🐛 Fix double stage redirect with V2 custom domain mapping

tests/test_handler.py

@@ -689,3 +689,40 @@ def test_wsgi_environ_fixes_double_prefix_bug(self):
         self.assertIn("SCRIPT_NAME='/dev'", response["body"])
         self.assertIn("PATH_INFO='/debug/wsgi/environ'", response["body"])  # FIXED: stage stripped
         self.assertIn("/dev/debug/wsgi/environ", response["body"])  # Correct single prefix!
+
+    def test_wsgi_v2_custom_domain_no_double_stage(self):
+        """
+        Test that API Gateway v2 with a custom domain mapping doesn't double the
+        stage in URLs (#1409). When a custom domain maps to a stage, API Gateway
+        strips the stage from rawPath, so SCRIPT_NAME should be empty.
+        """
+        lh = LambdaHandler("tests.test_wsgi_script_name_settings")
+
+        event = {
+            "version": "2.0",
+            "routeKey": "$default",
+            "rawPath": "/return/request/url",  # Custom domain: stage already stripped
+            "rawQueryString": "",
+            "headers": {
+                "host": "api.example.com",
+            },
+            "requestContext": {
+                "http": {
+                    "method": "GET",
+                    "path": "/return/request/url",
+                },
+                "stage": "dev",  # Stage is still present in requestContext
+                "domainName": "api.example.com",
+            },
+            "isBase64Encoded": False,
+            "body": "",
+        }
+        response = lh.handler(event, None)
+
+        self.assertEqual(response["statusCode"], 200)
+        # With custom domain, stage is NOT in rawPath, so SCRIPT_NAME should be empty
+        # and the URL should NOT contain /dev prefix
+        self.assertEqual(
+            response["body"],
+            "https://api.example.com/return/request/url",
+        )

zappa/handler.py

@@ -711,13 +711,16 @@ def handler(self, event, context):
                 stage = request_context.get("stage")
 
                 # For API Gateway v2, the stage is included in rawPath and we need to
-                # set script_name so it can be stripped from PATH_INFO
-                # For Function URLs (no stage), leave script_name empty
-                if stage:
-                    # API Gateway v2 with named stage - rawPath includes the stage
+                # set script_name so it can be stripped from PATH_INFO.
+                # When using a custom domain with API mapping, API Gateway already
+                # strips the stage from rawPath, so we detect this and skip setting
+                # script_name to avoid double-stage redirects (#1409).
+                raw_path = event.get("rawPath", "")
+                if stage and raw_path.startswith(f"/{stage}"):
+                    # Direct API Gateway v2 access - rawPath includes the stage
                     script_name = f"/{stage}"
                 else:
-                    # Function URL - no stage
+                    # Function URL or custom domain (stage already stripped)
                     script_name = ""
 
                 # ASGI path