Client socket must send data first

[Andrepuel]

Steps to reproduce:

1. Run ./ucat -d -l -p 5678
2. On another terminal, run ./ucat 127.0.0.1 -p 5678
   Working:
3. On the client terminal, send something to the server.
4. Now the communication can flow in any direction.
   Not working:
5. On the server terminal, send something to the client.
6. Now the communication will only work in one direction. The client will not receive any of the server messages, but the other way around works.

[ssiloti]

This is more-or-less by design. The UTP handshake is designed on the assumption that there will be an application layer handshake initiated by the client. If the server were to send data first it would make the protocol vulnerable to amplification attacks.

[inetic]

+1 to what @ssiloti said. My understanding is that it is directly related to this