Source file src/image/jpeg/reader_test.go

Documentation: image/jpeg

		 1  // Copyright 2012 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package jpeg
		 6  
		 7  import (
		 8  	"bytes"
		 9  	"encoding/base64"
		10  	"fmt"
		11  	"image"
		12  	"image/color"
		13  	"io"
		14  	"math/rand"
		15  	"os"
		16  	"strings"
		17  	"testing"
		18  	"time"
		19  )
		20  
		21  // TestDecodeProgressive tests that decoding the baseline and progressive
		22  // versions of the same image result in exactly the same pixel data, in YCbCr
		23  // space for color images, and Y space for grayscale images.
		24  func TestDecodeProgressive(t *testing.T) {
		25  	testCases := []string{
		26  		"../testdata/video-001",
		27  		"../testdata/video-001.q50.410",
		28  		"../testdata/video-001.q50.411",
		29  		"../testdata/video-001.q50.420",
		30  		"../testdata/video-001.q50.422",
		31  		"../testdata/video-001.q50.440",
		32  		"../testdata/video-001.q50.444",
		33  		"../testdata/video-005.gray.q50",
		34  		"../testdata/video-005.gray.q50.2x2",
		35  		"../testdata/video-001.separate.dc.progression",
		36  	}
		37  	for _, tc := range testCases {
		38  		m0, err := decodeFile(tc + ".jpeg")
		39  		if err != nil {
		40  			t.Errorf("%s: %v", tc+".jpeg", err)
		41  			continue
		42  		}
		43  		m1, err := decodeFile(tc + ".progressive.jpeg")
		44  		if err != nil {
		45  			t.Errorf("%s: %v", tc+".progressive.jpeg", err)
		46  			continue
		47  		}
		48  		if m0.Bounds() != m1.Bounds() {
		49  			t.Errorf("%s: bounds differ: %v and %v", tc, m0.Bounds(), m1.Bounds())
		50  			continue
		51  		}
		52  		// All of the video-*.jpeg files are 150x103.
		53  		if m0.Bounds() != image.Rect(0, 0, 150, 103) {
		54  			t.Errorf("%s: bad bounds: %v", tc, m0.Bounds())
		55  			continue
		56  		}
		57  
		58  		switch m0 := m0.(type) {
		59  		case *image.YCbCr:
		60  			m1 := m1.(*image.YCbCr)
		61  			if err := check(m0.Bounds(), m0.Y, m1.Y, m0.YStride, m1.YStride); err != nil {
		62  				t.Errorf("%s (Y): %v", tc, err)
		63  				continue
		64  			}
		65  			if err := check(m0.Bounds(), m0.Cb, m1.Cb, m0.CStride, m1.CStride); err != nil {
		66  				t.Errorf("%s (Cb): %v", tc, err)
		67  				continue
		68  			}
		69  			if err := check(m0.Bounds(), m0.Cr, m1.Cr, m0.CStride, m1.CStride); err != nil {
		70  				t.Errorf("%s (Cr): %v", tc, err)
		71  				continue
		72  			}
		73  		case *image.Gray:
		74  			m1 := m1.(*image.Gray)
		75  			if err := check(m0.Bounds(), m0.Pix, m1.Pix, m0.Stride, m1.Stride); err != nil {
		76  				t.Errorf("%s: %v", tc, err)
		77  				continue
		78  			}
		79  		default:
		80  			t.Errorf("%s: unexpected image type %T", tc, m0)
		81  			continue
		82  		}
		83  	}
		84  }
		85  
		86  func decodeFile(filename string) (image.Image, error) {
		87  	f, err := os.Open(filename)
		88  	if err != nil {
		89  		return nil, err
		90  	}
		91  	defer f.Close()
		92  	return Decode(f)
		93  }
		94  
		95  type eofReader struct {
		96  	data		 []byte // deliver from Read without EOF
		97  	dataEOF	[]byte // then deliver from Read with EOF on last chunk
		98  	lenAtEOF int
		99  }
	 100  
	 101  func (r *eofReader) Read(b []byte) (n int, err error) {
	 102  	if len(r.data) > 0 {
	 103  		n = copy(b, r.data)
	 104  		r.data = r.data[n:]
	 105  	} else {
	 106  		n = copy(b, r.dataEOF)
	 107  		r.dataEOF = r.dataEOF[n:]
	 108  		if len(r.dataEOF) == 0 {
	 109  			err = io.EOF
	 110  			if r.lenAtEOF == -1 {
	 111  				r.lenAtEOF = n
	 112  			}
	 113  		}
	 114  	}
	 115  	return
	 116  }
	 117  
	 118  func TestDecodeEOF(t *testing.T) {
	 119  	// Check that if reader returns final data and EOF at same time, jpeg handles it.
