✨ Add exclude_headers parameter (#280)

* Add exclude_headers parameter

* add tests

mangum/adapter.py

@@ -44,6 +44,7 @@ def __init__(
         api_gateway_base_path: str = "/",
         custom_handlers: Optional[List[Type[LambdaHandler]]] = None,
         text_mime_types: Optional[List[str]] = None,
+        exclude_headers: Optional[List[str]] = None,
     ) -> None:
         if lifespan not in ("auto", "on", "off"):
             raise ConfigurationError(
@@ -53,9 +54,11 @@ def __init__(
         self.app = app
         self.lifespan = lifespan
         self.custom_handlers = custom_handlers or []
+        exclude_headers = exclude_headers or []
         self.config = LambdaConfig(
             api_gateway_base_path=api_gateway_base_path or "/",
             text_mime_types=text_mime_types or [*DEFAULT_TEXT_MIME_TYPES],
+            exclude_headers=[header.lower() for header in exclude_headers],
         )
 
     def infer(self, event: LambdaEvent, context: LambdaContext) -> LambdaHandler:

mangum/handlers/alb.py

@@ -5,6 +5,7 @@
 from mangum.handlers.utils import (
     get_server_and_port,
     handle_base64_response_body,
+    handle_exclude_headers,
     maybe_encode_body,
 )
 from mangum.types import (
@@ -166,8 +167,10 @@ def __call__(self, response: Response) -> dict:
         # headers otherwise.
         multi_value_headers_enabled = "multiValueHeaders" in self.scope["aws.event"]
         if multi_value_headers_enabled:
-            out["multiValueHeaders"] = multi_value_headers
+            out["multiValueHeaders"] = handle_exclude_headers(
+                multi_value_headers, self.config
+            )
         else:
-            out["headers"] = finalized_headers
+            out["headers"] = handle_exclude_headers(finalized_headers, self.config)
 
         return out

mangum/handlers/api_gateway.py

@@ -4,6 +4,7 @@
 from mangum.handlers.utils import (
     get_server_and_port,
     handle_base64_response_body,
+    handle_exclude_headers,
     handle_multi_value_headers,
     maybe_encode_body,
     strip_api_gateway_path,
@@ -120,8 +121,10 @@ def __call__(self, response: Response) -> dict:
 
         return {
             "statusCode": response["status"],
-            "headers": finalized_headers,
-            "multiValueHeaders": multi_value_headers,
+            "headers": handle_exclude_headers(finalized_headers, self.config),
+            "multiValueHeaders": handle_exclude_headers(
+                multi_value_headers, self.config
+            ),
             "body": finalized_body,
             "isBase64Encoded": is_base64_encoded,
         }

mangum/handlers/lambda_at_edge.py

@@ -2,6 +2,7 @@
 
 from mangum.handlers.utils import (
     handle_base64_response_body,
+    handle_exclude_headers,
     handle_multi_value_headers,
     maybe_encode_body,
 )
@@ -88,7 +89,7 @@ def __call__(self, response: Response) -> dict:
 
         return {
             "status": response["status"],
-            "headers": finalized_headers,
+            "headers": handle_exclude_headers(finalized_headers, self.config),
             "body": response_body,
             "isBase64Encoded": is_base64_encoded,
         }

mangum/handlers/utils.py

@@ -1,8 +1,8 @@
 import base64
-from typing import Dict, List, Tuple, Union
+from typing import Any, Dict, List, Tuple, Union
 from urllib.parse import unquote
 
-from mangum.types import Headers
+from mangum.types import Headers, LambdaConfig
 
 
 def maybe_encode_body(body: Union[str, bytes], *, is_base64: bool) -> bytes:
@@ -81,3 +81,15 @@ def handle_base64_response_body(
             is_base64_encoded = True
 
     return output_body, is_base64_encoded
+
+
+def handle_exclude_headers(
+    headers: Dict[str, Any], config: LambdaConfig
+) -> Dict[str, Any]:
+    finalized_headers = {}
+    for header_key, header_value in headers.items():
+        if header_key in config["exclude_headers"]:
+            continue
+        finalized_headers[header_key] = header_value
+
+    return finalized_headers

