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From Ted Ross <tr...@redhat.com>
Subject Reply-To Addresses (was Re: Introducing Qpid Dispatch Router)
Date Thu, 26 Sep 2013 14:28:51 GMT

On 09/26/2013 08:23 AM, Gordon Sim wrote:
> On 09/26/2013 01:14 PM, Ted Ross wrote:
>> I'm putting a feature into Dispatch that allows a client to dynamically
>> obtain a routable reply-to address.  This will involve changes in
>> Messenger as well.
>
> I'd be interested in hearing a bit more about that, with a view to 
> making any necessary changes to the qpid::messaging library also.
>
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Here's how it looks from a protocol perspective:

                                              Server or
         Client                           First Intermediary
            |                                     |
            |-- Attach Sender  ------------------>|
            |<- Attach ---------------------------|
            |                                     |
            |-- Attach Receiver (src=_dyn_) ----->|
            |<- Attach (src=<temp>) --------------|
            |                                     |
            |-- Xfr (to=SVC, reply-to=<temp>) --->|
            |                                     |
            |<- Xfr (to=<temp>) ------------------|
            |                                     |

The client creates a pair of links, one to send the request and one to 
receive the response.  The source-terminus of the response link is 
flagged as dynamic.  The peer then assigns a temporary source address to 
the link.  This address is valid for the life of the link.  This 
temporary address can then be used as a reply-to in the request message.

 From an API perspective, it would be nice to hide as much of this 
detail as possible from the user.  It might be sufficient to allow a 
message to be tagged as "expecting a reply".  The client library could 
then do what is needed to set up the reply link and insert the reply-to 
field into the message.

-Ted


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