Please provide a link to the specification:
There is nothing in this specs that says a server should mask anything
This leads to connection abort with libsoup
Thanks for the report.
Problem seems to be that mod_websocket just returns the ping frame as is after changing opcode to pong,
which preserves the mask flag.
Fixed in https://hg.prosody.im/0.11/rev/10d6d0d91f4e despite being unable to reproduce the problem. The change doesn't appear to break anything tho and should be safe.
Reproduced with libsoup 2.68.2 in a Debian testing container.