Prior to this commit, the `ReactiveTypeHandler` would handle `Flux`-like
return types from controller methods and adapt them to SSE streams using
the `SseEmitter`/`ResponseBodyEmitter` APIs. In case an `IOException` is
thrown while writing to the HTTP response stream, the
`ReactiveTypeHandler` would rely on the Servlet container to call
`AsyncListener#onError` - this would be the signal for Spring MVC to
complete the async exchange. To prevent racing issues between this
signal and the actual handling of the exception, changes like gh-20173
were applied. Since then, robust checks were added with gh-32340 in
`StandardServletAsyncWebRequest.LifecycleHttpServletResponse`.
With Jetty 12, `AsyncListener#onError` would not be called as the error
would happen while writing in blocking mode to the response (so, not
using the Servlet WriteListener contract). But still, such `IOException`
would still result in the closing of the HTTP connection. As of Jetty
12.0.4, this is no longer the case and the party managing the async
lifecycle is in charge of completing the exchange, as it should. This
means that the current behavior leaks HTTP connections for these cases
and causes memory issues.
This commit ensures that such exceptions happening during response
writes are caught and result in the completion of the `SSEEmitter` and
the closing of the exchange. Even if other Servlet containers still
propagate the error `AsyncListener#onError`, competing signals are still
managed with gh-32340.
Closes gh-32629
c6b6ccdc89