The extra buffer used to decode the strings sent by the client
in the legacy ping protocol was never released. However, creating
an extra copy of the buffer just to decode it to a string isn't
actually necessary: We can just call toString() directly on the
original buffer.
Additionally, free the buffer in handlerRemoved() to handle cases
where the client never sends enough bytes to form a valid legacy
ping request.
This only impacted people who used our useSnapshots new API in a plugin,
which obviously was no one as the data result was completely broken.
Merged the NPE check patch into mine since it has to handle it too.
At the time this was re-added, there was concern around how the JIT
would handle the system property that enabled it.
This shouldn't be a problem, and as such we no longer need to block
access to it.
The Vanilla Method Profiler will not provide much to most users however
there is no harm in providing it as an option. For most users, the
recommended and supported method for determining performance issues with
Paper will continue to be Timings.
* Make the legacy ping handler more reliable
The Minecraft server often fails to respond to old ("legacy") pings
from old Minecraft versions using the protocol used before the switch
to Netty in Minecraft 1.7.
Due to packet fragmentation[1], we might not have all needed bytes
available when the LegacyPingHandler is called. In this case, it will
run into an error, remove the handler and continue using the modern
protocol.
This is unlikely to happen for the first two revisions of the legacy
ping protocol (used in Minecraft 1.5.x and older) since the request
consists of only one or two bytes, but happens frequently for the
last/third revision introduced in Minecraft 1.6.
It has much larger, variable packet sizes due to the inclusion of
the virtual host (the hostname/port used to connect to the server).
The solution[2] is simple: If we find more than two matching bytes,
we buffer the remaining bytes until we have enough to fully read and
respond to the request.
[1]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h3-11
[2]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h4-13
* Add legacy ping support to PaperServerListPingEvent
Add a new method to StatusClient check if the client is a legacy
client that does not support all of the features provided in the
event.
