feat: Add LangChain Provider for AI SDK

.release-please-manifest.json

@@ -1,22 +1,25 @@
 {
-  "packages/shared/common": "2.19.0",
-  "packages/shared/sdk-server": "2.16.2",
-  "packages/sdk/server-node": "9.10.2",
+  "packages/ai-providers/server-ai-langchain": "0.1.0-alpha.0",
+  "packages/sdk/akamai-base": "3.0.10",
+  "packages/sdk/akamai-edgekv": "1.4.12",
+  "packages/sdk/browser": "0.8.1",
   "packages/sdk/cloudflare": "2.7.10",
+  "packages/sdk/combined-browser": "0.0.0",
   "packages/sdk/fastly": "0.2.1",
-  "packages/shared/sdk-server-edge": "2.6.9",
+  "packages/sdk/react-native": "10.11.0",
+  "packages/sdk/react-universal": "0.0.1",
+  "packages/sdk/server-ai": "0.11.4",
+  "packages/sdk/server-node": "9.10.2",
+  "packages/sdk/svelte": "0.1.0",
   "packages/sdk/vercel": "1.3.34",
-  "packages/sdk/akamai-base": "3.0.10",
-  "packages/sdk/akamai-edgekv": "1.4.12",
   "packages/shared/akamai-edgeworker-sdk": "2.0.10",
+  "packages/shared/common": "2.19.0",
+  "packages/shared/sdk-client": "1.15.1",
+  "packages/shared/sdk-server": "2.16.2",
+  "packages/shared/sdk-server-edge": "2.6.9",
   "packages/store/node-server-sdk-dynamodb": "6.2.14",
   "packages/store/node-server-sdk-redis": "4.2.14",
-  "packages/shared/sdk-client": "1.15.1",
-  "packages/sdk/react-native": "10.11.0",
-  "packages/telemetry/node-server-sdk-otel": "1.3.2",
-  "packages/sdk/browser": "0.8.1",
-  "packages/sdk/server-ai": "0.11.4",
   "packages/telemetry/browser-telemetry": "1.0.11",
-  "packages/tooling/jest": "0.1.11",
-  "packages/sdk/combined-browser": "0.0.0"
+  "packages/telemetry/node-server-sdk-otel": "1.3.2",
+  "packages/tooling/jest": "0.1.11"
 }

package.json

@@ -1,6 +1,7 @@
 {
   "name": "@launchdarkly/js-core",
   "workspaces": [
+    "packages/ai-providers/server-ai-langchain",
     "packages/shared/common",
     "packages/shared/sdk-client",
     "packages/shared/sdk-server",

