QAbstractSocket: prevent waitForReadyRead() from early exit

According to documentation, waitForReadyRead() returns 'true' if
the readyRead() signal is emitted and there is new data available
for reading. Thus, waitForReadyRead() is being blocked in cycle
until canReadNotification() will return 'true'. This patch
adjusts canReadNotification() to return 'true' only when new data
arrives on buffered socket that ensures waitForReadyRead() to
succeed correctly.

Change-Id: Ic38c4a4dd8ef9128f04b6c1d5f3d03068f6c9894
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/src/network/socket/qabstractsocket.cpp b/src/network/socket/qabstractsocket.cpp
index 88237dc416..ccb63f4716 100644
--- a/src/network/socket/qabstractsocket.cpp
+++ b/src/network/socket/qabstractsocket.cpp
@@ -687,10 +687,11 @@ bool QAbstractSocketPrivate::canReadNotification()
         socketEngine->setReadNotificationEnabled(false);
 
     // If buffered, read data from the socket into the read buffer
-    qint64 newBytes = 0;
     if (isBuffered) {
+        const qint64 oldBufferSize = buffer.size();
+
         // Return if there is no space in the buffer
-        if (readBufferMaxSize && buffer.size() >= readBufferMaxSize) {
+        if (readBufferMaxSize && oldBufferSize >= readBufferMaxSize) {
 #if defined (QABSTRACTSOCKET_DEBUG)
             qDebug("QAbstractSocketPrivate::canReadNotification() buffer is full");
 #endif
@@ -699,7 +700,6 @@ bool QAbstractSocketPrivate::canReadNotification()
 
         // If reading from the socket fails after getting a read
         // notification, close the socket.
-        newBytes = buffer.size();
         if (!readFromSocket()) {
 #if defined (QABSTRACTSOCKET_DEBUG)
             qDebug("QAbstractSocketPrivate::canReadNotification() disconnecting socket");
@@ -707,7 +707,13 @@ bool QAbstractSocketPrivate::canReadNotification()
             q->disconnectFromHost();
             return false;
         }
-        newBytes = buffer.size() - newBytes;
+
+        // Return if there is no new data available.
+        if (buffer.size() == oldBufferSize) {
+            // If the socket is opened only for writing, return true
+            // to indicate that the data was discarded.
+            return !q->isReadable();
+        }
 
         // If read buffer is full, disable the read socket notifier.
         if (readBufferMaxSize && buffer.size() == readBufferMaxSize) {
@@ -715,9 +721,7 @@ bool QAbstractSocketPrivate::canReadNotification()
         }
     }
 
-    // Only emit readyRead() if there is data available.
-    if (newBytes > 0 || !isBuffered)
-        emitReadyRead();
+    emitReadyRead();
 
     // If we were closed as a result of the readyRead() signal,
     // return.