Fix MutationQueue issue resulting in re-sending acknowledged writes. (#909)

Port of: https://github.com/firebase/firebase-js-sdk/pull/559
Should address #772 once released.

getNextMutationBatchAfterBatchId() was not respecting
highestAcknowledgedBatchId and therefore we were resending writes after the
network was disabled / re-enabled.

2 files changed, 9 insertions, 4 deletions

diff --git a/Firestore/Source/Local/FSTLevelDBMutationQueue.mm b/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
index 575e98d..d7b5eca 100644
--- a/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
+++ b/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
@@ -315,7 +315,12 @@ static ReadOptions StandardReadOptions() {
 }
 
 - (nullable FSTMutationBatch *)nextMutationBatchAfterBatchID:(FSTBatchID)batchID {
-  std::string key = [self mutationKeyForBatchID:batchID + 1];
+  // All batches with batchID <= self.metadata.lastAcknowledgedBatchId have been acknowledged so
+  // the first unacknowledged batch after batchID will have a batchID larger than both of these
+  // values.
+  FSTBatchID nextBatchID = MAX(batchID, self.metadata.lastAcknowledgedBatchId) + 1;
+
+  std::string key = [self mutationKeyForBatchID:nextBatchID];
   std::unique_ptr<Iterator> it(_db->NewIterator(StandardReadOptions()));
   it->Seek(key);
 
@@ -336,7 +341,7 @@ static ReadOptions StandardReadOptions() {
     return nil;
   }
 
-  FSTAssert(rowKey.batchID > batchID, @"Should have found mutation after %d", batchID);
+  FSTAssert(rowKey.batchID >= nextBatchID, @"Should have found mutation after %d", nextBatchID);
   return [self decodedMutationBatch:it->value()];
 }
 
diff --git a/Firestore/Source/Local/FSTMemoryMutationQueue.mm b/Firestore/Source/Local/FSTMemoryMutationQueue.mm
index 5b2fca6..7e5cc02 100644
--- a/Firestore/Source/Local/FSTMemoryMutationQueue.mm
+++ b/Firestore/Source/Local/FSTMemoryMutationQueue.mm
@@ -192,10 +192,10 @@ static const NSComparator NumberComparator = ^NSComparisonResult(NSNumber *left,
 
   // All batches with batchID <= self.highestAcknowledgedBatchID have been acknowledged so the
   // first unacknowledged batch after batchID will have a batchID larger than both of these values.
-  batchID = MAX(batchID + 1, self.highestAcknowledgedBatchID);
+  FSTBatchID nextBatchID = MAX(batchID, self.highestAcknowledgedBatchID) + 1;
 
   // The requested batchID may still be out of range so normalize it to the start of the queue.
-  NSInteger rawIndex = [self indexOfBatchID:batchID];
+  NSInteger rawIndex = [self indexOfBatchID:nextBatchID];
   NSUInteger index = rawIndex < 0 ? 0 : (NSUInteger)rawIndex;
 
   // Finally return the first non-tombstone batch.