Method createConn

nats.go:2305–2374

createConn will connect to the server and wrap the appropriate bufio structures. It will do the right thing when an existing connection is in place.

()

// bufio structures. It will do the right thing when an existing
// connection is in place.
func (nc *Conn) createConn() (err error) {
	if nc.Opts.Timeout < 0 {
		return ErrBadTimeout
	}
	if _, cur := nc.currentServer(); cur == nil {
		return ErrNoServers
	}

	// If we have a reference to an in-process server then establish a
	// connection using that.
	if nc.Opts.InProcessServer != nil {
		conn, err := nc.Opts.InProcessServer.InProcessConn()
		if err != nil {
			return fmt.Errorf("failed to get in-process connection: %w", err)
		}
		nc.conn = conn
		nc.bindToNewConn()
		return nil
	}

	// We will auto-expand host names if they resolve to multiple IPs
	hosts := []string{}
	u := nc.current.URL

	if !nc.Opts.SkipHostLookup && net.ParseIP(u.Hostname()) == nil {
		addrs, _ := net.LookupHost(u.Hostname())
		for _, addr := range addrs {
			hosts = append(hosts, net.JoinHostPort(addr, u.Port()))
		}
	}
	// Fall back to what we were given.
	if len(hosts) == 0 {
		hosts = append(hosts, u.Host)
	}

	// CustomDialer takes precedence. If not set, use Opts.Dialer which
	// is set to a default *net.Dialer (in Connect()) if not explicitly
	// set by the user.
	dialer := nc.Opts.CustomDialer
	if dialer == nil {
		// We will copy and shorten the timeout if we have multiple hosts to try.
		copyDialer := *nc.Opts.Dialer
		copyDialer.Timeout = copyDialer.Timeout / time.Duration(len(hosts))
		dialer = &copyDialer
	}

	if len(hosts) > 1 && !nc.Opts.NoRandomize {
		rand.Shuffle(len(hosts), func(i, j int) {
			hosts[i], hosts[j] = hosts[j], hosts[i]
		})
	}
	for _, host := range hosts {
		nc.conn, err = dialer.Dial("tcp", host)
		if err == nil {
			break
		}
	}
	if err != nil {