Fire off just a SYN for TCP packets

[PaulMaddox]

At the moment, KnockSequence.java#166 attempts to open a full socket (read: full tcp handshake) with a 1000ms timeout to the knock destination for TCP packets, when all it actually needs to do is fire off a TCP SYN.

[etiago]

Here's a +1 for this to be added to the next milestone 👍 it actually doesn't work for me as is since my server's firewall is configured (purposefully) to drop all the ports by default. This seems to get in the way. It works with the knock client for OSX but not with this one.

[etiago]

It seems it's not trivial to send a TCP SYN on Java. I've gone as far as finding the RockSaw library which allows you to open raw sockets in Java. This should do the trick I'd hope...