Add Content-Disposition filename customization

image_type.go

@@ -76,21 +76,25 @@ func (it imageType) Mime() string {
 	return "application/octet-stream"
 }
 
-func (it imageType) ContentDisposition(imageURL string) string {
+func (it imageType) ContentDisposition(filename string) string {
 	format, ok := contentDispositionsFmt[it]
 	if !ok {
 		return "inline"
 	}
 
+	return fmt.Sprintf(format, filename)
+}
+
+func (it imageType) ContentDispositionFromURL(imageURL string) string {
 	url, err := url.Parse(imageURL)
 	if err != nil {
-		return fmt.Sprintf(format, contentDispositionFilenameFallback)
+		return it.ContentDisposition(contentDispositionFilenameFallback)
 	}
 
 	_, filename := filepath.Split(url.Path)
 	if len(filename) == 0 {
-		return fmt.Sprintf(format, contentDispositionFilenameFallback)
+		return it.ContentDisposition(contentDispositionFilenameFallback)
 	}
 
-	return fmt.Sprintf(format, strings.TrimSuffix(filename, filepath.Ext(filename)))
+	return it.ContentDisposition(strings.TrimSuffix(filename, filepath.Ext(filename)))
 }

processing_handler.go

@@ -46,10 +46,17 @@ func initProcessingHandler() {
 func respondWithImage(ctx context.Context, reqID string, r *http.Request, rw http.ResponseWriter, data []byte) {
 	po := getProcessingOptions(ctx)
 
+	var contentDisposition string
+	if len(po.Filename) > 0 {
+		contentDisposition = po.Format.ContentDisposition(po.Filename)
+	} else {
+		contentDisposition = po.Format.ContentDispositionFromURL(getImageURL(ctx))
+	}
+
 	rw.Header().Set("Expires", time.Now().Add(time.Second*time.Duration(conf.TTL)).Format(http.TimeFormat))
 	rw.Header().Set("Cache-Control", fmt.Sprintf("max-age=%d, public", conf.TTL))
 	rw.Header().Set("Content-Type", po.Format.Mime())
-	rw.Header().Set("Content-Disposition", po.Format.ContentDisposition(getImageURL(ctx)))
+	rw.Header().Set("Content-Disposition", contentDisposition)
 
 	if len(headerVaryValue) > 0 {
 		rw.Header().Set("Vary", headerVaryValue)

processing_options.go

@@ -125,6 +125,8 @@ type processingOptions struct {
 	PreferWebP  bool
 	EnforceWebP bool
 
+	Filename string
+
 	UsedPresets []string
 }
 
@@ -635,6 +637,16 @@ func applyCacheBusterOption(po *processingOptions, args []string) error {
 	return nil
 }
 
+func applyFilenameOption(po *processingOptions, args []string) error {
+	if len(args) > 1 {
+		return fmt.Errorf("Invalid filename arguments: %v", args)
+	}
+
+	po.Filename = args[0]
+
+	return nil
+}
+
 func applyProcessingOption(po *processingOptions, name string, args []string) error {
 	switch name {
 	case "format", "f", "ext":
@@ -709,6 +721,10 @@ func applyProcessingOption(po *processingOptions, name string, args []string) er
 		if err := applyCacheBusterOption(po, args); err != nil {
 			return err
 		}
+	case "filename", "fn":
+		if err := applyFilenameOption(po, args); err != nil {
+			return err
+		}
 	default:
 		return fmt.Errorf("Unknown processing option: %s", name)
 	}