WebSocket handlers should log unhandled errors

[Meemaw]

Was looking at the code, and it seems WebSocket original exception that happen when mapping the payload to gql message are "swallowed". On client, we just see a generic: Subscription error. This makes it almost impossible to debug, but also notice issues with messages.

Looking at the code, this seems to happen here:

https://github.com/spring-projects/spring-graphql/blob/main/spring-graphql/src/main/java/org/springframework/graphql/server/webmvc/GraphQlWebSocketHandler.java#L350

There should be an option to log an error here, this is an uncaught exception basically.

[rstoyanchev]

Indeed we should be logging an unresolved exception at that point. We'll fix that. Note that you can handle subscription exceptions, or if it is a controller method, you can also use an @GraphQlExceptionHandler method.