 8
				fmt.Fprintf(w, " %d", a)
			}
			io.WriteString(w, "}\n")
		}
	} else if strings.HasPrefix(filename, "ft") {
		if s, ok := fakebKGDs[filename]; ok {
			io.WriteString(w, s)
		}
		// We fake a tRNS chunk. The test files' grayscale and truecolor
		// transparent images all have their top left corner transparent.
		switch c := png.At(0, 0).(type) {
		case color.NRGBA:
			if c.A == 0 {
				useTransparent = true
				io.WriteString(w, "tRNS {\n")
				switch filename {
				case "ftbbn0g01", "ftbbn0g02", "ftbbn0g04":
					// The standard image package doesn't have a "gray with
					// alpha" type. Instead, we use an image.NRGBA.
					fmt.Fprintf(w, "    gray: %d;\n", c.R)
				default:
					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
				}
				io.WriteString(w, "}\n")
			}
		case color.NRGBA64:
			if c.A == 0 {
				useTransparent = true
				io.WriteString(w, "tRNS {\n")
				switch filename {
				case "ftbwn0g16":
					// The standard image package doesn't have a "gray16 with
					// alpha" type. Instead, we use an image.NRGBA64.
					fmt.Fprintf(w, "    gray: %d;\n", c.R)
				default:
					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
				}
				io.WriteString(w, "}\n")
			}
		}
	}

	// Write the IMAGE.
	io.WriteString(w, "IMAGE {\n    pixels hex\n")
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		switch {
		case cm == color.GrayModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray := png.At(x, y).(color.Gray)
				fmt.Fprintf(w, "%02x", gray.Y)
			}
		case cm == color.Gray16Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray16 := png.At(x, y).(color.Gray16)
				fmt.Fprintf(w, "%04x ", gray16.Y)
			}
		case cm == color.RGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba := png.At(x, y).(color.RGBA)
				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
			}
		case cm == color.RGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba64 := png.At(x, y).(color.RGBA64)
				fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
			}
		case cm == color.NRGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba := png.At(x, y).(color.NRGBA)
				switch filename {
				case "ftbbn0g01", "ftbbn0g02", "ftbbn0g04":
					fmt.Fprintf(w, "%02x", nrgba.R)
				default:
					if useTransparent {
						fmt.Fprintf(w, "%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B)
					} else {
						fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
					}
				}
			}
		case cm == color.NRGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba64 := png.At(x, y).(color.NRGBA64)
				switch filename {
				case "ftbwn0g16":
					fmt.Fprintf(w, "%04x ", nrgba64.R)
				default:
					if useTransparent {
						fmt.Fprintf(w, "%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B)
					} else {
						fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
					}
				}
			}
		case cpm != nil:
			var b, c int
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				b = b<<uint(bitdepth) | int(paletted.ColorIndexAt(x, y))
				c++
				if c == 8/bitdepth {
					fmt.Fprintf(w, "%02x", b)
					b = 0
					c = 0
				}
			}
			if c != 0 {
				for c != 8/bitdepth {
					b = b << uint(bitdepth)
					c++
				}
				fmt.Fprintf(w, "%02x", b)
			}
		}
		io.WriteString(w, "\n")
	}
	io.WriteString(w, "}\n")
}

func TestReader(t *testing.T) {
	names := filenames
	if testing.Short() {
		names = filenamesShort
	}
	for _, fn := range names {
		// Read the .png file.
		img, err := readPNG("testdata/pngsuite/" + fn + ".png")
		if err != nil {
			t.Error(fn, err)
			continue
		}

		if fn == "basn4a16" {
			// basn4a16.sng is gray + alpha but sng() will produce true color + alpha
			// so we just check a single random pixel.
			c := img.At(2, 1).(color.NRGBA64)
			if c.R != 0x11a7 || c.G != 0x11a7 || c.B != 0x11a7 || c.A != 0x1085 {
				t.Error(fn, fmt.Errorf("wrong pixel value at (2, 1): %x", c))
			}
			continue
		}

		piper, pipew := io.Pipe()
		pb := bufio.NewScanner(piper)
		go sng(pipew, fn, img)
		defer piper.Close()

		// Read the .sng file.
		sf, err := os.Open("testdata/pngsuite/" + fn + ".sng")
		if err != nil {
			t.Error(fn, err)
			continue
		}
		defer sf.Close()
		sb := bufio.NewScanner(sf)