	 120  	data, err := os.ReadFile("../testdata/video-001.jpeg")
	 121  	if err != nil {
	 122  		t.Fatal(err)
	 123  	}
	 124  
	 125  	n := len(data)
	 126  	for i := 0; i < n; {
	 127  		r := &eofReader{data[:n-i], data[n-i:], -1}
	 128  		_, err := Decode(r)
	 129  		if err != nil {
	 130  			t.Errorf("Decode with Read() = %d, EOF: %v", r.lenAtEOF, err)
	 131  		}
	 132  		if i == 0 {
	 133  			i = 1
	 134  		} else {
	 135  			i *= 2
	 136  		}
	 137  	}
	 138  }
	 139  
	 140  // check checks that the two pix data are equal, within the given bounds.
	 141  func check(bounds image.Rectangle, pix0, pix1 []byte, stride0, stride1 int) error {
	 142  	if stride0 <= 0 || stride0%8 != 0 {
	 143  		return fmt.Errorf("bad stride %d", stride0)
	 144  	}
	 145  	if stride1 <= 0 || stride1%8 != 0 {
	 146  		return fmt.Errorf("bad stride %d", stride1)
	 147  	}
	 148  	// Compare the two pix data, one 8x8 block at a time.
	 149  	for y := 0; y < len(pix0)/stride0 && y < len(pix1)/stride1; y += 8 {
	 150  		for x := 0; x < stride0 && x < stride1; x += 8 {
	 151  			if x >= bounds.Max.X || y >= bounds.Max.Y {
	 152  				// We don't care if the two pix data differ if the 8x8 block is
	 153  				// entirely outside of the image's bounds. For example, this can
	 154  				// occur with a 4:2:0 chroma subsampling and a 1x1 image. Baseline
	 155  				// decoding works on the one 16x16 MCU as a whole; progressive
	 156  				// decoding's first pass works on that 16x16 MCU as a whole but
	 157  				// refinement passes only process one 8x8 block within the MCU.
	 158  				continue
	 159  			}
	 160  
	 161  			for j := 0; j < 8; j++ {
	 162  				for i := 0; i < 8; i++ {
	 163  					index0 := (y+j)*stride0 + (x + i)
	 164  					index1 := (y+j)*stride1 + (x + i)
	 165  					if pix0[index0] != pix1[index1] {
	 166  						return fmt.Errorf("blocks at (%d, %d) differ:\n%sand\n%s", x, y,
	 167  							pixString(pix0, stride0, x, y),
	 168  							pixString(pix1, stride1, x, y),
	 169  						)
	 170  					}
	 171  				}
	 172  			}
	 173  		}
	 174  	}
	 175  	return nil
	 176  }
	 177  
	 178  func pixString(pix []byte, stride, x, y int) string {
	 179  	s := bytes.NewBuffer(nil)
	 180  	for j := 0; j < 8; j++ {
	 181  		fmt.Fprintf(s, "\t")
	 182  		for i := 0; i < 8; i++ {
	 183  			fmt.Fprintf(s, "%02x ", pix[(y+j)*stride+(x+i)])
	 184  		}
	 185  		fmt.Fprintf(s, "\n")
	 186  	}
	 187  	return s.String()
	 188  }
	 189  
	 190  func TestTruncatedSOSDataDoesntPanic(t *testing.T) {
	 191  	b, err := os.ReadFile("../testdata/video-005.gray.q50.jpeg")
	 192  	if err != nil {
	 193  		t.Fatal(err)
	 194  	}
	 195  	sosMarker := []byte{0xff, 0xda}
	 196  	i := bytes.Index(b, sosMarker)
	 197  	if i < 0 {
	 198  		t.Fatal("SOS marker not found")
	 199  	}
	 200  	i += len(sosMarker)
	 201  	j := i + 10
	 202  	if j > len(b) {
	 203  		j = len(b)
	 204  	}
	 205  	for ; i < j; i++ {
	 206  		Decode(bytes.NewReader(b[:i]))
	 207  	}
	 208  }
	 209  
	 210  func TestLargeImageWithShortData(t *testing.T) {
	 211  	// This input is an invalid JPEG image, based on the fuzzer-generated image
	 212  	// in issue 10413. It is only 504 bytes, and shouldn't take long for Decode
	 213  	// to return an error. The Start Of Frame marker gives the image dimensions
	 214  	// as 8192 wide and 8192 high, so even if an unreadByteStuffedByte bug
	 215  	// doesn't technically lead to an infinite loop, such a bug can still cause
	 216  	// an unreasonably long loop for such a short input.
