import { Transport } from "../shared/transport.js";
import { JSONRPCMessage, JSONRPCMessageSchema } from "../types.js";
const SUBPROTOCOL = "mcp";
/**
* Client transport for WebSocket: this will connect to a server over the WebSocket protocol.
*/
export class WebSocketClientTransport implements Transport {
private _socket?: WebSocket;
private _url: URL;
onclose?: () => void;
onerror?: (error: Error) => void;
onmessage?: (message: JSONRPCMessage) => void;
constructor(url: URL) {
this._url = url;
}
start(): Promise<void> {
if (this._socket) {
throw new Error(
"WebSocketClientTransport already started! If using Client class, note that connect() calls start() automatically.",
);
}
return new Promise((resolve, reject) => {
this._socket = new WebSocket(this._url, SUBPROTOCOL);
this._socket.onerror = (event) => {
const error =
"error" in event
? (event.error as Error)
: new Error(`WebSocket error: ${JSON.stringify(event)}`);
reject(error);
this.onerror?.(error);
};
this._socket.onopen = () => {
resolve();
};
this._socket.onclose = () => {
this.onclose?.();
};
this._socket.onmessage = (event: MessageEvent) => {
let message: JSONRPCMessage;
try {
message = JSONRPCMessageSchema.parse(JSON.parse(event.data));
} catch (error) {
this.onerror?.(error as Error);
return;
}
this.onmessage?.(message);
};
});
}
async close(): Promise<void> {
this._socket?.close();
}
send(message: JSONRPCMessage): Promise<void> {
return new Promise((resolve, reject) => {
if (!this._socket) {
reject(new Error("Not connected"));
return;
}
this._socket?.send(JSON.stringify(message));
resolve();
});
}
}