chore: Add example for LangChain provider integration

package.json

@@ -34,6 +34,7 @@
     "packages/sdk/server-ai/examples/bedrock",
     "packages/sdk/server-ai/examples/openai",
     "packages/sdk/server-ai/examples/vercel-ai",
+    "packages/sdk/server-ai/examples/langchain-chat",
     "packages/telemetry/browser-telemetry",
     "contract-tests",
     "packages/sdk/combined-browser"

packages/sdk/server-ai/examples/langchain-chat/README.md

@@ -0,0 +1,76 @@
+# LangChain Chat Example
+
+This example demonstrates how to use the LaunchDarkly AI SDK with LangChain for chat interactions.
+
+## Prerequisites
+
+1. A LaunchDarkly account and SDK key
+2. An OpenAI API key (for the LangChain integration)
+3. Node.js 16 or later
+
+## Setup
+
+1. Install dependencies:
+   ```bash
+   yarn install
+   ```
+
+2. Set up environment variables:
+   ```bash
+   cp .env.example .env
+   ```
+
+   Edit `.env` and add your keys:
+   ```
+   LAUNCHDARKLY_SDK_KEY=your-sdk-key-here
+   OPENAI_API_KEY=your-openai-api-key-here
+   LAUNCHDARKLY_AI_CONFIG_KEY=sample-ai-chat-config
+   ```
+
+3. Create an AI Config in LaunchDarkly with the key `sample-ai-config`:
+   ```json
+   {
+     "_ldMeta": {
+       "variationKey": "1234",
+       "enabled": true,
+       "version": 1
+     },
+     "messages": [
+       {
+         "content": "You are a helpful assistant for {{customerName}}. You should be friendly and informative.",
+         "role": "system"
+       }
+     ],
+     "model": {
+       "name": "gpt-3.5-turbo",
+       "parameters": {
+         "temperature": 0.7,
+         "maxTokens": 1000
+       }
+     },
+     "provider": {
+       "name": "langchain"
+     }
+   }
+   ```
+
+## Running the Example
+
+```bash
+yarn start
+```
+
+This will:
+1. Initialize the LaunchDarkly client
+2. Create a chat configuration using the AI Config
+3. Send a message to the AI and display the response
+4. Continue the conversation with a follow-up question
+5. Automatically track interaction metrics (duration, tokens, success/error)
+
+## Features Demonstrated
+
+- **AI Config Integration**: Using LaunchDarkly to configure AI models and prompts
+- **Variable Interpolation**: Using Mustache templates with runtime variables
+- **Chat Conversations**: Multi-turn conversations with message history
+- **Provider Integration**: Using LangChain as the AI provider
+- **Metrics Tracking**: Automatic tracking of token usage and performance

packages/sdk/server-ai/examples/langchain-chat/package.json

@@ -0,0 +1,24 @@
+{
+  "name": "langchain-chat-example",
+  "version": "1.0.0",
+  "description": "Example demonstrating LaunchDarkly AI SDK with LangChain",
+  "type": "module",
+  "scripts": {
+    "build": "tsc",
+    "start": "yarn build && node ./dist/index.js"
+  },
+  "dependencies": {
+    "@langchain/core": "^0.3.78",
+    "@langchain/google-genai": "^0.2.18",
+    "@launchdarkly/node-server-sdk": "^9.0.0",
+    "@launchdarkly/server-sdk-ai": "0.11.4",
+    "@launchdarkly/server-sdk-ai-langchain": "0.1.0",
+    "dotenv": "^16.0.0",
+    "langchain": "^0.1.0"
+  },
+  "devDependencies": {
+    "@types/node": "^20.0.0",
+    "tsx": "^4.0.0",
+    "typescript": "^5.0.0"
+  }
+}

packages/sdk/server-ai/examples/langchain-chat/src/index.ts

@@ -0,0 +1,74 @@
+/* eslint-disable no-console */
+import { init, type LDContext } from '@launchdarkly/node-server-sdk';
+import { initAi } from '@launchdarkly/server-sdk-ai';
+
+// Environment variables
+const sdkKey = process.env.LAUNCHDARKLY_SDK_KEY;
+const aiConfigKey = process.env.LAUNCHDARKLY_AI_CONFIG_KEY || 'sample-ai-config';
+
+// Validate required environment variables
+if (!sdkKey) {
+  console.error('*** Please set the LAUNCHDARKLY_SDK_KEY env first');
+  process.exit(1);
+}
+
+// Initialize LaunchDarkly client
+const ldClient = init(sdkKey, { eventsUri: 'https://fd9486c18583.ngrok-free.app' });
+
+// Set up the context properties. This context should appear on your LaunchDarkly contexts dashboard
+// soon after you run the demo.
+const context: LDContext = {
+  kind: 'user',
+  key: 'example-user-key',
+  name: 'Sandy',
+};
+
+async function main(): Promise<void> {
+  try {
+    await ldClient.waitForInitialization({ timeout: 10 });
+    console.log('*** SDK successfully initialized');
+  } catch (error) {
+    console.log(`*** SDK failed to initialize: ${error}`);
+    process.exit(1);
+  }
+
+  const aiClient = initAi(ldClient);
+  const defaultValue = {
+    enabled: true,
+    model: { name: 'gpt-3.5-turbo' },
+    messages: [{ role: 'system' as const, content: 'You are a helpful assistant.' }],
+    provider: { name: 'openai' },
+  };
+
+  // You provide a disabled default value
+  // const defaultValue = {
+  //   enabled: false,
+  // };
+
+  // Get AI chat configuration from LaunchDarkly
+  const chat = await aiClient.initChat(aiConfigKey, context, defaultValue, {
+    myVariable: 'My User Defined Variable',
+  });
+
+  if (!chat) {
+    console.log('*** AI chat configuration is not enabled');
+    process.exit(0);
+  }
+
+  // Example of using the chat functionality
+  console.log('\n*** Starting chat conversation:');
+  try {
+    const userInput = 'Hello! Can you help me understand what LaunchDarkly is?';
+    console.log('User Input:', userInput);
+
+    const response = await chat.invoke(userInput);
+
+    console.log('AI Response:', response.message.content);
+
+    console.log('Success.');
+  } catch (err) {
+    console.error('Error:', err);
+  }
+}
+
+main();

packages/sdk/server-ai/examples/langchain-chat/tsconfig.json

@@ -0,0 +1,18 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "node",
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "declaration": true,
+    "sourceMap": true
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}