		// Compare the two, in SNG format, line by line.
		for {
			pdone := !pb.Scan()
			sdone := !sb.Scan()
			if pdone && sdone {
				break
			}
			if pdone || sdone {
				t.Errorf("%s: Different sizes", fn)
				break
			}
			ps := pb.Text()
			ss := sb.Text()

			// Newer versions of the sng command line tool append an optional
			// color name to the RGB tuple. For example:
			//	# rgb = (0xff,0xff,0xff) grey100
			//	# rgb = (0x00,0x00,0xff) blue1
			// instead of the older version's plainer:
			//	# rgb = (0xff,0xff,0xff)
			//	# rgb = (0x00,0x00,0xff)
			// We strip any such name.
			if strings.Contains(ss, "# rgb = (") && !strings.HasSuffix(ss, ")") {
				if i := strings.LastIndex(ss, ") "); i >= 0 {
					ss = ss[:i+1]
				}
			}

			if ps != ss {
				t.Errorf("%s: Mismatch\n%s\nversus\n%s\n", fn, ps, ss)
				break
			}
		}
		if pb.Err() != nil {
			t.Error(fn, pb.Err())
		}
		if sb.Err() != nil {
			t.Error(fn, sb.Err())
		}
	}
}

var readerErrors = []struct {
	file string
	err  string
}{
	{"invalid-zlib.png", "zlib: invalid checksum"},
	{"invalid-crc32.png", "invalid checksum"},
	{"invalid-noend.png", "unexpected EOF"},
	{"invalid-trunc.png", "unexpected EOF"},
}

func TestReaderError(t *testing.T) {
	for _, tt := range readerErrors {
		img, err := readPNG("testdata/" + tt.file)
		if err == nil {
			t.Errorf("decoding %s: missing error", tt.file)
			continue
		}
		if !strings.Contains(err.Error(), tt.err) {
			t.Errorf("decoding %s: %s, want %s", tt.file, err, tt.err)
		}
		if img != nil {
			t.Errorf("decoding %s: have image + error", tt.file)
		}
	}
}

func TestPalettedDecodeConfig(t *testing.T) {
	for _, fn := range filenamesPaletted {
		f, err := os.Open("testdata/pngsuite/" + fn + ".png")
		if err != nil {
			t.Errorf("%s: open failed: %v", fn, err)
			continue
		}
		defer f.Close()
		cfg, err := DecodeConfig(f)
		if err != nil {
			t.Errorf("%s: %v", fn, err)
			continue
		}
		pal, ok := cfg.ColorModel.(color.Palette)
		if !ok {
			t.Errorf("%s: expected paletted color model", fn)
			continue
		}
		if pal == nil {
			t.Errorf("%s: palette not initialized", fn)
			continue
		}
	}
}

func TestInterlaced(t *testing.T) {
	a, err := readPNG("testdata/gray-gradient.png")
	if err != nil {
		t.Fatal(err)
	}
	b, err := readPNG("testdata/gray-gradient.interlaced.png")
	if err != nil {
		t.Fatal(err)
	}
	if !reflect.DeepEqual(a, b) {
		t.Fatalf("decodings differ:\nnon-interlaced:\n%#v\ninterlaced:\n%#v", a, b)
	}
}

func TestIncompleteIDATOnRowBoundary(t *testing.T) {
	// The following is an invalid 1x2 grayscale PNG image. The header is OK,
	// but the zlib-compressed IDAT payload contains two bytes "\x02\x00",
	// which is only one row of data (the leading "\x02" is a row filter).
	const (
		ihdr = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x02\x08\x00\x00\x00\x00\xbc\xea\xe9\xfb"
		idat = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"
		iend = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
	)
	_, err := Decode(strings.NewReader(pngHeader + ihdr + idat + iend))
	if err == nil {
		t.Fatal("got nil error, want non-nil")
	}
}

func TestTrailingIDATChunks(t *testing.T) {
	// The following is a valid 1x1 PNG image containing color.Gray{255} and
	// a trailing zero-length IDAT chunk (see PNG specification section 12.9):
	const (
		ihdr      = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08\x00\x00\x00\x00\x3a\x7e\x9b\x55"
		idatWhite = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\xfa\x0f\x08\x00\x00\xff\xff\x01\x05\x01\x02\x5a\xdd\x39\xcd"
		idatZero  = "\x00\x00\x00\x00IDAT\x35\xaf\x06\x1e"
		iend      = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
	)
	_, err := Decode(strings.NewReader(pngHeader + ihdr + idatWhite + idatZero + iend))
	if err != nil {
		t.Fatalf("decoding valid image: %v", err)
	}