packages/ai-providers/server-ai-langchain/__tests__/LangChainProvider.test.ts

@@ -0,0 +1,62 @@
+import { AIMessage, HumanMessage, SystemMessage } from 'langchain/schema';
+
+import { LangChainProvider } from '../src/LangChainProvider';
+
+describe('LangChainProvider', () => {
+  describe('convertMessagesToLangChain', () => {
+    it('converts system messages to SystemMessage', () => {
+      const messages = [{ role: 'system' as const, content: 'You are a helpful assistant.' }];
+      const result = LangChainProvider.convertMessagesToLangChain(messages);
+
+      expect(result).toHaveLength(1);
+      expect(result[0]).toBeInstanceOf(SystemMessage);
+      expect(result[0].content).toBe('You are a helpful assistant.');
+    });
+
+    it('converts user messages to HumanMessage', () => {
+      const messages = [{ role: 'user' as const, content: 'Hello, how are you?' }];
+      const result = LangChainProvider.convertMessagesToLangChain(messages);
+
+      expect(result).toHaveLength(1);
+      expect(result[0]).toBeInstanceOf(HumanMessage);
+      expect(result[0].content).toBe('Hello, how are you?');
+    });
+
+    it('converts assistant messages to AIMessage', () => {
+      const messages = [{ role: 'assistant' as const, content: 'I am doing well, thank you!' }];
+      const result = LangChainProvider.convertMessagesToLangChain(messages);
+
+      expect(result).toHaveLength(1);
+      expect(result[0]).toBeInstanceOf(AIMessage);
+      expect(result[0].content).toBe('I am doing well, thank you!');
+    });
+
+    it('converts multiple messages in order', () => {
+      const messages = [
+        { role: 'system' as const, content: 'You are a helpful assistant.' },
+        { role: 'user' as const, content: 'What is the weather like?' },
+        { role: 'assistant' as const, content: 'I cannot check the weather.' },
+      ];
+      const result = LangChainProvider.convertMessagesToLangChain(messages);
+
+      expect(result).toHaveLength(3);
+      expect(result[0]).toBeInstanceOf(SystemMessage);
+      expect(result[1]).toBeInstanceOf(HumanMessage);
+      expect(result[2]).toBeInstanceOf(AIMessage);
+    });
+
+    it('throws error for unsupported message role', () => {
+      const messages = [{ role: 'unknown' as any, content: 'Test message' }];
+
+      expect(() => LangChainProvider.convertMessagesToLangChain(messages)).toThrow(
+        'Unsupported message role: unknown'
+      );
+    });
+
+    it('handles empty message array', () => {
+      const result = LangChainProvider.convertMessagesToLangChain([]);
+
+      expect(result).toHaveLength(0);
+    });
+  });
+});

packages/ai-providers/server-ai-langchain/jest.config.js

@@ -0,0 +1,9 @@
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>/src'],
+  testMatch: ['**/__tests__/**/*.test.ts'],
+  collectCoverageFrom: ['src/**/*.ts', '!src/**/*.d.ts'],
+  coverageDirectory: 'coverage',
+  coverageReporters: ['text', 'lcov', 'html'],
+};

packages/ai-providers/server-ai-langchain/package.json

@@ -0,0 +1,55 @@
+{
+  "name": "@launchdarkly/server-sdk-ai-langchain",
+  "version": "0.1.0-alpha.0",
+  "description": "LaunchDarkly AI SDK LangChain Provider for Server-Side JavaScript",
+  "homepage": "https://github.com/launchdarkly/js-core/tree/main/packages/ai-providers/server-ai-langchain",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/launchdarkly/js-core.git"
+  },
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "type": "commonjs",
+  "scripts": {
+    "build": "npx tsc",
+    "lint": "npx eslint . --ext .ts",
+    "prettier": "prettier --write '**/*.@(js|ts|tsx|json|css)' --ignore-path ../../../.prettierignore",
+    "lint:fix": "yarn run lint --fix",
+    "check": "yarn prettier && yarn lint && yarn build && yarn test",
+    "test": "jest"
+  },
+  "keywords": [
+    "launchdarkly",
+    "ai",
+    "llm",
+    "langchain"
+  ],
+  "author": "LaunchDarkly",
+  "license": "Apache-2.0",
+  "dependencies": {
+    "@langchain/core": ">=0.2.21 <0.3.0",
+    "@launchdarkly/server-sdk-ai": "0.11.4",
+    "langchain": "^0.2.11"
+  },
+  "devDependencies": {
+    "@launchdarkly/js-server-sdk-common": "2.16.2",
+    "@trivago/prettier-plugin-sort-imports": "^4.1.1",
+    "@types/jest": "^29.5.3",
+    "@typescript-eslint/eslint-plugin": "^6.20.0",
+    "@typescript-eslint/parser": "^6.20.0",
+    "eslint": "^8.45.0",
+    "eslint-config-airbnb-base": "^15.0.0",
+    "eslint-config-airbnb-typescript": "^17.1.0",
+    "eslint-config-prettier": "^8.8.0",
+    "eslint-plugin-import": "^2.27.5",
+    "eslint-plugin-jest": "^27.6.3",
+    "eslint-plugin-prettier": "^5.0.0",
+    "jest": "^29.6.1",
+    "prettier": "^3.0.0",
+    "ts-jest": "^29.1.1",
+    "typescript": "5.1.6"
+  },
+  "peerDependencies": {
+    "@launchdarkly/js-server-sdk-common": "2.x"
+  }
+}

