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On 09/12/2014 09:50 AM, Flavio Percoco wrote:
> Zaqar supports once and only once delivery.

For the transfer from Zaqar to consumers it does (providing the claim id 
can be recovered). For transfer from producers to Zaqar I believe it is 
more limited.

If the connection to Zaqar fails during a post, the sender can't tell 
whether the message was successfully enqueued or not.

It could try to determine this is by browsing the entire queue looking 
for a matching body. However thatt would be awkward and in any case the 
absence of the message could mean that it wasn't enqueued or that it was 
already consumed and deleted.

One way of handling this is to have the post return a unique url to 
which the message(s) are put or posted. The sender can then repost 
(re-put) to this in the event of failure and the server can determine 
whether it already processed the publications. Alternatively the client 
can be required to generate a unique id on which the server can 
de-deduplicate.

The ActiveMQ REST interface supports both of these approaches: 
http://activemq.apache.org/restful-queue.html