	// Non-zero-length trailing IDAT chunks should be ignored (recoverable error).
	// The following chunk contains a single pixel with color.Gray{0}.
	const idatBlack = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"

	img, err := Decode(strings.NewReader(pngHeader + ihdr + idatWhite + idatBlack + iend))
	if err != nil {
		t.Fatalf("trailing IDAT not ignored: %v", err)
	}
	if img.At(0, 0) == (color.Gray{0}) {
		t.Fatal("decoded image from trailing IDAT chunk")
	}
}

func TestMultipletRNSChunks(t *testing.T) {
	/*
		The following is a valid 1x1 paletted PNG image with a 1-element palette
		containing color.NRGBA{0xff, 0x00, 0x00, 0x7f}:
			0000000: 8950 4e47 0d0a 1a0a 0000 000d 4948 4452  .PNG........IHDR
			0000010: 0000 0001 0000 0001 0803 0000 0028 cb34  .............(.4
			0000020: bb00 0000 0350 4c54 45ff 0000 19e2 0937  .....PLTE......7
			0000030: 0000 0001 7452 4e53 7f80 5cb4 cb00 0000  ....tRNS..\.....
			0000040: 0e49 4441 5478 9c62 6200 0400 00ff ff00  .IDATx.bb.......
			0000050: 0600 03fa d059 ae00 0000 0049 454e 44ae  .....Y.....IEND.
			0000060: 4260 82                                  B`.
		Dropping the tRNS chunk makes that color's alpha 0xff instead of 0x7f.
	*/
	const (
		ihdr = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08\x03\x00\x00\x00\x28\xcb\x34\xbb"
		plte = "\x00\x00\x00\x03PLTE\xff\x00\x00\x19\xe2\x09\x37"
		trns = "\x00\x00\x00\x01tRNS\x7f\x80\x5c\xb4\xcb"
		idat = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"
		iend = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
	)
	for i := 0; i < 4; i++ {
		var b []byte
		b = append(b, pngHeader...)
		b = append(b, ihdr...)
		b = append(b, plte...)
		for j := 0; j < i; j++ {
			b = append(b, trns...)
		}
		b = append(b, idat...)
		b = append(b, iend...)

		var want color.Color
		m, err := Decode(bytes.NewReader(b))
		switch i {
		case 0:
			if err != nil {
				t.Errorf("%d tRNS chunks: %v", i, err)
				continue
			}
			want = color.RGBA{0xff, 0x00, 0x00, 0xff}
		case 1:
			if err != nil {
				t.Errorf("%d tRNS chunks: %v", i, err)
				continue
			}
			want = color.NRGBA{0xff, 0x00, 0x00, 0x7f}
		default:
			if err == nil {
				t.Errorf("%d tRNS chunks: got nil error, want non-nil", i)
			}
			continue
		}
		if got := m.At(0, 0); got != want {
			t.Errorf("%d tRNS chunks: got %T %v, want %T %v", i, got, got, want, want)
		}
	}
}

func TestUnknownChunkLengthUnderflow(t *testing.T) {
	data := []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0xff, 0xff,
		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x06, 0xf4, 0x7c, 0x55, 0x04, 0x1a,
		0xd3, 0x11, 0x9a, 0x73, 0x00, 0x00, 0xf8, 0x1e, 0xf3, 0x2e, 0x00, 0x00,
		0x01, 0x00, 0xff, 0xff, 0xff, 0xff, 0x07, 0xf4, 0x7c, 0x55, 0x04, 0x1a,
		0xd3}
	_, err := Decode(bytes.NewReader(data))
	if err == nil {
		t.Errorf("Didn't fail reading an unknown chunk with length 0xffffffff")
	}
}

func TestPaletted8OutOfRangePixel(t *testing.T) {
	// IDAT contains a reference to a palette index that does not exist in the file.
	img, err := readPNG("testdata/invalid-palette.png")
	if err != nil {
		t.Errorf("decoding invalid-palette.png: unexpected error %v", err)
		return
	}

