Don't use IPv4 addresses when the user has enabled IPv6 address in the settings.

src/qtlibtorrent/qbtsession.cpp

@@ -1925,16 +1925,18 @@ void QBtSession::setListeningPort(int port) {
   QString ip;
   qDebug("This network interface has %d IP addresses", network_iface.addressEntries().size());
   foreach (const QNetworkAddressEntry &entry, network_iface.addressEntries()) {
-    if (!listen_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv6Protocol))
+    if ((!listen_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv6Protocol))
+        || (listen_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv4Protocol)))
       continue;
     qDebug("Trying to listen on IP %s (%s)", qPrintable(entry.ip().toString()), qPrintable(iface_name));
     s->listen_on(ports, ec, entry.ip().toString().toLatin1().constData(), session::listen_no_system_port);
     if (!ec) {
       ip = entry.ip().toString();
       addConsoleMessage(tr("qBittorrent is trying to listen on interface %1 port: %2", "e.g: qBittorrent is trying to listen on interface 192.168.0.1 port: TCP/6881").arg(ip).arg(QString::number(port)), "blue");
-      break;
+      return;
     }
   }
+  addConsoleMessage(tr("qBittorrent didn't find an %1 local address to listen on", "qBittorrent didn't find an IPv4 local address to listen on").arg(listen_ipv6 ? "IPv6" : "IPv4"), "red");
 }
 
 // Set download rate limit

src/smtp.cpp

@@ -81,13 +81,14 @@ QByteArray determineLocalAddress()
 {
   const Preferences* const pref = Preferences::instance();
   const QString iface_name = pref->getNetworkInterface();
-  const bool listen_ipv6 = pref->getListenIPv6();
+  const bool use_ipv6 = pref->getListenIPv6();
   QByteArray address = "127.0.0.1";
 
   if (iface_name.isEmpty()) {
     foreach (const QHostAddress& addr, QNetworkInterface::allAddresses()) {
       if (addr == QHostAddress::LocalHost || addr == QHostAddress::LocalHostIPv6
-          || (!listen_ipv6 && (addr.protocol() == QAbstractSocket::IPv6Protocol)))
+          || (!use_ipv6 && (addr.protocol() == QAbstractSocket::IPv6Protocol))
+          || (use_ipv6 && (addr.protocol() == QAbstractSocket::IPv4Protocol)))
         continue;
       address = addr.toString().toLatin1();
       break;
@@ -100,7 +101,8 @@ QByteArray determineLocalAddress()
 
     foreach (const QNetworkAddressEntry &entry, network_iface.addressEntries()) {
       if (entry.ip() == QHostAddress::LocalHost || entry.ip() == QHostAddress::LocalHostIPv6
-          || (!listen_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv6Protocol)))
+          || (!use_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv6Protocol))
+          || (use_ipv6 && (entry.ip().protocol() == QAbstractSocket::IPv4Protocol)))
         continue;
 
       address = entry.ip().toString().toLatin1();