	 217  	const input = "" +
	 218  		"\xff\xd8\xff\xe0\x00\x10\x4a\x46\x49\x46\x00\x01\x01\x00\x00\x01" +
	 219  		"\x00\x01\x00\x00\xff\xdb\x00\x43\x00\x10\x0b\x0c\x0e\x0c\x0a\x10" +
	 220  		"\x0e\x89\x0e\x12\x11\x10\x13\x18\xff\xd8\xff\xe0\x00\x10\x4a\x46" +
	 221  		"\x49\x46\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xdb\x00\x43" +
	 222  		"\x00\x10\x0b\x0c\x0e\x0c\x0a\x10\x0e\x0d\x0e\x12\x11\x10\x13\x18" +
	 223  		"\x28\x1a\x18\x16\x16\x18\x31\x23\x25\x1d\x28\x3a\x33\x3d\x3c\x39" +
	 224  		"\x33\x38\x37\x40\x48\x5c\x4e\x40\x44\x57\x45\x37\x38\x50\x6d\x51" +
	 225  		"\x57\x5f\x62\x67\x68\x67\x3e\x4d\x71\x79\x70\x64\x78\x5c\x65\x67" +
	 226  		"\x63\xff\xc0\x00\x0b\x08\x20\x00\x20\x00\x01\x01\x11\x00\xff\xc4" +
	 227  		"\x00\x1f\x00\x00\x01\x05\x01\x01\x01\x01\x01\x01\x00\x00\x00\x00" +
	 228  		"\x00\x00\x00\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\xff" +
	 229  		"\xc4\x00\xb5\x10\x00\x02\x01\x03\x03\x02\x04\x03\x05\x05\x04\x04" +
	 230  		"\x00\x00\x01\x7d\x01\x02\x03\x00\x04\x11\x05\x12\x21\x31\x01\x06" +
	 231  		"\x13\x51\x61\x07\x22\x71\x14\x32\x81\x91\xa1\x08\x23\xd8\xff\xdd" +
	 232  		"\x42\xb1\xc1\x15\x52\xd1\xf0\x24\x33\x62\x72\x82\x09\x0a\x16\x17" +
	 233  		"\x18\x19\x1a\x25\x26\x27\x28\x29\x2a\x34\x35\x36\x37\x38\x39\x3a" +
	 234  		"\x43\x44\x45\x46\x47\x48\x49\x4a\x53\x54\x55\x56\x57\x58\x59\x5a" +
	 235  		"\x00\x63\x64\x65\x66\x67\x68\x69\x6a\x73\x74\x75\x76\x77\x78\x79" +
	 236  		"\x7a\x83\x84\x85\x86\x87\x88\x89\x8a\x92\x93\x94\x95\x96\x97\x98" +
	 237  		"\x99\x9a\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xb2\xb3\xb4\xb5\xb6" +
	 238  		"\xb7\xb8\xb9\xba\xc2\xc3\xc4\xc5\xc6\xc7\xff\xd8\xff\xe0\x00\x10" +
	 239  		"\x4a\x46\x49\x46\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xdb" +
	 240  		"\x00\x43\x00\x10\x0b\x0c\x0e\x0c\x0a\x10\x0e\x0d\x0e\x12\x11\x10" +
	 241  		"\x13\x18\x28\x1a\x18\x16\x16\x18\x31\x23\x25\x1d\xc8\xc9\xca\xd2" +
	 242  		"\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8" +
	 243  		"\xe9\xea\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xff\xda\x00\x08" +
	 244  		"\x01\x01\x00\x00\x3f\x00\xb9\xeb\x50\xb0\xdb\xc8\xa8\xe4\x63\x80" +
	 245  		"\xdd\x31\xd6\x9d\xbb\xf2\xc5\x42\x1f\x6c\x6f\xf4\x34\xdd\x3c\xfc" +
	 246  		"\xac\xe7\x3d\x80\xa9\xcc\x87\x34\xb3\x37\xfa\x2b\x9f\x6a\xad\x63" +
