Send delivery receipts.

SignalServiceKit/src/Messages/OWSDeliveryReceiptManager.m

@@ -110,11 +110,11 @@ NSString *const kDeliveryReceiptManagerCollection = @"kDeliveryReceiptManagerCol
                                               usingBlock:^(NSString *key, id object, BOOL *stop) {
                                                   NSString *recipientId = key;
                                                   NSSet<NSNumber *> *timestamps = object;
-                                                  deliveryReceiptMap[recipientId] = timestamps;
+                                                  deliveryReceiptMap[recipientId] = [timestamps copy];
                                               }];
     }];
 
-    BOOL didWork = NO;
+    NSMutableArray<AnyPromise *> *sendPromises = [NSMutableArray array];
 
     for (NSString *recipientId in deliveryReceiptMap) {
         NSSet<NSNumber *> *timestamps = deliveryReceiptMap[recipientId];
@@ -128,30 +128,33 @@ NSString *const kDeliveryReceiptManagerCollection = @"kDeliveryReceiptManagerCol
             [OWSReceiptsForSenderMessage deliveryReceiptsForSenderMessageWithThread:thread
                                                                   messageTimestamps:timestamps.allObjects];
 
+        AnyPromise *sendPromise = [AnyPromise promiseWithResolverBlock:^(PMKResolver resolve) {
             [self.messageSender enqueueMessage:message
                 success:^{
                     OWSLogInfo(@"Successfully sent %lu delivery receipts to sender.", (unsigned long)timestamps.count);
+
+                    [self dequeueDeliveryReceiptsWithRecipientId:recipientId timestamps:timestamps];
+
+                    // The value doesn't matter, we just need any non-NSError value.
+                    resolve(@(1));
                 }
                 failure:^(NSError *error) {
                     OWSLogError(@"Failed to send delivery receipts to sender with error: %@", error);
-            }];
-
-        didWork = YES;
-    }
 
-    // Now that they've been processed, remove all enqueued delivery receipts.
+                    resolve(error);
-    //
+                }];
-    // NOTE: we don't need to worry about race conditions; this
-    // collection will only be mutated on serialQueue.
-    [self.dbConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
-        [transaction removeAllObjectsInCollection:kDeliveryReceiptManagerCollection];
         }];
+        [sendPromises addObject:sendPromise];
+    }
 
-    if (!didWork) {
+    if (sendPromises.count < 1) {
+        // No work to do; abort.
         self.isProcessing = NO;
         return;
     }
 
+    AnyPromise *completionPromise = PMKJoin(sendPromises);
+    completionPromise.always(^() {
         // Wait N seconds before processing delivery receipts again.
         // This allows time for a batch to accumulate.
         //
@@ -159,10 +162,13 @@ NSString *const kDeliveryReceiptManagerCollection = @"kDeliveryReceiptManagerCol
         // delivery receipts without being so high that we risk not sending delivery
         // receipts due to app exit.
         const CGFloat kProcessingFrequencySeconds = 3.f;
-    dispatch_after(
+        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(kProcessingFrequencySeconds * NSEC_PER_SEC)),
-        dispatch_time(DISPATCH_TIME_NOW, (int64_t)(kProcessingFrequencySeconds * NSEC_PER_SEC)), self.serialQueue, ^{
+            self.serialQueue,
+            ^{
                 [self process];
             });
+    });
+    [completionPromise retainUntilComplete];
 }
 
 - (void)envelopeWasReceived:(SSKProtoEnvelope *)envelope {