	// Expect that the palette is extended with opaque black.
	want := color.RGBA{0x00, 0x00, 0x00, 0xff}
	if got := img.At(15, 15); got != want {
		t.Errorf("got %F %v, expected %T %v", got, got, want, want)
	}
}

func TestGray8Transparent(t *testing.T) {
	// These bytes come from https://golang.org/issues/19553
	m, err := Decode(bytes.NewReader([]byte{
		0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
		0x00, 0x00, 0x00, 0x0f, 0x00, 0x00, 0x00, 0x0b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x85, 0x2c, 0x88,
		0x80, 0x00, 0x00, 0x00, 0x02, 0x74, 0x52, 0x4e, 0x53, 0x00, 0xff, 0x5b, 0x91, 0x22, 0xb5, 0x00,
		0x00, 0x00, 0x02, 0x62, 0x4b, 0x47, 0x44, 0x00, 0xff, 0x87, 0x8f, 0xcc, 0xbf, 0x00, 0x00, 0x00,
		0x09, 0x70, 0x48, 0x59, 0x73, 0x00, 0x00, 0x0a, 0xf0, 0x00, 0x00, 0x0a, 0xf0, 0x01, 0x42, 0xac,
		0x34, 0x98, 0x00, 0x00, 0x00, 0x07, 0x74, 0x49, 0x4d, 0x45, 0x07, 0xd5, 0x04, 0x02, 0x12, 0x11,
		0x11, 0xf7, 0x65, 0x3d, 0x8b, 0x00, 0x00, 0x00, 0x4f, 0x49, 0x44, 0x41, 0x54, 0x08, 0xd7, 0x63,
		0xf8, 0xff, 0xff, 0xff, 0xb9, 0xbd, 0x70, 0xf0, 0x8c, 0x01, 0xc8, 0xaf, 0x6e, 0x99, 0x02, 0x05,
		0xd9, 0x7b, 0xc1, 0xfc, 0x6b, 0xff, 0xa1, 0xa0, 0x87, 0x30, 0xff, 0xd9, 0xde, 0xbd, 0xd5, 0x4b,
		0xf7, 0xee, 0xfd, 0x0e, 0xe3, 0xef, 0xcd, 0x06, 0x19, 0x14, 0xf5, 0x1e, 0xce, 0xef, 0x01, 0x31,
		0x92, 0xd7, 0x82, 0x41, 0x31, 0x9c, 0x3f, 0x07, 0x02, 0xee, 0xa1, 0xaa, 0xff, 0xff, 0x9f, 0xe1,
		0xd9, 0x56, 0x30, 0xf8, 0x0e, 0xe5, 0x03, 0x00, 0xa9, 0x42, 0x84, 0x3d, 0xdf, 0x8f, 0xa6, 0x8f,
		0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
	}))
	if err != nil {
		t.Fatalf("Decode: %v", err)
	}

	const hex = "0123456789abcdef"
	var got []byte
	bounds := m.Bounds()
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			if r, _, _, a := m.At(x, y).RGBA(); a != 0 {
				got = append(got,
					hex[0x0f&(r>>12)],
					hex[0x0f&(r>>8)],
					' ',
				)
			} else {
				got = append(got,
					'.',
					'.',
					' ',
				)
			}
		}
		got = append(got, '\n')
	}

	const want = "" +
		".. .. .. ce bd bd bd bd bd bd bd bd bd bd e6 \n" +
		".. .. .. 7b 84 94 94 94 94 94 94 94 94 6b bd \n" +
		".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
		".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
		".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
		"e6 bd bd 7b a5 bd bd f7 .. .. .. .. .. 8c bd \n" +
		"bd 6b 94 94 94 94 5a ef .. .. .. .. .. 8c bd \n" +
		"bd 8c .. .. .. .. 63 ad ad ad ad ad ad 73 bd \n" +
		"bd 8c .. .. .. .. 63 9c 9c 9c 9c 9c 9c 9c de \n" +
		"bd 6b 94 94 94 94 5a ef .. .. .. .. .. .. .. \n" +
		"e6 b5 b5 b5 b5 b5 b5 f7 .. .. .. .. .. .. .. \n"

	if string(got) != want {
		t.Errorf("got:\n%swant:\n%s", got, want)
	}
}

func TestDimensionOverflow(t *testing.T) {
	maxInt32AsInt := int((1 << 31) - 1)
	have32BitInts := 0 > (1 + maxInt32AsInt)

