Sample code in RunnableWithMessageHistory not working through langserve

[harris]

I am using the code from the sample section of the RunnableWithMessageHistory. it works perfectly if I invoke the chain manually by calling in python code directly. It DOES NOT work when calling through the langserve API. hopefully I am not mistaken but i believe the dictionary parsing in langserve probably not able to recognize the dict properly. Attach is the error I am encountering also.

This works:

print(chain_with_history.invoke(  # noqa: T201
    {"ability": "math", "question": "What's its inverse"},
    config={"configurable": {"session_id": "foo"}}
))

with the samples from the RunnableWithMessageHistory file

from typing import List
from langchain_openai.chat_models import ChatOpenAI

from langchain_core.chat_history import BaseChatMessageHistory
from langchain_core.messages import BaseMessage, AIMessage
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.pydantic_v1 import BaseModel, Field
from langchain_core.runnables.history import RunnableWithMessageHistory

def example_history(settings):
    class InMemoryHistory(BaseChatMessageHistory, BaseModel):
        messages: List[BaseMessage] = Field(default_factory=list)

        def add_messages(self, messages: List[BaseMessage]) -> None:
            self.messages.extend(messages)

        def clear(self) -> None:
            self.messages = []

    # Here we use a global variable to store the chat message history.
    # This will make it easier to inspect it to see the underlying results.
    store = {}

    def get_by_session_id(session_id: str) -> BaseChatMessageHistory:
        if session_id not in store:
            store[session_id] = InMemoryHistory()
        return store[session_id]

    history = get_by_session_id("1")
    history.add_message(AIMessage(content="hello"))
    # print(store)  # noqa: T201

    prompt = ChatPromptTemplate.from_messages([
        ("system", "You're an assistant who's good at {ability}"),
        MessagesPlaceholder(variable_name="history"),
        ("human", "{question}"),
    ])
    model = ChatOpenAI(temperature=0, openai_api_key=settings.OPENAI_API_KEY)

    chain = prompt | model

    chain_with_history = RunnableWithMessageHistory(
        chain,
        # Uses the get_by_session_id function defined in the example
        # above.
        get_by_session_id,
        input_messages_key="question",
        history_messages_key="history",
    )
    return chain_with_history

However, it will fail if call through the api through langserve.

await fetch(`localhost:8000/example_history/invoke`, {
			method: 'POST',
			headers: { accept: 'application/json', 'Content-Type': 'application/json' },
			body: JSON.stringify({
				input: { ability: 'math', question: "What's its inverse?" },
				config: {
					configurable: {
						session_id: "something_random",
					}
				}
			}),
		});

This produces the following errors:

ne 65, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 64, in wrapped_app
    raise exc
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    await app(scope, receive, sender)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/routing.py", line 756, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/routing.py", line 776, in app
    await route.handle(scope, receive, send)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/routing.py", line 297, in handle
    await self.app(scope, receive, send)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/routing.py", line 77, in app
    await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 64, in wrapped_app
    raise exc
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    await app(scope, receive, sender)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/starlette/routing.py", line 72, in app
    response = await func(request)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/fastapi/routing.py", line 278, in app
    raw_response = await run_endpoint_function(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/fastapi/routing.py", line 191, in run_endpoint_function
    return await dependant.call(**values)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langserve/server.py", line 530, in invoke
    return await api_handler.invoke(request)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langserve/api_handler.py", line 833, in invoke
    output = await invoke_coro
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 4529, in ainvoke
    return await self.bound.ainvoke(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 4529, in ainvoke
    return await self.bound.ainvoke(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 2536, in ainvoke
    input = await step.ainvoke(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 4529, in ainvoke
    return await self.bound.ainvoke(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 2536, in ainvoke
    input = await step.ainvoke(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/prompts/base.py", line 143, in ainvoke
    return await self._acall_with_config(
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 1677, in _acall_with_config
    output = await coro
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/prompts/base.py", line 117, in _aformat_prompt_with_error_handling
    _inner_input = self._validate_input(inner_input)
  File "/Users/harris/code/meow/.venv/lib/python3.10/site-packages/langchain_core/prompts/base.py", line 103, in _validate_input
    raise KeyError(
KeyError: "Input to ChatPromptTemplate is missing variables {'ability'}.  Expected: ['ability', 'history', 'question'] Received: ['question', 'history']"

[harris]

one thing I notice is the input in BasePromptTemplate::invoke would get parsed properly with ability while BasePromptTemplate::ainvoke would not include it.

    def invoke(
        self, input: Dict, config: Optional[RunnableConfig] = None
    ) -> PromptValue:
        config = ensure_config(config)
        if self.metadata:
            config["metadata"] = {**config["metadata"], **self.metadata}
        if self.tags:
            config["tags"] = config["tags"] + self.tags
        return self._call_with_config(
            self._format_prompt_with_error_handling,
            input,
            config,
            run_type="prompt",
        )

    async def ainvoke(
        self, input: Dict, config: Optional[RunnableConfig] = None, **kwargs: Any
    ) -> PromptValue:
        config = ensure_config(config)
        if self.metadata:
            config["metadata"].update(self.metadata)
        if self.tags:
            config["tags"].extend(self.tags)
        return await self._acall_with_config(
            self._aformat_prompt_with_error_handling,
            input,
            config,
            run_type="prompt",
        )

[harris]

I am able to bypass the input_schema validation so the data would flow through in this PR: #631

please let me know the proper fix.

[ZohaibRamzan]

looking for the solution!!! Anyone able to manage session id based chat history(each user specific) or pipeline state(langgraph) if we deploy through langserve