Building LangChain-Based Bots#

In this section, let’s build a bot that uses a LangChain runnable to drive the conversation. We will build a LangChain agent that performs DuckDuckGo searches and answers questions in the context of the conversation. You can swap out this agent with their own chains/agents in this tutorial. You can learn about LangChain Runnable Interface, LangServe, LangGraph, and a few other terminologies mentioned by following LangChain Documentation. You can cross reference the DuckDuckGo LangChain Sample bot for code or any issues in the tutorial steps.

The interaction with the LangChain runnable will happen via a custom Plugin server. In this tutorial, we will define a LangChain runnable directly in the custom Plugin server. However, you can also choose to deploy your LangChain runnables via LangServe and have your custom Plugins interact with the LangServe APIs using remote runnables.

The minimal file structure of the LangChain bot looks like this:

samples
└── langchain_tutorial_bot
    └── plugin
        └── langchain_agent.py
        └── schemas.py
    └── plugin_config.yaml
    └── speech_config.yaml
    └── model_config.yaml

Create an empty directory called samples/langchain_tutorial_bot and perform the following steps for updating bot configurations.

For the LangChain or custom RAG pipelines that do not require processing or guardrailing with Colang, you can directly connect the Chat Controller to the Plugin server. Follow the plugin server architecture section for more information. We will demonstrate this approach below.

Creating the LangChain Plugin#

In this section, let’s build the custom LangChain Plugin and test it as a standalone component.

  1. Define the input and output API schemas used by ACE Agent for communication with the Plugin server and Chat Controller. Update plugin/schemas.py with the following contents.

    from pydantic import BaseModel, Field
from typing import Optional, Dict, List, Any


class ChatRequest(BaseModel):
    Query: Optional[str] = Field(default="", description="The user query which needs to be processed.")
    UserId: str = Field(
        description="Mandatory unique identifier to recognize which user is interacting with the Chat Engine."
    )
Metadata: Optional[Dict[str, Any]] = Field(
    default={},
    description="Any additional information related to the request.",
)


class EventRequest(BaseModel):
    EventType: str = Field(default="", description="The event name which needs to be processed.")
    UserId: str = Field(
        description="Mandatory unique identifier to recognize which user is interacting with the Chat Engine."
    )


class ResponseField(BaseModel):
    Text: str = Field(
        default="",
        description="Text response to be sent out. This field will also be picked by a Text to Speech Synthesis module if enabled for speech based bots.",
    )
    CleanedText: str = Field(
        default="", description="Text response from the Chat Engine with all SSML/HTML tags removed."
    )
    NeedUserResponse: Optional[bool] = Field(
        default=True,
        description="This field can be used by end user applications to deduce if user response is needed or not for a dialog initiated query. This is set to true automatically if form filling is active and one or more slots are missing.",
    )
    IsFinal: bool = Field(
        default=False,
        description="This field to indicate the final response chunk when streaming. The chunk with IsFinal=true will contain the full Chat Engine response attributes.",
    )


class ChatResponse(BaseModel):
    UserId: str = Field(
        default="",
        description="Unique identifier to recognize which user is interacting with the Chat Engine. This is populated from the request JSON.",
    )
    QueryId: str = Field(
        default="",
        description="Unique identifier for the user query assigned automatically by the Chat Engine unless specified in request JSON.",
    )
    Response: ResponseField = Field(
        default=ResponseField(),
        description="Final response template from the Chat Engine. This field can be picked up from domain rule files or can be formulated directly from custom plugin modules.",
    )
    Metadata: Optional[Dict[str, Any]] = Field(
        default={"SessionId": "", "StreamId": ""},
        description="Any additional information related to the request.",
    )


class EventResponse(BaseModel):
    UserId: str = Field(
        default="",
        description="Unique identifier to recognize which user is interacting with the Chat Engine. This is populated from the request JSON.",
    )
    Events: List[Dict[str, Any]] = Field(
        default=[], description="The generated event list for the provided EventType from Chat Engine."
    )
    Response: ResponseField = Field(
        default=ResponseField(),
        description="Final response template from the Chat Engine. This field can be picked up from domain rule files or can be formulated directly from custom plugin modules.",
    )

    Let’s understand the APIs and their schemas a little. There are two APIs used by the Chat Controller microservice: /chat and /event.

    1. Events such as pipeline creation and deletion are sent by the Chat Controller to the /event endpoint. In most cases, you will not need to modify the default /event endpoint that we will define in the next step.

    2. User questions are sent by the Chat Controller to the /chat endpoint, along with the UserId and an optional QueryId. The response schema for this API contains a Response attribute, which contains the details of the response. In this tutorial, we only need to manage two sub-fields: Response.Text (which contains the chunk that we are streaming) and Response.IsFinal (which indicates whether the stream is complete).

