Improve EXIF UserComment handling

ALso regenerate and clean up the `gen/testdata` folder.

gen/main.go

@@ -18,7 +18,7 @@ func main() {
 	}
 	base := "../testdata"
 
-	if err := filepath.Walk(base, func(path string, info os.FileInfo, err error) error {
+	if err := filepath.Walk(filepath.Join(base, "images"), func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
 		}

gen/testdata_exiftool/images/huge_tag_exif.jpg.json → gen/testdata_exiftool/images/corrupt/huge_tag_exif.jpg.json

@@ -1,12 +1,12 @@
 [{
-  "SourceFile": "../testdata/images/huge_tag_exif.jpg",
+  "SourceFile": "../testdata/images/corrupt/huge_tag_exif.jpg",
   "ExifTool": {
     "ExifToolVersion": 12.76,
     "Warning": "JPEG format error"
   },
   "File": {
     "FileName": "huge_tag_exif.jpg",
-    "Directory": "../testdata/images",
+    "Directory": "../testdata/images/corrupt",
     "FileSize": 65536,
     "FilePermissions": 100644,
     "FileType": "JPEG",

gen/testdata_exiftool/images/infinite_loop_exif.jpg.json → gen/testdata_exiftool/images/corrupt/infinite_loop_exif.jpg.json

@@ -1,12 +1,12 @@
 [{
-  "SourceFile": "../testdata/images/infinite_loop_exif.jpg",
+  "SourceFile": "../testdata/images/corrupt/infinite_loop_exif.jpg",
   "ExifTool": {
     "ExifToolVersion": 12.76,
     "Warning": "Suspicious IFD0 offset for XResolution"
   },
   "File": {
     "FileName": "infinite_loop_exif.jpg",
-    "Directory": "../testdata/images",
+    "Directory": "../testdata/images/corrupt",
     "FileSize": 3738,
     "FilePermissions": 100644,
     "FileType": "JPEG",

gen/testdata_exiftool/images/max_uint32_exif.jpg.json → gen/testdata_exiftool/images/corrupt/max_uint32_exif.jpg.json

@@ -1,12 +1,12 @@
 [{
-  "SourceFile": "../testdata/images/max_uint32_exif.jpg",
+  "SourceFile": "../testdata/images/corrupt/max_uint32_exif.jpg",
   "ExifTool": {
     "ExifToolVersion": 12.76,
     "Warning": "JPEG format error"
   },
   "File": {
     "FileName": "max_uint32_exif.jpg",
-    "Directory": "../testdata/images",
+    "Directory": "../testdata/images/corrupt",
     "FileSize": 65536,
     "FilePermissions": 100644,
     "FileType": "JPEG",

gen/testdata_exiftool/images/hugo-issue-12669.jpg.json

@@ -0,0 +1,87 @@
+[{
+  "SourceFile": "../testdata/images/hugo-issue-12669.jpg",
+  "ExifTool": {
+    "ExifToolVersion": 12.76
+  },
+  "File": {
+    "FileName": "hugo-issue-12669.jpg",
+    "Directory": "../testdata/images",
+    "FileSize": 5772106,
+    "FilePermissions": 100644,
+    "FileType": "JPEG",
+    "FileTypeExtension": "JPG",
+    "MIMEType": "image/jpeg",
+    "ExifByteOrder": "II",
+    "ImageWidth": 4032,
+    "ImageHeight": 2268,
+    "EncodingProcess": 0,
+    "BitsPerSample": 8,
+    "ColorComponents": 3,
+    "YCbCrSubSampling": "2 2"
+  },
+  "EXIF": {
+    "ImageWidth": 4032,
+    "ImageHeight": 2268,
+    "Make": "samsung",
+    "Model": "SM-G950U",
+    "Orientation": 1,
+    "XResolution": 72,
+    "YResolution": 72,
+    "ResolutionUnit": 2,
+    "Software": "G950USQS8DTJ1",
+    "ModifyDate": "2021:01:17 11:34:47",
+    "YCbCrPositioning": 1,
+    "ExposureTime": 0.0003172588832,
+    "FNumber": 1.7,
+    "ExposureProgram": 2,
+    "ISO": 50,
+    "ExifVersion": "0220",
+    "DateTimeOriginal": "2021:01:17 11:34:47",
+    "CreateDate": "2021:01:17 11:34:47",
+    "ComponentsConfiguration": "1 2 3 0",
+    "ShutterSpeedValue": "0.000317270278919785",
+    "ApertureValue": 1.6993699982773,
+    "BrightnessValue": 8.98,
+    "ExposureCompensation": 0,
+    "MaxApertureValue": 1.6993699982773,
+    "MeteringMode": 2,
+    "LightSource": 0,
+    "Flash": 0,
+    "FocalLength": 4.25,
+    "UserComment": "\n",
+    "FlashpixVersion": "0100",
+    "ColorSpace": 1,
+    "ExifImageWidth": 4032,
+    "ExifImageHeight": 2268,
+    "InteropIndex": "R98",
+    "InteropVersion": "0100",
+    "SensingMethod": 2,
+    "SceneType": 1,
+    "ExposureMode": 0,
+    "WhiteBalance": 0,
+    "FocalLengthIn35mmFormat": 26,
+    "SceneCaptureType": 0,
+    "ImageUniqueID": "F12QSJA00SM F12QSKB01SB",
+    "GPSVersionID": "2 2 0 0",
+    "GPSLatitudeRef": "N",
+    "GPSLatitude": 0,
+    "GPSLongitudeRef": "E",
+    "GPSLongitude": 0,
+    "GPSAltitudeRef": 0,
+    "GPSAltitude": 0,
+    "GPSTimeStamp": "18:34:47",
+    "GPSDateStamp": "2021:01:17",
+    "Compression": 6,
+    "ThumbnailOffset": 6312,
+    "ThumbnailLength": 16863
+  },
+  "MakerNotes": {
+    "MakerNoteVersion": "0100",
+    "DeviceType": 73728,
+    "RawDataByteOrder": 0,
+    "RawDataCFAPattern": 1,
+    "FaceDetect": 0,
+    "TimeStamp": "2021:01:17 19:34:47.374+01:00",
+    "MCCData": 310
+  }
+}]

helpers.go

@@ -276,6 +276,31 @@ func (vc) convertStringToInt(ctx valueConverterContext, v any) any {
 	return i
 }
 
+func (c vc) convertUserComment(ctx valueConverterContext, v any) any {
+	// UserComment tag is identified based on an ID code in a fixed 8-byte area at the start of the tag data area.
+	b, ok := typeAssert[[]byte](ctx, v)
+	if !ok {
+		return ""
+	}
+	if len(b) < 8 {
+		return ""
+	}
+	id := string(b[:8])
+
+	switch id {
+	case "ASCII\x00\x00\x00":
+		s := printableString(string(trimBytesNulls(b[8:])))
+		if !isASCII(s) {
+			return ""
+		}
+		return s
+	case "UNICODE\x00":
+		return printableString(string(trimBytesNulls(b[8:])))
+	default:
+		return ""
+	}
+}
+
 func (vc) ratNum(v any) any {
 	switch vv := v.(type) {
 	case Rat[uint32]:
@@ -357,6 +382,15 @@ func (c vc) toDegrees(v any) (float64, error) {
 	}
 }
 
+func isASCII(s string) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] > unicode.MaxASCII {
+			return false
+		}
+	}
+	return true
+}
+
 func printableString(s string) string {
 	ss := strings.Map(func(r rune) rune {
 		if unicode.IsGraphic(r) {