1 files changed, 371 insertions, 0 deletions
diff --git a/packages/server/src/tools/mcp-client.test.ts b/packages/server/src/tools/mcp-client.test.ts
new file mode 100644
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--- /dev/null
+++ b/packages/server/src/tools/mcp-client.test.ts
@@ -0,0 +1,371 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+  Mocked,
+} from 'vitest';
+import { discoverMcpTools } from './mcp-client.js';
+import { Config, MCPServerConfig } from '../config/config.js';
+import { ToolRegistry } from './tool-registry.js';
+import { DiscoveredMCPTool } from './mcp-tool.js';
+import { Client } from '@modelcontextprotocol/sdk/client/index.js';
+import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
+import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js';
+import { parse, ParseEntry } from 'shell-quote';
+
+// Mock dependencies
+vi.mock('shell-quote');
+
+vi.mock('@modelcontextprotocol/sdk/client/index.js', () => {
+  const MockedClient = vi.fn();
+  MockedClient.prototype.connect = vi.fn();
+  MockedClient.prototype.listTools = vi.fn();
+  // Ensure instances have an onerror property that can be spied on or assigned to
+  MockedClient.mockImplementation(() => ({
+    connect: MockedClient.prototype.connect,
+    listTools: MockedClient.prototype.listTools,
+    onerror: vi.fn(), // Each instance gets its own onerror mock
+  }));
+  return { Client: MockedClient };
+});
+
+// Define a global mock for stderr.on that can be cleared and checked
+const mockGlobalStdioStderrOn = vi.fn();
+
+vi.mock('@modelcontextprotocol/sdk/client/stdio.js', () => {
+  // This is the constructor for StdioClientTransport
+  const MockedStdioTransport = vi.fn().mockImplementation(function (
+    this: any,
+    options: any,
+  ) {
+    // Always return a new object with a fresh reference to the global mock for .on
+    this.options = options;
+    this.stderr = { on: mockGlobalStdioStderrOn };
+    return this;
+  });
+  return { StdioClientTransport: MockedStdioTransport };
+});
+
+vi.mock('@modelcontextprotocol/sdk/client/sse.js', () => {
+  const MockedSSETransport = vi.fn();
+  return { SSEClientTransport: MockedSSETransport };
+});
+
+vi.mock('./tool-registry.js');
+
+describe('discoverMcpTools', () => {
+  let mockConfig: Mocked<Config>;
+  let mockToolRegistry: Mocked<ToolRegistry>;
+
+  beforeEach(() => {
+    mockConfig = {
+      getMcpServers: vi.fn().mockReturnValue({}),
+      getMcpServerCommand: vi.fn().mockReturnValue(undefined),
+    } as any;
+
+    mockToolRegistry = new (ToolRegistry as any)(
+      mockConfig,
+    ) as Mocked<ToolRegistry>;
+    mockToolRegistry.registerTool = vi.fn();
+
+    vi.mocked(parse).mockClear();
+    vi.mocked(Client).mockClear();
+    vi.mocked(Client.prototype.connect)
+      .mockClear()
+      .mockResolvedValue(undefined);
+    vi.mocked(Client.prototype.listTools)
+      .mockClear()
+      .mockResolvedValue({ tools: [] });
+
+    vi.mocked(StdioClientTransport).mockClear();
+    mockGlobalStdioStderrOn.mockClear(); // Clear the global mock in beforeEach
+
+    vi.mocked(SSEClientTransport).mockClear();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('should do nothing if no MCP servers or command are configured', async () => {
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+    expect(mockConfig.getMcpServers).toHaveBeenCalledTimes(1);
+    expect(mockConfig.getMcpServerCommand).toHaveBeenCalledTimes(1);
+    expect(Client).not.toHaveBeenCalled();
+    expect(mockToolRegistry.registerTool).not.toHaveBeenCalled();
+  });
+
+  it('should discover tools via mcpServerCommand', async () => {
+    const commandString = 'my-mcp-server --start';
+    const parsedCommand = ['my-mcp-server', '--start'] as ParseEntry[];
+    mockConfig.getMcpServerCommand.mockReturnValue(commandString);
+    vi.mocked(parse).mockReturnValue(parsedCommand);
+
+    const mockTool = {
+      name: 'tool1',
+      description: 'desc1',
+      inputSchema: { type: 'object' as const, properties: {} },
+    };
+    vi.mocked(Client.prototype.listTools).mockResolvedValue({
+      tools: [mockTool],
+    });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(parse).toHaveBeenCalledWith(commandString, process.env);
+    expect(StdioClientTransport).toHaveBeenCalledWith({
+      command: parsedCommand[0],
+      args: parsedCommand.slice(1),