	 247  		"\x20\x36\x9f\x78\x64\x75\xe6\xab\x7d\xb2\xde\x29\x70\xd3\x20\x27" +
	 248  		"\xde\xaf\xa4\xf0\xca\x9f\x24\xa8\xdf\x46\xa8\x24\x84\x96\xe3\x77" +
	 249  		"\xf9\x2e\xe0\x0a\x62\x7f\xdf\xd9"
	 250  	c := make(chan error, 1)
	 251  	go func() {
	 252  		_, err := Decode(strings.NewReader(input))
	 253  		c <- err
	 254  	}()
	 255  	select {
	 256  	case err := <-c:
	 257  		if err == nil {
	 258  			t.Fatalf("got nil error, want non-nil")
	 259  		}
	 260  	case <-time.After(3 * time.Second):
	 261  		t.Fatalf("timed out")
	 262  	}
	 263  }
	 264  
	 265  func TestPaddedRSTMarker(t *testing.T) {
	 266  	// This test image comes from golang.org/issue/28717
	 267  	const base64EncodedImage = `
	 268  /9j/4AAhQVZJMQABAQEAeAB4AAAAAAAAAAAAAAAAAAAAAAAAAP/bAEMABAIDAwMCBAMDAwQEBAQGCgYG
	 269  BQUGDAgJBwoODA8PDgwODxASFxMQERURDQ4UGhQVFxgZGhkPExweHBkeFxkZGP/bAEMBBAQEBgUGCwYG
	 270  CxgQDhAYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGBgYGP/EAaIA
	 271  AAEFAQEBAQEBAAAAAAAAAAABAgMEBQYHCAkKCxAAAgEDAwIEAwUFBAQAAAF9AQIDAAQRBRIhMUEGE1Fh
	 272  ByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVWV1hZWmNk
	 273  ZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT
	 274  1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6AQADAQEBAQEBAQEBAAAAAAAAAQIDBAUGBwgJCgsRAAIB
	 275  AgQEAwQHBQQEAAECdwABAgMRBAUhMQYSQVEHYXETIjKBCBRCkaGxwQkjM1LwFWJy0QoWJDThJfEXGBka
	 276  JicoKSo1Njc4OTpDREVGR0hJSlNUVVZXWFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZ
	 277  mqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/dAAQA
	 278  Cv/gAAQAAP/AABEIALABQAMBIQACEQEDEQH/2gAMAwEAAhEDEQA/APnCFTk5BPPGKliAB718W7H2j3Ip
	 279  VUuwJxzTfKXacde9VBhYRUBAyO3pTmUAbSMU5WGmybywzHGAMdelPVFC+n1qXZCuyaJADxjj2qzbBMAP
	 280  xz1rKaVib6ltLcFvlIx2pLy0dwuAMMBnH1rFON9RNsszAZPFEYHldPzrOy3KewmBk9qUABugxjtTVmiW
	 281  xWRcjp+VJtHXgVL3K6AgBDdM9eRTNzAZViOe1VyxaJavuf/Q8aW4mUcSGpo764AyHz+FfnnJBvVH1UsN
	 282  CS1Q/wDte4Trip49ecA7g3FSqMW9zlqZandxJ4/EKADcSPqKni8QQMT865qOSUNjiqZdNbFiHWYXz84N
	 283  WE1KNsfMKj2zirHHPDSj0JFvo2H36d9pUjg1sqykYOm0KbgY60omXPXmr9pFkco3zBnrQzjGcnrRzp9S
	 284  bEbuOvao3fisZSXUpIYWGKGcbetTCSswsxnmACkYrtNSpJ2YNM//0fnK1BD7sDg9KmUHeOe/Svid3qfb
	 285  SdmQ3AHmnr1pGBC5z19a0hohNiJkensM1J0yCKmY0yZR82e+BT1BxnpmpepN9SRCR0NSpweOoPWs6isr
	 286  ijuWIZGBA/lVwzMVFY8ibuhXEfr+tOz8hIqUymhRnJGTSc5wBVRRDFPXBHJpB3qdmV0EX7vXmoyfl685
