Fix QSocketEngineBackend::nativeBytesAvaible for UDP sockets

On OS X ioctl(... FIONREAD) on UDP socket returns more than expected:

"SO_NREAD returns the amount of data in the input buffer that is available to be received
 For datagram oriented sockets, SO_NREAD returns the size of the first packet -- this dif-
 fers from the ioctl() command FIONREAD that returns the total amount of data available."
(man getsockopt). On OS X bytesAvailable for UDP socket seems to include some headers also:
for a datagram of size 1 - bytesAvailable == 17, 2 - bytesAvailable == 18 etc.
Found in a broken tst_qudpsocket test.

Change-Id: I88be827c66208835ed10b010f13d9dc70576fea4
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/src/network/socket/qnativesocketengine_unix.cpp b/src/network/socket/qnativesocketengine_unix.cpp
index 8fe0bb4aad..1b7dfe53ff 100644
--- a/src/network/socket/qnativesocketengine_unix.cpp
+++ b/src/network/socket/qnativesocketengine_unix.cpp
@@ -745,14 +745,23 @@ qint64 QNativeSocketEnginePrivate::nativeBytesAvailable() const
 {
     int nbytes = 0;
     // gives shorter than true amounts on Unix domain sockets.
-    qint64 available = 0;
-    if (qt_safe_ioctl(socketDescriptor, FIONREAD, (char *) &nbytes) >= 0)
-        available = (qint64) nbytes;
+    qint64 available = -1;
+
+#if defined (SO_NREAD)
+    if (socketType == QAbstractSocket::UdpSocket) {
+        socklen_t sz = sizeof nbytes;
+        if (!::getsockopt(socketDescriptor, SOL_SOCKET, SO_NREAD, &nbytes, &sz))
+            available = nbytes;
+    }
+#endif
+
+    if (available == -1 && qt_safe_ioctl(socketDescriptor, FIONREAD, (char *) &nbytes) >= 0)
+        available = nbytes;
 
 #if defined (QNATIVESOCKETENGINE_DEBUG)
     qDebug("QNativeSocketEnginePrivate::nativeBytesAvailable() == %lli", available);
 #endif
-    return available;
+    return available > 0 ? available : 0;
 }
 
 bool QNativeSocketEnginePrivate::nativeHasPendingDatagrams() const