Attach extension to ID for known image types

store/store.go

@@ -57,12 +57,32 @@ func (s *Store) Get(id string) (*Image, bool) {
 	return image, true
 }
 
+// isImageContentType checks if the content type is a valid image
+func extFromContentType(contentType string) (string, bool) {
+	val, ok := map[string]string{
+		"image/jpeg": "jpg",
+		"image/jpg":  "jpg",
+		"image/png":  "png",
+		"image/gif":  "gif",
+		"image/webp": "webp",
+		"image/bmp":  "bmp",
+	}[contentType]
+	return val, ok
+}
+
 // Save stores an image and returns its ID
 func (s *Store) Save(data []byte, contentType string) string {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	id := uuid.New().String()
+	ext, ok := extFromContentType(contentType)
+	if !ok {
+		ext = ""
+	} else {
+		ext = "." + ext
+	}
+
+	id := uuid.New().String() + ext
 	s.images[id] = &Image{
 		Data:        data,
 		ContentType: contentType,