examples/widgets/chat/message_list/server.py

#!/usr/bin/env python
"""Example of a simple chatbot that just passes current conversation
state back and forth between server and client.
"""
from typing import List, Union

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from langchain_anthropic import ChatAnthropic
from langchain_core.messages import AIMessage, HumanMessage, SystemMessage
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from pydantic import BaseModel, Field

from langserve import add_routes

app = FastAPI(
    title="LangChain Server",
    version="1.0",
    description="Spin up a simple api server using Langchain's Runnable interfaces",
)


# Set all CORS enabled origins
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
    expose_headers=["*"],
)


# Declare a chain
prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "You are a helpful assisstant named Cob."),
        MessagesPlaceholder(variable_name="messages"),
    ]
)

chain = prompt | ChatAnthropic(model="claude-2.1") | StrOutputParser()


class InputChat(BaseModel):
    """Input for the chat endpoint."""

    messages: List[Union[HumanMessage, AIMessage, SystemMessage]] = Field(
        ...,
        description="The chat messages representing the current conversation.",
        extra={"widget": {"type": "chat", "input": "messages"}},
    )


add_routes(
    app,
    chain.with_types(input_type=InputChat),
)

if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app, host="localhost", port=8000)