Connecting P2P over NAT

[longfin]

Currently, the implementation of P2P through Swarm assumes that the peer can connect via TCP with public IP. however, clients targeted by libplanet are not directly connected to the Internet with such public IP, but are often connected through NAT. In such a connection method, it is often difficult for one peer to directly access another peer.

Using techniques such as UDP hole punching, it is necessary to support natural connections in these environments.

[longfin]

I've researched about it and leave note as below.

• Option 1: we can modify Swarm to act as a repeater.
  • it changes Swarm's basic communications to broadcast and peers with public IP help communication with peer that don't
  • there is no need for an external server or entity, but the implementation is complicated and the load on peer with public IP is increased.
  • to be honest, I'm not sure if the implementation is possible. 😕
• Option 2: we can modify Swarm to rely STUN / TURN protocols.
  • Swarm uses STUN to determine its public IP and NAT type to traversal.
  • Swarm uses TURN to send actual packet with relay.
  • although it requires two type of external servers (STUN / TURN), it's an open protocol as rfc and can be operated by anyone who wants to operate (including us).
    • but there is not a lot of public TURN servers (compared to STUN).

[longfin]

I've made #117 for sharing progress to other teammates.

[longfin]

Related PRs have been merged. (#117 , #130) so let's close this issue and try it for real game implementation. 😄