Port #426 Autobahn WebSocket server from ros1 to ros2

Description

The issue described in https://github.com/RobotWebTools/rosbridge_suite/issues/425 and fixed in https://github.com/RobotWebTools/rosbridge_suite/pull/426 still persists in ros2 because the fix was not ported to ros2. There was a request made in https://github.com/RobotWebTools/rosbridge_suite/pull/426#issuecomment-532471720 but I do not see any issue tracking the progress of porting the changes to ros2.

• Library Version: 1.1.2-1focal.20220126.193440
• ROS Version: Rolling
• Platform / OS: Ubuntu 20.04

Steps To Reproduce

I can reproduce issues by performing rapid connect/disconnect while topics are actively being published. I launch the websocket server while other nodes are publishing. Then I have a browser web page that opens a websocket connection and subscribes to topics using https://github.com/RobotWebTools/roslibjs. I can refresh the page rapidly a few times and then observe the websocket server print errors and then no longer accept new websocket connections.

Expected Behavior

The server should recover from websocket disconnect errors mid-write without locking the entire websocket server.

Actual Behavior

The server becomes locked due to the _write_lock never being released because of exception handling logic in the prewrite_message method.

Here is an example trace of the exception:

ERROR:tornado.application:Exception in callback functools.partial(<function wrap.<locals>.null_wrapper at 0x7f75d8f4d700>, <Future finished exception=WebSocketClosedError()>)
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/tornado/websocket.py", line 867, in write_message
    fut = self._write_frame(True, opcode, message, flags=flags)
  File "/usr/lib/python3/dist-packages/tornado/websocket.py", line 846, in _write_frame
    return self.stream.write(frame)
  File "/usr/lib/python3/dist-packages/tornado/iostream.py", line 570, in write
    self._check_closed()
  File "/usr/lib/python3/dist-packages/tornado/iostream.py", line 1112, in _check_closed
    raise StreamClosedError(real_error=self.error)
tornado.iostream.StreamClosedError: Stream is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/tornado/ioloop.py", line 758, in _run_callback
    ret = callback()
  File "/usr/lib/python3/dist-packages/tornado/stack_context.py", line 300, in null_wrapper
    return fn(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/tornado/ioloop.py", line 779, in _discard_future_result
    future.result()
  File "/usr/lib/python3/dist-packages/tornado/gen.py", line 326, in wrapper
    yielded = next(result)
  File "/opt/colcon_ws/install/rosbridge_server/lib/python3.8/site-packages/rosbridge_server/websocket_handler.py", line 197, in prewrite_message
    future = self.write_message(message, binary)
  File "/usr/lib/python3/dist-packages/tornado/websocket.py", line 262, in write_message
    return self.ws_connection.write_message(message, binary=binary)
  File "/usr/lib/python3/dist-packages/tornado/websocket.py", line 869, in write_message
    raise WebSocketClosedError()
tornado.websocket.WebSocketClosedError
ERROR:tornado.application:Exception in callback functools.partial(<function wrap.<locals>.null_wrapper at 0x7f75d8f2d0d0>, <Future finished exception=WebSocketClosedError()>)
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/tornado/ioloop.py", line 758, in _run_callback
    ret = callback()
  File "/usr/lib/python3/dist-packages/tornado/stack_context.py", line 300, in null_wrapper
    return fn(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/tornado/ioloop.py", line 779, in _discard_future_result
    future.result()
  File "/usr/lib/python3/dist-packages/tornado/gen.py", line 326, in wrapper
    yielded = next(result)
  File "/opt/colcon_ws/install/rosbridge_server/lib/python3.8/site-packages/rosbridge_server/websocket_handler.py", line 197, in prewrite_message
    future = self.write_message(message, binary)
  File "/usr/lib/python3/dist-packages/tornado/websocket.py", line 259, in write_message
    raise WebSocketClosedError()
tornado.websocket.WebSocketClosedError

[v-kiniv]

I tried unsuccessfully to get Rosbridge to work stable with ROS2, and ended up writing bridge in C++, it’s ROS2 only (tested on Galactic): https://github.com/v-kiniv/rws

Give it a try if you have problems with Rosbridge and ROS2.

p.s. Sorry for the off-topic comment, but I think it might useful for others who will came here looking for a solution for the Rosbridge+ROS2 issues.

[achim-k]

I think it makes sense to get #741 in first, before trying to migrate to autobahn. I will look into that