packages/ai-providers/server-ai-langchain/src/LangChainProvider.ts

@@ -0,0 +1,123 @@
+import { BaseChatModel } from '@langchain/core/language_models/chat_models';
+import { AIMessage, HumanMessage, SystemMessage } from '@langchain/core/messages';
+import { initChatModel } from 'langchain/chat_models/universal';
+
+import {
+  LDAIConfig,
+  LDAIConfigTracker,
+  LDMessage,
+  LDTokenUsage,
+} from '@launchdarkly/server-sdk-ai';
+
+/**
+ * LangChain provider utilities and helper functions.
+ */
+export class LangChainProvider {
+  /**
+   * Map LaunchDarkly provider names to LangChain provider names.
+   * This method enables seamless integration between LaunchDarkly's standardized
+   * provider naming and LangChain's naming conventions.
+   */
+  static mapProvider(ldProviderName: string): string {
+    const lowercasedName = ldProviderName.toLowerCase();
+
+    const mapping: Record<string, string> = {
+      gemini: 'google-genai',
+    };
+
+    return mapping[lowercasedName] || lowercasedName;
+  }
+
+  /**
+   * Create token usage information from a LangChain provider response.
+   * This method extracts token usage information from LangChain responses
+   * and returns a LaunchDarkly TokenUsage object.
+   */
+  static createTokenUsage(langChainResponse: AIMessage): LDTokenUsage | undefined {
+    if (!langChainResponse?.response_metadata?.tokenUsage) {
+      return undefined;
+    }
+
+    const { tokenUsage } = langChainResponse.response_metadata;
+
+    return {
+      total: tokenUsage.totalTokens || 0,
+      input: tokenUsage.promptTokens || 0,
+      output: tokenUsage.completionTokens || 0,
+    };
+  }
+
+  /**
+   * Convert LaunchDarkly messages to LangChain messages.
+   * This helper method enables developers to work directly with LangChain message types
+   * while maintaining compatibility with LaunchDarkly's standardized message format.
+   */
+  static convertMessagesToLangChain(
+    messages: LDMessage[],
+  ): (HumanMessage | SystemMessage | AIMessage)[] {
+    return messages.map((msg) => {
+      switch (msg.role) {
+        case 'system':
+          return new SystemMessage(msg.content);
+        case 'user':
+          return new HumanMessage(msg.content);
+        case 'assistant':
+          return new AIMessage(msg.content);
+        default:
+          throw new Error(`Unsupported message role: ${msg.role}`);
+      }
+    });
+  }
+
+  /**
+   * Track metrics for a LangChain callable execution.
+   * This helper method enables developers to work directly with LangChain callables
+   * while ensuring consistent tracking behavior.
+   */
+  static async trackMetricsOf(
+    tracker: LDAIConfigTracker,
+    callable: () => Promise<AIMessage>,
+  ): Promise<AIMessage> {
+    return tracker.trackDurationOf(async () => {
+      try {
+        const result = await callable();
+
+        // Extract and track token usage if available
+        const tokenUsage = this.createTokenUsage(result);
+        if (tokenUsage) {
+          tracker.trackTokens({
+            total: tokenUsage.total,
+            input: tokenUsage.input,
+            output: tokenUsage.output,
+          });
+        }
+
+        tracker.trackSuccess();
+        return result;
+      } catch (error) {
+        tracker.trackError();
+        throw error;
+      }
+    });
+  }
+
+  /**
+   * Create a LangChain model from an AI configuration.
+   * This public helper method enables developers to initialize their own LangChain models
+   * using LaunchDarkly AI configurations.
+   *
+   * @param aiConfig The LaunchDarkly AI configuration
+   * @returns A Promise that resolves to a configured LangChain BaseChatModel
+   */
+  static async createLangChainModel(aiConfig: LDAIConfig): Promise<BaseChatModel> {
+    const modelName = aiConfig.model?.name || '';
+    const provider = aiConfig.provider?.name || '';
+    const parameters = aiConfig.model?.parameters || {};
+
+    // Use LangChain's universal initChatModel to support multiple providers
+    return initChatModel(modelName, {
+      modelProvider: this.mapProvider(provider),
+      ...parameters,
+    });
+  }
+}

