Hopefully fix closed group handling bug

Session/Utilities/BackgroundPoller.swift

@@ -43,7 +43,7 @@ public final class BackgroundPoller : NSObject {
     }
     
     private static func getMessages(for publicKey: String) -> Promise<Void> {
-        return SnodeAPI.getSwarm(for: publicKey).then2 { swarm -> Promise<Void> in
+        return SnodeAPI.getSwarm(for: publicKey).then(on: DispatchQueue.main) { swarm -> Promise<Void> in
             guard let snode = swarm.randomElement() else { throw SnodeAPI.Error.generic }
             return SnodeAPI.getRawMessages(from: snode, associatedWith: publicKey).then(on: DispatchQueue.main) { rawResponse -> Promise<Void> in
                 let messages = SnodeAPI.parseRawMessagesResponse(rawResponse, from: snode, associatedWith: publicKey)

SessionMessagingKit/Sending & Receiving/MessageReceiver.swift

@@ -54,11 +54,6 @@ public enum MessageReceiver {
         // Parse the envelope
         let envelope = try SNProtoEnvelope.parseData(data)
         let storage = SNMessagingKitConfiguration.shared.storage
-        // If the message failed to process the first time around we retry it later (if the error is retryable). In this case the timestamp
-        // will already be in the database but we don't want to treat the message as a duplicate. The isRetry flag is a simple workaround
-        // for this issue.
-        guard !Set(storage.getReceivedMessageTimestamps(using: transaction)).contains(envelope.timestamp) || isRetry else { throw Error.duplicateMessage }
-        storage.addReceivedMessageTimestamp(envelope.timestamp, using: transaction)
         // Decrypt the contents
         guard let ciphertext = envelope.content else { throw Error.noData }
         var plaintext: Data!
@@ -159,6 +154,19 @@ public enum MessageReceiver {
             guard isValid else {
                 throw Error.invalidMessage
             }
+            // If the message failed to process the first time around we retry it later (if the error is retryable). In this case the timestamp
+            // will already be in the database but we don't want to treat the message as a duplicate. The isRetry flag is a simple workaround
+            // for this issue.
+            if let message = message as? ClosedGroupControlMessage, case .new = message.kind {
+                // Allow duplicates in this case to avoid the following situation:
+                // • The app performed a background poll or received a push notification
+                // • This method was invoked and the received message timestamps table was updated
+                // • Processing wasn't finished
+                // • The user doesn't see the new closed group
+            } else {
+                guard !Set(storage.getReceivedMessageTimestamps(using: transaction)).contains(envelope.timestamp) || isRetry else { throw Error.duplicateMessage }
+                storage.addReceivedMessageTimestamp(envelope.timestamp, using: transaction)
+            }
             // Return
             return (message, proto)
         } else {