fix: expose request body schema in Swagger for unannotated endpoints #667

src/litserve/server.py

@@ -32,7 +32,7 @@
 from collections.abc import Callable, Iterable, Mapping, Sequence
 from contextlib import asynccontextmanager
 from queue import Queue
-from typing import TYPE_CHECKING, Literal, Optional, Union
+from typing import TYPE_CHECKING, Any, Literal, Optional, Union
 
 import uvicorn
 import uvicorn.server
@@ -296,6 +296,8 @@ def __init__(self, lit_api: LitAPI, server: "LitServer"):
 
     async def _prepare_request(self, request, request_type) -> dict:
         """Common request preparation logic."""
+        if isinstance(request, dict):
+            return request
         if request_type == Request:
             content_type = request.headers.get("Content-Type", "")
             if content_type == "application/x-www-form-urlencoded" or content_type.startswith("multipart/form-data"):
@@ -1103,8 +1105,12 @@ def _register_api_endpoints(self, lit_api: LitAPI, request_type, response_type):
         # Create handlers
         handler = StreamingRequestHandler(lit_api, self) if lit_api.stream else RegularRequestHandler(lit_api, self)
 
+        # When no Pydantic model is annotated, use Dict[str, Any] so Swagger renders a request body form.
+        # FastAPI will parse the JSON body into a dict automatically in this case.
+        swagger_request_type = dict[str, Any] if request_type is Request else request_type
+
         # Create endpoint function
-        async def endpoint_handler(request: request_type) -> response_type:
+        async def endpoint_handler(request: swagger_request_type) -> response_type:
             return await handler.handle_request(request, request_type)
 
         # Register endpoint

tests/unit/test_pydantic.py

@@ -45,3 +45,21 @@ def test_pydantic():
     with wrap_litserve_start(server) as server, TestClient(server.app) as client:
         response = client.post("/predict", json={"input": 4.0})
         assert response.json() == {"output": 16.0}
+
+
+class NoAnnotationLitAPI(LitAPI):
+    def setup(self, device):
+        pass
+
+    def predict(self, request):
+        return {"output": request["input"] ** 2}
+
+
+def test_swagger_request_body_without_decode_request_annotation():
+    """Regression test for https://github.com/Lightning-AI/LitServe/issues/667.
+    When decode_request has no type annotation, Swagger should still expose a request body form."""
+    server = LitServer(NoAnnotationLitAPI(), accelerator="cpu", devices=1, timeout=5)
+    schema = server.app.openapi()
+    predict_post = schema["paths"]["/predict"]["post"]
+    assert "requestBody" in predict_post, "Swagger must expose a requestBody for /predict"
+    assert "application/json" in predict_post["requestBody"]["content"]