Use custom converter for catch-all index path

#3045 fixed the 404 errors for non-existent urls but the implementation
masks CORS issues with other endpoints. The catch-all index_pages endpoint
, by default, has provide_automatic_options enabled and as a result it
matches OPTIONS requests for non-existent urls or any other endpoints that
have CORS incompletely configured. This makes it harder to debug CORS
issues. To avoid this instead of throwing a 404 after matching, we need
to throw the error during matching itself. Hence, use a custom path
converter that matches all paths except those starting with the api prefix.

listenbrainz/webserver/__init__.py

@@ -13,6 +13,7 @@
 from listenbrainz import db
 from listenbrainz.db import create_test_database_connect_strings, timescale, donation
 from listenbrainz.db.timescale import create_test_timescale_connect_strings
+from listenbrainz.webserver.converters import NotApiPathConverter
 
 API_PREFIX = '/1'
 
@@ -108,6 +109,8 @@ def create_app(debug=None):
         logger = logging.getLogger('listenbrainz')
         logger.setLevel(logging.DEBUG)
 
+    app.url_map.converters["not_api_path"] = NotApiPathConverter
+
     # initialize Flask-DebugToolbar if the debug option is True
     if app.debug and app.config['SECRET_KEY']:
         app.init_debug_toolbar()

listenbrainz/webserver/converters.py

@@ -0,0 +1,10 @@
+from werkzeug.routing import PathConverter, ValidationError
+
+
+class NotApiPathConverter(PathConverter):
+
+    def to_python(self, path):
+        print(path)
+        if path.startswith('1/'):
+            raise ValidationError()
+        return path

listenbrainz/webserver/views/index.py

@@ -274,12 +274,10 @@ def _get_user_count():
 
 
 @index_bp.route("/",  defaults={'path': ''})
-@index_bp.route('/<path:path>/')
+@index_bp.route('/<not_api_path:path>/')
 @web_listenstore_needed
 def index_pages(path):
     # this is a catch-all route, all unmatched urls match this route instead of raising a 404
     # at least in the case the of API urls, we don't want this behavior. hence detect api urls
-    # and raise 404 errors manually
-    if path.startswith("1/"):
-        raise APINotFound(f"Page not found: {path}")
+    # in the custom NotApiConverter and raise 404 errors manually
     return render_template("index.html")