Openfire currently uses Jetty 9.2.9. Quite some work has been done on Jetty since that release.
Although the current 9.3 and upcoming 9.4 branch differ significantly, the 9.2 branch also had a good number (70+) of improvements.
We should upgrade Jetty from 9.2.9 to the latest version of the 9.2 branch, which is 9.2.14 at the time of writing.
A direct cause for me to raise this issue is a problem with asynchronous processing of POST requests with no/empty bodies. This was fixed in 9.2.10
Pushed to master as well as 4.0 branch.