Image streaming over websocket

[iche033]

depends on gazebosim/gz-common#139

🎉 New feature

Summary

Adds support for streaming images from an ign topic.

Added keyword image for requesting data from an image topic. The websocket server plugin will subscribe to the topic in the request and republish the image data over to the client.

A better solution maybe to use a proper streaming server like HTTP Live Streaming (HLS) protocol in the future.

Test it

Launch ign gazebo camera sensor example world:

ign gazebo -v 4 -r src/ign-gazebo/examples/worlds/camera_sensor.sdf

Launch ign websocket server example launch file

ign launch -v 4 src/ign-launch/examples/websocket.ign

See the image stream using this demo image_stream_websocket_client.html file

Note the red and blue channels are reversed in the image stream, which may be fixed by gazebosim/gz-common#162

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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

Note to maintainers: Remember to use Squash-Merge

[nkoenig]

Would it be more efficient to base64 encode the image on the server side rather than on the client side? This could also be captured as a future improvement.

[codecov]

Codecov Report

Merging #97 (3461c90) into ign-launch3 (77f736a) will not change coverage.
The diff coverage is n/a.

❗ Current head 3461c90 differs from pull request most recent head 8dbdb23. Consider uploading reports for the commit 8dbdb23 to get more accurate results

@@             Coverage Diff              @@
##           ign-launch3      #97   +/-   ##
============================================
  Coverage        30.24%   30.24%           
============================================
  Files                3        3           
  Lines              734      734           
============================================
  Hits               222      222           
  Misses             512      512           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 77f736a...8dbdb23. Read the comment docs.