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From Michael Goulish <mgoul...@redhat.com>
Subject Re: What is x-amqp-to?
Date Tue, 27 Jan 2015 14:44:10 GMT

I use this field in my 'topologist' gadget that reads topology
information from a network of qdrouters.

I only have a connection to router A, but I am able to make topo
requests of the other routers (after I learn their names) by setting
the x-amqp-to field to a value like  "amqp:/_topo/0/QDR.B" .

This causes my local router to forward the request to router B
(to which I have no connection), B consumes the request, 
and I get the answer back.





----- Original Message -----
> On 01/23/2015 01:53 PM, Alan Conway wrote:
> > I'm trying to determine if the message header x-amqp-to has any use or
> > if it's a historical leftover. Here's what I found in the 3 qpid
> > projects:
> >
> > == proton
> > == dispatch
> > doc/book/release-0.1.md:        request.setProperty("x-amqp-to",
> > "amqp:/_local/$management");
> > doc/book/using.md:        request.setProperty("x-amqp-to",
> > "amqp:/_local/$management");
> > == qpid
> > qpid/cpp/AMQP_1.0:for the header section, and x-amqp-to,
> > x-amqp-absolute-expiry-time,
> > qpid/cpp/src/qpid/messaging/amqp/EncodedMessage.cpp:
> > map["x-amqp-to"] = to.str();
> > qpid/cpp/src/qpid/messaging/amqp/SenderContext.cpp:const std::string
> > X_AMQP_TO("x-amqp-to");
> >
> > I believe the dispatch documentation references are incorrect and should
> > be setting the normal "to" address for the message, not the x-amqp-to
> > property. I'll test that and correct if its the case.
> >
> > I followed the bread crumbs in the qpid code base and all I could find
> > was (a lot of) code for propagating this property along the message
> > encoding and transformation path and making it available in the Message
> > API. I couldn't find any code that actually *uses* it.
> >
> > Does anyone know if I'm missing something or can we get rid of it
> > entirely?
> 
> The qpid::messaging::Message class has no 'to' field. However the AMQP
> 1.0 specification does have such a field in the properties section. The
> 'x-amqp-to' label is a special key allowing the AMQP 1.0 field to be
> accessed (for both incoming and outgoing messages) as a special property
> (via Message::getProperty()/setProperty()).
> 
> It should not be needed outside the qpid::messaging client (but within
> that it is still needed).
> 
> 
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