Websocket connect, clear error response

[raspberry-jenshen]

First of all, want to say thank you all for the impressive and powerful framework!
I like it! Keep rocking!

Issue:

Evvironment

flutter 3.0.0 (latest)
dart 2.17.0 (latest)

Use case

When connecting to WebSocket there is no way to understand why it's failing during updating to WebSocket.

1. In case the backend is down (500 error)
2. Connecting via WebSocket.connect
3. Getting an error
   ` WebSocketException: Connection to 'https://....../sockets#' was not upgraded to web socket

No response code.
No response body.
Just hardcoded error message each time.

What will be if I want to have a different logic based on the server error code?
All existing WebSockets for various platforms has this option.

Proposal

To have a root cause in WebSocketException or even create a separate WebSocketUpgradeException

class WebSocketException implements IOException {
  final String message;
  /// The exception that caused this one, if available.
  final Object? inner;
.....

Improve the error exposing like:

class _WebSocketImpl {
   ..... 
   static Future<WebSocket> connect(....) {
    ......
    Future<WebSocket> error(Exception message) {
        // Flush data.
        response.detachSocket().then((socket) {
          socket.destroy();
        });
        return Future<WebSocket>.error(message, callerStackTrace);
      }

      var connectionHeader = response.headers[HttpHeaders.connectionHeader];
      if (response.statusCode != HttpStatus.switchingProtocols ||
          connectionHeader == null ||
          !connectionHeader.any((value) => value.toLowerCase() == "upgrade") ||
          response.headers.value(HttpHeaders.upgradeHeader)!.toLowerCase() !=
              "websocket") {

        final stringData = await response.transform(utf8.decoder).join();
        final exception = WebSocketUpgradeException(
            message: "Connection to '$uri' was not upgraded to websocket",
            statusCode: response.statusCode,
            data: stringData,
        );
        return error(exception);
      }
  }
}

Thank you in advance!

BTW I haven't found any way how to contribute to the sky_engine package. Cloud you also advise on that?

[chinmaygarde]

cc @brianquinlan

[blablabla123-cell]

Same issue, in case of providing secure websocket connection with JWT. When token is expired server not upgrades the connection but the client (flutter) doenst recieve any message or status codes, error just pops up and cant be handled

[philos3]

Same issue,any updated?

[philos3]

dart-lang/sdk#52890