From 24095740e7c12220a8ca5cc14766cf0ec95764ca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Janek=20Nouvertn=C3=A9?= <provinzkraut@posteo.de>
Date: Wed, 3 Jan 2024 20:16:31 +0100
Subject: [PATCH] fix: #2867 - Ensure `type_encoders` are passed to exception
 response (#2941)
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* Pass type_encoders to exception handling response

---------

Signed-off-by: Janek Nouvertné <25355197+provinzkraut@users.noreply.github.com>
---
 .../middleware/exceptions/_debug_response.py   | 18 +++++++++++++++++-
 litestar/middleware/exceptions/middleware.py   |  7 ++++---
 .../test_exception_handler_middleware.py       | 17 +++++++++++++++++
 3 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/litestar/middleware/exceptions/_debug_response.py b/litestar/middleware/exceptions/_debug_response.py
index 3cdd86dc6f..d80ea4bde9 100644
--- a/litestar/middleware/exceptions/_debug_response.py
+++ b/litestar/middleware/exceptions/_debug_response.py
@@ -26,6 +26,7 @@
     from inspect import FrameInfo
 
     from litestar.connection import Request
+    from litestar.types import TypeEncodersMap
 
 tpl_dir = Path(__file__).parent / "templates"
 
@@ -191,4 +192,19 @@ def create_debug_response(request: Request, exc: Exception) -> Response:
         content = create_plain_text_response_content(exc)
         media_type = MediaType.TEXT
 
-    return Response(content=content, media_type=media_type, status_code=HTTP_500_INTERNAL_SERVER_ERROR)
+    return Response(
+        content=content,
+        media_type=media_type,
+        status_code=HTTP_500_INTERNAL_SERVER_ERROR,
+        type_encoders=_get_type_encoders_for_request(request) if request is not None else None,
+    )
+
+
+def _get_type_encoders_for_request(request: Request) -> TypeEncodersMap | None:
+    try:
+        return request.route_handler.resolve_type_encoders()
+    # we might be in a 404, or before we could resolve the handler, so this
+    # could potentially error out. In this case we fall back on the application
+    # type encoders
+    except (KeyError, AttributeError):
+        return request.app.type_encoders
diff --git a/litestar/middleware/exceptions/middleware.py b/litestar/middleware/exceptions/middleware.py
index 97dacbeb99..4828cfd8d5 100644
--- a/litestar/middleware/exceptions/middleware.py
+++ b/litestar/middleware/exceptions/middleware.py
@@ -11,7 +11,7 @@
 from litestar.enums import MediaType, ScopeType
 from litestar.exceptions import WebSocketException
 from litestar.middleware.cors import CORSMiddleware
-from litestar.middleware.exceptions._debug_response import create_debug_response
+from litestar.middleware.exceptions._debug_response import _get_type_encoders_for_request, create_debug_response
 from litestar.serialization import encode_json
 from litestar.status_codes import HTTP_500_INTERNAL_SERVER_ERROR
 from litestar.utils.deprecation import warn_deprecation
@@ -85,7 +85,7 @@ class ExceptionResponseContent:
     extra: dict[str, Any] | list[Any] | None = field(default=None)
     """An extra mapping to attach to the exception."""
 
-    def to_response(self) -> Response:
+    def to_response(self, request: Request | None = None) -> Response:
         """Create a response from the model attributes.
 
         Returns:
@@ -103,6 +103,7 @@ def to_response(self) -> Response:
             headers=self.headers,
             status_code=self.status_code,
             media_type=self.media_type,
+            type_encoders=_get_type_encoders_for_request(request) if request is not None else None,
         )
 
 
@@ -139,7 +140,7 @@ def create_exception_response(request: Request[Any, Any, Any], exc: Exception) -
         extra=getattr(exc, "extra", None),
         media_type=media_type,
     )
-    return content.to_response()
+    return content.to_response(request=request)
 
 
 class ExceptionHandlerMiddleware:
diff --git a/tests/unit/test_middleware/test_exception_handler_middleware.py b/tests/unit/test_middleware/test_exception_handler_middleware.py
index 7f2cae85d1..cb53adc88a 100644
--- a/tests/unit/test_middleware/test_exception_handler_middleware.py
+++ b/tests/unit/test_middleware/test_exception_handler_middleware.py
@@ -362,3 +362,20 @@ def method(self) -> None:
     if exc is not None and exc.__traceback__ is not None:
         frame = getinnerframes(exc.__traceback__, 2)[-1]
         assert get_symbol_name(frame) == "Test.method"
+
+
+def test_serialize_custom_types() -> None:
+    # ensure type encoders are passed down to the created response so custom types that
+    # might end up as part of a ValidationException are handled properly
+    # https://github.com/litestar-org/litestar/issues/2867
+    class Foo:
+        def __init__(self, value: str) -> None:
+            self.value = value
+
+    @get()
+    def handler() -> None:
+        raise ValidationException(extra={"foo": Foo("bar")})
+
+    with create_test_client([handler], type_encoders={Foo: lambda f: f.value}) as client:
+        res = client.get("/")
+        assert res.json()["extra"] == {"foo": "bar"}