Guard inner flush in ServerCall.writeResponseBody for Jetty 12 compatibility

[nico-mayora]

The aim

Stop spurious SEVERE log entries and bogus 500 retries on every Restlet response served via the Jetty 12 connector. The wire response is already correct, only logging and the retry path misbehave.

The solution

Guard the inner responseEntityStream.flush() in ServerCall.writeResponseBody with a try/catch that logs at FINE, mirroring the pattern already used by sendResponse()'s finally block two methods up.

org.eclipse.jetty.io.content.BufferedContentSink in Jetty 12 strictly enforces the Content.Sink contract: once a write with last=true has occurred, any subsequent write or flush completes the callback with IOException("complete"). Under Jetty 9 / 11 the same flush was silently tolerated.

That IOException propagates from writeResponseBody up to ServerAdapter.commit, where it's caught and logged at SEVERE as "An exception occurred writing the response entity" and triggers a retry against a response whose body bytes are already on the wire.

The outer flush+close in sendResponse()'s finally block already wraps the same operation:

  } catch (IOException ioe) {
      getLogger().log(Level.FINE,
              "The stream was probably already closed by the connector. "
                      + "Probably OK, low message priority.", ioe);
  }

This patch mirrors that exact treatment on the inner flush:

protected void writeResponseBody(Representation entity, OutputStream responseEntityStream) throws IOException {
    // Send the entity to the client
    if (responseEntityStream != null) {
        entity.write(responseEntityStream);
        try {
            responseEntityStream.flush();
        } catch (IOException ioe) {
            getLogger().log(Level.FINE, "Unable to flush the entity stream.", ioe);
        }
    }
}

Reproduction

• Jetty 12.1.9 + org.restlet.ext.jetty 2.6.0.
• Mount any ServerResource returning a simple representation, e.g.

public class Hello extends ServerResource {
    @Get
    public Representation hello() {
        return new StringRepresentation("hi");
    }
}

• curl it. Without this patch, the response body is hi (correct) but the server logs:

SEVERE: An exception occurred writing the response entity
java.io.IOException: complete
    at org.eclipse.jetty.io.content.BufferedContentSink._lastWritten(...)
    at org.eclipse.jetty.io.content.BufferedContentSink.flush(...)
    at org.restlet.engine.adapter.ServerCall.writeResponseBody(ServerCall.java:...)
    ...

• With the patch: response unchanged, no SEVERE entry, no retry.

Check-list

• PR size
  • Under 300 lines ✅
  • Can't be split without complicating the process even more
• Tests
  • Added
  • Not applicable: exercising this path requires a live Jetty 12 server in the Restlet test harness; the analogous existing guard in sendResponse() is also untested, and this change is mechanically the same one method down
• Doc
  • Added
  • Not applicable
• Reviewer
  • Asked for a review
  • Added label DO NOT REVIEW

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud