Enable configurable by default langserve side (#219)

* Enable configurable key by default
* Should be safe to enable by default since the user is already marking
the runnable as configurable (when they make it configurable)
* Raise an client side error if the client specifies a `configurable`
key but the server does not accept it (will help in debugging)

langserve/server.py

@@ -97,7 +97,7 @@ def _config_from_hash(config_hash: str) -> Dict[str, Any]:
 
 def _unpack_request_config(
     *configs: Union[BaseModel, Mapping, str],
-    keys: Sequence[str],
+    config_keys: Sequence[str],
     model: Type[BaseModel],
     request: Request,
     per_req_config_modifier: Optional[PerRequestConfigModifier],
@@ -114,7 +114,15 @@ def _unpack_request_config(
         else:
             raise TypeError(f"Expected a string, dict or BaseModel got {type(config)}")
     config = merge_configs(*config_dicts)
-    projected_config = {k: config[k] for k in keys if k in config}
+    if "configurable" in config and config["configurable"]:
+        if "configurable" not in config_keys:
+            raise HTTPException(
+                422,
+                "The config field `configurable` has been disallowed by the server. "
+                "This can be modified server side by adding `configurable` to the list "
+                "of `config_keys` argument in `add_routes`",
+            )
+    projected_config = {k: config[k] for k in config_keys if k in config}
     return (
         per_req_config_modifier(projected_config, request)
         if per_req_config_modifier
@@ -405,7 +413,7 @@ def add_routes(
     path: str = "",
     input_type: Union[Type, Literal["auto"], BaseModel] = "auto",
     output_type: Union[Type, Literal["auto"], BaseModel] = "auto",
-    config_keys: Sequence[str] = (),
+    config_keys: Sequence[str] = ("configurable",),
     include_callback_events: bool = False,
     enable_feedback_endpoint: bool = False,
     per_req_config_modifier: Optional[PerRequestConfigModifier] = None,
@@ -438,7 +446,8 @@ def add_routes(
             Favor using runnable.with_types(input_type=..., output_type=...) instead.
             This parameter may get deprecated!
         config_keys: list of config keys that will be accepted, by default
-                     no config keys are accepted.
+            will accept `configurable` key in the config. Will only be used
+            if the runnable is configurable.
         include_callback_events: Whether to include callback events in the response.
             If true, the client will be able to show trace information
             including events that occurred on the server side.
@@ -569,7 +578,7 @@ async def _get_config_and_input(
             config = _unpack_request_config(
                 config_hash,
                 body.config,
-                keys=config_keys,
+                config_keys=config_keys,
                 model=ConfigPayload,
                 request=request,
                 per_req_config_modifier=per_req_config_modifier,
@@ -654,7 +663,7 @@ async def batch(
                     _unpack_request_config(
                         config_hash,
                         config,
-                        keys=config_keys,
+                        config_keys=config_keys,
                         model=ConfigPayload,
                         request=request,
                         per_req_config_modifier=per_req_config_modifier,
@@ -665,7 +674,7 @@ async def batch(
                 configs = _unpack_request_config(
                     config_hash,
                     config,
-                    keys=config_keys,
+                    config_keys=config_keys,
                     model=ConfigPayload,
                     request=request,
                     per_req_config_modifier=per_req_config_modifier,
@@ -935,7 +944,7 @@ async def input_schema(request: Request, config_hash: str = "") -> Any:
         with _with_validation_error_translation():
             config = _unpack_request_config(
                 config_hash,
-                keys=config_keys,
+                config_keys=config_keys,
                 model=ConfigPayload,
                 request=request,
                 per_req_config_modifier=per_req_config_modifier,
@@ -958,7 +967,7 @@ async def output_schema(request: Request, config_hash: str = "") -> Any:
         with _with_validation_error_translation():
             config = _unpack_request_config(
                 config_hash,
-                keys=config_keys,
+                config_keys=config_keys,
                 model=ConfigPayload,
                 request=request,
                 per_req_config_modifier=per_req_config_modifier,
@@ -978,7 +987,7 @@ async def config_schema(request: Request, config_hash: str = "") -> Any:
         with _with_validation_error_translation():
             config = _unpack_request_config(
                 config_hash,
-                keys=config_keys,
+                config_keys=config_keys,
                 model=ConfigPayload,
                 request=request,
                 per_req_config_modifier=per_req_config_modifier,
@@ -997,7 +1006,7 @@ async def playground(
         with _with_validation_error_translation():
             config = _unpack_request_config(
                 config_hash,
-                keys=config_keys,
+                config_keys=config_keys,
                 model=ConfigPayload,
                 request=request,
                 per_req_config_modifier=per_req_config_modifier,

tests/unit_tests/test_server_client.py

@@ -1084,7 +1084,7 @@ async def test_configurable_runnables(event_loop: AbstractEventLoop) -> None:
     assert chain.invoke({"name": "cat"}) == "say cat"
 
     app = FastAPI()
-    add_routes(app, chain, config_keys=["tags", "configurable"])
+    add_routes(app, chain)
 
     async with get_async_remote_runnable(app) as remote_runnable:
         # Test with hard-coded LLM
@@ -1094,19 +1094,30 @@ async def test_configurable_runnables(event_loop: AbstractEventLoop) -> None:
         assert (
             await remote_runnable.ainvoke(
                 {"name": "foo"},
-                {"configurable": {"template": "hear {name}"}, "tags": ["h"]},
+                {"configurable": {"template": "hear {name}"}},
             )
             == "hear foo"
         )
         # Test with alternative passthrough LLM
         assert (
             await remote_runnable.ainvoke(
                 {"name": "foo"},
-                {"configurable": {"llm": "hardcoded_llm"}, "tags": ["h"]},
+                {"configurable": {"llm": "hardcoded_llm"}},
             )
             == "hello Mr. Kitten!"
         )
 
+    add_routes(app, chain, path="/no_config", config_keys=["tags"])
+
+    async with get_async_remote_runnable(app, path="/no_config") as remote_runnable:
+        with pytest.raises(httpx.HTTPError) as cb:
+            await remote_runnable.ainvoke(
+                {"name": "foo"},
+                {"configurable": {"template": "hear {name}"}},
+            )
+
+        assert cb.value.response.status_code == 422
+
 
 # Test for utilities
 

tests/unit_tests/test_validation.py

@@ -157,7 +157,7 @@ def test_invoke_request_with_runnables() -> None:
             Model(
                 input={"name": "bob"},
             ).config,
-            keys=[],
+            config_keys=[],
             model=config,
             request=MagicMock(Request),
             per_req_config_modifier=lambda x, y: x,
@@ -184,7 +184,7 @@ def test_invoke_request_with_runnables() -> None:
 
     assert _unpack_request_config(
         request.config,
-        keys=["configurable"],
+        config_keys=["configurable"],
         model=config,
         request=MagicMock(Request),
         per_req_config_modifier=lambda x, y: x,