Expose favicon URL in instance API

lib/pleroma/web/mastodon_api/views/instance_view.ex

@@ -56,7 +56,10 @@ def render("show.json", _) do
         },
         stats: %{mau: Pleroma.User.active_user_count()},
         vapid_public_key: Keyword.get(Pleroma.Web.Push.vapid_config(), :public_key),
-        oauth_consumer_strategies: Pleroma.Config.oauth_consumer_strategies()
+        oauth_consumer_strategies: Pleroma.Config.oauth_consumer_strategies(),
+        favicon:
+          URI.merge(Pleroma.Web.Endpoint.url(), Keyword.get(instance, :favicon))
+          |> to_string
       },
       configuration: configuration(),
       soapbox: %{

test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs

@@ -19,6 +19,7 @@ test "get instance information", %{conn: conn} do
     email = Pleroma.Config.get([:instance, :email])
     thumbnail = Pleroma.Web.Endpoint.url() <> Pleroma.Config.get([:instance, :instance_thumbnail])
     background = Pleroma.Web.Endpoint.url() <> Pleroma.Config.get([:instance, :background_image])
+    favicon = Pleroma.Web.Endpoint.url() <> Pleroma.Config.get([:instance, :favicon])
 
     # Note: not checking for "max_toot_chars" since it's optional
     assert %{
@@ -44,7 +45,10 @@ test "get instance information", %{conn: conn} do
              "background_image" => from_config_background,
              "shout_limit" => _,
              "description_limit" => _,
-             "rules" => _
+             "rules" => _,
+             "pleroma" => %{
+               "favicon" => from_config_favicon
+             }
            } = result
 
     assert result["version"] =~ "Pleroma"
@@ -60,6 +64,7 @@ test "get instance information", %{conn: conn} do
     assert email == from_config_email
     assert thumbnail == from_config_thumbnail
     assert background == from_config_background
+    assert favicon == from_config_favicon
   end
 
   test "get instance stats", %{conn: conn} do