feat(api-gateway): add common service errors (#506)

Author: Michael Brewer

aws_lambda_powertools/event_handler/__init__.py

@@ -2,6 +2,7 @@
 Event handler decorators for common Lambda events
 """
 
+from .api_gateway import ApiGatewayResolver
 from .appsync import AppSyncResolver
 
-__all__ = ["AppSyncResolver"]
+__all__ = ["AppSyncResolver", "ApiGatewayResolver"]

aws_lambda_powertools/event_handler/api_gateway.py

@@ -4,8 +4,11 @@
 import re
 import zlib
 from enum import Enum
+from http import HTTPStatus
 from typing import Any, Callable, Dict, List, Optional, Set, Union
 
+from aws_lambda_powertools.event_handler import content_types
+from aws_lambda_powertools.event_handler.exceptions import ServiceError
 from aws_lambda_powertools.shared.json_encoder import Encoder
 from aws_lambda_powertools.utilities.data_classes import ALBEvent, APIGatewayProxyEvent, APIGatewayProxyEventV2
 from aws_lambda_powertools.utilities.data_classes.common import BaseProxyEvent
@@ -466,19 +469,28 @@ def _not_found(self, method: str) -> ResponseBuilder:
 
         return ResponseBuilder(
             Response(
-                status_code=404,
-                content_type="application/json",
+                status_code=HTTPStatus.NOT_FOUND.value,
+                content_type=content_types.APPLICATION_JSON,
                 headers=headers,
-                body=json.dumps({"message": "Not found"}),
+                body=self._json_dump({"statusCode": HTTPStatus.NOT_FOUND.value, "message": "Not found"}),
             )
         )
 
     def _call_route(self, route: Route, args: Dict[str, str]) -> ResponseBuilder:
         """Actually call the matching route with any provided keyword arguments."""
-        return ResponseBuilder(self._to_response(route.func(**args)), route)
+        try:
+            return ResponseBuilder(self._to_response(route.func(**args)), route)
+        except ServiceError as e:
+            return ResponseBuilder(
+                Response(
+                    status_code=e.status_code,
+                    content_type=content_types.APPLICATION_JSON,
+                    body=self._json_dump({"statusCode": e.status_code, "message": e.msg}),
+                ),
+                route,
+            )
 
-    @staticmethod
-    def _to_response(result: Union[Dict, Response]) -> Response:
+    def _to_response(self, result: Union[Dict, Response]) -> Response:
         """Convert the route's result to a Response
 
          2 main result types are supported:
@@ -493,6 +505,11 @@ def _to_response(result: Union[Dict, Response]) -> Response:
         logger.debug("Simple response detected, serializing return before constructing final response")
         return Response(
             status_code=200,
-            content_type="application/json",
-            body=json.dumps(result, separators=(",", ":"), cls=Encoder),
+            content_type=content_types.APPLICATION_JSON,
+            body=self._json_dump(result),
         )
+
+    @staticmethod
+    def _json_dump(obj: Any) -> str:
+        """Does a concise json serialization"""
+        return json.dumps(obj, separators=(",", ":"), cls=Encoder)

aws_lambda_powertools/event_handler/content_types.py

@@ -0,0 +1,2 @@
+APPLICATION_JSON = "application/json"
+PLAIN_TEXT = "plain/text"

aws_lambda_powertools/event_handler/exceptions.py

@@ -0,0 +1,45 @@
+from http import HTTPStatus
+
+
+class ServiceError(Exception):
+    """Service Error"""
+
+    def __init__(self, status_code: int, msg: str):
+        """
+        Parameters
+        ----------
+        status_code: int
+            Http status code
+        msg: str
+            Error message
+        """
+        self.status_code = status_code
+        self.msg = msg
+
+
+class BadRequestError(ServiceError):
+    """Bad Request Error"""
+
+    def __init__(self, msg: str):
+        super().__init__(HTTPStatus.BAD_REQUEST, msg)
+
+
+class UnauthorizedError(ServiceError):
+    """Unauthorized Error"""
+
+    def __init__(self, msg: str):
+        super().__init__(HTTPStatus.UNAUTHORIZED, msg)
+
+
+class NotFoundError(ServiceError):
+    """Not Found Error"""
+
+    def __init__(self, msg: str = "Not found"):
+        super().__init__(HTTPStatus.NOT_FOUND, msg)
+
+
+class InternalServerError(ServiceError):
+    """Internal Server Error"""
+
+    def __init__(self, message: str):
+        super().__init__(HTTPStatus.INTERNAL_SERVER_ERROR, message)

