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/**
* @license
* Copyright 2025 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
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 } from 'shell-quote';
import { Config, MCPServerConfig } from '../config/config.js';
import { DiscoveredMCPTool } from './mcp-tool.js';
import { ToolRegistry } from './tool-registry.js';
export async function discoverMcpTools(
config: Config,
toolRegistry: ToolRegistry,
): Promise<void> {
const mcpServers = config.getMcpServers() || {};
if (config.getMcpServerCommand()) {
const cmd = config.getMcpServerCommand()!;
const args = parse(cmd, process.env) as string[];
if (args.some((arg) => typeof arg !== 'string')) {
throw new Error('failed to parse mcpServerCommand: ' + cmd);
}
// use generic server name 'mcp'
mcpServers['mcp'] = {
command: args[0],
args: args.slice(1),
};
}
const discoveryPromises = Object.entries(mcpServers).map(
([mcpServerName, mcpServerConfig]) =>
connectAndDiscover(
mcpServerName,
mcpServerConfig,
toolRegistry,
mcpServers,
),
);
await Promise.all(discoveryPromises);
}
async function connectAndDiscover(
mcpServerName: string,
mcpServerConfig: MCPServerConfig,
toolRegistry: ToolRegistry,
mcpServers: Record<string, MCPServerConfig>,
): Promise<void> {
let transport;
if (mcpServerConfig.url) {
transport = new SSEClientTransport(new URL(mcpServerConfig.url));
} else if (mcpServerConfig.command) {
transport = new StdioClientTransport({
command: mcpServerConfig.command,
args: mcpServerConfig.args || [],
env: {
...process.env,
...(mcpServerConfig.env || {}),
} as Record<string, string>,
cwd: mcpServerConfig.cwd,
stderr: 'pipe',
});
} else {
console.error(
`MCP server '${mcpServerName}' has invalid configuration: missing both url (for SSE) and command (for stdio). Skipping.`,
);
return; // Return a resolved promise as this path doesn't throw.
}
const mcpClient = new Client({
name: 'gemini-cli-mcp-client',
version: '0.0.1',
});
try {
await mcpClient.connect(transport);
} catch (error) {
console.error(
`failed to start or connect to MCP server '${mcpServerName}' ` +
`${JSON.stringify(mcpServerConfig)}; \n${error}`,
);
return; // Return a resolved promise, let other MCP servers be discovered.
}
mcpClient.onerror = (error) => {
console.error('MCP ERROR', error.toString());
};
if (transport instanceof StdioClientTransport && transport.stderr) {
transport.stderr.on('data', (data) => {
if (!data.toString().includes('] INFO')) {
console.debug('MCP STDERR', data.toString());
}
});
}
try {
const result = await mcpClient.listTools();
for (const tool of result.tools) {
// Recursively remove additionalProperties and $schema from the inputSchema
// eslint-disable-next-line @typescript-eslint/no-explicit-any -- This function recursively navigates a deeply nested and potentially heterogeneous JSON schema object. Using 'any' is a pragmatic choice here to avoid overly complex type definitions for all possible schema variations.
const removeSchemaProps = (obj: any) => {
if (typeof obj !== 'object' || obj === null) {
return;
}
if (Array.isArray(obj)) {
obj.forEach(removeSchemaProps);
} else {
delete obj.additionalProperties;
delete obj.$schema;
Object.values(obj).forEach(removeSchemaProps);
}
};
removeSchemaProps(tool.inputSchema);
// if there are multiple MCP servers, prefix tool name with mcpServerName to avoid collisions
let toolNameForModel = tool.name;
if (Object.keys(mcpServers).length > 1) {
toolNameForModel = mcpServerName + '__' + toolNameForModel;
}
// replace invalid characters (based on 400 error message) with underscores
toolNameForModel = toolNameForModel.replace(/[^a-zA-Z0-9_.-]/g, '_');
// if longer than 63 characters, replace middle with '___'
// note 400 error message says max length is 64, but actual limit seems to be 63
if (toolNameForModel.length > 63) {
toolNameForModel =
toolNameForModel.slice(0, 28) + '___' + toolNameForModel.slice(-32);
}
toolRegistry.registerTool(
new DiscoveredMCPTool(
mcpClient,
toolNameForModel,
tool.description ?? '',
tool.inputSchema,
tool.name,
mcpServerConfig.timeout,
),
);
}
} catch (error) {
console.error(
`Failed to list or register tools for MCP server '${mcpServerName}': ${error}`,
);
// Do not re-throw, allow other servers to proceed.
}
}
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