#185 add case mutation code back for alb when multi value headers is not set (#186)

Author: nathanglover

mangum/handlers/aws_alb.py

@@ -1,11 +1,30 @@
 import base64
 import urllib.parse
-from typing import Dict, Any
+from typing import Any, Dict, Generator, List, Tuple
 
 from .abstract_handler import AbstractHandler
 from .. import Response, Request
 
 
+def all_casings(input_string: str) -> Generator:
+    """
+    Permute all casings of a given string.
+    A pretty algoritm, via @Amber
+    http://stackoverflow.com/questions/6792803/finding-all-possible-case-permutations-in-python
+    """
+    if not input_string:
+        yield ""
+    else:
+        first = input_string[:1]
+        if first.lower() == first.upper():
+            for sub_casing in all_casings(input_string[1:]):
+                yield first + sub_casing
+        else:
+            for sub_casing in all_casings(input_string[1:]):
+                yield first.lower() + sub_casing
+                yield first.upper() + sub_casing
+
+
 class AwsAlb(AbstractHandler):
     """
     Handles AWS Elastic Load Balancer, really Application Load Balancer events
@@ -66,10 +85,27 @@ def body(self) -> bytes:
 
         return body
 
-    def transform_response(self, response: Response) -> Dict[str, Any]:
+    def handle_headers(
+        self,
+        response_headers: List[List[bytes]],
+    ) -> Tuple[Dict[str, str], Dict[str, List[str]]]:
         headers, multi_value_headers = self._handle_multi_value_headers(
-            response.headers
+            response_headers
         )
+        if "multiValueHeaders" not in self.trigger_event:
+            # If there are multiple occurrences of headers, create case-mutated
+            # variations: https://github.com/logandk/serverless-wsgi/issues/11
+            for key, values in multi_value_headers.items():
+                if len(values) > 1:
+                    for value, cased_key in zip(values, all_casings(key)):
+                        headers[cased_key] = value
+
+            multi_value_headers = {}
+
+        return headers, multi_value_headers
+
+    def transform_response(self, response: Response) -> Dict[str, Any]:
+        headers, multi_value_headers = self.handle_headers(response.headers)
 
         body, is_base64_encoded = self._handle_base64_response_body(
             response.body, headers

tests/handlers/test_aws_alb.py

@@ -5,9 +5,14 @@
 
 
 def get_mock_aws_alb_event(
-    method, path, multi_value_query_parameters, body, body_base64_encoded
+    method,
+    path,
+    multi_value_query_parameters,
+    body,
+    body_base64_encoded,
+    multi_value_headers=True,
 ):
-    return {
+    event = {
         "requestContext": {
             "elb": {
                 "targetGroupArn": "arn:aws:elasticloadbalancing:us-east-2:123456789012:targetgroup/lambda-279XGJDqGZ5rsrHC2Fjr/49e9d65c45c6791a"  # noqa: E501
@@ -38,6 +43,10 @@ def get_mock_aws_alb_event(
         "body": body,
         "isBase64Encoded": body_base64_encoded,
     }
+    if multi_value_headers:
+        event["multiValueHeaders"] = {}
+
+    return event
 
 
 def test_aws_alb_basic():
@@ -226,7 +235,7 @@ def test_aws_alb_scope_real(
         assert handler.body == b""
 
 
-def test_aws_alb_set_cookies() -> None:
+def test_aws_alb_set_cookies_multiValueHeaders() -> None:
     async def app(scope, receive, send):
         await send(
             {
@@ -255,6 +264,39 @@ async def app(scope, receive, send):
     }
 
 
+def test_aws_alb_set_cookies_headers() -> 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"set-cookie", b"cookie1=cookie1; Secure"],
+                    [b"set-cookie", b"cookie2=cookie2; Secure"],
+                ],
+            }
+        )
+        await send({"type": "http.response.body", "body": b"Hello, world!"})
+
+    handler = Mangum(app, lifespan="off")
+    event = get_mock_aws_alb_event(
+        "GET", "/test", {}, None, False, multi_value_headers=False
+    )
+    response = handler(event, {})
+    assert response == {
+        "statusCode": 200,
+        "isBase64Encoded": False,
+        "headers": {
+            "content-type": "text/plain; charset=utf-8",
+            "set-cookie": "cookie1=cookie1; Secure",
+            "Set-cookie": "cookie2=cookie2; Secure",
+        },
+        "multiValueHeaders": {},
+        "body": "Hello, world!",
+    }
+
+
 @pytest.mark.parametrize(
     "method,content_type,raw_res_body,res_body,res_base64_encoded",
     [