	testCases := []struct {
		src               []byte
		unsupportedConfig bool
		width             int
		height            int
	}{
		// These bytes come from https://golang.org/issues/22304
		//
		// It encodes a 2147483646 × 2147483646 (i.e. 0x7ffffffe × 0x7ffffffe)
		// NRGBA image. The (width × height) per se doesn't overflow an int64, but
		// (width × height × bytesPerPixel) will.
		{
			src: []byte{
				0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
				0x7f, 0xff, 0xff, 0xfe, 0x7f, 0xff, 0xff, 0xfe, 0x08, 0x06, 0x00, 0x00, 0x00, 0x30, 0x57, 0xb3,
				0xfd, 0x00, 0x00, 0x00, 0x15, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x62, 0x62, 0x20, 0x12, 0x8c,
				0x2a, 0xa4, 0xb3, 0x42, 0x40, 0x00, 0x00, 0x00, 0xff, 0xff, 0x13, 0x38, 0x00, 0x15, 0x2d, 0xef,
				0x5f, 0x0f, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
			},
			// It's debatable whether DecodeConfig (which does not allocate a
			// pixel buffer, unlike Decode) should fail in this case. The Go
			// standard library has made its choice, and the standard library
			// has compatibility constraints.
			unsupportedConfig: true,
			width:             0x7ffffffe,
			height:            0x7ffffffe,
		},

		// The next three cases come from https://golang.org/issues/38435

		{
			src: []byte{
				0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
				0x00, 0x00, 0xb5, 0x04, 0x00, 0x00, 0xb5, 0x04, 0x08, 0x06, 0x00, 0x00, 0x00, 0xf5, 0x60, 0x2c,
				0xb8, 0x00, 0x00, 0x00, 0x15, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x62, 0x62, 0x20, 0x12, 0x8c,
				0x2a, 0xa4, 0xb3, 0x42, 0x40, 0x00, 0x00, 0x00, 0xff, 0xff, 0x13, 0x38, 0x00, 0x15, 0x2d, 0xef,
				0x5f, 0x0f, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
			},
			// Here, width * height = 0x7ffea810, just under MaxInt32, but at 4
			// bytes per pixel, the number of pixels overflows an int32.
			unsupportedConfig: have32BitInts,
			width:             0x0000b504,
			height:            0x0000b504,
		},

		{
			src: []byte{
				0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
				0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x08, 0x06, 0x00, 0x00, 0x00, 0x30, 0x6e, 0xc5,
				0x21, 0x00, 0x00, 0x00, 0x15, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x62, 0x62, 0x20, 0x12, 0x8c,
				0x2a, 0xa4, 0xb3, 0x42, 0x40, 0x00, 0x00, 0x00, 0xff, 0xff, 0x13, 0x38, 0x00, 0x15, 0x2d, 0xef,
				0x5f, 0x0f, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
			},
			unsupportedConfig: false,
			width:             0x04000000,
			height:            0x00000001,
		},

		{
			src: []byte{
				0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
				0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x08, 0x06, 0x00, 0x00, 0x00, 0xaa, 0xd4, 0x7c,
				0xda, 0x00, 0x00, 0x00, 0x15, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x62, 0x66, 0x20, 0x12, 0x30,
				0x8d, 0x2a, 0xa4, 0xaf, 0x42, 0x40, 0x00, 0x00, 0x00, 0xff, 0xff, 0x14, 0xd2, 0x00, 0x16, 0x00,
				0x00, 0x00,
			},
			unsupportedConfig: false,
			width:             0x08000000,
			height:            0x00000001,
		},
	}

	for i, tc := range testCases {
		cfg, err := DecodeConfig(bytes.NewReader(tc.src))
		if tc.unsupportedConfig {
			if err == nil {
				t.Errorf("i=%d: DecodeConfig: got nil error, want non-nil", i)
			} else if _, ok := err.(UnsupportedError); !ok {
				t.Fatalf("Decode: got %v (of type %T), want non-nil error (of type png.UnsupportedError)", err, err)
			}
			continue
		} else if err != nil {
			t.Errorf("i=%d: DecodeConfig: %v", i, err)
			continue
		} else if cfg.Width != tc.width {
			t.Errorf("i=%d: width: got %d, want %d", i, cfg.Width, tc.width)
			continue
		} else if cfg.Height != tc.height {
			t.Errorf("i=%d: height: got %d, want %d", i, cfg.Height, tc.height)
			continue
		}

