From ffdd115ded596f53085a37afbda9bcba7ea353a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alin=20Tr=C4=83istaru?= <github@cevreau.eu>
Date: Mon, 5 May 2025 12:20:54 +0200
Subject: [PATCH] [client] set TLS ServerName for hostname-based QUIC
 connections (#3673)

* fix: set TLS ServerName for hostname-based QUIC connections

When connecting to a relay server by hostname, certificates are
validated against the IP address instead of the hostname.
This change sets ServerName in the TLS config when connecting
via hostname, ensuring proper certificate validation.

* use default port if port is missing in URL string
---
 relay/client/dialer/quic/quic.go | 37 +++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/relay/client/dialer/quic/quic.go b/relay/client/dialer/quic/quic.go
index 7fd486f87..3fd48fb19 100644
--- a/relay/client/dialer/quic/quic.go
+++ b/relay/client/dialer/quic/quic.go
@@ -28,6 +28,16 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 		return nil, err
 	}
 
+	// Get the base TLS config
+	tlsClientConfig := quictls.ClientQUICTLSConfig()
+
+	// Set ServerName to hostname if not an IP address
+	host, _, splitErr := net.SplitHostPort(quicURL)
+	if splitErr == nil && net.ParseIP(host) == nil {
+		// It's a hostname, not an IP - modify directly
+		tlsClientConfig.ServerName = host
+	}
+
 	quicConfig := &quic.Config{
 		KeepAlivePeriod:   30 * time.Second,
 		MaxIdleTimeout:    4 * time.Minute,
@@ -47,7 +57,7 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 		return nil, err
 	}
 
-	session, err := quic.Dial(ctx, udpConn, udpAddr, quictls.ClientQUICTLSConfig(), quicConfig)
+	session, err := quic.Dial(ctx, udpConn, udpAddr, tlsClientConfig, quicConfig)
 	if err != nil {
 		if errors.Is(err, context.Canceled) {
 			return nil, err
@@ -61,12 +71,29 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 }
 
 func prepareURL(address string) (string, error) {
-	if !strings.HasPrefix(address, "rel://") && !strings.HasPrefix(address, "rels://") {
+	var host string
+	var defaultPort string
+
+	switch {
+	case strings.HasPrefix(address, "rels://"):
+		host = address[7:]
+		defaultPort = "443"
+	case strings.HasPrefix(address, "rel://"):
+		host = address[6:]
+		defaultPort = "80"
+	default:
 		return "", fmt.Errorf("unsupported scheme: %s", address)
 	}
 
-	if strings.HasPrefix(address, "rels://") {
-		return address[7:], nil
+	finalHost, finalPort, err := net.SplitHostPort(host)
+	if err != nil {
+		if strings.Contains(err.Error(), "missing port") {
+			return host + ":" + defaultPort, nil
+		}
+
+		// return any other split error as is
+		return "", err
 	}
-	return address[6:], nil
+
+	return finalHost + ":" + finalPort, nil
 }