Fix Android Connectivity Monitor (v2)

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/AbstractStream.java

@@ -177,7 +177,8 @@ public void run() {
   /**
    * Maximum backoff time for reconnecting when we know the connection is failed on the client-side.
    */
-  private static final long DNS_FAILURE_BACKOFF_MAX_DELAY_MS = TimeUnit.SECONDS.toMillis(10);
+  private static final long BACKOFF_CLIENT_NETWORK_FAILURE_MAX_DELAY_MS =
+      TimeUnit.SECONDS.toMillis(10);
 
   @Nullable private DelayedTask idleTimer;
 
@@ -308,8 +309,9 @@ private void close(State finalState, Status status) {
     } else if (code == Code.UNAVAILABLE) {
       // This exception is thrown when the gRPC connection fails on the client side, To shorten
       // reconnect time, we can use a shorter max delay when reconnecting.
-      if (status.getCause() instanceof java.net.UnknownHostException) {
-        backoff.setTemporaryMaxDelay(DNS_FAILURE_BACKOFF_MAX_DELAY_MS);
+      if (status.getCause() instanceof java.net.UnknownHostException
+          || status.getCause() instanceof java.net.ConnectException) {
+        backoff.setTemporaryMaxDelay(BACKOFF_CLIENT_NETWORK_FAILURE_MAX_DELAY_MS);
       }
     }
 

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/GrpcCallProvider.java

@@ -58,6 +58,7 @@ public class GrpcCallProvider {
   // This timeout is used when attempting to establish a connection in gRPC. If a connection attempt
   // does not succeed in CONNECTIVITY_ATTEMPT_TIMEOUT_MS, we restart the channel and try
   // reconnecting again, rather than waiting up to 2+ minutes for gRPC to timeout.
+  // More details about usage can be found in GrpcCallProvider.onConnectivityStateChanged().
   private static final int CONNECTIVITY_ATTEMPT_TIMEOUT_MS = 15 * 1000;
   private DelayedTask connectivityAttemptTimer;
 
@@ -201,6 +202,21 @@ void shutdown() {
     }
   }
 
+  /**
+   * Monitors the connectivity state of the gRPC channel and resets the channel when gRPC fails to
+   * connect.
+   *
+   * <p>We currently cannot configure timeouts in connection attempts for gRPC
+   * (https://github.com/grpc/grpc-java/issues/1943), and until they support doing so, the gRPC
+   * connection can stay open for up to 2+ minutes before shutting down.
+   *
+   * <p>We start a timer when the channel enters ConnectivityState.CONNECTING. If the timer elapses,
+   * we reset the channel by shutting it down and reinitializing the channelTask. Changes to the
+   * connectivity state will clear the timer and start a new one-time listener for the next
+   * ConnectivityState change.
+   *
+   * @param channel The channel to monitor the connectivity state of.
+   */
   private void onConnectivityStateChange(ManagedChannel channel) {
     ConnectivityState newState = channel.getState(true);
     Logger.debug(LOG_TAG, "Current gRPC connectivity state: " + newState);
@@ -216,24 +232,18 @@ private void onConnectivityStateChange(ManagedChannel channel) {
               CONNECTIVITY_ATTEMPT_TIMEOUT_MS,
               () -> {
                 Logger.debug(LOG_TAG, "connectivityAttemptTimer elapsed. Resetting the channel.");
-                clearConnectivityTimer();
+                clearConnectivityAttemptTimer();
                 resetChannel(channel);
               });
     } else {
       // Clear the timer otherwise, so we don't end up with multiple connectivityAttemptTimers.
-      clearConnectivityTimer();
+      clearConnectivityAttemptTimer();
     }
     // Re-listen for next state change.
     channel.notifyWhenStateChanged(
         newState, () -> asyncQueue.enqueueAndForget(() -> onConnectivityStateChange(channel)));
   }
 
-  /**
-   * Shuts down and reinitializes the channel.
-   *
-   * <p>This is used when the connectivity attempt timer elapses and we need to reset the gRPC
-   * channel to reestablish connectivity.
-   */
   private void resetChannel(ManagedChannel channel) {
     asyncQueue.enqueueAndForget(
         () -> {
@@ -264,8 +274,7 @@ private void initChannelTask() {
             });
   }
 
-  /** Clears the connectivity timer if it exists. */
-  private void clearConnectivityTimer() {
+  private void clearConnectivityAttemptTimer() {
     if (connectivityAttemptTimer != null) {
       Logger.debug(LOG_TAG, "Clearing the connectivityAttemptTimer");
       connectivityAttemptTimer.cancel();

firebase-firestore/src/main/java/com/google/firebase/firestore/util/ExponentialBackoff.java

@@ -29,15 +29,22 @@ public class ExponentialBackoff {
 
   public static final double DEFAULT_BACKOFF_FACTOR = 1.5;
 
-  /** Maximum backoff time in milliseconds */
   public static final long DEFAULT_BACKOFF_MAX_DELAY_MS = 60 * 1000;
 
   private final AsyncQueue queue;
   private final TimerId timerId;
   private final long initialDelayMs;
   private final double backoffFactor;
 
-  private long maxDelayMs;
+  /** The maximum backoff time in milliseconds. */
+  private final long maxDelayMs;
+
+  /**
+   * The maximum backoff time used when calculating the next backoff. This value can be changed for
+   * a single backoffAndRun call, after which it resets to maxDelayMs.
+   */
+  private long nextMaxDelayMs;
+
   private long currentBaseMs;
   private long lastAttemptTime;
   private DelayedTask timerTask;
@@ -71,6 +78,7 @@ public ExponentialBackoff(
     this.initialDelayMs = initialDelayMs;
     this.backoffFactor = backoffFactor;
     this.maxDelayMs = maxDelayMs;
+    this.nextMaxDelayMs = maxDelayMs;
     this.lastAttemptTime = new Date().getTime();
 
     reset();
@@ -100,7 +108,7 @@ public void reset() {
    * Resets the backoff delay to the maximum delay (e.g. for use after a RESOURCE_EXHAUSTED error).
    */
   public void resetToMax() {
-    currentBaseMs = maxDelayMs;
+    currentBaseMs = nextMaxDelayMs;
   }
 
   /**
@@ -110,7 +118,7 @@ public void resetToMax() {
    * @param newMax The temporary maximum delay to set.
    */
   public void setTemporaryMaxDelay(long newMax) {
-    maxDelayMs = newMax;
+    nextMaxDelayMs = newMax;
   }
 
   /**
@@ -158,12 +166,12 @@ public void backoffAndRun(Runnable task) {
     currentBaseMs = (long) (currentBaseMs * backoffFactor);
     if (currentBaseMs < initialDelayMs) {
       currentBaseMs = initialDelayMs;
-    } else if (currentBaseMs > maxDelayMs) {
-      currentBaseMs = maxDelayMs;
+    } else if (currentBaseMs > nextMaxDelayMs) {
+      currentBaseMs = nextMaxDelayMs;
     }
 
     // Reset max delay to the default.
-    maxDelayMs = DEFAULT_BACKOFF_MAX_DELAY_MS;
+    nextMaxDelayMs = maxDelayMs;
   }
 
   public void cancel() {