+      env: expect.any(Object),
+      cwd: undefined,
+      stderr: 'pipe',
+    });
+    expect(Client.prototype.connect).toHaveBeenCalledTimes(1);
+    expect(Client.prototype.listTools).toHaveBeenCalledTimes(1);
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledTimes(1);
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledWith(
+      expect.any(DiscoveredMCPTool),
+    );
+    const registeredTool = mockToolRegistry.registerTool.mock
+      .calls[0][0] as DiscoveredMCPTool;
+    expect(registeredTool.name).toBe('tool1');
+    expect(registeredTool.serverToolName).toBe('tool1');
+  });
+
+  it('should discover tools via mcpServers config (stdio)', async () => {
+    const serverConfig: MCPServerConfig = {
+      command: './mcp-stdio',
+      args: ['arg1'],
+    };
+    mockConfig.getMcpServers.mockReturnValue({ 'stdio-server': serverConfig });
+
+    const mockTool = {
+      name: 'tool-stdio',
+      description: 'desc-stdio',
+      inputSchema: { type: 'object' as const, properties: {} },
+    };
+    vi.mocked(Client.prototype.listTools).mockResolvedValue({
+      tools: [mockTool],
+    });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(StdioClientTransport).toHaveBeenCalledWith({
+      command: serverConfig.command,
+      args: serverConfig.args,
+      env: expect.any(Object),
+      cwd: undefined,
+      stderr: 'pipe',
+    });
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledWith(
+      expect.any(DiscoveredMCPTool),
+    );
+    const registeredTool = mockToolRegistry.registerTool.mock
+      .calls[0][0] as DiscoveredMCPTool;
+    expect(registeredTool.name).toBe('tool-stdio');
+  });
+
+  it('should discover tools via mcpServers config (sse)', async () => {
+    const serverConfig: MCPServerConfig = { url: 'http://localhost:1234/sse' };
+    mockConfig.getMcpServers.mockReturnValue({ 'sse-server': serverConfig });
+
+    const mockTool = {
+      name: 'tool-sse',
+      description: 'desc-sse',
+      inputSchema: { type: 'object' as const, properties: {} },
+    };
+    vi.mocked(Client.prototype.listTools).mockResolvedValue({
+      tools: [mockTool],
+    });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(SSEClientTransport).toHaveBeenCalledWith(new URL(serverConfig.url!));
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledWith(
+      expect.any(DiscoveredMCPTool),
+    );
+    const registeredTool = mockToolRegistry.registerTool.mock
+      .calls[0][0] as DiscoveredMCPTool;
+    expect(registeredTool.name).toBe('tool-sse');
+  });
+
+  it('should prefix tool names if multiple MCP servers are configured', async () => {
+    const serverConfig1: MCPServerConfig = { command: './mcp1' };
+    const serverConfig2: MCPServerConfig = { url: 'http://mcp2/sse' };
+    mockConfig.getMcpServers.mockReturnValue({
+      server1: serverConfig1,
+      server2: serverConfig2,
+    });
+
+    const mockTool1 = {
+      name: 'toolA',
+      description: 'd1',
+      inputSchema: { type: 'object' as const, properties: {} },
+    };
+    const mockTool2 = {
+      name: 'toolB',
+      description: 'd2',
+      inputSchema: { type: 'object' as const, properties: {} },
+    };
+
+    vi.mocked(Client.prototype.listTools)
+      .mockResolvedValueOnce({ tools: [mockTool1] })
+      .mockResolvedValueOnce({ tools: [mockTool2] });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledTimes(2);
+    const registeredTool1 = mockToolRegistry.registerTool.mock
+      .calls[0][0] as DiscoveredMCPTool;
+    const registeredTool2 = mockToolRegistry.registerTool.mock
+      .calls[1][0] as DiscoveredMCPTool;
+
+    expect(registeredTool1.name).toBe('server1__toolA');
+    expect(registeredTool1.serverToolName).toBe('toolA');
+    expect(registeredTool2.name).toBe('server2__toolB');
+    expect(registeredTool2.serverToolName).toBe('toolB');
+  });
+
+  it('should clean schema properties ($schema, additionalProperties)', async () => {
+    const serverConfig: MCPServerConfig = { command: './mcp-clean' };
+    mockConfig.getMcpServers.mockReturnValue({ 'clean-server': serverConfig });
+
+    const rawSchema = {
+      type: 'object' as const,
+      $schema: 'http://json-schema.org/draft-07/schema#',
+      additionalProperties: true,
+      properties: {
+        prop1: { type: 'string', $schema: 'remove-this' },
+        prop2: {
+          type: 'object' as const,
