Add system console switch for enabling link previews (#5663)

api/post.go

@@ -452,6 +452,11 @@ func getFileInfosForPost(c *Context, w http.ResponseWriter, r *http.Request) {
 }
 
 func getOpenGraphMetadata(c *Context, w http.ResponseWriter, r *http.Request) {
+	if !*utils.Cfg.ServiceSettings.EnableLinkPreviews {
+		c.Err = model.NewAppError("getOpenGraphMetadata", "api.post.link_preview_disabled.app_error", nil, "", http.StatusNotImplemented)
+		return
+	}
+
 	props := model.StringInterfaceFromJson(r.Body)
 
 	ogJSONGeneric, ok := openGraphDataCache.Get(props["url"])

api/post_test.go

@@ -1307,6 +1307,12 @@ func TestGetOpenGraphMetadata(t *testing.T) {
 	th := Setup().InitBasic()
 	Client := th.BasicClient
 
+	enableLinkPreviews := *utils.Cfg.ServiceSettings.EnableLinkPreviews
+	defer func() {
+		*utils.Cfg.ServiceSettings.EnableLinkPreviews = enableLinkPreviews
+	}()
+	*utils.Cfg.ServiceSettings.EnableLinkPreviews = true
+
 	ogDataCacheMissCount := 0
 
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -1355,4 +1361,9 @@ func TestGetOpenGraphMetadata(t *testing.T) {
 			))
 		}
 	}
+
+	*utils.Cfg.ServiceSettings.EnableLinkPreviews = false
+	if _, err := Client.DoApiPost("/get_opengraph_metadata", "{\"url\":\"/og-data/\"}"); err == nil || err.StatusCode != http.StatusNotImplemented {
+		t.Fatal("should have failed with 501 - disabled link previews")
+	}
 }