Proper error handling

[ekuiter]

The editor does not do much error handling right now. In particular, these issues have to be addressed:

• errors returned by the server (thrown exceptions) are not shown in the UI at all. Global errors (toast or dialog) should be shown as well as local errors (attached to particular UI elements, see WebSocket request/response model #9)
• right now, exceptions on the server are essentially RuntimeExceptions attached with a somewhat helpful English string. Instead, we should have a proper exception hierarchy attached with metadata so that the client can parse and handle the errors individually. Also error codes should be sent instead of messages (see Internationalization #10)
• WebSocket issues are not handled at all (only relevant in multi-user mode, not on localhost). We need to handle cases such as
  • losing a network connection
  • changing networks (e.g., Wi-Fi to GSM)
  • the server crashes
  • automatically reconnect when the connection is lost, or offer the user an option to reconnect easily
  • when reconnecting, "repair" the application state (introduce the concept of "reconnecting" to the server)

[ekuiter]

Regarding WebSockets: With Sockette, we can reconnect on a closed connection. But rn, we don't distinguish between a new WebSocket and a reconnecting one, and the reconnecting client is assigned a new user name etc.

[ekuiter]

Improved in 0402bff.

[ekuiter]

WebSockets improved since adding the Clojure kernel, but still no sanity checks for generated operations (such as cycle check on move).