feat: add keepalive feature to tear down streams in their absence

Author: SamuelSchaub

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/StreamingSubscriberConnection.java

@@ -63,6 +63,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
@@ -95,6 +96,7 @@ final class StreamingSubscriberConnection extends AbstractApiService implements
 
   private final SubscriberStub subscriberStub;
   private final int channelAffinity;
+  private final long protocolVersion;
   private final String subscription;
   private final SubscriptionName subscriptionNameObject;
   private final ScheduledExecutorService systemExecutor;
@@ -127,6 +129,15 @@ final class StreamingSubscriberConnection extends AbstractApiService implements
   private OpenTelemetryPubsubTracer tracer = new OpenTelemetryPubsubTracer(null, false);
   private final SubscriberShutdownSettings subscriberShutdownSettings;
 
+  private final boolean enableKeepalive;
+  private static final long KEEP_ALIVE_SUPPORT_VERSION = 2;
+  private static final Duration CLIENT_PING_INTERVAL = Duration.ofSeconds(30);
+  private ScheduledFuture<?> pingSchedulerHandle;
+
+  private static final Duration SERVER_TIMEOUT_DURATION = Duration.ofSeconds(45);
+  private final AtomicLong lastServerResponseTime;
+  private ScheduledFuture<?> serverMonitorHandle;
+
   private StreamingSubscriberConnection(Builder builder) {
     subscription = builder.subscription;
     subscriptionNameObject = SubscriptionName.parse(builder.subscription);
@@ -154,6 +165,7 @@ private StreamingSubscriberConnection(Builder builder) {
 
     subscriberStub = builder.subscriberStub;
     channelAffinity = builder.channelAffinity;
+    protocolVersion = builder.protocolVersion;
 
     MessageDispatcher.Builder messageDispatcherBuilder;
     if (builder.receiver != null) {
@@ -190,6 +202,8 @@ private StreamingSubscriberConnection(Builder builder) {
 
     flowControlSettings = builder.flowControlSettings;
     useLegacyFlowControl = builder.useLegacyFlowControl;
+    enableKeepalive = protocolVersion >= KEEP_ALIVE_SUPPORT_VERSION;
+    lastServerResponseTime = new AtomicLong(clock.nanoTime());
   }
 
   public StreamingSubscriberConnection setExactlyOnceDeliveryEnabled(
@@ -218,6 +232,12 @@ protected void doStop() {
     } finally {
       lock.unlock();
     }
+
+    if (enableKeepalive) {
+      stopClientPinger();
+      stopServerMonitor();
+    }
+
     runShutdown();
     notifyStopped();
   }
@@ -266,6 +286,10 @@ public void onStart(StreamController controller) {
 
     @Override
     public void onResponse(StreamingPullResponse response) {
+      if (enableKeepalive) {
+        lastServerResponseTime.set(clock.nanoTime());
+      }
+
       channelReconnectBackoffMillis.set(INITIAL_CHANNEL_RECONNECT_BACKOFF.toMillis());
 
       boolean exactlyOnceDeliveryEnabledResponse =
@@ -295,11 +319,19 @@ public void onResponse(StreamingPullResponse response) {
 
     @Override
     public void onError(Throwable t) {
+      if (enableKeepalive) {
+        stopClientPinger();
+        stopServerMonitor();
+      }
       errorFuture.setException(t);
     }
 
     @Override
     public void onComplete() {
+      if (enableKeepalive) {
+        stopClientPinger();
+        stopServerMonitor();
+      }
       logger.fine("Streaming pull terminated successfully!");
       errorFuture.set(null);
     }
@@ -336,6 +368,7 @@ private void initialize() {
                 this.useLegacyFlowControl
                     ? 0
                     : valueOrZero(flowControlSettings.getMaxOutstandingRequestBytes()))
+            .setProtocolVersion(protocolVersion)
             .build());
 
     /**
@@ -350,6 +383,11 @@ private void initialize() {
       lock.unlock();
     }
 
+    if (enableKeepalive) {
+      startClientPinger();
+      startServerMonitor();
+    }
+
     ApiFutures.addCallback(
         errorFuture,
         new ApiFutureCallback<Void>() {
@@ -366,6 +404,10 @@ public void onSuccess(@Nullable Void result) {
 
