Generic adapter for TCP / UDP / serial communications?

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At least for serial there have been some, and the velodyne_driver package follows a similar design pattern (ie: dedicated nodelet handles network traffic and (initial) deserialisation, other nodelet(s) convert to ROS msgs).

I'm not aware of anything that would be a standard "goto implementation" you could reuse (but that doesn't mean there aren't any of course).

Three reasons why I believe node authors often decide to not separate these concerns:

1. the effort needed to write good networking code is often underestimated
2. if using something like asio for C++ or pyserial for Python, it takes only a few lines of code to get something to work
3. unless you take care (by using nodelets fi), interposing an intermediary node to handle the conversion to and from your external comms infrastructure/transport will introduce latency and jitter, and will add one more component which can fail.

Finally: network and ...(more)

.. typically not examples of shared resources, and require specific interaction patterns to function correctly. Both at the level of the transport, and at the level of communication with whatever is "on the other side".

While that does seem like a responsibility/concern which could be nicely separated -- and some packages that bridge systems like CAN(open)/Ethercat/etc do just that -- it also has a tendency to couple nodes (ie: the bridge and the nodes talking to the bridge), as now two nodes need to work together to maintain proper ordering of messages (fi). This is especially true if the transport/comms channel being wrapped/bridged has no or a different concept of addressing, or doesn't support asynchronous messaging.

Note: I'm not saying your idea is not a good one. I just wanted to discuss it a bit.

That's also why this is not an answer.

I ...(more)