Jetty 12 is missing a way to record server latencies

[lorban]

Jetty version(s)
12.0.x

Description
12.0.x currently does not have anything equivalent to 11's HttpChannel.Listener API which is needed at least to record server latencies with our performance tests.

[lorban]

This actually can be done with the existing wrapper mechanisms by creating a Handler.Wrapper that adds a stream wrapper:

    @Override
    public Request.Processor handle(Request request) throws Exception
    {
        long before = System.nanoTime();
        Request.Processor processor = super.handle(request);
        if (processor == null)
            return null;

        request.addHttpStreamWrapper(httpStream -> new HttpStream.Wrapper(httpStream)
        {
            @Override
            public void succeeded()
            {
                super.succeeded();
                recordLatency(System.nanoTime() - before);
            }

            @Override
            public void failed(Throwable x)
            {
                super.failed(x);
                recordLatency(System.nanoTime() - before);
            }
        });

        return processor;
    }

[sbordet]

@lorban can you make this a utility Handler with overridable methods such as onRequestBegin(), etc. so people that wants to use it can do so overriding only the few methods they need?

[gregw]

It could have a bunch of overridable methods that correspond to the previous listener events... or is that just adding complexity.
Perhaps just have an extensible method that creates the actual listener would be sufficient?

[sbordet]

@gregw won't you still need a Listener interface with all the onXYZ() methods?

[gregw]

It could be done with a new listener interface, or just an extendible method to create the stream listener.

My preference is to avoid lots of lists of listeners that we must iterate over.

[lorban]

Introduced AbstractLatencyRecordingHandler in #9172