Add net.Dialer DualStack config option.

client/connection.go

@@ -82,6 +82,11 @@ type Config struct {
 	// Local address to bind to when connecting to the server.
 	LocalAddr string
 
+	// To attempt RFC6555 parallel IPv4 and IPv6 connections if both
+	// address families are returned for a hostname, set this to true.
+	// Passed through to https://golang.org/pkg/net/#Dialer
+	DualStack bool
+
 	// Replaceable function to customise the 433 handler's new nick.
 	// By default an underscore "_" is appended to the current nick.
 	NewNick func(string) string
@@ -160,6 +165,7 @@ func Client(cfg *Config) *Conn {
 
 	dialer := new(net.Dialer)
 	dialer.Timeout = cfg.Timeout
+	dialer.DualStack = cfg.DualStack
 	if cfg.LocalAddr != "" {
 		if !hasPort(cfg.LocalAddr) {
 			cfg.LocalAddr += ":0"