What I do is stop and face the dog. If it stops and doesn’t show signs of aggression, I back up a little, and soon go on my way. Shooting it, even if I happened to be armed, does not occur to me as a first response. But then I’m not a cop with control issues. Precisely. I would add that if you did shoot a dog under the circumstances decribed, this very cop would put your face in the dirt, cuff you and throw your can in jail.
To quote Orwell, "Some animals are more equal than other animals."