QAbstractSocket: fix writing to socket in HostLookup state

After calling connectToHost(), the socket enters HostLookup state. At this
stage, the socket engine was not created yet, and writing to the socket
should result in either data buffering or an error. So, add a check for
d->socketEngine to prevent a crash on unbuffered sockets.

Task-number: QTBUG-48356
Change-Id: I15ea9ce7de97ce6d7e13e358eca5350745b556bb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Richard J. Moore <rich@kde.org>

2 files changed, 18 insertions, 4 deletions

diff --git a/src/network/socket/qabstractsocket.cpp b/src/network/socket/qabstractsocket.cpp
index d93150799c..5b1c5fa601 100644
--- a/src/network/socket/qabstractsocket.cpp
+++ b/src/network/socket/qabstractsocket.cpp
@@ -2456,13 +2456,15 @@ qint64 QAbstractSocket::readLineData(char *data, qint64 maxlen)
 qint64 QAbstractSocket::writeData(const char *data, qint64 size)
 {
     Q_D(QAbstractSocket);
-    if (d->state == QAbstractSocket::UnconnectedState) {
+    if (d->state == QAbstractSocket::UnconnectedState
+        || (!d->socketEngine && d->socketType != TcpSocket && !d->isBuffered)) {
         d->socketError = QAbstractSocket::UnknownSocketError;
         setErrorString(tr("Socket is not connected"));
         return -1;
     }
 
-    if (!d->isBuffered && d->socketType == TcpSocket && d->writeBuffer.isEmpty()) {
+    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);
         if (written < 0) {
@@ -2473,8 +2475,7 @@ qint64 QAbstractSocket::writeData(const char *data, qint64 size)
             // Buffer what was not written yet
             char *ptr = d->writeBuffer.reserve(size - written);
             memcpy(ptr, data + written, size - written);
-            if (d->socketEngine)
-                d->socketEngine->setWriteNotificationEnabled(true);
+            d->socketEngine->setWriteNotificationEnabled(true);
         }
         return size; // size=actually written + what has been buffered
     } else if (!d->isBuffered && d->socketType != TcpSocket) {
diff --git a/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp b/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
index a4695955af..6f96e6d6f5 100644
--- a/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
+++ b/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
@@ -117,6 +117,7 @@ private slots:
     void readyRead();
     void readyReadForEmptyDatagram();
     void asyncReadDatagram();
+    void writeInHostLookupState();
 
 protected slots:
     void empty_readyReadSlot();
@@ -1725,5 +1726,17 @@ void tst_QUdpSocket::asyncReadDatagram()
     delete m_asyncReceiver;
 }
 
+void tst_QUdpSocket::writeInHostLookupState()
+{
+    QFETCH_GLOBAL(bool, setProxy);
+    if (setProxy)
+        return;
+
+    QUdpSocket socket;
+    socket.connectToHost("nosuchserver.qt-project.org", 80);
+    QCOMPARE(socket.state(), QUdpSocket::HostLookupState);
+    QVERIFY(!socket.putChar('0'));
+}
+
 QTEST_MAIN(tst_QUdpSocket)
 #include "tst_qudpsocket.moc"