microsoft/playwright · error · Error

Can only connect to the server once

Error message

Can only connect to the server once

What it means

Error "Can only connect to the server once" thrown in microsoft/playwright.

Source

Thrown at packages/injected/src/webSocketMock.ts:267

      // Calling "sendToPage()" from the route handler. Allow this for easier testing.
      this._ensureOpened();
      if (this.readyState !== WebSocketMock.OPEN)
        throw new DOMException(`WebSocket is already in CLOSING or CLOSED state.`);
      this.dispatchEvent(new MessageEvent('message', { data: message, origin: this._origin, cancelable: true }));
    }

    _apiSendToServer(message: WebSocketMessage) {
      if (!this._ws)
        throw new Error('Cannot send a message before connecting to the server');
      if (this._ws.readyState === WebSocketMock.CONNECTING)
        this._wsBufferedMessages.push(message);
      else
        this._ws.send(message);
    }

    _apiConnect() {
      if (this._ws)
        throw new Error('Can only connect to the server once');

      this._ws = new NativeWebSocket(this.url, this._protocols);
      this._ws.binaryType = this._binaryType;

      this._ws.onopen = () => {
        for (const message of this._wsBufferedMessages)
          this._ws!.send(message);
        this._wsBufferedMessages = [];
        this._ensureOpened();
      };

      this._ws.onclose = event => {
        this._onWSClose(event.code, event.reason, event.wasClean);
      };

      this._ws.onmessage = event => {
        if (this._passthrough)
          this._apiSendToPage(event.data);

View on GitHub (pinned to c8fc3bf8d3)

When it happens

Trigger: Thrown at packages/injected/src/webSocketMock.ts:267 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/4e945186c6819e94. Report an issue: GitHub.