Method start

src/client/stdio.ts:112–163

* Starts the server process and prepares to communicate with it.

()

     * Starts the server process and prepares to communicate with it.
     */
    async start(): Promise<void> {
        if (this._process) {
            throw new Error(
                'StdioClientTransport already started! If using Client class, note that connect() calls start() automatically.'
            );
        }

        return new Promise((resolve, reject) => {
            this._process = spawn(this._serverParams.command, this._serverParams.args ?? [], {
                // merge default env with server env because mcp server needs some env vars
                env: {
                    ...getDefaultEnvironment(),
                    ...this._serverParams.env
                },
                stdio: ['pipe', 'pipe', this._serverParams.stderr ?? 'inherit'],
                shell: false,
                windowsHide: process.platform === 'win32',
                cwd: this._serverParams.cwd
            });

            this._process.on('error', error => {
                reject(error);
                this.onerror?.(error);
            });

            this._process.on('spawn', () => {
                resolve();
            });

            this._process.on('close', _code => {
                this._process = undefined;
                this.onclose?.();
            });

            this._process.stdin?.on('error', error => {
                this.onerror?.(error);
            });

            this._process.stdout?.on('data', chunk => {
                this._readBuffer.append(chunk);
                this.processReadBuffer();
            });

            this._process.stdout?.on('error', error => {
                this.onerror?.(error);
            });

            if (this._stderrStream && this._process.stderr) {
                this._process.stderr.pipe(this._stderrStream);
            }
        });
    }

    /**
     * The stderr stream of the child process, if `StdioServerParameters.stderr` was set to "pipe" or "overlapped".