minor addition to #8238

app/post.go

@@ -894,14 +894,10 @@ func (a *App) ImageProxyAdder() func(string) string {
 	}
 
 	return func(url string) string {
-		if url == "" || strings.HasPrefix(url, siteURL) || strings.HasPrefix(url, proxyURL) {
+		if url == "" || url[0] == '/' || strings.HasPrefix(url, siteURL) || strings.HasPrefix(url, proxyURL) {
 			return url
 		}
 
-		if url[0] == '/' {
-			url = siteURL + url[1:]
-		}
-
 		switch proxyType {
 		case "atmos/camo":
 			mac := hmac.New(sha1.New, []byte(options))

app/post_test.go

@@ -221,6 +221,12 @@ func TestImageProxy(t *testing.T) {
 			ImageURL:        "http://mymattermost.com/myimage",
 			ProxiedImageURL: "http://mymattermost.com/myimage",
 		},
+		"willnorris/imageproxy_PathOnly": {
+			ProxyType:       "willnorris/imageproxy",
+			ProxyURL:        "https://127.0.0.1",
+			ImageURL:        "/myimage",
+			ProxiedImageURL: "/myimage",
+		},
 		"willnorris/imageproxy_EmptyImageURL": {
 			ProxyType:       "willnorris/imageproxy",
 			ProxyURL:        "https://127.0.0.1",