		if nPixels := int64(cfg.Width) * int64(cfg.Height); nPixels > 0x7f000000 {
			// In theory, calling Decode would succeed, given several gigabytes
			// of memory. In practice, trying to make a []uint8 big enough to
			// hold all of the pixels can often result in OOM (out of memory).
			// OOM is unrecoverable; we can't write a test that passes when OOM
			// happens. Instead we skip the Decode call (and its tests).
			continue
		} else if testing.Short() {
			// Even for smaller image dimensions, calling Decode might allocate
			// 1 GiB or more of memory. This is usually feasible, and we want
			// to check that calling Decode doesn't panic if there's enough
			// memory, but we provide a runtime switch (testing.Short) to skip
			// these if it would OOM. See also http://golang.org/issue/5050
			// "decoding... images can cause huge memory allocations".
			continue
		}

		// Even if we don't panic, these aren't valid PNG images.
		if _, err := Decode(bytes.NewReader(tc.src)); err == nil {
			t.Errorf("i=%d: Decode: got nil error, want non-nil", i)
		}
	}

	if testing.Short() {
		t.Skip("skipping tests which allocate large pixel buffers")
	}
}

func TestDecodePalettedWithTransparency(t *testing.T) {
	// These bytes come from https://go.dev/issue/54325
	//
	// Per the PNG spec, a PLTE chunk contains 3 (not 4) bytes per palette
	// entry: RGB (not RGBA). The alpha value comes from the optional tRNS
	// chunk. Here, the PLTE chunk (0x50, 0x4c, 0x54, 0x45, etc) has 16 entries
	// (0x30 = 48 bytes) and the tRNS chunk (0x74, 0x52, 0x4e, 0x53, etc) has 1
	// entry (0x01 = 1 byte) that sets the first palette entry's alpha to zero.
	//
	// Both Decode and DecodeConfig should pick up that the first palette
	// entry's alpha is zero.
	src := []byte{
		0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
		0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x20, 0x04, 0x03, 0x00, 0x00, 0x00, 0x81, 0x54, 0x67,
		0xc7, 0x00, 0x00, 0x00, 0x30, 0x50, 0x4c, 0x54, 0x45, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x0e,
		0x00, 0x23, 0x27, 0x7b, 0xb1, 0x2d, 0x0a, 0x49, 0x3f, 0x19, 0x78, 0x5f, 0xcd, 0xe4, 0x69, 0x69,
		0xe4, 0x71, 0x59, 0x53, 0x80, 0x11, 0x14, 0x8b, 0x00, 0xa9, 0x8d, 0x95, 0xcb, 0x99, 0x2f, 0x6b,
		0xd7, 0x29, 0x91, 0xd7, 0x7b, 0xba, 0xff, 0xe3, 0xd7, 0x13, 0xc6, 0xd3, 0x58, 0x00, 0x00, 0x00,
		0x01, 0x74, 0x52, 0x4e, 0x53, 0x00, 0x40, 0xe6, 0xd8, 0x66, 0x00, 0x00, 0x00, 0xfd, 0x49, 0x44,
		0x41, 0x54, 0x28, 0xcf, 0x63, 0x60, 0x00, 0x83, 0x55, 0x0c, 0x68, 0x60, 0x9d, 0x02, 0x9a, 0x80,
		0xde, 0x23, 0x74, 0x15, 0xef, 0x50, 0x94, 0x70, 0x2d, 0xd2, 0x7b, 0x87, 0xa2, 0x84, 0xeb, 0xee,
		0xbb, 0x77, 0x6f, 0x51, 0x94, 0xe8, 0xbd, 0x7d, 0xf7, 0xee, 0x12, 0xb2, 0x80, 0xd2, 0x3d, 0x54,
		0x01, 0x26, 0x10, 0x1f, 0x59, 0x40, 0x0f, 0xc8, 0xd7, 0x7e, 0x84, 0x70, 0x1c, 0xd7, 0xba, 0xb7,
		0x4a, 0xda, 0xda, 0x77, 0x11, 0xf6, 0xac, 0x5a, 0xa5, 0xf4, 0xf9, 0xbf, 0xfd, 0x3d, 0x24, 0x6b,
		0x98, 0x94, 0xf4, 0xff, 0x7f, 0x52, 0x42, 0x16, 0x30, 0x0e, 0xd9, 0xed, 0x6a, 0x8c, 0xec, 0x10,
		0x65, 0x53, 0x97, 0x60, 0x23, 0x64, 0x1d, 0x8a, 0x2e, 0xc6, 0x2e, 0x42, 0x08, 0x3d, 0x4c, 0xca,
		0x81, 0xc1, 0x82, 0xa6, 0xa2, 0x46, 0x08, 0x3d, 0x4a, 0xa1, 0x82, 0xc6, 0x82, 0xa1, 0x4a, 0x08,
		0x3d, 0xfa, 0xa6, 0x81, 0xa1, 0xa2, 0xc1, 0x9f, 0x10, 0x66, 0xd4, 0x2b, 0x87, 0x0a, 0x86, 0x1a,
		0x7d, 0x57, 0x80, 0x9b, 0x99, 0xaf, 0x62, 0x1a, 0x1a, 0xec, 0xf0, 0x0d, 0x66, 0x2a, 0x7b, 0x5a,
		0xba, 0xd2, 0x64, 0x63, 0x4b, 0xa6, 0xb2, 0xb4, 0x02, 0xa8, 0x12, 0xb5, 0x24, 0xa5, 0x99, 0x2e,
		0x33, 0x95, 0xd4, 0x92, 0x10, 0xee, 0xd0, 0x59, 0xb9, 0x6a, 0xd6, 0x21, 0x24, 0xb7, 0x33, 0x9d,
		0x01, 0x01, 0x64, 0xbf, 0xac, 0x59, 0xb2, 0xca, 0xeb, 0x14, 0x92, 0x80, 0xd6, 0x9a, 0x53, 0x4a,
		0x6b, 0x4e, 0x2d, 0x42, 0x52, 0xa1, 0x73, 0x28, 0x54, 0xe7, 0x90, 0x6a, 0x00, 0x92, 0x92, 0x45,
		0xa1, 0x40, 0x84, 0x2c, 0xe0, 0xc4, 0xa0, 0xb2, 0x28, 0x14, 0xc1, 0x67, 0xe9, 0x50, 0x60, 0x60,
		0xea, 0x70, 0x40, 0x12, 0x00, 0x79, 0x54, 0x09, 0x22, 0x00, 0x00, 0x30, 0xf3, 0x52, 0x87, 0xc6,
		0xe4, 0xbd, 0x70, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
	}