	 287  p2dxWR//0vFsHZ9TQv3T618Bqz7PSwwn1phPXpSWrQEUhIx0NVXc7j0rSNwViCS4dWYpJj3BpBqVzGy7
	 288  ZmHSq9kpblSpxkveQ+PX7uMf6wEDtU0fi24TAkX8jTeCjJaaHDUwFN7aFq28aL/GCMGrtr4xtHGGkA+t
	 289  YTy+a+E82eAa2LsXiWzI5mXPHercOsW8hwJB+dcUqVSCOKVFxdmiwl7E2MOPzp4nQ9GH51jzNbmUoOIC
	 290  TI4okOaUXoybDCevNBPHX8qIO4mf/9P52i4dix5zjp/n1qZFBCmviL6an2kt9CGcYnJznJpOBwegq4vQ
	 291  L9xIUytSkfu/bv70p7j6EnQgjHSpFGVqXclkkaHb1+makUHgdazm7IFuSKOasrnjis2+oDm9qnIHlgd/
	 292  es7gxqjkt1NLwH4xTTEhjkhutM3D15oGhkcnBGRTDKu3A7H1rS3cLn//1PEhJ8uM557UvmDaa/P7a3Ps
	 293  xpZcZ6mo5WG45pdUC2K8ko5JIzWfcTqu7HPHrW9OLbKWhSluVLNz3wKrS3I3KfcV1Rg9CrpXK8l0F7io
	 294  pLnLnJHGOldMYJGMpu5XNwuxjyRTBcAAjd1HWtfZmPORy3WAWWQDOM4PWtHRru6DFlmY88ZqKsVyXaKp
	 295  QjOoa7axe28G/cWqhoHjO/n1WeJwSkS9c981wUcFCopPayFj8JC8VFbs6e38VldvmHHFaMHimAoCzDB6
	 296  V5U8FKz5TlrZU4/CXYtdtnXIarEepW7jAcfnXGqEoKx5tfBzh0P/1fnqEAsc/wB6pI9owAD1618Qn3Ps
	 297  35EE4UzHrx79aXaMcdaqAMWIADvj271IMeXg59KUmNLQkUDfjb1FSLxzg0pWJRLGAQAeMVIoA+uaxlaw
	 298  0SoF/u1KowwwDUcwuo9wMjrUrY2ZPOKy0KY1T1NMdwG/CtBEFzMqnIPNUZ75FBJP5mtIQvYfoU21JFVs
	 299  N271AurRE/e611xw73Yj/9b50GsQhOXHWnpq8JX7w4PWvjPq76H2fzHjVYCud9Q3GrRAZDUvq75kNbMz
	 300  7vV0zjdjNZ82pqzMcj7tdlPDtIiVWKKct+AxwRxUbXi7VPJAIrZUdEZOsrsga8DFgelQtd98g5P6V0Qp
	 301  GE6qIUut2cZ470kd2FjYc4Oce1bSpJ3Rzxq21GNcDZhSeg710ujKRbKzAg5rkxceWnqd+XtOo7bD9cl8
	 302  qxLDPHasXwUvmyXU7Lgl8cegrnw2lGbZ14l3rU0bl3gMQCRgVU1y7WytUZQzMRwBXPRhzWRvVny3ZW8N
	 303  6xPdXBikiZc5IOa6GG6nDsd5xnAyfaliqEacrGOHarx5pI//1/nuL754HWngEkYx1r4VWsfaMjk4mP8A
	 304  OgnjPH1rRMLKwR4A2jH1FPA+TNRIa0ROvQcY4p4GF/pUskmi6+gqRACvPrWMnpca3JABjFSKCQOnFS2u
	 305  o7E3XBOKcR8ucdKzUkDGSHGemKpXchVuP0rSmDMfUrl1J5rn9TvnVCc9OtelhoJtDekW0Yb6pId3zdRw
	 306  RVT+0pAPvc57CvbhQVrHlTxD3P8A/9D4tbUpTH1I7cU/7ZdMnyqcdsV5vsErXPbWJbHLdXzYQDBY8c02
	 307  6udQjyGVuD1FHsqfMridepZ6ED3s4IDqeD0I68VEt7J5hy3GO9aKkuhPt2BumeRjnv3pJLlgwBYE8ZqH
	 308  T2GqujYLcuWYbhj0zTHm5B/vcGtVBLYzdRtEcUueoGB3FOjmBjcBhx2NNx1IhO+uwtqd93EgA5YcV32n
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	 422  Sqm7JH//2Q==
	 423  `
	 424  
	 425  	data, err := base64.StdEncoding.DecodeString(base64EncodedImage)
	 426  	if err != nil {
	 427  		t.Fatalf("base64 DecodeString: %v", err)
	 428  	}
	 429  	if _, err = Decode(bytes.NewReader(data)); err != nil {
	 430  		t.Fatalf("Decode: %v", err)
	 431  	}
	 432  }
	 433  
	 434  func TestExtraneousData(t *testing.T) {
	 435  	// Encode a 1x1 red image.