tests/functional/event_handler/test_api_gateway.py

@@ -5,13 +5,21 @@
 from pathlib import Path
 from typing import Dict
 
+from aws_lambda_powertools.event_handler import content_types
 from aws_lambda_powertools.event_handler.api_gateway import (
     ApiGatewayResolver,
     CORSConfig,
     ProxyEventType,
     Response,
     ResponseBuilder,
 )
+from aws_lambda_powertools.event_handler.exceptions import (
+    BadRequestError,
+    InternalServerError,
+    NotFoundError,
+    ServiceError,
+    UnauthorizedError,
+)
 from aws_lambda_powertools.shared.json_encoder import Encoder
 from aws_lambda_powertools.utilities.data_classes import ALBEvent, APIGatewayProxyEvent, APIGatewayProxyEventV2
 from tests.functional.utils import load_event
@@ -24,7 +32,6 @@ def read_media(file_name: str) -> bytes:
 
 LOAD_GW_EVENT = load_event("apiGatewayProxyEvent.json")
 TEXT_HTML = "text/html"
-APPLICATION_JSON = "application/json"
 
 
 def test_alb_event():
@@ -55,15 +62,15 @@ def test_api_gateway_v1():
     def get_lambda() -> Response:
         assert isinstance(app.current_event, APIGatewayProxyEvent)
         assert app.lambda_context == {}
-        return Response(200, APPLICATION_JSON, json.dumps({"foo": "value"}))
+        return Response(200, content_types.APPLICATION_JSON, json.dumps({"foo": "value"}))
 
     # WHEN calling the event handler
     result = app(LOAD_GW_EVENT, {})
 
     # THEN process event correctly
     # AND set the current_event type as APIGatewayProxyEvent
     assert result["statusCode"] == 200
-    assert result["headers"]["Content-Type"] == APPLICATION_JSON
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
 
 
 def test_api_gateway():
@@ -93,15 +100,15 @@ def test_api_gateway_v2():
     def my_path() -> Response:
         assert isinstance(app.current_event, APIGatewayProxyEventV2)
         post_data = app.current_event.json_body
-        return Response(200, "plain/text", post_data["username"])
+        return Response(200, content_types.PLAIN_TEXT, post_data["username"])
 
     # WHEN calling the event handler
     result = app(load_event("apiGatewayProxyV2Event.json"), {})
 
     # THEN process event correctly
     # AND set the current_event type as APIGatewayProxyEventV2
     assert result["statusCode"] == 200
-    assert result["headers"]["Content-Type"] == "plain/text"
+    assert result["headers"]["Content-Type"] == content_types.PLAIN_TEXT
     assert result["body"] == "tom"
 
 
@@ -215,7 +222,7 @@ def test_compress():
 
     @app.get("/my/request", compress=True)
     def with_compression() -> Response:
-        return Response(200, APPLICATION_JSON, expected_value)
+        return Response(200, content_types.APPLICATION_JSON, expected_value)
 
     def handler(event, context):
         return app.resolve(event, context)
@@ -261,7 +268,7 @@ def test_compress_no_accept_encoding():
 
     @app.get("/my/path", compress=True)
     def return_text() -> Response:
-        return Response(200, "text/plain", expected_value)
+        return Response(200, content_types.PLAIN_TEXT, expected_value)
 
     # WHEN calling the event handler
     result = app({"path": "/my/path", "httpMethod": "GET", "headers": {}}, None)
@@ -327,7 +334,7 @@ def rest_func() -> Dict:
 
     # THEN automatically process this as a json rest api response
     assert result["statusCode"] == 200
-    assert result["headers"]["Content-Type"] == APPLICATION_JSON
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
     expected_str = json.dumps(expected_dict, separators=(",", ":"), indent=None, cls=Encoder)
     assert result["body"] == expected_str
 
