Fix multicastMembershipHelper to not assume addresses are IPv4

Make it iterate the addresses available looking for an IPv4 address,
when that's what it needs, instead of just assuming the first entry in
the list (when non-empty) is IPv4.

Based on a suggestion by Dmitry Pankratov.

Task-number: QTBUG-27641
Change-Id: I1920f68ade44a996ea5c2ed691a87ff3e686f35a
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 20 insertions, 8 deletions

diff --git a/src/network/socket/qnativesocketengine_unix.cpp b/src/network/socket/qnativesocketengine_unix.cpp
index d1efc21e09..e140b33ce9 100644
--- a/src/network/socket/qnativesocketengine_unix.cpp
+++ b/src/network/socket/qnativesocketengine_unix.cpp
@@ -679,10 +679,16 @@ static bool multicastMembershipHelper(QNativeSocketEnginePrivate *d,
 
         if (interface.isValid()) {
             const QList<QNetworkAddressEntry> addressEntries = interface.addressEntries();
-            if (!addressEntries.isEmpty()) {
-                QHostAddress firstIP = addressEntries.first().ip();
-                mreq4.imr_interface.s_addr = htonl(firstIP.toIPv4Address());
-            } else {
+            bool found = false;
+            for (const QNetworkAddressEntry &entry : addressEntries) {
+                const QHostAddress ip = entry.ip();
+                if (ip.protocol() == QAbstractSocket::IPv4Protocol) {
+                    mreq4.imr_interface.s_addr = htonl(ip.toIPv4Address());
+                    found = true;
+                    break;
+                }
+            }
+            if (!found) {
                 d->setError(QAbstractSocket::NetworkError,
                             QNativeSocketEnginePrivate::NetworkUnreachableErrorString);
                 return false;
diff --git a/src/network/socket/qnativesocketengine_win.cpp b/src/network/socket/qnativesocketengine_win.cpp
index 5a9641a9fe..e203571a63 100644
--- a/src/network/socket/qnativesocketengine_win.cpp
+++ b/src/network/socket/qnativesocketengine_win.cpp
@@ -959,10 +959,16 @@ static bool multicastMembershipHelper(QNativeSocketEnginePrivate *d,
 
         if (iface.isValid()) {
             const QList<QNetworkAddressEntry> addressEntries = iface.addressEntries();
-            if (!addressEntries.isEmpty()) {
-                QHostAddress firstIP = addressEntries.first().ip();
-                mreq4.imr_interface.s_addr = htonl(firstIP.toIPv4Address());
-            } else {
+            bool found = false;
+            for (const QNetworkAddressEntry &entry : addressEntries) {
+                const QHostAddress ip = entry.ip();
+                if (ip.protocol() == QAbstractSocket::IPv4Protocol) {
+                    mreq4.imr_interface.s_addr = htonl(ip.toIPv4Address());
+                    found = true;
+                    break;
+                }
+            }
+            if (!found) {
                 d->setError(QAbstractSocket::NetworkError,
                             QNativeSocketEnginePrivate::NetworkUnreachableErrorString);
                 return false;