Check if a port is being used.

port_in_use.rb

require "socket"

def detect_port!
  hostname = Snowpacker.config.hostname || "localhost"
  port = Snowpacker.config.port || 4035
  server = TCPServer.new(hostname, port)
  server.close
rescue Errno::EADDRINUSE
  puts "#{port} is currently being used"
  exit!
end