Considering you were attacked first and the attacker was using a weapon, pulling a knife could constitute self defence. As long as the weapon is legal in your state, I don't see how you can be charged with anything.
Also, since the guy who attacked you did so for no reason and with a dog chain, he is probably uncultured and likely not wealthy. This would mean he would be unable to afford a good lawyer if you press charges and would have to rely on a crappy public defender. For this reason, it is unlikely he will press charges (if an investigation occurs it looks like he would be screwed too).
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