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Is there a way to check for dropped messages that don't have headers?

asked 2011-03-20 12:18:57 -0500

updated 2014-01-28 17:09:23 -0500

ngrennan gravatar image

In particular, I am sending some joy/Joy messages over a WLAN and am hinting ros::TransportHints().unreliable() in the subscriber (the publisher is a joy/joy_node).

I've occasionally seen a delay of > 0.5 s, where the in the received messages based on timing within the subscriber's callback, and I'd like to see if that might have to do with dropped UDP packets. I was thinking that I would just look at the header.seq field in each received message, looking for and increment greater than 1, and then realized that joy/Joy messages have no header.

Am I SOL or is there some way to determine whether messages are being dropped?

I also wonder about out-of-order messages which I think are theoretically possible with UDP and was hoping to also watch out for those in a similar manner. Maybe a Header could be added to joy/Joy in a future release?

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answered 2011-03-20 14:13:01 -0500

joq gravatar image

Adding a Header seems like the best solution to me.

For backwards compatibility, maybe create a JoyStamped message.

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Would backwards compatibility really be an issue, though? Usually you wouldn't have one part of a system running say, C-Turtle, and the other Diamondback. Creating a new message type would mean that all publishers and subscribers would have to be recoded. Just changing the message, they wouldn't.
Patrick Bouffard gravatar image Patrick Bouffard  ( 2011-03-20 16:09:17 -0500 )edit
I'm planning on putting a timestamp on a the Joy msg in the next release. These is a ticket here:
mmwise gravatar image mmwise  ( 2011-05-04 10:21:51 -0500 )edit

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Asked: 2011-03-20 12:18:57 -0500

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Last updated: Mar 20 '11