libsweep does not handle unexpected unplug gracefully

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Root cause of: https://github.com/scanse/sweep-ros/issues/11

libsweep version + affected bindings

This is an issue in the libsweep software package

operating system

I've only tested on Linux, current Windows behavior in the same situation is unknown

Description:

I have determined the root cause of the issue to be here: https://github.com/scanse/sweep-sdk/blob/master/libsweep/src/unix/serial.cc#L332

When the device is unplugged this results in an EOF event where all calls to wait_readable will return true but calls to read returns zero bytes. This sends us into an infinite loop as this specific failure mode is not addressed at all in the loop so we're stuck here forever.

Repro steps

• Plugin sensor
• Start a system monitor: htop
• Start sweep_node roslaunch sweep_ros sweep.launch
• Wait until scans are collected(1-5s): rostopic hz /pc2
• Unplug sensor

Observed result

• CPU usage goes from ~0.1% to over 90%
• No error messages in /rosout or log files
• Node stops publishing to /pc2 topic

Expected result

• Error message indicating some form of sensor failure/read timeout
• CPU usage unchanged

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Examining other failure modes in libsweep it appears the right thing here is to throw an exception(possibly causing the calling process to terminate abruptly). I will produce a patched version to bring this failure mode inline with the behavior I see employed elsewhere.