           @Override
           public void onFailure(Throwable cause) {
+            if (enableKeepalive) {
+              stopClientPinger();
+              stopServerMonitor();
+            }
             if (!isAlive()) {
               // we don't care about subscription failures when we're no longer running.
               logger.log(Level.FINE, "pull failure after service no longer running", cause);
@@ -410,6 +452,93 @@ private boolean isAlive() {
     return state == State.RUNNING || state == State.STARTING;
   }
 
+  private void startClientPinger() {
+    if (pingSchedulerHandle != null) {
+      pingSchedulerHandle.cancel(false);
+    }
+
+    pingSchedulerHandle =
+        systemExecutor.scheduleAtFixedRate(
+            () -> {
+              try {
+                lock.lock();
+                try {
+                  if (clientStream != null && isAlive()) {
+                    clientStream.send(StreamingPullRequest.newBuilder().build());
+                    logger.log(Level.FINEST, "Sent client keepalive ping");
+                  }
+                } finally {
+                  lock.unlock();
+                }
+              } catch (Exception e) {
+                logger.log(Level.FINE, "Error sending client keepalive ping", e);
+              }
+            },
+            CLIENT_PING_INTERVAL.getSeconds(),
+            CLIENT_PING_INTERVAL.getSeconds(),
+            TimeUnit.SECONDS);
+  }
+
+  private void stopClientPinger() {
+    if (pingSchedulerHandle != null) {
+      pingSchedulerHandle.cancel(false);
+      pingSchedulerHandle = null;
+    }
+  }
+
+  private void startServerMonitor() {
+    if (serverMonitorHandle != null) {
+      serverMonitorHandle.cancel(false);
+    }
+
+    Duration checkInterval = Duration.ofSeconds(15);
+    serverMonitorHandle =
+        systemExecutor.scheduleAtFixedRate(
+            () -> {
+              try {
+                if (!isAlive()) {
+                  return;
+                }
+
+                long now = clock.nanoTime();
+                long lastResponse = lastServerResponseTime.get();
+                Duration elapsed = Duration.ofNanos(now - lastResponse);
+
+                if (elapsed.compareTo(SERVER_TIMEOUT_DURATION) > 0) {
+                  logger.log(
+                      Level.WARNING,
+                      "No response from server for {0} seconds. Closing stream.",
+                      elapsed.getSeconds());
+
+                  lock.lock();
+                  try {
+                    if (clientStream != null) {
+                      clientStream.closeSendWithError(
+                          Status.UNAVAILABLE
+                              .withDescription("Keepalive timeout with server")
+                              .asException());
+                    }
+                  } finally {
+                    lock.unlock();
+                  }
+                  stopServerMonitor();
+                }
+              } catch (Exception e) {
+                logger.log(Level.FINE, "Error in server keepaliver monitor", e);
+              }
+            },
+            checkInterval.getSeconds(),
+            checkInterval.getSeconds(),
+            TimeUnit.SECONDS);
+  }
+
+  private void stopServerMonitor() {
+    if (serverMonitorHandle != null) {
+      serverMonitorHandle.cancel(false);
+      serverMonitorHandle = null;
+    }
+  }
+
   public void setResponseOutstandingMessages(AckResponse ackResponse) {
     // We will close the futures with ackResponse - if there are multiple references to the same
     // future they will be handled appropriately
@@ -769,6 +898,7 @@ public static final class Builder {
     private Distribution ackLatencyDistribution;
     private SubscriberStub subscriberStub;
     private int channelAffinity;
+    private long protocolVersion;
     private FlowController flowController;
     private FlowControlSettings flowControlSettings;
     private boolean useLegacyFlowControl;
@@ -840,6 +970,11 @@ public Builder setChannelAffinity(int channelAffinity) {
       return this;
     }
 
+    public Builder setProtocolVersion(long protocolVersion) {
+      this.protocolVersion = protocolVersion;
+      return this;
+    }
+
     public Builder setFlowController(FlowController flowController) {
       this.flowController = flowController;
       return this;