code: func DialerFromEnvironment(addr string) Dialer {
  	// Try and get proxy addr from the environment.
  	proxyAddr := getProxyAddress(addr)
  
  	// If no proxy settings are in environment return regular ssh dialer,
  	// otherwise return a proxy dialer.
  	if proxyAddr == "" {
  		log.Debugf("No proxy set in environment, returning direct dialer.")
  		return directDial{}
  	}
  	log.Debugf("Found proxy %q in environment, returning proxy dialer.", proxyAddr)
  	return proxyDial{proxyHost: proxyAddr}
  }
docs: // DialerFromEnvironment returns a Dial function. If the https_proxy or http_proxy
  // environment variable are set, it returns a function that will dial through
  // said proxy server. If neither variable is set, it will connect to the SSH
  // server directly.