On 08/29/2014 04:57 PM, Rob Godfrey wrote:
On 29 August 2014 17:39, Gordon Sim <[email protected]> wrote:
I'm not opposed to change. However I don't think the use of subject for
what might be termed 'routing' is obviously wrong or unintended by the
current spec and therefore an illogical choice for anything 'designed
around AMQP 1.0'.
I'm not saying it's wrong...
I think you are (and that in itself I don't object to):
On 08/29/2014 03:42 PM, Rob Godfrey wrote:
On 29 August 2014 16:24, Gordon Sim <[email protected]> wrote:
On 08/29/2014 03:12 PM, Rob Godfrey wrote:
If an application is designed around using AMQP 1.0, I would not normally
expect them to be putting routing information in the subject field.
That depends on what you define to be routing information. I think it is a
perfectly sensible approach to use the subject to indicate some sort of
logical category and then have the broker be configured to 'route' messages
according to that logical category.
I think that's one choice you could make, certainly. I just think it's a
bad choice for the general case.
You also appeared to be implying that the definitions of the 'to' and
'subject' fields in the specification backed this view up. That's where
I disagreed with you.
I can accept that using the subject may not be the best approach for
other reasons, i.e. that it is wrong. What I objected to is the notion
that it is *obviously* wrong based on a reading of the specification and
therefore somehow not really AMQP 1.0.
And indeed originally I was very much of the
opinion that subject was a surrogate for the routing-key in 0.10 (which is
why I originally implemented filters in that way).
I think those legacy filters turned out to be a mistake. I quite agree
that a convention around the address (either of the source/target, or of
the 'to' field on the message) leads to a simpler (yet also more
flexible and powerful) solution for the use cases the direct and topic
exchanges were intended to support.
The description in the spec for the 'to' field is again in hindsight not
a good one (not entirely sure its the best choice of name either), and
it may indeed have been better to leave the subject field out entirely.
[...]
However I think the potentially
more contentious question is actually message translation.
I doubt it's that contentious :-)
Behaviour of
exchanges can be considered a property of a given exchange/node/address
whatever you want to call it. Message translation is externally visible
and obviously we should be striving to have commonality there. Given an
AMQP 1.0 message how does one translate that into an AMQP 0-9-1 or 0-10
message (along with their associated delivery headers). In particular for
reply to... I am translating an AMQP 0-10 exchange + routing-key combo into
and AMQP 1.0 address of "exchange/routing-key" ... How does the C++ broker
translate the replyTo address?
It does the same thing.
I've actually described the mapping for the qpid::messaging API and the
c++ brokers behaviours onto 1.0 on this list in past threads and in a
readme:
http://svn.apache.org/viewvc/qpid/trunk/qpid/cpp/AMQP_1.0?view=markup.
My hope in doing so was that it would allow others to comment and
criticise the choices made, suggesting alternatives or enhancements
(indeed Fraser's feedback was very valuable) and that this would
encourage more open analysis and discussion around AMQP 1.0 extended
semantics which I feel is sorely lacking. Sadly this failed.
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