Extend websocket server to support message limits and throttling

[iche033]

Summary

Added 3 new features:

• setting max msg queue size

  • Msg published to websocket clients can now have a msg queue size limit to prevent the queue from infinitely growing. You can now set this by specifying:

    <queue_size_per_connection>10</queue_size_per_connection>
  

  • see Limit websocket publish rate and message queue size osrf/subt#950
  • To test, run web app, and navigate to the websocket visualizer page. Connect to a point cloud topic, then use browser debugger to pause the page and verify that memory usage does not keep growing.

• throttling publish rate for topics

  • Added a keyword throttle that can be used by clients to limit the publish rate of a specific topic. This is initiated by the websocket client and it affects all clients who are subscribed to that topic.
  • see related pull request in web app

• limiting number of subscriptions per msg type

  • some msg types have large message size. So this configuration allows users to limit the number of subscriptions that each connection can open for a particular msg type, e.g. the following limits each client to subscribe to only 1 point cloud topic

  <subscription_limit_per_connection>
    <subscription>
      <msg_type>ignition.msgs.PointCloudPacked</msg_type>
      <limit>1</limit>
    </subscription>
  </subscription_limit_per_connection>
  

  • see Limit websocket publish rate and message queue size osrf/subt#950
  • To test, run web app, go to cloudsim's websocket visualizer, and try to connect to multiple point cloud topics. With the above configuration, only one can be visualized.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[nkoenig]

One minor comment

Changes resolved.