fix(event_handler): omit Content-Type header from OpenAPI

aws_lambda_powertools/event_handler/openapi/schema_generator.py

@@ -174,9 +174,15 @@ def _build_operation_parameters(
             continue
 
         if _is_pydantic_model_param(field_info):
-            parameters.extend(_expand_pydantic_model_parameters(field_info))
+            generated_parameters = _expand_pydantic_model_parameters(field_info)
         else:
-            parameters.append(_create_regular_parameter(param, model_name_map, field_mapping))
+            generated_parameters = [_create_regular_parameter(param, model_name_map, field_mapping)]
+
+        parameters.extend(
+            parameter
+            for parameter in generated_parameters
+            if not (parameter["in"] == "header" and parameter["name"].lower() == "content-type")
+        )
 
     return parameters
 

tests/functional/event_handler/_pydantic/test_openapi_params.py

@@ -1,7 +1,7 @@
 import json
 from dataclasses import dataclass
 from datetime import datetime
-from typing import List, Optional, Tuple
+from typing import List, Literal, Optional, Tuple
 
 import pytest
 from pydantic import BaseModel, Field
@@ -915,6 +915,24 @@ def mixed_body_endpoint(user_data: Annotated[UserData, Body(media_type="applicat
     assert "application/json" in request_body.content
 
 
+def test_openapi_excludes_content_type_header_parameter():
+    """Content-Type is described by requestBody content, not an OpenAPI header parameter."""
+    app = APIGatewayRestResolver(enable_validation=True)
+
+    @app.patch("/json-patch")
+    def json_patch(
+        operations: Annotated[list[dict], Body(media_type="application/json-patch+json")],
+        content_type: Annotated[Literal["application/json-patch+json"], Header(alias="Content-Type")],
+    ):
+        return {"status": "updated"}
+
+    schema = app.get_openapi_schema()
+    patch_op = schema.paths["/json-patch"].patch
+
+    assert "application/json-patch+json" in patch_op.requestBody.content
+    assert all(parameter.name.lower() != "content-type" for parameter in patch_op.parameters or [])
+
+
 def test_openapi_form_parameter_edge_cases():
     """Test Form parameters with various edge cases."""
 
@@ -986,7 +1004,7 @@ def get_items(params: Annotated[QueryParams, Query()]):
 
 
 def test_openapi_pydantic_header_with_alias():
-    """Test that Pydantic field aliases work correctly in Header parameters"""
+    """Test that Pydantic header aliases are emitted, except Content-Type."""
     app = APIGatewayRestResolver()
 
     class HeaderParams(BaseModel):
@@ -1003,7 +1021,7 @@ def test_handler(headers: Annotated[HeaderParams, Header()]):
 
     # Check that aliases are used as parameter names
     param_names = [param.name for param in get_operation.parameters]
-    assert "content-type" in param_names
+    assert "content-type" not in param_names
     assert "user-agent" in param_names
     assert "content_type" not in param_names  # Original field name should not be used
     assert "user_agent" not in param_names

tests/functional/event_handler/_pydantic/test_openapi_validation_middleware.py

@@ -59,6 +59,27 @@ def handler(user_id: int):
     assert any(text in result["body"] for text in ["type_error.integer", "int_parsing"])
 
 
+def test_content_type_header_validation_remains_enabled(gw_event):
+    """Content-Type header validation remains available when it is omitted from the OpenAPI schema."""
+    app = APIGatewayRestResolver(enable_validation=True)
+
+    @app.patch("/json-patch")
+    def json_patch(
+        operations: Annotated[list[dict], Body(media_type="application/json-patch+json")],
+        content_type: Annotated[Literal["application/json-patch+json"], Header(alias="Content-Type")],
+    ):
+        return {"status": "updated"}
+
+    gw_event["httpMethod"] = "PATCH"
+    gw_event["path"] = "/json-patch"
+    gw_event["headers"]["Content-Type"] = "application/json"
+    gw_event["body"] = '[{"op": "replace"}]'
+
+    result = app(gw_event, {})
+
+    assert result["statusCode"] == 422
+
+
 def test_validate_pydantic_query_params(gw_event):
     """Test that Pydantic models in Query parameters are validated correctly"""