	cfg, err := DecodeConfig(bytes.NewReader(src))
	if err != nil {
		t.Fatalf("DecodeConfig: %v", err)
	} else if _, _, _, alpha := cfg.ColorModel.(color.Palette)[0].RGBA(); alpha != 0 {
		t.Errorf("DecodeConfig: got %d, want 0", alpha)
	}

	img, err := Decode(bytes.NewReader(src))
	if err != nil {
		t.Fatalf("Decode: %v", err)
	} else if _, _, _, alpha := img.ColorModel().(color.Palette)[0].RGBA(); alpha != 0 {
		t.Errorf("Decode: got %d, want 0", alpha)
	}
}

func benchmarkDecode(b *testing.B, filename string, bytesPerPixel int) {
	data, err := os.ReadFile(filename)
	if err != nil {
		b.Fatal(err)
	}
	cfg, err := DecodeConfig(bytes.NewReader(data))
	if err != nil {
		b.Fatal(err)
	}
	b.SetBytes(int64(cfg.Width * cfg.Height * bytesPerPixel))
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		Decode(bytes.NewReader(data))
	}
}

func BenchmarkDecodeGray(b *testing.B) {
	benchmarkDecode(b, "testdata/benchGray.png", 1)
}

func BenchmarkDecodeNRGBAGradient(b *testing.B) {
	benchmarkDecode(b, "testdata/benchNRGBA-gradient.png", 4)
}

func BenchmarkDecodeNRGBAOpaque(b *testing.B) {
	benchmarkDecode(b, "testdata/benchNRGBA-opaque.png", 4)
}

func BenchmarkDecodePaletted(b *testing.B) {
	benchmarkDecode(b, "testdata/benchPaletted.png", 1)
}

func BenchmarkDecodeRGB(b *testing.B) {
	benchmarkDecode(b, "testdata/benchRGB.png", 4)
}

func BenchmarkDecodeInterlacing(b *testing.B) {
	benchmarkDecode(b, "testdata/benchRGB-interlace.png", 4)
}