mangum/types.py

@@ -117,6 +117,7 @@ class Response(TypedDict):
 class LambdaConfig(TypedDict):
     api_gateway_base_path: str
     text_mime_types: List[str]
+    exclude_headers: List[str]
 
 
 class LambdaHandler(Protocol):

tests/handlers/test_alb.py

@@ -372,3 +372,40 @@ async def app(scope, receive, send):
         "headers": {"content-type": content_type.decode()},
         "body": utf_res_body,
     }
+
+
+@pytest.mark.parametrize("multi_value_headers_enabled", (True, False))
+def test_aws_alb_exclude_headers(multi_value_headers_enabled) -> None:
+    async def app(scope, receive, send):
+        await send(
+            {
+                "type": "http.response.start",
+                "status": 200,
+                "headers": [
+                    [b"content-type", b"text/plain; charset=utf-8"],
+                    [b"x-custom-header", b"test"],
+                ],
+            }
+        )
+        await send({"type": "http.response.body", "body": b"Hello, world!"})
+
+    handler = Mangum(app, lifespan="off", exclude_headers=["x-custom-header"])
+    event = get_mock_aws_alb_event(
+        "GET", "/test", {}, None, None, False, multi_value_headers_enabled
+    )
+    response = handler(event, {})
+
+    expected_response = {
+        "statusCode": 200,
+        "isBase64Encoded": False,
+        "body": "Hello, world!",
+    }
+    if multi_value_headers_enabled:
+        expected_response["multiValueHeaders"] = {
+            "content-type": ["text/plain; charset=utf-8"],
+        }
+    else:
+        expected_response["headers"] = {
+            "content-type": "text/plain; charset=utf-8",
+        }
+    assert response == expected_response

tests/handlers/test_api_gateway.py

@@ -401,3 +401,31 @@ async def app(scope, receive, send):
         "multiValueHeaders": {},
         "body": utf_res_body,
     }
+
+
+def test_aws_api_gateway_exclude_headers():
+    async def app(scope, receive, send):
+        await send(
+            {
+                "type": "http.response.start",
+                "status": 200,
+                "headers": [
+                    [b"content-type", b"text/plain; charset=utf-8"],
+                    [b"x-custom-header", b"test"],
+                ],
+            }
+        )
+        await send({"type": "http.response.body", "body": b"Hello world"})
+
+    event = get_mock_aws_api_gateway_event("GET", "/test", {}, None, False)
+
+    handler = Mangum(app, lifespan="off", exclude_headers=["X-CUSTOM-HEADER"])
+
+    response = handler(event, {})
+    assert response == {
+        "statusCode": 200,
+        "isBase64Encoded": False,
+        "headers": {"content-type": b"text/plain; charset=utf-8".decode()},
+        "multiValueHeaders": {},
+        "body": "Hello world",
+    }

tests/handlers/test_lambda_at_edge.py

@@ -342,3 +342,34 @@ async def app(scope, receive, send):
         },
         "body": utf_res_body,
     }
+
+
+def test_aws_lambda_at_edge_exclude_():
+    async def app(scope, receive, send):
+        await send(
+            {
+                "type": "http.response.start",
+                "status": 200,
+                "headers": [
+                    [b"content-type", b"text/plain; charset=utf-8"],
+                    [b"x-custom-header", b"test"],
+                ],
+            }
+        )
+        await send({"type": "http.response.body", "body": b"Hello world"})
+
+    event = mock_lambda_at_edge_event("GET", "/test", {}, None, False)
+
+    handler = Mangum(app, lifespan="off", exclude_headers=["x-custom-header"])
+
+    response = handler(event, {})
+    assert response == {
+        "status": 200,
+        "isBase64Encoded": False,
+        "headers": {
+            "content-type": [
+                {"key": "content-type", "value": b"text/plain; charset=utf-8".decode()}
+            ]
+        },
+        "body": "Hello world",
+    }

tests/test_adapter.py

@@ -14,6 +14,7 @@ def test_default_settings():
     assert handler.lifespan == "auto"
     assert handler.config["api_gateway_base_path"] == "/"
     assert sorted(handler.config["text_mime_types"]) == sorted(DEFAULT_TEXT_MIME_TYPES)
+    assert handler.config["exclude_headers"] == []
 
 
 @pytest.mark.parametrize(