[logstash-input] Handle connection errors correctly

[ash-darin]

Current handling of connection errors results in a log message that the case is handled, followed by an error and stack trace because it is not handled.

This change handles this by correcting the logging to indicate when an Error is handled and when it isn't.

Here is an example of connection resets that are not handled because the are not as the expected ones, observed in the wild:

[2026-04-14T10:01:18,143][INFO ][org.logstash.beats.BeatsHandler][pipeline-name][0091cc855ef1087f43a697aa15a65059dde76fb10db72eac9d82c3a650a9376e] [local: 192.168.0.2:5001, remote: 192.168.0.11:36316] Handling exception: java.net.SocketException: Connection reset (caused by: java.net.SocketException: Connection reset)
[2026-04-14T10:01:18,143][WARN ][io.netty.channel.DefaultChannelPipeline][pipeline-name][0091cc855ef1087f43a697aa15a65059dde76fb10db72eac9d82c3a650a9376e] An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
java.net.SocketException: Connection reset
[..]

Added 07.2026: The above error is caused by winlogbeat 8.17.10. It is unclear why as I have found no reference to it anywhere and goes away with an update to > 8.18.0 Might be an artifact of virtualized machines. Removed original handling of this error from PR as it's fixed by a client upgrade.

P.S. Please backport to 8.x

[Copilot]

Pull request overview

Updates the Beats input’s Netty exception handling to better classify/handle connection reset scenarios and to log handled vs. unhandled exceptions more clearly, avoiding misleading “handled” logs followed by Netty pipeline warnings.

Changes:

• Adjusts exceptionCaught logging to log “Handling exception” only for handled RejectedExecutionExceptions, and “Unhandled exception” when forwarding to Netty.
• Extends noisy-exception detection to treat SocketException: Connection reset as a connection reset case.

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[ash-darin]

Hi @robbavey ,

am I missing anything to move this forward? I do not know which other files changed or prerequisites should be fulfilled for this. Thank you.