  2. Create the actual custom Plugin with the LangChain agent and the /chat and /event APIs. Update plugin/langchain_agent.py with the following code:

    from fastapi import APIRouter, status, Body, Response
from fastapi.responses import StreamingResponse
import logging
import os
import sys
from typing_extensions import Annotated
from typing import Union, Dict
import json

from langchain_community.chat_models import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.output_parsers import StrOutputParser
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain.memory import ChatMessageHistory
from langchain.tools.ddg_search import DuckDuckGoSearchRun
from langchain_core.runnables import (
    RunnableParallel,
    RunnablePassthrough,
)
from langchain.tools import tool

logger = logging.getLogger("plugin")
router = APIRouter()

sys.path.append(os.path.dirname(__file__))

from schemas import ChatRequest, EventRequest, EventResponse, ChatResponse

EVENTS_NOT_REQUIRING_RESPONSE = [
    "system.event_pipeline_acquired",
    "system.event_pipeline_released",
    "system.event_exit",
]

duckduckgo = DuckDuckGoSearchRun()


@tool
def ddg_search(query: str):
    """Performs a duckduck go search"""

    logger.info(f"Input to DDG: {query}")
    answer = duckduckgo.run(query)
    logger.info(f"Answer from DDG: {answer}")
    return answer


rephraser_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            f"You are an assistant whose job is to rephrase the question into a standalone question, based on the conversation history."
            f"The rephrased question should be as short and simple as possible. Do not attempt to provide an answer of your own!",
        ),
        MessagesPlaceholder(variable_name="history"),
        ("human", "{query}"),
    ]
)

wiki_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "Answer the given question from the provided context. Only use the context to form an answer.\nContext: {context}",
        ),
        ("user", "{query}"),
    ]
)

chat_history_map = {}
llm = ChatOpenAI(model="gpt-4-turbo")
output_parser = StrOutputParser()

chain = (
    rephraser_prompt
    | llm
    | output_parser
    | RunnableParallel({"context": ddg_search, "query": RunnablePassthrough()})
    | wiki_prompt
    | llm
    | output_parser
)

chain_with_history = RunnableWithMessageHistory(
    chain,
    lambda session_id: chat_history_map.get(session_id),
    input_messages_key="query",
    history_messages_key="history",
)


@router.post(
    "/chat",
    status_code=status.HTTP_200_OK,
)
async def chat(
    request: Annotated[
        ChatRequest,
        Body(
            description="Chat Engine Request JSON. All the fields populated as part of this JSON is also available as part of request JSON."
        ),
    ],
    response: Response,
) -> StreamingResponse:
    """
    This endpoint can be used to provide response to query driven user request.
    """

    req = request.dict(exclude_none=True)
    logger.info(f"Received request JSON at /chat endpoint: {json.dumps(req, indent=4)}")

    try:

        session_id = req["UserId"]
        question = req["Query"]

        if session_id not in chat_history_map:
            chat_history_map[session_id] = ChatMessageHistory(messages=[])

        def generator(question: str, session_id: str):
            full_response = ""
            if question:
                for chunk in chain_with_history.stream(
                    {"query": question}, config={"configurable": {"session_id": session_id}}
                ):
                    if not chunk:
                        continue
                    full_response += chunk

                    json_chunk = ChatResponse()
                    json_chunk.Response.Text = chunk
                    json_chunk = json.dumps(json_chunk.dict())
                    yield json_chunk

            json_chunk = ChatResponse()
            json_chunk.Response.IsFinal = True
            json_chunk.Response.CleanedText = full_response
            json_chunk = json.dumps(json_chunk.dict())
            yield json_chunk

        return StreamingResponse(generator(question, session_id), media_type="text/event-stream")

    except Exception as e:
        response.status_code = status.HTTP_500_INTERNAL_SERVER_ERROR
        return {"StatusMessage": str(e)}


@router.post("/event", status_code=status.HTTP_200_OK)
async def event(
    request: Annotated[
        EventRequest,
        Body(
            description="Chat Engine Request JSON. All the fields populated as part of this JSON is also available as part of request JSON."
        ),
    ],
    response: Response,
) -> Union[EventResponse, Dict[str, str]]:
    """
    This endpoint can be used to provide response to an event driven user request.
    """

    req = request.dict(exclude_none=True)
    logger.info(f"Received request JSON at /event endpoint: {json.dumps(req, indent=4)}")

    try:
        resp = EventResponse()
        resp.UserId = req["UserId"]
        resp.Response.IsFinal = True

        if req["EventType"] in EVENTS_NOT_REQUIRING_RESPONSE:
            resp.Response.NeedUserResponse = False

        return resp
    except Exception as e:
        response.status_code = status.HTTP_500_INTERNAL_SERVER_ERROR
        return {"StatusMessage": str(e)}

    Let’s understand the above code.

