Server response to legacy ping (fe and fe01) packets

[deathcap]

Implements server-side support for #332 FE legacy ping support

Supports type 0 (fe) and type 1 (fe01) pings, testing with https://github.com/deathcap/node-minecraft-ping:

node-minecraft-protocol $ NODE_DEBUG=mc-proto node examples/server/server.js
node-minecraft-ping $   node demo.js localhost 25565
received ping_fe01fa { pingVersion: 1,
  protocolVersion: 47,
  gameVersion: '1.8.8',
  motd: 'Vox Industries',
  playersOnline: 0,
  maxPlayers: 12 }
received ping_fe { pingVersion: 0,
  motd: 'Vox Industries',
  playersOnline: 0,
  maxPlayers: 12 }
received ping_fe01 { pingVersion: 1,
  protocolVersion: 47,
  gameVersion: '1.8.8',
  motd: 'Vox Industries',
  playersOnline: 0,
  maxPlayers: 12 }

Some notes about issues/limitations with this pull request:

• The deserializer cannot parse legacy ping packets, because of the missing varint packet type header, so I worked around by having the splitter prepend a varint packet id. Ideally minecraft-data could specify how to parse these packets: Legacy ping protocol minecraft-data#95 but idk how
• minecraft-data specifies server_legacy_list_ping as requiring a ubyte payload, but for ping type 0 it is not, so I fill in a \0 in the ping payload to avoid deserialization errors. Also would need changes to Legacy ping protocol minecraft-data#95
• Serializer is not used to write the ping responses (or the ping requests, which aren't supported in this PR) for the same reason; client.writeRaw() is also unsuitable because it prepends length, so I use client.socket.write(). Maybe this could be refactored further, a new "legacy" packet state, which doesn't have length varints? Could be revisited later if/once pre-Netty protocol support is added.
• Node.js has utf16le support in Buffer but not utf16be (UCS2 big endian encoding for buffer nodejs/node-v0.x-archive#1684); encoded hackishly updated to use native utf16le + swap with https://github.com/substack/endian-toggle, works well
• No client support for sending legacy ping requests or parsing legacy ping responses (can use n-mc-ping, but would be nice to have in nmp)

but it is functional

[rom1504]

isn't state === states.HANDSHAKING always true at that point ?

edit:nevermind

[rom1504]

This is kind of a hack, but well, so is that packet. It would be ideal to handle this kind of thing properly directly in protodef, but let's do that later in #332