QAbstractSocket: avoid unspecified behavior in writing on TCP

Passing zero as size parameter to QAbstractSocketEngine::write() has
unspecified behavior, at least for TCP sockets. This could happen on
flush() when writeBuffer is empty or on writeData() with size 0. Avoid
by explicitly checking against zero size.

Change-Id: I070630d244ce6c3de3da94f84c2cded2c7a4b081
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/network/socket/qabstractsocket.cpp b/src/network/socket/qabstractsocket.cpp
index 3d665270fd..f28dc6698a 100644
--- a/src/network/socket/qabstractsocket.cpp
+++ b/src/network/socket/qabstractsocket.cpp
@@ -881,7 +881,7 @@ bool QAbstractSocketPrivate::flush()
     const char *ptr = writeBuffer.readPointer();
 
     // Attempt to write it all in one chunk.
-    qint64 written = socketEngine->write(ptr, nextSize);
+    qint64 written = nextSize ? socketEngine->write(ptr, nextSize) : Q_INT64_C(0);
     if (written < 0) {
 #if defined (QABSTRACTSOCKET_DEBUG)
         qDebug() << "QAbstractSocketPrivate::flush() write error, aborting." << socketEngine->errorString();
@@ -2477,7 +2477,7 @@ qint64 QAbstractSocket::writeData(const char *data, qint64 size)
     if (!d->isBuffered && d->socketType == TcpSocket
         && d->socketEngine && d->writeBuffer.isEmpty()) {
         // This code is for the new Unbuffered QTcpSocket use case
-        qint64 written = d->socketEngine->write(data, size);
+        qint64 written = size ? d->socketEngine->write(data, size) : Q_INT64_C(0);
         if (written < 0) {
             d->setError(d->socketEngine->error(), d->socketEngine->errorString());
             return written;