Fix for b/74749605: Cancel pending backoff operations when closing streams. (#958)

Port of https://github.com/firebase/firebase-js-sdk/pull/564.

3 files changed, 20 insertions, 4 deletions

diff --git a/Firestore/Source/Remote/FSTExponentialBackoff.h b/Firestore/Source/Remote/FSTExponentialBackoff.h
index 03558ee..3beafbf 100644
--- a/Firestore/Source/Remote/FSTExponentialBackoff.h
+++ b/Firestore/Source/Remote/FSTExponentialBackoff.h
@@ -76,6 +76,9 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)backoffAndRunBlock:(void (^)(void))block;
 
+/** Cancels any pending backoff block scheduled via backoffAndRunBlock:. */
+- (void)cancel;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/Firestore/Source/Remote/FSTExponentialBackoff.mm b/Firestore/Source/Remote/FSTExponentialBackoff.mm
index dddf164..20b50a5 100644
--- a/Firestore/Source/Remote/FSTExponentialBackoff.mm
+++ b/Firestore/Source/Remote/FSTExponentialBackoff.mm
@@ -66,9 +66,8 @@ using firebase::firestore::util::SecureRandom;
 }
 
 - (void)backoffAndRunBlock:(void (^)(void))block {
-  if (self.timerCallback) {
-    [self.timerCallback cancel];
-  }
+  [self cancel];
+
   // First schedule the block using the current base (which may be 0 and should be honored as such).
   NSTimeInterval delayWithJitter = _currentBase + [self jitterDelay];
   if (_currentBase > 0) {
@@ -89,6 +88,13 @@ using firebase::firestore::util::SecureRandom;
   }
 }
 
+- (void)cancel {
+  if (self.timerCallback) {
+    [self.timerCallback cancel];
+    self.timerCallback = nil;
+  }
+}
+
 /** Returns a random value in the range [-currentBase/2, currentBase/2] */
 - (NSTimeInterval)jitterDelay {
   std::uniform_real_distribution<double> dist;
diff --git a/Firestore/Source/Remote/FSTStream.mm b/Firestore/Source/Remote/FSTStream.mm
index a5c36c8..f65230b 100644
--- a/Firestore/Source/Remote/FSTStream.mm
+++ b/Firestore/Source/Remote/FSTStream.mm
@@ -326,7 +326,8 @@ static const NSTimeInterval kIdleTimeout = 60.0;
 /** Resumes stream start after backing off. */
 - (void)resumeStartFromBackoffWithDelegate:(id)delegate {
   if (self.state == FSTStreamStateStopped) {
-    // Streams can be stopped while waiting for backoff to complete.
+    // We should have canceled the backoff timer when the stream was closed, but just in case we
+    // make this a no-op.
     return;
   }
 
@@ -367,8 +368,14 @@ static const NSTimeInterval kIdleTimeout = 60.0;
             @"Can't provide an error when not in an error state.");
 
   [self.workerDispatchQueue verifyIsCurrentQueue];
+
+  // The stream will be closed so we don't need our idle close timer anymore.
   [self cancelIdleCheck];
 
+  // Ensure we don't leave a pending backoff operation queued (in case close()
+  // was called while we were waiting to reconnect).
+  [self.backoff cancel];
+
   if (finalState != FSTStreamStateError) {
     // If this is an intentional close ensure we don't delay our next connection attempt.
     [self.backoff reset];