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Does a node receive messages sent by itself on a topic that it is both publishing and subscribing to?

asked 2016-04-30 04:21:31 -0500

luketheduke gravatar image

updated 2022-02-22 11:26:51 -0500

lucasw gravatar image

I am working on writing some code for a project, but I have a node that will be continuously publishing(30 Hz) to a topic while also subscribing to the same topic to listen for a different pub from a different node. Basically, node A is listening to topic X and publishing to topic X. Meanwhile another node, node B, will at some time, publish a message to topic X. Will the subscriber callback in node A be triggered every time it publishes sometime? Also, will it be able to pick up the message if node B only publishes once? Thanks, luketheduke

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May I suggest a title change? Your question seems to be really about whether a node receives its own messages if it publishes on a topic it also subscribes to. You can't actually 'receive callbacks', just messages.

gvdhoorn gravatar image gvdhoorn  ( 2016-05-01 01:29:16 -0500 )edit

Thanks for the suggestion! It's changed.

luketheduke gravatar image luketheduke  ( 2016-05-01 13:30:07 -0500 )edit

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answered 2016-04-30 04:33:39 -0500

If a node publishes on a topic and also has a subscriber for it, it will receive "it's own" message. This is a feature, as components in the publish/subscribe system should not need to care about where a message originates from.

Even though this probably is best avoided, you can check for the origin of a message using the MessageEvent mechanism (e.g. if it originates from the same node) as in this example.

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Thanks for the quick reply!

luketheduke gravatar image luketheduke  ( 2016-04-30 04:42:51 -0500 )edit

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Asked: 2016-04-30 04:21:31 -0500

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Last updated: May 01 '16