Move write of incoming messages off main thread.

// FREEBIE

SignalServiceKit/src/Network/WebSockets/TSSocketManager.m

@@ -381,6 +381,8 @@ NSString *const kNSNotification_SocketManagerStateDidChange = @"kNSNotification_
 
     if ([message.path isEqualToString:@"/api/v1/message"] && [message.verb isEqualToString:@"PUT"]) {
 
+        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+
             NSData *decryptedPayload =
                 [Cryptography decryptAppleMessagePayload:message.body withSignalingKey:TSStorageManager.signalingKey];
 
@@ -393,8 +395,11 @@ NSString *const kNSNotification_SocketManagerStateDidChange = @"kNSNotification_
             OWSSignalServiceProtosEnvelope *envelope = [OWSSignalServiceProtosEnvelope parseFromData:decryptedPayload];
 
             [self.messageReceiver handleReceivedEnvelope:envelope];
-        [self sendWebSocketMessageAcknowledgement:message];
 
+            dispatch_async(dispatch_get_main_queue(), ^{
+                [self sendWebSocketMessageAcknowledgement:message];
+            });
+        });
     } else {
         DDLogWarn(@"%@ Unsupported WebSocket Request", self.tag);