feat(event-handler): allow for a custom serializer

Author: Michael Brewer

aws_lambda_powertools/event_handler/api_gateway.py

@@ -6,6 +6,7 @@
 import traceback
 import zlib
 from enum import Enum
+from functools import partial
 from http import HTTPStatus
 from typing import Any, Callable, Dict, List, Optional, Set, Union
 
@@ -263,6 +264,7 @@ def __init__(
         proxy_type: Enum = ProxyEventType.APIGatewayProxyEvent,
         cors: Optional[CORSConfig] = None,
         debug: Optional[bool] = None,
+        serializer: Optional[Callable[[Dict], str]] = None,
     ):
         """
         Parameters
@@ -284,6 +286,14 @@ def __init__(
             env=os.getenv(constants.EVENT_HANDLER_DEBUG_ENV, "false"), choice=debug
         )
 
+        if serializer:
+            self._serializer = serializer
+        elif self._debug:
+            """Does a concise json serialization or pretty print when in debug mode"""
+            self._serializer = partial(json.dumps, indent=4, cls=Encoder)
+        else:
+            self._serializer = partial(json.dumps, separators=(",", ":"), cls=Encoder)
+
     def get(self, rule: str, cors: Optional[bool] = None, compress: bool = False, cache_control: Optional[str] = None):
         """Get route decorator with GET `method`
 
@@ -592,8 +602,4 @@ def _to_response(self, result: Union[Dict, Response]) -> Response:
         )
 
     def _json_dump(self, obj: Any) -> str:
-        """Does a concise json serialization or pretty print when in debug mode"""
-        if self._debug:
-            return json.dumps(obj, indent=4, cls=Encoder)
-        else:
-            return json.dumps(obj, separators=(",", ":"), cls=Encoder)
+        return self._serializer(obj)

tests/functional/event_handler/test_api_gateway.py

@@ -3,6 +3,8 @@
 import zlib
 from copy import deepcopy
 from decimal import Decimal
+from enum import Enum
+from json import JSONEncoder
 from pathlib import Path
 from typing import Dict
 
@@ -728,3 +730,39 @@ def get_account(account_id: str):
 
     ret = app.resolve(event, None)
     assert ret["statusCode"] == 200
+
+
+def test_custom_serializer():
+    class Color(Enum):
+        RED = 1
+        BLUE = 2
+
+    class CustomEncoder(JSONEncoder):
+        def default(self, data):
+            if isinstance(data, Enum):
+                return data.value
+            try:
+                iterable = iter(data)
+            except TypeError:
+                pass
+            else:
+                return list(iterable)
+            return JSONEncoder.default(self, data)
+
+    def custom_serializer(data) -> str:
+        return json.dumps(data, cls=CustomEncoder)
+
+    app = ApiGatewayResolver(serializer=custom_serializer)
+
+    @app.get("/colors")
+    def get_color() -> Dict:
+        return {
+            "color": Color.RED,
+            "variations": {"light", "dark"},
+        }
+
+    response = app({"httpMethod": "GET", "path": "/colors"}, None)
+
+    body = response["body"]
+    expected = '{"color": 1, "variations": ["light", "dark"]}'
+    assert expected == body