On non-HG this is on the only recognized failure state so we can return more information in the error result.
On HG there are multiple failure states which would require more work to distinguish, so currently return the unsatisfying "Internal Error" like some other existing calls.
This currently prints caps requests received and handled, so that overload of received compared to handled or deadlock can be detected.
This involves making BaseStreamHandler and BaseOutputStream record the ints, which means inheritors should subclass ProcessRequest() instead of Handle()
However, existing inheriting classes overriding Handle() will still work, albeit without stats recording.
"show caps" becomes "show caps list" to disambiguate between show caps commands
Justin Clark-Casey (justincc)