Re: Source/Target Question
On Mon, Feb 24, 2014 at 8:37 AM, Ken Giusti kgiu...@redhat.com wrote: +1 this question - I've never quite understood Messenger's current behavior w.r.t. setting the source and target to the same value. I don't think there is a good reason, I think it's just an accident of history. As far as interpreting the behavior of a subscription, and the interaction with the API, I would think the most 'natural' approach would be: sub = M.subscribe(amqp://~0.0.0.0/name) would imply: I am a service called 'name' and I wish to begin receiving messages and sub = M.subscribe(amqp://0.0.0.0/name) would imply: I wish to receive messages from a node called 'name'. As the ~ causes Messenger to open a TCP listener on the address, and the absence of ~ causes Messenger to initiate a connection attempt to the address. In the two cases, I agree with Ted's point that only the Target or Source should be set. My opinion: set them based on the subscription's mode: Target should be set in the case of ~, Source in the case of !~. Thoughts? When a ~ is used messenger is not the one establishing the link, the remote peer establishes the link so it's the remote peer that is going to end up supplying the source and target. Currently messenger just copies whatever the remote peer supplies and proceeds to pass through any and all incoming messages. As for the original question, in the general case we need to think about local terminus/remote terminus rather than source/target as messenger has similar behaviour for outgoing links as well as incoming links. This is even true for ~ URLs since you can send messages to them and they will get held in the messenger's message store until someone connects and grabs them. Given that in many respects messenger will behave like an embedded broker rather than just a simple client, it would in some sense be consistent for messenger to set the local terminus to the name of the messenger unless otherwise overridden. This is consistent with what a broker would do, e.g. when a broker sends messages from a queue, the local terminus is the name of the queue, when a broker receives messages into a queue, the local terminus is still the name of the queue. Regardless of the default though, I think we probably need a mechanism for explicitly controlling both ends, e.g. something like M.subscribe(source-target) for when you want a non default target. --Rafael
Re: Source/Target Question
+1 this question - I've never quite understood Messenger's current behavior w.r.t. setting the source and target to the same value. As far as interpreting the behavior of a subscription, and the interaction with the API, I would think the most 'natural' approach would be: sub = M.subscribe(amqp://~0.0.0.0/name) would imply: I am a service called 'name' and I wish to begin receiving messages and sub = M.subscribe(amqp://0.0.0.0/name) would imply: I wish to receive messages from a node called 'name'. As the ~ causes Messenger to open a TCP listener on the address, and the absence of ~ causes Messenger to initiate a connection attempt to the address. In the two cases, I agree with Ted's point that only the Target or Source should be set. My opinion: set them based on the subscription's mode: Target should be set in the case of ~, Source in the case of !~. Thoughts? -K - Original Message - From: Ted Ross tr...@redhat.com To: proton@qpid.apache.org Sent: Friday, February 21, 2014 3:42:21 PM Subject: Re: Source/Target Question Based on a discussion with Gordon, I'm not going to use source vs. target to infer any intent on the part of the peer node. I am, however, still interested in the answer to the question. -Ted On 02/21/2014 03:02 PM, Ted Ross wrote: I'm working on a feature for Dispatch Router that will allow it to intermediate between clients and brokers. This raises a question about how Proton Messenger handles targets and sources in links. Consider a subscriber using Messenger: from proton import Messenger M = Messenger() M.start() sub = M.subscribe(amqp://0.0.0.0/name) The resulting incoming link (from Messenger's perspective) has a source of name and a target of name. The above code can have two meanings: I am a service called 'name' and I wish to begin receiving messages or I wish to receive messages from a node called 'name'. As I understand it, the first meaning should be indicated by setting the target and the second meaning by setting the source. Since both source and target are set, the intent of the node is ambiguous. From an API perspective, how should a Messenger program indicate which flavor of subscription it is establishing? -Ted -- -K
Source/Target Question
I'm working on a feature for Dispatch Router that will allow it to intermediate between clients and brokers. This raises a question about how Proton Messenger handles targets and sources in links. Consider a subscriber using Messenger: from proton import Messenger M = Messenger() M.start() sub = M.subscribe(amqp://0.0.0.0/name) The resulting incoming link (from Messenger's perspective) has a source of name and a target of name. The above code can have two meanings: I am a service called 'name' and I wish to begin receiving messages or I wish to receive messages from a node called 'name'. As I understand it, the first meaning should be indicated by setting the target and the second meaning by setting the source. Since both source and target are set, the intent of the node is ambiguous. From an API perspective, how should a Messenger program indicate which flavor of subscription it is establishing? -Ted
Re: Source/Target Question
Based on a discussion with Gordon, I'm not going to use source vs. target to infer any intent on the part of the peer node. I am, however, still interested in the answer to the question. -Ted On 02/21/2014 03:02 PM, Ted Ross wrote: I'm working on a feature for Dispatch Router that will allow it to intermediate between clients and brokers. This raises a question about how Proton Messenger handles targets and sources in links. Consider a subscriber using Messenger: from proton import Messenger M = Messenger() M.start() sub = M.subscribe(amqp://0.0.0.0/name) The resulting incoming link (from Messenger's perspective) has a source of name and a target of name. The above code can have two meanings: I am a service called 'name' and I wish to begin receiving messages or I wish to receive messages from a node called 'name'. As I understand it, the first meaning should be indicated by setting the target and the second meaning by setting the source. Since both source and target are set, the intent of the node is ambiguous. From an API perspective, how should a Messenger program indicate which flavor of subscription it is establishing? -Ted
