feat(event-handler): prefixes to strip for custom mappings (#579)

Author: Michael Brewer

aws_lambda_powertools/event_handler/api_gateway.py

@@ -37,7 +37,7 @@ class ProxyEventType(Enum):
     ALBEvent = "ALBEvent"
 
 
-class CORSConfig(object):
+class CORSConfig:
     """CORS Config
 
     Examples
@@ -265,6 +265,7 @@ def __init__(
         cors: Optional[CORSConfig] = None,
         debug: Optional[bool] = None,
         serializer: Optional[Callable[[Dict], str]] = None,
+        strip_prefixes: Optional[List[str]] = None,
     ):
         """
         Parameters
@@ -276,6 +277,11 @@ def __init__(
         debug: Optional[bool]
             Enables debug mode, by default False. Can be also be enabled by "POWERTOOLS_EVENT_HANDLER_DEBUG"
             environment variable
+        serializer : Callable, optional
+            function to serialize `obj` to a JSON formatted `str`, by default json.dumps
+        strip_prefixes: List[str], optional
+            optional list of prefixes to be removed from the request path before doing the routing. This is often used
+            with api gateways with multiple custom mappings.
         """
         self._proxy_type = proxy_type
         self._routes: List[Route] = []
@@ -285,6 +291,7 @@ def __init__(
         self._debug = resolve_truthy_env_var_choice(
             env=os.getenv(constants.EVENT_HANDLER_DEBUG_ENV, "false"), choice=debug
         )
+        self._strip_prefixes = strip_prefixes
 
         # Allow for a custom serializer or a concise json serialization
         self._serializer = serializer or partial(json.dumps, separators=(",", ":"), cls=Encoder)
@@ -521,7 +528,7 @@ def _to_proxy_event(self, event: Dict) -> BaseProxyEvent:
     def _resolve(self) -> ResponseBuilder:
         """Resolves the response or return the not found response"""
         method = self.current_event.http_method.upper()
-        path = self.current_event.path
+        path = self._remove_prefix(self.current_event.path)
         for route in self._routes:
             if method != route.method:
                 continue
@@ -533,6 +540,25 @@ def _resolve(self) -> ResponseBuilder:
         logger.debug(f"No match found for path {path} and method {method}")
         return self._not_found(method)
 
+    def _remove_prefix(self, path: str) -> str:
+        """Remove the configured prefix from the path"""
+        if not isinstance(self._strip_prefixes, list):
+            return path
+
+        for prefix in self._strip_prefixes:
+            if self._path_starts_with(path, prefix):
+                return path[len(prefix) :]
+
+        return path
+
+    @staticmethod
+    def _path_starts_with(path: str, prefix: str):
+        """Returns true if the `path` starts with a prefix plus a `/`"""
+        if not isinstance(prefix, str) or len(prefix) == 0:
+            return False
+
+        return path.startswith(prefix + "/")
+
     def _not_found(self, method: str) -> ResponseBuilder:
         """Called when no matching route was found and includes support for the cors preflight response"""
         headers = {}

tests/functional/event_handler/test_api_gateway.py

@@ -769,3 +769,57 @@ def get_color() -> Dict:
     body = response["body"]
     expected = '{"color": 1, "variations": ["dark", "light"]}'
     assert expected == body
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        pytest.param("/pay/foo", id="path matched pay prefix"),
+        pytest.param("/payment/foo", id="path matched payment prefix"),
+        pytest.param("/foo", id="path does not start with any of the prefixes"),
+    ],
+)
+def test_remove_prefix(path: str):
+    # GIVEN events paths `/pay/foo`, `/payment/foo` or `/foo`
+    # AND a configured strip_prefixes of `/pay` and `/payment`
+    app = ApiGatewayResolver(strip_prefixes=["/pay", "/payment"])
+
+    @app.get("/pay/foo")
+    def pay_foo():
+        raise ValueError("should not be matching")
+
+    @app.get("/foo")
+    def foo():
+        ...
+
+    # WHEN calling handler
+    response = app({"httpMethod": "GET", "path": path}, None)
+
+    # THEN a route for `/foo` should be found
+    assert response["statusCode"] == 200
+
+
+@pytest.mark.parametrize(
+    "prefix",
+    [
+        pytest.param("/foo", id="String are not supported"),
+        pytest.param({"/foo"}, id="Sets are not supported"),
+        pytest.param({"foo": "/foo"}, id="Dicts are not supported"),
+        pytest.param(tuple("/foo"), id="Tuples are not supported"),
+        pytest.param([None, 1, "", False], id="List of invalid values"),
+    ],
+)
+def test_ignore_invalid(prefix):
+    # GIVEN an invalid prefix
+    app = ApiGatewayResolver(strip_prefixes=prefix)
+
+    @app.get("/foo/status")
+    def foo():
+        ...
+
+    # WHEN calling handler
+    response = app({"httpMethod": "GET", "path": "/foo/status"}, None)
+
+    # THEN a route for `/foo/status` should be found
+    # so no prefix was stripped from the request path
+    assert response["statusCode"] == 200