index,camtool: try and cope better with broken exif

http://camlistore.org/issue/493

Change-Id: I40aebd67252cf82a3a5a143af6c258d7ed2aecda

cmd/camtool/exif.go

@@ -32,9 +32,18 @@ func showEXIF(file string) {
 	defer f.Close()
 	ex, err := exif.Decode(f)
 	if err != nil {
-		log.Fatalf("exif.Decode: %v", err)
+		if exif.IsCriticalError(err) {
+			log.Fatalf("exif.Decode, critical error: %v", err)
+		}
+		log.Printf("exif.Decode, warning: %v", err)
+	}
+	fmt.Printf("%v\n", ex)
+	if exif.IsExifError(err) {
+		// the error happened while decoding the EXIF sub-IFD, so as DateTime is
+		// part of it, we have to assume (until there's a better "decode effort"
+		// strategy in goexif) that it's not usable.
+		return
 	}
-	fmt.Printf("exif.Decode = %#v\n", ex)
 	ct, err := ex.DateTime()
 	fmt.Printf("exif.DateTime = %v, %v\n", ct, err)
 }

pkg/index/receive.go

@@ -410,6 +410,7 @@ func (ix *Index) populateFile(fetcher blob.Fetcher, b *schema.Blob, mm *mutation
 			log.Printf("filename %q exif = %v, %v", b.FileName(), ft, err)
 		}
 
+		// TODO(mpl): find (generate?) more broken EXIF images to experiment with.
 		err = indexEXIF(wholeRef, bytes.NewReader(imageBuf.Bytes), mm)
 		if err == io.EOF {
 			var fr *schema.FileReader
@@ -472,9 +473,14 @@ func (f exifWalkFunc) Walk(name exif.FieldName, tag *tiff.Tag) error { return f(
 var errEXIFPanic = errors.New("EXIF library panicked while walking fields")
 
 func indexEXIF(wholeRef blob.Ref, reader io.Reader, mm *mutationMap) (err error) {
+	var tiffErr error
 	ex, err := exif.Decode(reader)
 	if err != nil {
-		return
+		tiffErr = err
+		if exif.IsCriticalError(err) {
+			return
+		}
+		log.Printf("Non critical TIFF decoding error: %v", err)
 	}
 	defer func() {
 		// The EXIF library panics if you access a field past
@@ -549,6 +555,10 @@ func indexEXIF(wholeRef blob.Ref, reader io.Reader, mm *mutationMap) (err error)
 		return
 	}
 
+	if exif.IsGPSError(tiffErr) {
+		log.Printf("Invalid EXIF GPS data: %v", tiffErr)
+		return nil
+	}
 	if lat, long, err := ex.LatLong(); err == nil {
 		mm.Set(keyEXIFGPS.Key(wholeRef), keyEXIFGPS.Val(fmt.Sprint(lat), fmt.Sprint(long)))
 	} else if !exif.IsTagNotPresentError(err) {

pkg/schema/schema.go

@@ -958,9 +958,13 @@ func FileTime(f io.ReaderAt) (time.Time, error) {
 		size = 256 << 10 // enough to get the EXIF
 	}
 	r := io.NewSectionReader(f, 0, size)
+	var tiffErr error
 	ex, err := exif.Decode(r)
 	if err != nil {
-		return defaultTime()
+		tiffErr = err
+		if exif.IsCriticalError(err) || exif.IsExifError(err) {
+			return defaultTime()
+		}
 	}
 	ct, err = ex.DateTime()
 	if err != nil {
@@ -969,6 +973,10 @@ func FileTime(f io.ReaderAt) (time.Time, error) {
 	// If the EXIF file only had local timezone, but it did have
 	// GPS, then lookup the timezone and correct the time.
 	if ct.Location() == time.Local {
+		if exif.IsGPSError(tiffErr) {
+			log.Printf("Invalid EXIF GPS data: %v", tiffErr)
+			return ct, nil
+		}
 		if lat, long, err := ex.LatLong(); err == nil {
 			if loc := lookupLocation(latlong.LookupZoneName(lat, long)); loc != nil {
 				if t, err := exifDateTimeInLocation(ex, loc); err == nil {