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/**
* @license
* Copyright 2025 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
import * as vscode from 'vscode';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import express, { Request, Response } from 'express';
import { randomUUID } from 'node:crypto';
import {
isInitializeRequest,
type JSONRPCNotification,
} from '@modelcontextprotocol/sdk/types.js';
export async function startIDEServer(context: vscode.ExtensionContext) {
const app = express();
app.use(express.json());
const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
const disposable = vscode.window.onDidChangeActiveTextEditor((editor) => {
const filePath = editor ? editor.document.uri.fsPath : null;
const notification: JSONRPCNotification = {
jsonrpc: '2.0',
method: 'ide/activeFileChanged',
params: { filePath },
};
for (const transport of Object.values(transports)) {
transport.send(notification);
}
});
context.subscriptions.push(disposable);
app.post('/mcp', async (req: Request, res: Response) => {
const sessionId = req.headers['mcp-session-id'] as string | undefined;
let transport: StreamableHTTPServerTransport;
if (sessionId && transports[sessionId]) {
transport = transports[sessionId];
} else if (!sessionId && isInitializeRequest(req.body)) {
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID(),
onsessioninitialized: (newSessionId) => {
transports[newSessionId] = transport;
const editor = vscode.window.activeTextEditor;
const filePath = editor ? editor.document.uri.fsPath : null;
const notification: JSONRPCNotification = {
jsonrpc: '2.0',
method: 'ide/activeFileChanged',
params: { filePath },
};
transport.send(notification);
},
});
transport.onclose = () => {
if (transport.sessionId) {
delete transports[transport.sessionId];
}
};
const server = createMcpServer();
server.connect(transport);
} else {
res.status(400).json({
jsonrpc: '2.0',
error: {
code: -32000,
message:
'Bad Request: No valid session ID provided for non-initialize request.',
},
id: null,
});
return;
}
try {
await transport.handleRequest(req, res, req.body);
} catch (error) {
console.error('Error handling MCP request:', error);
if (!res.headersSent) {
res.status(500).json({
jsonrpc: '2.0' as const,
error: {
code: -32603,
message: 'Internal server error',
},
id: null,
});
}
}
});
const handleSessionRequest = async (req: Request, res: Response) => {
const sessionId = req.headers['mcp-session-id'] as string | undefined;
if (!sessionId || !transports[sessionId]) {
res.status(400).send('Invalid or missing session ID');
return;
}
const transport = transports[sessionId];
try {
await transport.handleRequest(req, res);
} catch (error) {
console.error('Error handling MCP GET request:', error);
if (!res.headersSent) {
res.status(400).send('Bad Request');
}
}
};
app.get('/mcp', handleSessionRequest);
// TODO(#3918): Generate dynamically and write to env variable
const PORT = 3000;
app.listen(PORT, (error?: Error) => {
if (error) {
console.error('Failed to start server:', error);
vscode.window.showErrorMessage(
`Companion server failed to start on port ${PORT}: ${error.message}`,
);
}
console.log(`MCP Streamable HTTP Server listening on port ${PORT}`);
});
}
const createMcpServer = () => {
const server = new McpServer(
{
name: 'gemini-cli-companion-mcp-server',
version: '1.0.0',
},
{ capabilities: { logging: {} } },
);
server.registerTool(
'getActiveFile',
{
description:
'(IDE Tool) Get the path of the file currently active in VS Code.',
inputSchema: {},
},
async () => {
try {
const activeEditor = vscode.window.activeTextEditor;
const filePath = activeEditor
? activeEditor.document.uri.fsPath
: undefined;
if (filePath) {
return {
content: [{ type: 'text', text: `Active file: ${filePath}` }],
};
} else {
return {
content: [
{
type: 'text',
text: 'No file is currently active in the editor.',
},
],
};
}
} catch (error) {
return {
content: [
{
type: 'text',
text: `Failed to get active file: ${
(error as Error).message || 'Unknown error'
}`,
},
],
};
}
},
);
return server;
};
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