api: add @schema endpoint for cards (#46999)

tests/test_api.py

@@ -3195,6 +3195,12 @@ def test_cards(pub, local_user):
     assert resp.json['data'][0]['digest'] == formdata.digest
     assert resp.json['data'][0]['text'] == formdata.digest
 
+    # get schema
+    resp = get_app(pub).get(sign_uri('/api/cards/test/@schema'), status=200)
+    assert len(resp.json['fields']) == 1
+    assert resp.json['fields'][0]['label'] == 'foobar'
+    assert resp.json['fields'][0]['varname'] == 'foo'
+
 
 def test_api_invalid_http_basic_auth(pub, local_user, admin_user, ics_data):
     app = get_app(pub)

wcs/api.py

@@ -229,6 +229,11 @@ class ApiFormPage(BackofficeFormPage):
 
 class ApiCardPage(ApiFormPage):
     formdef_class = CardDef
+    _q_exports = [('list', 'json'), 'geojson', 'ods', ('@schema', 'schema')]  # restrict to API endpoints
+
+    def schema(self):
+        get_response().set_content_type('application/json')
+        return self.formdef.export_to_json(anonymise=not is_url_signed())
 
 
 class ApiFormsDirectory(Directory):