Message reader

A message box reader reads messages from one or more message boxes, and passes them to a delegate for further processing.

Instance creation

MessageBoxReader messageBoxReader = new MessageBoxReader(keyPair, accountWithKey);

var messageBoxReader = new cds.MessageBoxReader(keyPair, accountWithKey);

my $messageBoxReader = CDS::MessageBoxReader->new($keyPair, $accountWithKey, $delegate);

Creates a message reader for reading messages addressed to the key pair.

Perl uses structural delegates, i.e. the delegate is defined when creating the structure. Since it is single-threaded, the program flow is defined by the control flow. The Java implementation uses operation delegates. The delegate is passed with an asynchronous operation (e.g. read). The control flow returns immediately, and the program logic flow continues in one or more of the delegate functions.

Reading messages

messageBoxReader.read(delegate);

messageBoxReader.read(accountWithKey);

$messageBoxReader->read($accountWithKey);

Starts reading the message box of account with key, unless a read operation for that account is already ongoing.

A read operation first lists the message box. If listing fails, onInQueueListFailed is called on the delegate, and the read operation stops immediately.

The reader then processes each message. Up to approximately 4 messages are processed in parallel.

For each message, the envelope is retrieved from the store and parsed. If the envelope is complete, onInQueueVerifyStore is called on the delegate to resolve the sender's store. If the delegate returns nullundef, the message is treated as invalid.

Otherwise, the sender's public key is retrieved from the store, the signature is verified, the AES key decrypted, and the content retrieved.

Once everything is ready onInQueueMessage is called for further processing.

When a read operation starts, on the delegate, indicating the store. Similarly, onInQueueReadingStarts is called when the

boolean isReading = messageBoxReader.isReading(store);

var isReading = messageBoxReader.isReading(store);

my $isReading = $messageBoxReader->isReading($store);

Indicates whether a read operation for the indicated store is ongoing.

Implementing a delegate

		@Override
		public boolean onInQueueVerifyStore(HashReference source, Record envelope, String storeUrl) {
			// Allow HTTP stores
			return storeUrl.startsWith("http://") || storeUrl.startsWith("https://");
		}

		@Override
		void onInQueueMessage(ReceivedMessage message) {
			// Process the message, and call one of the following
			message.processed();
			message.remove();
			message.failed(error);
			message.postpone(Duration.MINUTE * 10);
		}

		@Override
		void onInQueueMessageInvalid(HashReference source, String reason) {
			// An invalid message was found. Such messages are deleted.
			// This could be shown on the user interface, or logged.
		}

		@Override
		void onInQueueMessageFailed(HashReference source, String error) {
			// A message could not be retrieved due to a store error.
			// Such messages are put on hold, and will be tried later.
			// This could be shown on the user interface, or logged.
		}

		@Override
		void onInQueueListFailed(AccountWithKey accountWithKey, String error) {
			// Listing failed. This could be shown on the user interface.
		}

		@Override
		void onInQueueReadingDone(AccountWithKey accountWithKey) {
			// All messages have been read. This could be shown on the user interface.
		}