+          additionalProperties: false,
+          properties: { nested: { type: 'number' } },
+        },
+      },
+    };
+    const mockTool = {
+      name: 'cleanTool',
+      description: 'd',
+      inputSchema: JSON.parse(JSON.stringify(rawSchema)),
+    };
+    vi.mocked(Client.prototype.listTools).mockResolvedValue({
+      tools: [mockTool],
+    });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(mockToolRegistry.registerTool).toHaveBeenCalledTimes(1);
+    const registeredTool = mockToolRegistry.registerTool.mock
+      .calls[0][0] as DiscoveredMCPTool;
+    const cleanedParams = registeredTool.schema.parameters as any;
+
+    expect(cleanedParams).not.toHaveProperty('$schema');
+    expect(cleanedParams).not.toHaveProperty('additionalProperties');
+    expect(cleanedParams.properties.prop1).not.toHaveProperty('$schema');
+    expect(cleanedParams.properties.prop2).not.toHaveProperty(
+      'additionalProperties',
+    );
+    expect(cleanedParams.properties.prop2.properties.nested).not.toHaveProperty(
+      '$schema',
+    );
+    expect(cleanedParams.properties.prop2.properties.nested).not.toHaveProperty(
+      'additionalProperties',
+    );
+  });
+
+  it('should handle error if mcpServerCommand parsing fails', async () => {
+    const commandString = 'my-mcp-server "unterminated quote';
+    mockConfig.getMcpServerCommand.mockReturnValue(commandString);
+    vi.mocked(parse).mockImplementation(() => {
+      throw new Error('Parsing failed');
+    });
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    await expect(
+      discoverMcpTools(mockConfig, mockToolRegistry),
+    ).rejects.toThrow('Parsing failed');
+    expect(mockToolRegistry.registerTool).not.toHaveBeenCalled();
+    expect(console.error).not.toHaveBeenCalled();
+  });
+
+  it('should log error and skip server if config is invalid (missing url and command)', async () => {
+    mockConfig.getMcpServers.mockReturnValue({ 'bad-server': {} as any });
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(console.error).toHaveBeenCalledWith(
+      expect.stringContaining(
+        "MCP server 'bad-server' has invalid configuration",
+      ),
+    );
+    // Client constructor should not be called if config is invalid before instantiation
+    expect(Client).not.toHaveBeenCalled();
+  });
+
+  it('should log error and skip server if mcpClient.connect fails', async () => {
+    const serverConfig: MCPServerConfig = { command: './mcp-fail-connect' };
+    mockConfig.getMcpServers.mockReturnValue({
+      'fail-connect-server': serverConfig,
+    });
+    vi.mocked(Client.prototype.connect).mockRejectedValue(
+      new Error('Connection refused'),
+    );
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(console.error).toHaveBeenCalledWith(
+      expect.stringContaining(
+        "failed to start or connect to MCP server 'fail-connect-server'",
+      ),
+    );
+    expect(Client.prototype.listTools).not.toHaveBeenCalled();
+    expect(mockToolRegistry.registerTool).not.toHaveBeenCalled();
+  });
+
+  it('should log error and skip server if mcpClient.listTools fails', async () => {
+    const serverConfig: MCPServerConfig = { command: './mcp-fail-list' };
+    mockConfig.getMcpServers.mockReturnValue({
+      'fail-list-server': serverConfig,
+    });
+    vi.mocked(Client.prototype.listTools).mockRejectedValue(
+      new Error('ListTools error'),
+    );
+    vi.spyOn(console, 'error').mockImplementation(() => {});
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    expect(console.error).toHaveBeenCalledWith(
+      expect.stringContaining(
+        "Failed to list or register tools for MCP server 'fail-list-server'",
+      ),
+    );
+    expect(mockToolRegistry.registerTool).not.toHaveBeenCalled();
+  });
+
+  it('should assign mcpClient.onerror handler', async () => {
+    const serverConfig: MCPServerConfig = { command: './mcp-onerror' };
+    mockConfig.getMcpServers.mockReturnValue({
+      'onerror-server': serverConfig,
+    });
+
+    await discoverMcpTools(mockConfig, mockToolRegistry);
+
+    const clientInstances = vi.mocked(Client).mock.results;
+    expect(clientInstances.length).toBeGreaterThan(0);
+    const lastClientInstance =
+      clientInstances[clientInstances.length - 1]?.value;
+    expect(lastClientInstance?.onerror).toEqual(expect.any(Function));
+  });
+});