#8069 add latency recording handler

Signed-off-by: Ludovic Orban <[email protected]>

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/AbstractLatencyRecordingHandler.java

@@ -0,0 +1,86 @@
+//
+// ========================================================================
+// Copyright (c) 1995-2022 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.server.handler;
+
+import java.util.function.Function;
+
+import org.eclipse.jetty.server.Handler;
+import org.eclipse.jetty.server.HttpStream;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.Response;
+import org.eclipse.jetty.util.Callback;
+import org.eclipse.jetty.util.NanoTime;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A <code>Handler</code> that allows recording the latencies of the requests executed by the wrapped handler.
+ */
+public abstract class AbstractLatencyRecordingHandler extends Handler.Wrapper
+{
+    private static final Logger LOG = LoggerFactory.getLogger(AbstractLatencyRecordingHandler.class);
+
+    private final Function<HttpStream, HttpStream> recordingWrapper;
+
+    public AbstractLatencyRecordingHandler()
+    {
+        this.recordingWrapper = httpStream -> new HttpStream.Wrapper(httpStream)
+        {
+            @Override
+            public void succeeded()
+            {
+                long begin = httpStream.getNanoTime();
+                super.succeeded();
+                try
+                {
+                    onRequestComplete(NanoTime.since(begin));
+                }
+                catch (Throwable t)
+                {
+                    if (LOG.isDebugEnabled())
+                        LOG.debug("Error thrown by onRequestComplete", t);
+                }
+            }
+
+            @Override
+            public void failed(Throwable x)
+            {
+                long begin = httpStream.getNanoTime();
+                super.failed(x);
+                try
+                {
+                    onRequestComplete(NanoTime.since(begin));
+                }
+                catch (Throwable t)
+                {
+                    if (LOG.isDebugEnabled())
+                        LOG.debug("Error thrown by onRequestComplete", t);
+                }
+            }
+        };
+    }
+
+    @Override
+    public boolean process(Request request, Response response, Callback callback) throws Exception
+    {
+        request.addHttpStreamWrapper(recordingWrapper);
+        return super.process(request, response, callback);
+    }
+
+    /**
+     * Called back for each completed request with its execution's duration.
+     * @param durationInNs the duration in nanoseconds of the completed request
+     */
+    protected abstract void onRequestComplete(long durationInNs);
+}