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Developing with LangChain

LangChain is an open-source framework for developing LLM applications, providing rich components and toolchains. CloudBase offers the @cloudbase/agent-adapter-langchain adapter, enabling LangChain Agents to seamlessly connect with the AG-UI protocol.

Prerequisites​

Install Dependencies​

npm install @cloudbase/agent-adapter-langchain @cloudbase/agent-server langchain @langchain/openai @langchain/langgraph express

Quick Start​

1. Create LangChain Agent​

// agent.ts
import { createAgent as createLangchainAgent } from "langchain";
import { MemorySaver } from "@langchain/langgraph";
import { ChatOpenAI } from "@langchain/openai";
import { clientTools } from "@cloudbase/agent-adapter-langchain";

const checkpointer = new MemorySaver();

export function createAgent() {
  // Use CloudBase's built-in LLM endpoint
  const model = new ChatOpenAI({
    model: process.env.TCB_AI_MODEL || "deepseek-v4-flash",
    apiKey: process.env.TCB_API_KEY!,
    configuration: {
      baseURL: `https://${process.env.TCB_ENV_ID}.api.tcloudbasegateway.com/v1/ai/cloudbase`,
    },
  });

  // Create Agent with clientTools middleware for client-side tool support
  return createLangchainAgent({
    model,
    checkpointer,
    middleware: [clientTools()],
  });
}
tip

CloudBase provides a unified LLM HTTP endpoint supporting models like Tencent Hunyuan and DeepSeek. The endpoint format is:

https://<ENV_ID>.api.tcloudbasegateway.com/v1/ai/<PROVIDER>

Where PROVIDER can be cloudbase.

2. Wrap and Deploy as HTTP Service​

// index.ts
import { createExpressRoutes } from "@cloudbase/agent-server";
import { LangchainAgent } from "@cloudbase/agent-adapter-langchain";
import { createAgent as createLangchainAgent } from "./agent.js";
import express from "express";

function createAgent() {
  const lcAgent = createLangchainAgent();

  return {
    agent: new LangchainAgent({
      agent: lcAgent,
    }),
  };
}

const app = express();

createExpressRoutes({
  createAgent,
  express: app,
});

app.listen(9000, () => console.log("Listening on 9000!"));

3. Configure Environment Variables​

Create a .env file:

TCB_ENV_ID=your-env-id          # CloudBase environment ID
TCB_API_KEY=your-api-key        # CloudBase API Key
TCB_AI_MODEL=deepseek-v4-flash       # Model name

For supported models, refer to the LLM Configuration Guide.

4. Start the Service​

npx tsx src/index.ts

Core API​

LangchainAgent​

Wraps a LangChain Agent as an AG-UI compatible Agent:

import { LangchainAgent } from "@cloudbase/agent-adapter-langchain";

const agent = new LangchainAgent({
  agent: lcAgent,  // LangChain Agent returned by createAgent()
});

Constructor Parameters:

ParameterTypeDescription
agentReturnType<typeof createAgent>Return value from LangChain's createAgent()

clientTools()​

Creates a middleware that allows clients to dynamically inject tools into Agent calls:

import { clientTools } from "@cloudbase/agent-adapter-langchain";

const agent = createLangchainAgent({
  model,
  checkpointer,
  middleware: [clientTools()],
});

Purpose:

  • Allows frontend clients to define tools and pass them dynamically to the Agent at call time
  • The Agent will merge client-side tools with server-side tools

Advanced Usage​

Agent with Server-Side Tools​

import { createAgent as createLangchainAgent } from "langchain";
import { MemorySaver } from "@langchain/langgraph";
import { ChatOpenAI } from "@langchain/openai";
import { tool } from "@langchain/core/tools";
import { z } from "zod";

const checkpointer = new MemorySaver();

// Define server-side tools
const weatherTool = tool(
  async ({ city }) => {
    // In real projects, call a weather API
    return JSON.stringify({
      city,
      temperature: "25°C",
      weather: "Sunny",
    });
  },
  {
    name: "get_weather",
    description: "Get weather information for a specified city",
    schema: z.object({
      city: z.string().describe("City name"),
    }),
  }
);

export function createAgent() {
  const model = new ChatOpenAI({
    model: process.env.OPENAI_MODEL!,
    apiKey: process.env.OPENAI_API_KEY!,
  });

  return createLangchainAgent({
    model,
    checkpointer,
    tools: [weatherTool],
  });
}

Multi-Model Support​

CloudBase has built-in support for multiple LLMs, accessible through a unified HTTP endpoint:

import { ChatOpenAI } from "@langchain/openai";

const envId = process.env.TCB_ENV_ID;
const apiKey = process.env.TCB_API_KEY;

// Tencent Hunyuan
const hunyuanModel = new ChatOpenAI({
  model: "deepseek-v4-flash",
  apiKey,
  configuration: {
    baseURL: `https://${envId}.api.tcloudbasegateway.com/v1/ai/cloudbase`,
  },
});

// DeepSeek
const deepseekModel = new ChatOpenAI({
  model: "deepseek-r1-0528",  // Options: deepseek-r1-0528, deepseek-v3-0324, deepseek-v3.2
  apiKey,
  configuration: {
    baseURL: `https://${envId}.api.tcloudbasegateway.com/v1/ai/cloudbase`,
  },
});

If you need to use external model APIs, you can configure them yourself:

import { ChatOpenAI } from "@langchain/openai";
import { ChatAnthropic } from "@langchain/anthropic";

// OpenAI (requires your own API Key)
const openaiModel = new ChatOpenAI({
  model: "gpt-4",
  apiKey: process.env.OPENAI_API_KEY,
});

// Anthropic (requires your own API Key)
const anthropicModel = new ChatAnthropic({
  model: "claude-3-opus-20240229",
  apiKey: process.env.ANTHROPIC_API_KEY,
});

Streaming Output​

LangchainAgent supports streaming output by default, requiring no additional configuration. Clients will receive streaming TEXT_MESSAGE_CONTENT events.

Deployment​

Cloud Function Deployment​

Refer to HTTP Cloud Function Deployment

CloudRun Deployment​

Refer to CloudRun Deployment

Best Practices​

1. Use Environment Variables​

const model = new ChatOpenAI({
  model: process.env.TCB_AI_MODEL || "deepseek-v4-flash",
  apiKey: process.env.TCB_API_KEY,
  configuration: {
    baseURL: `https://${process.env.TCB_ENV_ID}.api.tcloudbasegateway.com/v1/ai/cloudbase`,
  },
});

2. Set Temperature Appropriately​

  • For deterministic output (e.g., tool calls): temperature: 0
  • For creative output (e.g., writing): temperature: 0.7-1.0

3. Timeout Control​

const model = new ChatOpenAI({
  model: "gpt-4",
  timeout: 30000, // 30 seconds timeout
});

Observability​

CloudBase provides built-in observability capabilities for LangChain applications, configurable via environment variables or code.

# Enable console output
AUTO_TRACES_STDOUT=true

No code changes needed; the SDK will automatically read environment variables and enable tracing.

Code Configuration Method​

import { createExpressRoutes } from "@cloudbase/agent-server";
import { ExporterType } from "@cloudbase/agent-observability/server";

createExpressRoutes({
  createAgent,
  express: app,
  observability: { type: ExporterType.Console }
});

For more configuration options (OTLP export, Serverless considerations, etc.), refer to the Agent Observability Guide.