    1. The ddg_search tool takes in the query, performs a DuckDuckGo search, and returns the top responses.

    2. The rephraser_prompt is used to rephrase the current question into a single, simple question based on the conversation history, represented by the history placeholder.

    3. The chain runnable performs rephrasing of the query, passes the rephrased to the ddg_search tool, and finally calls the LLM again to fetch the answer from the DuckDuckGo search results.

    4. The chain_with_history is the actual runnable that we will be using to generate answers. It fetches the correct conversation history based on the session_id and populates the rephraser_prompt with the right inputs.

    5. Finally, the /chat endpoint invokes the chain_with_history with the right inputs. In this case, we return a generator where we call the stream method of the runnable, format the response into the ChatResponse schema, and push the chunk into the response stream.

    If you are using a custom LangChain runnable or if you want to modify the way you call the runnable, you will only need to make changes in the generator method.

  3. Register this plugin. Add the following to plugin_config.yaml.

    config:
  workers: 1
  timeout: 30

plugins:
  - name: langchain
    path: ./plugin/langchain_agent.py

  4. Add the Python dependencies used by this runnable in deploy/docker/dockerfiles/plugin_server.Dockerfile. This will install the custom dependencies when the Plugin server is being built.

    ##############################
# Install custom dependencies
##############################
RUN pip install langchain==0.1.1 \
    langchain-community==0.0.13 \
    langchain-core==0.1.12 \
    duckduckgo-search==5.3.1b1

Note

If you see a crash in the plugin server or an issue with fetching a response from DuckDuckGo, try using a more recent duckduckgo-search version.

  1. Deploy the Plugin server for testing.

    1. Set the OpenAI API key if it is not already set.

      export OPENAI_API_KEY=...

    2. Run the bot using the Docker Environment.

      export BOT_PATH=./samples/langchain_tutorial_bot
source deploy/docker/docker_init.sh
docker compose -f deploy/docker/docker-compose.yml up --build plugin-server -d

  2. We can test the endpoint by running the following CURL command:

    curl -X 'POST' \
  'http://localhost:9002/langchain/chat' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "Query": "Who is the president of the United States?",
  "UserId": "user1"
}'

  3. After you are done testing the plugin, to stop the server, run:

    docker compose -f deploy/docker/docker-compose.yml down

Connecting the Plugin to the Chat Controller#

Now that the Plugin is functional, let’s create the configs to connect the Chat Controller to the Plugin server, as well as enable speech.

  1. Copy the model_config.yaml and speech_config.yaml files from samples/chitchat_bot. They represent the common settings for a speech pipeline.

  2. Update the server URL in the dialog_manager component in the speech_config.yaml file to point to the plugin we created in the previous section.

    dialog_manager:
  DialogManager:
    server: "http://localhost:9002/langchain"
    use_streaming: true

    With this change, the Chat Controller will directly call the /chat and /event endpoints of the Plugin server.

  3. Deploy the bot using the Docker environment.

  4. Set the environment variables required for the docker-compose.yml file.

    export BOT_PATH=./samples/langchain_tutorial_bot/
source deploy/docker/docker_init.sh

  5. For Plugin Server Architecture bots, we need to use the speech_lite pipeline configuration for the Chat Controller microservice. Update the PIPELINE variable in deploy/docker/docker_init.sh or override by setting the PIPELINE environment variable manually.

    export PIPELINE=speech_lite

  6. Deploy the Riva ASR and TTS speech models.

    docker compose -f deploy/docker/docker-compose.yml up model-utils-speech

  7. Deploy the Plugin server with the LangChain plugin.

    docker compose -f deploy/docker/docker-compose.yml up --build plugin-server -d

  8. Deploy the Chat Controller microservice with the gRPC interface.

    docker compose -f deploy/docker/docker-compose.yml up chat-controller -d

  9. Deploy the speech sample frontend application.

    docker compose -f deploy/docker/docker-compose.yml up bot-web-ui-client bot-web-ui-speech -d

    Notice that we are not deploying the Chat Engine microservice at all.

    You can interact with the bot using your browser at http://<YOUR_IP_ADDRESS>:7006.

Here’s an example dialog with the bot.

LangChain Bot

Note

If you want to utilize Colang along with the LangChain Agent or you want to add more modalities, refer to the Building a Bot using Colang 2.0 and Event Interface and Building a Low Latency Speech-To-Speech RAG Bot tutorials.

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