Service Bus - Retrieve message from session by sequence number

Question

I am currently trying to retrieve a specific message from a session .

To do so I use want to use the . Receive ( Int64 ) on the MessageSession where I pass in the sequence number of the message.

Here is my code -

long msgSequenceNr = 1337;

QueueClient queueClient = QueueClient.CreateFromConnectionString(Constants.ServiceBusConnectionString, Constants.TestQueueEntityName, ReceiveMode.PeekLock);
MessageSession msgSession = queueClient.AcceptMessageSession(Constants.TestSessionId);

var peekedMsg = msgSession.Peek(msgSequenceNr); // <-- Works fine!
var receivedMsg = msgSession.Receive(msgSequenceNr); // <-- MessageNotFoundException

Unfortunately the Receive will result in a MessageNotFoundException while the Peek works fine. Is this a limitation that I missed or is there another way to achieve this.

Note that it is possible that there are multiple messages in the session

Answer 1

Receive with the SequenceNumber can only be used in combination with the Defer method. This is how you would implement it:

1. Message received, but it can't be processed right now (maybe it's waiting for a different process to complete).
2. Persist the SequenceNumber in some persistent storage (Table Storage, SQL Database, ...)
3. When you know that processing can continue (eg: the dependent process is complete), load all SequenceNumbers from your persistent storage.
4. Use Receive(int sequenceNumber) or ReceiveBatch(int[] sequenceNumbers) to received and process your deferred messages.

Sample application: https://code.msdn.microsoft.com/windowsazure/Brokered-Messaging-ccc4f879#content

Update:

Form your comment I noticed that "undeferring" a deferred message could be a solution. Here's some sample code to undefer the message which copies the deferred message to a new message, Completes the deferred message and sends the new message back in the queue. This uses a TransactionScope to transactionally Complete and Resend the message to avoid the risk of losing the message:

    var messageId = "12434539828282";

    // Send.
    var msg = new BrokeredMessage {SessionId = "user1", MessageId = messageId };
    msg.Properties.Add("Language", "Dutch");
    queue.Send(msg);

    // Receive.
    var session = queue.AcceptMessageSession();
    msg = session.Receive();

    // Store the sequence number.
    var sequenceNumber = msg.SequenceNumber;

    // Defer.
    msg.Defer();

    // Change to true to test if the transaction worked.
    var shouldThrow = false;

    // Later processing of deferred message.
    msg = session.Receive(sequenceNumber);

    try
    {
        using (var ts = new TransactionScope())
        {
            // Create a new message.
            var undeferredMessage = new BrokeredMessage {SessionId = msg.SessionId, MessageId = msg.MessageId};
            foreach (var prop in msg.Properties)
                undeferredMessage.Properties.Add(prop);

            // Complete and send within the same transaction.
            msg.Complete();
            if (shouldThrow)
                throw new InvalidOperationException("Some error");
            queue.Send(undeferredMessage);

            // Complete the transaction.
            ts.Complete();
        }
    }
    catch (Exception ex)
    {
        msg.Abandon();
    }

    if (shouldThrow)
    {
        msg = session.Receive(sequenceNumber);
        Console.WriteLine(msg.MessageId + " should match: " + messageId);
    }
    else
    {
        try
        {
            msg = session.Receive(sequenceNumber);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Message not found, transaction worked OK.");
        }
    }

Note: here I'm simply taking a copy of the Properties. Keep into account that you might want to copy the Body and any other additional information.