Prefer ipv6 setting

proxy/telegram.go

@@ -7,24 +7,37 @@ import (
 	"github.com/juju/errors"
 )
 
-var telegramDCIPs = [5]string{
-	"149.154.175.50:443",
-	"149.154.167.51:443",
-	"149.154.175.100:443",
-	"149.154.167.91:443",
-	"149.154.171.5:443",
+type TelegramAddress struct {
+	v4 string
+	v6 string
 }
 
+func (t *TelegramAddress) IPv4() string {
+	return net.JoinHostPort(t.v4, telegramPort)
+}
+
+func (t *TelegramAddress) IPv6() string {
+	return net.JoinHostPort(t.v6, telegramPort)
+}
+
+var TelegramAddresses = []TelegramAddress{
+	TelegramAddress{v4: "149.154.175.50", v6: "2001:b28:f23d:f001::a"},
+	TelegramAddress{v4: "149.154.167.51", v6: "2001:67c:04e8:f002::a"},
+	TelegramAddress{v4: "149.154.175.100", v6: "2001:b28:f23d:f003::a"},
+	TelegramAddress{v4: "149.154.167.91", v6: "2001:67c:04e8:f004::a"},
+	TelegramAddress{v4: "149.154.171.5", v6: "2001:b28:f23f:f005::a"},
+}
+
+const telegramPort = "443"
+
 const telegramKeepAlive = 30 * time.Second
 
-func dialToTelegram(dcIdx int16, timeout time.Duration) (net.Conn, error) {
+func dialToTelegram(ipv6 bool, dcIdx int16, timeout time.Duration) (net.Conn, error) {
 	if dcIdx < 0 || dcIdx >= 5 {
 		return nil, errors.New("Incorrect DC IDX")
 	}
 
-	dialer := net.Dialer{Timeout: timeout}
-	rawConn, err := dialer.Dial("tcp", telegramDCIPs[dcIdx])
-	conn := rawConn.(*net.TCPConn)
+	conn, err := doDial(ipv6, dcIdx, timeout)
 	if err != nil {
 		return nil, errors.Annotate(err, "Cannot dial")
 	}
@@ -38,3 +51,20 @@ func dialToTelegram(dcIdx int16, timeout time.Duration) (net.Conn, error) {
 
 	return conn, nil
 }
+
+func doDial(ipv6 bool, dcIdx int16, timeout time.Duration) (*net.TCPConn, error) {
+	dialer := net.Dialer{Timeout: timeout}
+	addr := TelegramAddresses[dcIdx]
+
+	if ipv6 {
+		if conn, err := dialer.Dial("tcp", addr.IPv6()); err == nil {
+			return conn.(*net.TCPConn), nil
+		}
+	}
+
+	conn, err := dialer.Dial("tcp", addr.IPv4())
+	if err == nil {
+		return conn.(*net.TCPConn), nil
+	}
+	return nil, err
+}