	 436  	src := image.NewRGBA(image.Rect(0, 0, 1, 1))
	 437  	src.Set(0, 0, color.RGBA{0xff, 0x00, 0x00, 0xff})
	 438  	buf := new(bytes.Buffer)
	 439  	if err := Encode(buf, src, nil); err != nil {
	 440  		t.Fatalf("encode: %v", err)
	 441  	}
	 442  	enc := buf.String()
	 443  	// Sanity check that the encoded JPEG is long enough, that it ends in a
	 444  	// "\xff\xd9" EOI marker, and that it contains a "\xff\xda" SOS marker
	 445  	// somewhere in the final 64 bytes.
	 446  	if len(enc) < 64 {
	 447  		t.Fatalf("encoded JPEG is too short: %d bytes", len(enc))
	 448  	}
	 449  	if got, want := enc[len(enc)-2:], "\xff\xd9"; got != want {
	 450  		t.Fatalf("encoded JPEG ends with %q, want %q", got, want)
	 451  	}
	 452  	if s := enc[len(enc)-64:]; !strings.Contains(s, "\xff\xda") {
	 453  		t.Fatalf("encoded JPEG does not contain a SOS marker (ff da) near the end: % x", s)
	 454  	}
	 455  	// Test that adding some random junk between the SOS marker and the
	 456  	// EOI marker does not affect the decoding.
	 457  	rnd := rand.New(rand.NewSource(1))
	 458  	for i, nerr := 0, 0; i < 1000 && nerr < 10; i++ {
	 459  		buf.Reset()
	 460  		// Write all but the trailing "\xff\xd9" EOI marker.
	 461  		buf.WriteString(enc[:len(enc)-2])
	 462  		// Write some random extraneous data.
	 463  		for n := rnd.Intn(10); n > 0; n-- {
	 464  			if x := byte(rnd.Intn(256)); x != 0xff {
	 465  				buf.WriteByte(x)
	 466  			} else {
	 467  				// The JPEG format escapes a SOS 0xff data byte as "\xff\x00".
	 468  				buf.WriteString("\xff\x00")
	 469  			}
	 470  		}
	 471  		// Write the "\xff\xd9" EOI marker.
	 472  		buf.WriteString("\xff\xd9")
	 473  
	 474  		// Check that we can still decode the resultant image.
	 475  		got, err := Decode(buf)
	 476  		if err != nil {
	 477  			t.Errorf("could not decode image #%d: %v", i, err)
	 478  			nerr++
	 479  			continue
	 480  		}
	 481  		if got.Bounds() != src.Bounds() {
	 482  			t.Errorf("image #%d, bounds differ: %v and %v", i, got.Bounds(), src.Bounds())
	 483  			nerr++
	 484  			continue
	 485  		}
	 486  		if averageDelta(got, src) > 2<<8 {
	 487  			t.Errorf("image #%d changed too much after a round trip", i)
	 488  			nerr++
	 489  			continue
	 490  		}
	 491  	}
	 492  }
	 493  
	 494  func benchmarkDecode(b *testing.B, filename string) {
	 495  	data, err := os.ReadFile(filename)
	 496  	if err != nil {
	 497  		b.Fatal(err)
	 498  	}
	 499  	cfg, err := DecodeConfig(bytes.NewReader(data))
	 500  	if err != nil {
	 501  		b.Fatal(err)
	 502  	}
	 503  	b.SetBytes(int64(cfg.Width * cfg.Height * 4))
	 504  	b.ReportAllocs()
	 505  	b.ResetTimer()
	 506  	for i := 0; i < b.N; i++ {
	 507  		Decode(bytes.NewReader(data))
	 508  	}
	 509  }
	 510  
	 511  func BenchmarkDecodeBaseline(b *testing.B) {
	 512  	benchmarkDecode(b, "../testdata/video-001.jpeg")
	 513  }
	 514  
	 515  func BenchmarkDecodeProgressive(b *testing.B) {
	 516  	benchmarkDecode(b, "../testdata/video-001.progressive.jpeg")
	 517  }
	 518  

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