@@ -382,7 +389,7 @@ def another_one():
     # THEN routes by default return the custom cors headers
     assert "headers" in result
     headers = result["headers"]
-    assert headers["Content-Type"] == APPLICATION_JSON
+    assert headers["Content-Type"] == content_types.APPLICATION_JSON
     assert headers["Access-Control-Allow-Origin"] == cors_config.allow_origin
     expected_allows_headers = ",".join(sorted(set(allow_header + cors_config._REQUIRED_HEADERS)))
     assert headers["Access-Control-Allow-Headers"] == expected_allows_headers
@@ -429,6 +436,7 @@ def test_no_matches_with_cors():
     # AND cors headers are returned
     assert result["statusCode"] == 404
     assert "Access-Control-Allow-Origin" in result["headers"]
+    assert "Not found" in result["body"]
 
 
 def test_cors_preflight():
@@ -490,3 +498,87 @@ def custom_method():
     assert headers["Content-Type"] == TEXT_HTML
     assert "Access-Control-Allow-Origin" in result["headers"]
     assert headers["Access-Control-Allow-Methods"] == "CUSTOM"
+
+
+def test_service_error_responses():
+    # SCENARIO handling different kind of service errors being raised
+    app = ApiGatewayResolver(cors=CORSConfig())
+
+    def json_dump(obj):
+        return json.dumps(obj, separators=(",", ":"))
+
+    # GIVEN an BadRequestError
+    @app.get(rule="/bad-request-error", cors=False)
+    def bad_request_error():
+        raise BadRequestError("Missing required parameter")
+
+    # WHEN calling the handler
+    # AND path is /bad-request-error
+    result = app({"path": "/bad-request-error", "httpMethod": "GET"}, None)
+    # THEN return the bad request error response
+    # AND status code equals 400
+    assert result["statusCode"] == 400
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
+    expected = {"statusCode": 400, "message": "Missing required parameter"}
+    assert result["body"] == json_dump(expected)
+
+    # GIVEN an UnauthorizedError
+    @app.get(rule="/unauthorized-error", cors=False)
+    def unauthorized_error():
+        raise UnauthorizedError("Unauthorized")
+
+    # WHEN calling the handler
+    # AND path is /unauthorized-error
+    result = app({"path": "/unauthorized-error", "httpMethod": "GET"}, None)
+    # THEN return the unauthorized error response
+    # AND status code equals 401
+    assert result["statusCode"] == 401
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
+    expected = {"statusCode": 401, "message": "Unauthorized"}
+    assert result["body"] == json_dump(expected)
+
+    # GIVEN an NotFoundError
+    @app.get(rule="/not-found-error", cors=False)
+    def not_found_error():
+        raise NotFoundError
+
+    # WHEN calling the handler
+    # AND path is /not-found-error
+    result = app({"path": "/not-found-error", "httpMethod": "GET"}, None)
+    # THEN return the not found error response
+    # AND status code equals 404
+    assert result["statusCode"] == 404
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
+    expected = {"statusCode": 404, "message": "Not found"}
+    assert result["body"] == json_dump(expected)
+
+    # GIVEN an InternalServerError
+    @app.get(rule="/internal-server-error", cors=False)
+    def internal_server_error():
+        raise InternalServerError("Internal server error")
+
+    # WHEN calling the handler
+    # AND path is /internal-server-error
+    result = app({"path": "/internal-server-error", "httpMethod": "GET"}, None)
+    # THEN return the internal server error response
+    # AND status code equals 500
+    assert result["statusCode"] == 500
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
+    expected = {"statusCode": 500, "message": "Internal server error"}
+    assert result["body"] == json_dump(expected)
+
+    # GIVEN an ServiceError with a custom status code
+    @app.get(rule="/service-error", cors=True)
+    def service_error():
+        raise ServiceError(502, "Something went wrong!")
+
+    # WHEN calling the handler
+    # AND path is /service-error
+    result = app({"path": "/service-error", "httpMethod": "GET"}, None)
+    # THEN return the service error response
+    # AND status code equals 502
+    assert result["statusCode"] == 502
+    assert result["headers"]["Content-Type"] == content_types.APPLICATION_JSON
+    assert "Access-Control-Allow-Origin" in result["headers"]
+    expected = {"statusCode": 502, "message": "Something went wrong!"}
+    assert result["body"] == json_dump(expected)