check if the incoming message is already in database before persisting

SessionMessagingKit/Database/Storage+Messaging.swift

@@ -42,6 +42,7 @@ extension Storage {
             }
             tsMessage = tsOutgoingMessage
         } else {
+            if let _ = TSIncomingMessage.find(withAuthorId: message.sender!, timestamp: message.sentTimestamp!, transaction: transaction) { return nil }
             tsMessage = TSIncomingMessage.from(message, quotedMessage: quotedMessage, linkPreview: linkPreview, associatedWith: thread)
         }
         tsMessage.save(with: transaction)

SessionMessagingKit/Sending & Receiving/MessageReceiver+Handling.swift

@@ -365,7 +365,7 @@ extension MessageReceiver {
         }
         // Persist the message
         guard let tsMessageID = storage.persist(message, quotedMessage: tsQuotedMessage, linkPreview: owsLinkPreview,
-            groupPublicKey: message.groupPublicKey, openGroupID: openGroupID, using: transaction) else { throw Error.noThread }
+            groupPublicKey: message.groupPublicKey, openGroupID: openGroupID, using: transaction) else { throw Error.duplicateMessage }
         message.threadID = threadID
         // Start attachment downloads if needed
         let isContactTrusted = Storage.shared.getContact(with: message.sender!)?.isTrusted ?? false