Add ALPN support

This should make go-sendxmpp work on servers using ALPN e.g. when
using sslh on port 443 to use a httpd and XMPP over TLS on the
same port.

go-sendxmpp.go

@@ -83,7 +83,7 @@ func parseConfig(configPath string) (configuration, error) {
 
 	// Read config file per line.
 	for scanner.Scan() {
-		if strings.HasPrefix(scanner.Text(), "#"){
+		if strings.HasPrefix(scanner.Text(), "#") {
 			continue
 		}
 
@@ -100,7 +100,7 @@ func parseConfig(configPath string) (configuration, error) {
 			output.port = row[1]
 		default:
 			if len(row) >= 2 {
-				if strings.Contains(scanner.Text(), ";"){
+				if strings.Contains(scanner.Text(), ";") {
 					output.username = strings.Split(row[0], ";")[0]
 					output.jserver = strings.Split(row[0], ";")[1]
 					output.password = row[1]
@@ -238,15 +238,21 @@ func main() {
 		password = *flagPassword
 	}
 
+	// Use ALPN
+	tlsConfig := xmpp.DefaultConfig
+	tlsConfig.ServerName = strings.Split(server, ":")[0]
+	tlsConfig.NextProtos = append(tlsConfig.NextProtos, "xmpp-client")
+
 	// Set XMPP connection options.
 	options := xmpp.Options{
-		Host:     server,
-		User:     user,
-		Resource: *flagResource,
-		Password: password,
-		NoTLS:    !*flagTLS,
-		StartTLS: *flagStartTLS,
-		Debug:    *flagDebug,
+		Host:      server,
+		User:      user,
+		Resource:  *flagResource,
+		Password:  password,
+		NoTLS:     !*flagTLS,
+		StartTLS:  *flagStartTLS,
+		Debug:     *flagDebug,
+		TLSConfig: &tlsConfig,
 	}
 
 	// Read message from file.