QAbstractSocket: Add socketOption for the Path MTU

This allow retrieving the value of the known PMTU for the current
socket. This works on Linux (IPv6 and IPv4) and FreeBSD (IPv6 only) --
the other OSes don't have the necessary API.

Note: do we need add IP_MTU_DISCOVER?

Change-Id: I6e9274c1e7444ad48c81fffd14dcaf97a18ce335
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/network/socket/qnativesocketengine_win.cpp b/src/network/socket/qnativesocketengine_win.cpp
index 1ec3df842f..fb31607e2c 100644
--- a/src/network/socket/qnativesocketengine_win.cpp
+++ b/src/network/socket/qnativesocketengine_win.cpp
@@ -209,7 +209,7 @@ static inline void qt_socket_getPortAndAddress(SOCKET socketDescriptor, const qt
 static void convertToLevelAndOption(QNativeSocketEngine::SocketOption opt,
                                     QAbstractSocket::NetworkLayerProtocol socketProtocol, int &level, int &n)
 {
-    n = 0;
+    n = -1;
     level = SOL_SOCKET; // default
 
     switch (opt) {
@@ -281,6 +281,9 @@ static void convertToLevelAndOption(QNativeSocketEngine::SocketOption opt,
             n = IP_HOPLIMIT;
         }
         break;
+
+    case QAbstractSocketEngine::PathMtuInformation:
+        break;          // not supported on Windows
     }
 }
 
@@ -471,9 +474,11 @@ int QNativeSocketEnginePrivate::option(QNativeSocketEngine::SocketOption opt) co
     QT_SOCKOPTLEN_T len = sizeof(v);
 
     convertToLevelAndOption(opt, socketProtocol, level, n);
-    if (getsockopt(socketDescriptor, level, n, (char *) &v, &len) == 0)
-        return v;
-    WS_ERROR_DEBUG(WSAGetLastError());
+    if (n != -1) {
+        if (getsockopt(socketDescriptor, level, n, (char *) &v, &len) == 0)
+            return v;
+        WS_ERROR_DEBUG(WSAGetLastError());
+    }
     return -1;
 }
 
@@ -514,6 +519,8 @@ bool QNativeSocketEnginePrivate::setOption(QNativeSocketEngine::SocketOption opt
 
     int n, level;
     convertToLevelAndOption(opt, socketProtocol, level, n);
+    if (n == -1)
+        return false;
     if (::setsockopt(socketDescriptor, level, n, (char*)&v, sizeof(v)) != 0) {
         WS_ERROR_DEBUG(WSAGetLastError());
         return false;