add mimetype to service response

pkg/thumbnails/encoding.go

@@ -14,6 +14,8 @@ type Encoder interface {
 	Encode(io.Writer, image.Image) error
 	// Types returns the formats suffixes.
 	Types() []string
+	// MimeType returns the mimetype used by the encoder.
+	MimeType() string
 }
 
 // PngEncoder encodes to png
@@ -29,6 +31,11 @@ func (e PngEncoder) Types() []string {
 	return []string{"png"}
 }
 
+// MimeType returns the mimetype for png files.
+func (e PngEncoder) MimeType() string {
+	return "image/png"
+}
+
 // JpegEncoder encodes to jpg.
 type JpegEncoder struct{}
 
@@ -42,6 +49,11 @@ func (e JpegEncoder) Types() []string {
 	return []string{"jpeg", "jpg"}
 }
 
+// MimeType returns the mimetype for jpg files.
+func (e JpegEncoder) MimeType() string {
+	return "image/jpeg"
+}
+
 // EncoderForType returns the encoder for a given file type
 // or nil if the type is not supported.
 func EncoderForType(fileType string) Encoder {