packages/ai-providers/server-ai-langchain/src/LangChainTrackedChat.ts

@@ -0,0 +1,86 @@
+import { BaseChatModel } from '@langchain/core/language_models/chat_models';
+import { AIMessage, HumanMessage, SystemMessage } from '@langchain/core/messages';
+
+import {
+  BaseTrackedChat,
+  ChatResponse,
+  LDAIConfig,
+  LDAIConfigTracker,
+  LDMessage,
+} from '@launchdarkly/server-sdk-ai';
+
+import { LangChainProvider } from './LangChainProvider';
+
+/**
+ * LangChain-specific implementation of TrackedChat.
+ * This implementation integrates LangChain models with LaunchDarkly's tracking capabilities.
+ */
+export class LangChainTrackedChat extends BaseTrackedChat {
+  private _llm: BaseChatModel;
+
+  constructor(aiConfig: LDAIConfig, tracker: LDAIConfigTracker, llm: BaseChatModel) {
+    super(aiConfig, tracker);
+    this._llm = llm;
+  }
+
+  /**
+   * Provider-specific implementation that converts LDMessage[] to LangChain format,
+   * invokes the model, and returns a ChatResponse.
+   */
+  protected async invokeModel(messages: LDMessage[]): Promise<ChatResponse> {
+    // Convert LDMessage[] to LangChain messages
+    const langchainMessages = LangChainProvider.convertMessagesToLangChain(messages);
+
+    // Get the LangChain response
+    const response = await this._llm.invoke(langchainMessages);
+
+    // Extract token usage if available using the helper method
+    const usage = LangChainProvider.createTokenUsage(response);
+
+    // Handle different content types from LangChain
+    let content: string;
+    if (typeof response.content === 'string') {
+      content = response.content;
+    } else if (Array.isArray(response.content)) {
+      // Handle complex content (e.g., with images)
+      content = response.content
+        .map((item: any) => {
+          if (typeof item === 'string') return item;
+          if (item.type === 'text') return item.text;
+          return '';
+        })
+        .join('');
+    } else {
+      content = String(response.content);
+    }
+
+    // Create the assistant message
+    const assistantMessage: LDMessage = {
+      role: 'assistant',
+      content,
+    };
+
+    return {
+      message: assistantMessage,
+      usage,
+    };
+  }
+
+  /**
+   * LangChain-specific invoke method that accepts LangChain-native message types.
+   * This is the main implementation that does all the tracking and LangChain logic.
+   */
+  async trackLangChainInvoke(
+    messages: (HumanMessage | SystemMessage | AIMessage)[],
+  ): Promise<AIMessage> {
+    // Use the trackMetricsOf helper to handle all tracking automatically
+    return LangChainProvider.trackMetricsOf(this.tracker, () => this._llm.invoke(messages));
+  }
+
+  /**
+   * Get the underlying LangChain model instance.
+   */
+  async getChatModel(): Promise<BaseChatModel> {
+    return this._llm;
+  }
+}

packages/ai-providers/server-ai-langchain/src/index.ts

@@ -0,0 +1,11 @@
+/**
+ * This is the API reference for the LaunchDarkly AI SDK LangChain Provider for Server-Side JavaScript.
+ *
+ * This package provides LangChain integration for the LaunchDarkly AI SDK, allowing you to use
+ * LangChain models and chains with LaunchDarkly's tracking and configuration capabilities.
+ *
+ * @packageDocumentation
+ */
+
+export * from './LangChainTrackedChat';
+export * from './LangChainProvider';