Service Bus - Retrieve message from session by sequence number - session

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:
Message received, but it can't be processed right now (maybe it's waiting for a different process to complete).
Persist the SequenceNumber in some persistent storage (Table Storage, SQL Database, ...)
When you know that processing can continue (eg: the dependent process is complete), load all SequenceNumbers from your persistent storage.
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.