[Metrics] Add a few WebSocket metrics

- open connections count
- requests count

metrics/metrics-api/src/main/java/org/apache/james/metrics/api/Metric.java

@@ -46,4 +46,13 @@ public interface Metric {
     default double movingAverage() {
         return Long.valueOf(getCount()).doubleValue();
     }
+
+    /**
+     * Mean rate of the events happen in one second.
+     *
+     * Default to count (naive implementation with period starting at boot time)
+     */
+    default double meanRate() {
+        return Long.valueOf(getCount()).doubleValue();
+    }
 }

metrics/metrics-dropwizard/src/main/java/org/apache/james/metrics/dropwizard/DropWizardMetric.java

@@ -72,4 +72,9 @@ public long getCount() {
     public double movingAverage() {
         return meter.getFiveMinuteRate();
     }
+
+    @Override
+    public double meanRate() {
+        return meter.getMeanRate();
+    }
 }

server/protocols/jmap-rfc-8621/src/main/scala/org/apache/james/jmap/routes/WebSocketRoutes.scala

@@ -41,6 +41,7 @@ import org.apache.james.jmap.http.{Authenticator, UserProvisioning}
 import org.apache.james.jmap.json.{PushSerializer, ResponseSerializer}
 import org.apache.james.jmap.{Endpoint, JMAPRoute, JMAPRoutes, InjectionKeys => JMAPInjectionKeys}
 import org.apache.james.mailbox.MailboxSession
+import org.apache.james.metrics.api.{Metric, MetricFactory}
 import org.apache.james.user.api.DelegationStore
 import org.slf4j.{Logger, LoggerFactory}
 import play.api.libs.json.Json
@@ -79,7 +80,10 @@ class WebSocketRoutes @Inject() (@Named(InjectionKeys.RFC_8621) val authenticato
                                  emailChangeRepository: EmailChangeRepository,
                                  pushSerializer: PushSerializer,
                                  typeStateFactory: TypeStateFactory,
-                                 delegationStore: DelegationStore) extends JMAPRoutes {
+                                 delegationStore: DelegationStore,
+                                 metricFactory: MetricFactory) extends JMAPRoutes {
+  private val openingConnectionsMetric: Metric = metricFactory.generate("jmap_websocket_opening_connections_count")
+  private val requestCountMetric: Metric = metricFactory.generate("jmap_websocket_requests_count")
 
   override def routes(): stream.Stream[JMAPRoute] = stream.Stream.of(
     JMAPRoute.builder
@@ -91,16 +95,17 @@ class WebSocketRoutes @Inject() (@Named(InjectionKeys.RFC_8621) val authenticato
       .action(JMAPRoutes.CORS_CONTROL)
       .corsHeaders())
 
-  private def handleWebSockets(httpServerRequest: HttpServerRequest, httpServerResponse: HttpServerResponse): Mono[Void] = {
+  private def handleWebSockets(httpServerRequest: HttpServerRequest, httpServerResponse: HttpServerResponse): Mono[Void] =
     SMono(authenticator.authenticate(httpServerRequest))
       .flatMap((mailboxSession: MailboxSession) => userProvisioner.provisionUser(mailboxSession)
         .`then`
         .`then`(SMono(httpServerResponse.addHeader(HttpHeaderNames.SEC_WEBSOCKET_PROTOCOL, "jmap")
-            .sendWebsocket((in, out) => handleWebSocketConnection(mailboxSession)(in, out)))))
+          .sendWebsocket((in, out) => handleWebSocketConnection(mailboxSession)(in, out)))
+          .doOnSubscribe(_ => openingConnectionsMetric.increment())
+          .doOnTerminate(() => openingConnectionsMetric.decrement())))
       .onErrorResume(throwable => handleHttpHandshakeError(throwable, httpServerResponse))
       .asJava()
       .`then`()
-  }
 
   private def handleWebSocketConnection(session: MailboxSession)(in: WebsocketInbound, out: WebsocketOutbound): Mono[Void] = {
     val sink: Sinks.Many[OutboundMessage] = Sinks.many().unicast().onBackpressureBuffer()
@@ -113,6 +118,7 @@ class WebSocketRoutes @Inject() (@Named(InjectionKeys.RFC_8621) val authenticato
         frame.content().readBytes(bytes)
         new String(bytes, StandardCharsets.UTF_8)
       })
+      .doOnNext(_ => requestCountMetric.increment())
       .flatMap(message => handleClientMessages(context)(message))
       .doOnTerminate(context.clean)
       .doOnCancel(context.clean)