OpenSubsonic: report HTTP form POST extension as supported

Funkwhale already supports passing parameters as application/x-www-form-urlencoded

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2695>

api/funkwhale_api/subsonic/views.py

@@ -189,8 +189,7 @@ class SubsonicViewSet(viewsets.GenericViewSet):
     )
     def get_open_subsonic_extensions(self, request, *args, **kwargs):
         data = {
-            # No specific extensions are currently supported
-            "openSubsonicExtensions": [""],
+            "openSubsonicExtensions": [{"name": "formPost", "versions": [1]}],
         }
         return response.Response(data, status=200)
 

api/tests/subsonic/test_views.py

@@ -97,6 +97,23 @@ def test_ping(f, db, api_client):
     assert response.data == expected
 
 
+@pytest.mark.parametrize("f", ["xml", "json"])
+def test_get_open_subsonic_extensions(f, db, api_client):
+    url = reverse("api:subsonic:subsonic-get_open_subsonic_extensions")
+    response = api_client.get(url, {"f": f})
+
+    expected = {
+        "openSubsonicExtensions": [
+            {
+                "name": "formPost",
+                "versions": [1],
+            }
+        ],
+    }
+    assert response.status_code == 200
+    assert response.data == expected
+
+
 @pytest.mark.parametrize("f", ["json"])
 def test_get_artists(
     f, db, logged_in_api_client, factories, mocker, queryset_equal_queries