feat: Add LangChain Provider for AI SDK

.github/workflows/release-please.yml

@@ -27,6 +27,7 @@ jobs:
       package-react-universal-release: ${{ steps.release.outputs['packages/sdk/react-universal--release_created'] }}
       package-browser-released: ${{ steps.release.outputs['packages/sdk/browser--release_created'] }}
       package-server-ai-released: ${{ steps.release.outputs['packages/sdk/server-ai--release_created'] }}
+      package-server-ai-langchain-released: ${{ steps.release.outputs['packages/ai-providers/server-ai-langchain--release_created'] }}
       package-browser-telemetry-released: ${{ steps.release.outputs['packages/telemetry/browser-telemetry--release_created'] }}
       package-combined-browser-released: ${{ steps.release.outputs['packages/sdk/combined-browser--release_created'] }}
     steps:
@@ -460,3 +461,23 @@ jobs:
         with:
           workspace_path: packages/sdk/combined-browser
           aws_assume_role: ${{ vars.AWS_ROLE_ARN }}
+
+  release-server-ai-langchain:
+    runs-on: ubuntu-latest
+    needs: ['release-please', 'release-server-ai']
+    permissions:
+      id-token: write
+      contents: write
+    if: ${{ always() && !failure() && !cancelled() && needs.release-please.outputs.package-server-ai-langchain-released == 'true'}}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22.x
+          registry-url: 'https://registry.npmjs.org'
+      - id: release-server-ai-langchain
+        name: Full release of packages/ai-providers/server-ai-langchain
+        uses: ./actions/full-release
+        with:
+          workspace_path: packages/ai-providers/server-ai-langchain
+          aws_assume_role: ${{ vars.AWS_ROLE_ARN }}

.release-please-manifest.json

@@ -1,22 +1,23 @@
 {
-  "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": "0.0.0",
+  "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/server-ai": "0.12.0",
+  "packages/sdk/server-node": "9.10.2",
   "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": "0.12.0",
   "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 +1,179 @@
+import { AIMessage, HumanMessage, SystemMessage } from '@langchain/core/messages';
+
+import { LangChainProvider } from '../src/LangChainProvider';
+
+// Mock LangChain dependencies
+jest.mock('langchain/chat_models/universal', () => ({
+  initChatModel: jest.fn(),
+}));
+
+// Mock logger
+const mockLogger = {
+  warn: jest.fn(),
+  info: jest.fn(),
+  error: jest.fn(),
+  debug: jest.fn(),
+};
+
+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);
+    });
+  });
+
+  describe('createAIMetrics', () => {
+    it('creates metrics with success=true and token usage', () => {
+      const mockResponse = new AIMessage('Test response');
+      mockResponse.response_metadata = {
+        tokenUsage: {
+          totalTokens: 100,
+          promptTokens: 50,
+          completionTokens: 50,
+        },
+      };
+
+      const result = LangChainProvider.createAIMetrics(mockResponse);
+
+      expect(result).toEqual({
+        success: true,
+        usage: {
+          total: 100,
+          input: 50,
+          output: 50,
+        },
+      });
+    });
+
+    it('creates metrics with success=true and no usage when metadata is missing', () => {
+      const mockResponse = new AIMessage('Test response');
+
+      const result = LangChainProvider.createAIMetrics(mockResponse);
+
+      expect(result).toEqual({
+        success: true,
+        usage: undefined,
+      });
+    });
+  });
+
+  describe('invokeModel', () => {
+    let mockLLM: any;
+    let provider: LangChainProvider;
+
+    beforeEach(() => {
+      mockLLM = {
+        invoke: jest.fn(),
+      };
+      provider = new LangChainProvider(mockLLM, mockLogger);
+      jest.clearAllMocks();
+    });
+
+    it('returns success=true for string content', async () => {
+      const mockResponse = new AIMessage('Test response');
+      mockLLM.invoke.mockResolvedValue(mockResponse);
+
+      const messages = [{ role: 'user' as const, content: 'Hello' }];
+      const result = await provider.invokeModel(messages);
+
+      expect(result.metrics.success).toBe(true);
+      expect(result.message.content).toBe('Test response');
+      expect(mockLogger.warn).not.toHaveBeenCalled();
+    });
+
+    it('returns success=false for non-string content and logs warning', async () => {
+      const mockResponse = new AIMessage({ type: 'image', data: 'base64data' } as any);
+      mockLLM.invoke.mockResolvedValue(mockResponse);
+
+      const messages = [{ role: 'user' as const, content: 'Hello' }];
+      const result = await provider.invokeModel(messages);
+
+      expect(result.metrics.success).toBe(false);
+      expect(result.message.content).toBe('');
+      expect(mockLogger.warn).toHaveBeenCalledWith(
+        'Multimodal response not supported, expecting a string. Content type: object, Content:',
+        JSON.stringify({ type: 'image', data: 'base64data' }, null, 2),
+      );
+    });
+
+    it('returns success=false for array content and logs warning', async () => {
+      const mockResponse = new AIMessage(['text', { type: 'image', data: 'base64data' }] as any);
+      mockLLM.invoke.mockResolvedValue(mockResponse);
+
+      const messages = [{ role: 'user' as const, content: 'Hello' }];
+      const result = await provider.invokeModel(messages);
+
+      expect(result.metrics.success).toBe(false);
+      expect(result.message.content).toBe('');
+      expect(mockLogger.warn).toHaveBeenCalledWith(
+        'Multimodal response not supported, expecting a string. Content type: object, Content:',
+        JSON.stringify(['text', { type: 'image', data: 'base64data' }], null, 2),
+      );
+    });
+  });
+
+  describe('mapProvider', () => {
+    it('maps gemini to google-genai', () => {
+      expect(LangChainProvider.mapProvider('gemini')).toBe('google-genai');
+      expect(LangChainProvider.mapProvider('Gemini')).toBe('google-genai');
+      expect(LangChainProvider.mapProvider('GEMINI')).toBe('google-genai');
+    });
+
+    it('returns provider name unchanged for unmapped providers', () => {
+      expect(LangChainProvider.mapProvider('openai')).toBe('openai');
+      expect(LangChainProvider.mapProvider('anthropic')).toBe('anthropic');
+      expect(LangChainProvider.mapProvider('unknown')).toBe('unknown');
+    });
+  });
+});

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

@@ -0,0 +1,7 @@
+module.exports = {
+  transform: { '^.+\\.ts?$': 'ts-jest' },
+  testMatch: ['**/__tests__/**/*test.ts?(x)'],
+  testEnvironment: 'node',
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
+  collectCoverageFrom: ['src/**/*.ts'],
+};

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

@@ -0,0 +1,55 @@
+{
+  "name": "@launchdarkly/server-sdk-ai-langchain",
+  "version": "0.0.0",
+  "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": "^0.12.0",
+    "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"
+  }
+}