Continue on unknown tiff tag type

When a tag with unknown tag type is encountered, skip tag and parse
other fields.

exif/exif_test.go

@@ -183,7 +183,7 @@ func TestHugeTagError(t *testing.T) {
 	}
 }
 
-// Check for a 0-length tag value
+// Even though the image contains a 0-length tag value, we continue and get some data
 func TestZeroLengthTagError(t *testing.T) {
 	name := filepath.Join(*dataDir, "corrupt/infinite_loop_exif.jpg")
 	f, err := os.Open(name)
@@ -196,7 +196,7 @@ func TestZeroLengthTagError(t *testing.T) {
 	if err == nil {
 		t.Fatal("no error on bad exif data")
 	}
-	if !strings.Contains(err.Error(), "zero length tag value") {
+	if !strings.Contains(err.Error(), "short read") {
 		t.Fatal("wrong error:", err.Error())
 	}
 }

exif/regress_expected_test.go

@@ -2078,6 +2078,42 @@ var regressExpected = map[string]map[FieldName]string{
 		Contrast:                         `0`,
 		FocalLengthIn35mmFilm:            `36`,
 	},
+	"exif-zero-length.jpg": map[FieldName]string{
+		ColorSpace:                       `1`,
+		ComponentsConfiguration:          `""`,
+		CustomRendered:                   `0`,
+		DateTime:                         `"2010:11:07 13:32:41"`,
+		DateTimeDigitized:                `"2010:11:07 13:32:41"`,
+		DateTimeOriginal:                 `"2010:11:07 13:32:41"`,
+		DigitalZoomRatio:                 `"100/100"`,
+		ExifIFDPointer:                   `182`,
+		ExifVersion:                      `"0220"`,
+		ExposureBiasValue:                `"0/65536"`,
+		ExposureMode:                     `0`,
+		ExposureTime:                     `"257/20000"`,
+		FNumber:                          `"28/10"`,
+		Flash:                            `16`,
+		FlashpixVersion:                  `"0100"`,
+		FocalLength:                      `"465/100"`,
+		ISOSpeedRatings:                  `50`,
+		ImageDescription:                 `""`,
+		LightSource:                      `0`,
+		Make:                             `"SEMC"`,
+		MeteringMode:                     `2`,
+		Model:                            `"X10i"`,
+		Orientation:                      `1`,
+		PixelXDimension:                  `3264`,
+		PixelYDimension:                  `2448`,
+		ResolutionUnit:                   `2`,
+		SceneCaptureType:                 `0`,
+		ShutterSpeedValue:                `"411787/65536"`,
+		ThumbJPEGInterchangeFormat:       `670`,
+		ThumbJPEGInterchangeFormatLength: `6101`,
+		WhiteBalance:                     `0`,
+		XResolution:                      `"72/1"`,
+		YCbCrPositioning:                 `2`,
+		YResolution:                      `"72/1"`,
+	},
 	"FailedHash-NoDate-sep-remembory.jpg": map[FieldName]string{
 		Model:           `"MFC-7840W"`,
 		YResolution:     `"150/1"`,

tiff/tag.go

@@ -25,7 +25,10 @@ const (
 	OtherVal
 )
 
-var ErrShortReadTagValue = errors.New("tiff: short read of tag value")
+var (
+	ErrShortReadTagValue = errors.New("tiff: short read of tag value")
+	errUnhandledTagType  = errors.New("tiff: unhandled tag type")
+)
 
 var formatNames = map[Format]string{
 	IntVal:    "int",
@@ -138,11 +141,17 @@ func DecodeTag(r ReadAtReader, order binary.ByteOrder) (*Tag, error) {
 		return t, errors.New("invalid Count offset in tag")
 	}
 
-	valLen := typeSize[t.Type] * t.Count
-	if valLen == 0 {
-		return t, errors.New("zero length tag value")
+	// Ignore the value/offset if we don't know about the size of the type.
+	size, ok := typeSize[t.Type]
+	if !ok {
+		var ignore [4]byte
+		if _, err = io.ReadFull(r, ignore[:]); err != nil {
+			return t, errors.New("tiff: unknown tag offset read failed: " + err.Error())
+		}
+		return nil, errUnhandledTagType
 	}
 
+	valLen := size * t.Count
 	if valLen > 4 {
 		binary.Read(r, order, &t.ValOffset)
 

tiff/tiff.go

@@ -129,7 +129,9 @@ func DecodeDir(r ReadAtReader, order binary.ByteOrder) (d *Dir, offset int32, er
 	// load tags
 	for n := 0; n < int(nTags); n++ {
 		t, err := DecodeTag(r, order)
-		if err != nil {
+		if err == errUnhandledTagType {
+			continue
+		} else if err != nil {
 			return nil, 0, err
 		}
 		d.Tags = append(d.Tags, t)