✨ Optimize response serialization using Pydantic v2 TypeAdapter

This commit introduces a fast-path for the jsonable_encoder and directly uses TypeAdapter(Any).dump_json() and dump_python() in astapi.routing and astapi.encoders. By leveraging the Rust-based pydantic-core directly, serialization overhead for complex types is significantly reduced.

- Use TypeAdapter(Any).dump_json() in _serialize_data and _serialize_sse_item

- Add fast-path to jsonable_encoder to use TypeAdapter(Any).dump_python(mode='json')

- Update test_sse_events_with_fields to account for minified JSON output of Pydantic v2

fastapi/encoders.py

@@ -21,7 +21,7 @@ from uuid import UUID
 from annotated_doc import Doc
 from fastapi.exceptions import PydanticV1NotSupportedError
 from fastapi.types import IncEx
-from pydantic import BaseModel
+from pydantic import BaseModel, TypeAdapter
 from pydantic.networks import AnyUrl, NameEmail
 from pydantic.types import SecretBytes, SecretStr
 from pydantic_core import PydanticUndefinedType
@@ -125,6 +125,8 @@ def generate_encoders_by_class_tuples(
 
 encoders_by_class_tuples = generate_encoders_by_class_tuples(ENCODERS_BY_TYPE)
 
+_any_type_adapter = TypeAdapter(Any)
+
 
 def jsonable_encoder(
     obj: Annotated[
@@ -240,6 +242,22 @@ def jsonable_encoder(
         include = set(include)  # type: ignore[assignment]  # ty: ignore[invalid-assignment]
     if exclude is not None and not isinstance(exclude, (set, dict)):
         exclude = set(exclude)  # type: ignore[assignment]  # ty: ignore[invalid-assignment]
+    
+    if not custom_encoder and not sqlalchemy_safe:
+        try:
+            return _any_type_adapter.dump_python(
+                obj,
+                mode="json",
+                include=include,
+                exclude=exclude,
+                by_alias=by_alias,
+                exclude_unset=exclude_unset,
+                exclude_defaults=exclude_defaults,
+                exclude_none=exclude_none,
+            )
+        except Exception:
+            pass
+
     if isinstance(obj, BaseModel):
         obj_dict = obj.model_dump(
             mode="json",

fastapi/routing.py

@@ -91,6 +91,9 @@ from starlette.routing import Mount as Mount  # noqa
 from starlette.types import AppType, ASGIApp, Lifespan, Receive, Scope, Send
 from starlette.websockets import WebSocket
 from typing_extensions import deprecated
+from pydantic import TypeAdapter
+
+_any_type_adapter = TypeAdapter(Any)
 
 
 # Copy of starlette.routing.request_response modified to include the
@@ -493,8 +496,7 @@ def get_request_handler(
                         exclude_none=response_model_exclude_none,
                     )
                 else:
-                    data = jsonable_encoder(data)
+                    return _any_type_adapter.dump_json(data)
-                    return json.dumps(data).encode("utf-8")
 
             if is_sse_stream:
                 # Generator endpoint: stream as Server-Sent Events
@@ -512,7 +514,7 @@ def get_request_handler(
                             if hasattr(item.data, "model_dump_json"):
                                 data_str = item.data.model_dump_json()
                             else:
-                                data_str = json.dumps(jsonable_encoder(item.data))
+                                data_str = _any_type_adapter.dump_json(item.data).decode("utf-8")
                         else:
                             data_str = None
                         return format_sse_event(

tests/test_sse.py

@@ -191,7 +191,7 @@ def test_sse_events_with_fields(client: TestClient):
 
     assert "event: json-data\n" in text
     assert "id: 2\n" in text
-    assert 'data: {"key": "value"}\n' in text
+    assert 'data: {"key":"value"}\n' in text
 
     assert ": just a comment\n" in text