Improves "Could not reach Firestore backend." log message. (#1455)

Port of https://github.com/firebase/firebase-js-sdk/pull/864

3 files changed, 24 insertions, 11 deletions

diff --git a/Firestore/Source/Remote/FSTOnlineStateTracker.h b/Firestore/Source/Remote/FSTOnlineStateTracker.h
index 2521c84..340b641 100644
--- a/Firestore/Source/Remote/FSTOnlineStateTracker.h
+++ b/Firestore/Source/Remote/FSTOnlineStateTracker.h
@@ -57,7 +57,7 @@ NS_ASSUME_NONNULL_BEGIN
  * We then may allow multiple failures (based on kMaxWatchStreamFailures) before we actually
  * transition to FSTOnlineStateOffline.
  */
-- (void)handleWatchStreamFailure;
+- (void)handleWatchStreamFailure:(NSError *)error;
 
 /**
  * Explicitly sets the FSTOnlineState to the specified state.
diff --git a/Firestore/Source/Remote/FSTOnlineStateTracker.mm b/Firestore/Source/Remote/FSTOnlineStateTracker.mm
index fb993e5..a5c2b38 100644
--- a/Firestore/Source/Remote/FSTOnlineStateTracker.mm
+++ b/Firestore/Source/Remote/FSTOnlineStateTracker.mm
@@ -84,11 +84,10 @@ static const NSTimeInterval kOnlineStateTimeout = 10;
                        HARD_ASSERT(
                            self.state == FSTOnlineStateUnknown,
                            "Timer should be canceled if we transitioned to a different state.");
-                       LOG_DEBUG(
-                           "Watch stream didn't reach Online or Offline within %s seconds. "
-                           "Considering client offline.",
-                           kOnlineStateTimeout);
-                       [self logClientOfflineWarningIfNecessary];
+                       [self logClientOfflineWarningIfNecessaryWithReason:
+                                 [NSString
+                                     stringWithFormat:@"Backend didn't respond within %f seconds.",
+                                                      kOnlineStateTimeout]];
                        [self setAndBroadcastState:FSTOnlineStateOffline];
 
                        // NOTE: handleWatchStreamFailure will continue to increment
@@ -98,7 +97,7 @@ static const NSTimeInterval kOnlineStateTimeout = 10;
   }
 }
 
-- (void)handleWatchStreamFailure {
+- (void)handleWatchStreamFailure:(NSError *)error {
   if (self.state == FSTOnlineStateOnline) {
     [self setAndBroadcastState:FSTOnlineStateUnknown];
 
@@ -110,7 +109,9 @@ static const NSTimeInterval kOnlineStateTimeout = 10;
     self.watchStreamFailures++;
     if (self.watchStreamFailures >= kMaxWatchStreamFailures) {
       [self clearOnlineStateTimer];
-      [self logClientOfflineWarningIfNecessary];
+      [self logClientOfflineWarningIfNecessaryWithReason:
+                [NSString stringWithFormat:@"Connection failed %d times. Most recent error: %@",
+                                           kMaxWatchStreamFailures, error]];
       [self setAndBroadcastState:FSTOnlineStateOffline];
     }
   }
@@ -136,10 +137,18 @@ static const NSTimeInterval kOnlineStateTimeout = 10;
   }
 }
 
-- (void)logClientOfflineWarningIfNecessary {
+- (void)logClientOfflineWarningIfNecessaryWithReason:(NSString *)reason {
+  NSString *message = [NSString
+      stringWithFormat:
+          @"Could not reach Cloud Firestore backend. %@\n This typically indicates that your "
+          @"device does not have a healthy Internet connection at the moment. The client will "
+          @"operate in offline mode until it is able to successfully connect to the backend.",
+          reason];
   if (self.shouldWarnClientIsOffline) {
-    LOG_WARN("Could not reach Firestore backend.");
+    LOG_WARN("%s", message);
     self.shouldWarnClientIsOffline = NO;
+  } else {
+    LOG_DEBUG("%s", message);
   }
 }
 
diff --git a/Firestore/Source/Remote/FSTRemoteStore.mm b/Firestore/Source/Remote/FSTRemoteStore.mm
index 4309c74..4d8aa7e 100644
--- a/Firestore/Source/Remote/FSTRemoteStore.mm
+++ b/Firestore/Source/Remote/FSTRemoteStore.mm
@@ -323,11 +323,15 @@ static const int kMaxPendingWrites = 10;
               "enabled");
 
   [self cleanUpWatchStreamState];
-  [self.onlineStateTracker handleWatchStreamFailure];
 
   // If the watch stream closed due to an error, retry the connection if there are any active
   // watch targets.
   if ([self shouldStartWatchStream]) {
+    if (error) {
+      // There should generally be an error if the watch stream was closed when it's still needed,
+      // but it's not quite worth asserting.
+      [self.onlineStateTracker handleWatchStreamFailure:error];
+    }
     [self startWatchStream];
   } else {
     // We don't need to restart the watch stream because there are no active targets. The online