5 files changed, 29 insertions, 1 deletions

diff --git a/src/corelib/io/qfiledevice.cpp b/src/corelib/io/qfiledevice.cpp
index e1f1db9ead..fc1bc6009a 100644
--- a/src/corelib/io/qfiledevice.cpp
+++ b/src/corelib/io/qfiledevice.cpp
@@ -459,6 +459,8 @@ qint64 QFileDevice::readLineData(char *data, qint64 maxlen)
 qint64 QFileDevice::readData(char *data, qint64 len)
 {
     Q_D(QFileDevice);
+    if (!len)
+        return 0;
     unsetError();
     if (!d->ensureFlushed())
         return -1;
diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index 03bf59ed9d..a60aee1ebe 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -772,6 +772,8 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
             printf("%p \tread 0x%hhx (%c) returning 1 (shortcut)\n", this,
                    int(c), isprint(c) ? c : '?');
 #endif
+            if (d->buffer.isEmpty())
+                readData(data, 0);
             return qint64(1);
         }
     }
@@ -786,8 +788,11 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
             *d->pPos += lastReadChunkSize;
             readSoFar += lastReadChunkSize;
             // fast exit when satisfied by buffer
-            if (lastReadChunkSize == maxSize && !(d->openMode & Text))
+            if (lastReadChunkSize == maxSize && !(d->openMode & Text)) {
+                if (d->buffer.isEmpty())
+                    readData(data, 0);
                 return readSoFar;
+            }
 
             data += lastReadChunkSize;
             maxSize -= lastReadChunkSize;
@@ -906,6 +911,10 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
            int(readSoFar), int(d->pos), d->buffer.size());
     debugBinaryString(data - readSoFar, readSoFar);
 #endif
+
+    if (d->buffer.isEmpty())
+        readData(data, 0);
+
     return readSoFar;
 }
 
@@ -1083,6 +1092,8 @@ qint64 QIODevice::readLine(char *data, qint64 maxSize)
     qint64 readSoFar = 0;
     if (!d->buffer.isEmpty()) {
         readSoFar = d->buffer.readLine(data, maxSize);
+        if (d->buffer.isEmpty())
+            readData(data,0);
         if (!sequential)
             d->pos += readSoFar;
 #if defined QIODEVICE_DEBUG
@@ -1622,6 +1633,9 @@ QString QIODevice::errorString() const
     all the requested information was read and therefore does not retry reading
     if there was a problem.
 
+    This function will be called with maxSize 0 when the device is
+    buffered and the buffer was emptied by a call to read().
+
     \sa read(), readLine(), writeData()
 */
 
diff --git a/src/corelib/io/qprocess.cpp b/src/corelib/io/qprocess.cpp
index de8e3d4b49..7228ceca78 100644
--- a/src/corelib/io/qprocess.cpp
+++ b/src/corelib/io/qprocess.cpp
@@ -1774,6 +1774,8 @@ void QProcess::setupChildProcess()
 qint64 QProcess::readData(char *data, qint64 maxlen)
 {
     Q_D(QProcess);
+    if (!maxlen)
+        return 0;
     QRingBuffer *readBuffer = (d->processChannel == QProcess::StandardError)
                               ? &d->errorReadBuffer
                               : &d->outputReadBuffer;
diff --git a/src/network/socket/qabstractsocket.cpp b/src/network/socket/qabstractsocket.cpp
index 3959419fed..8f290f6e2f 100644
--- a/src/network/socket/qabstractsocket.cpp
+++ b/src/network/socket/qabstractsocket.cpp
@@ -2324,6 +2324,13 @@ qint64 QAbstractSocket::readData(char *data, qint64 maxSize)
 {
     Q_D(QAbstractSocket);
 
+    // Check if the read notifier can be enabled again.
+    if (d->socketEngine && !d->socketEngine->isReadNotificationEnabled() && d->socketEngine->isValid())
+        d->socketEngine->setReadNotificationEnabled(true);
+
+    if (!maxSize)
+        return 0;
+
     // This is for a buffered QTcpSocket
     if (d->isBuffered && d->buffer.isEmpty())
         // if we're still connected, return 0 indicating there may be more data in the future
diff --git a/src/network/socket/qlocalsocket_win.cpp b/src/network/socket/qlocalsocket_win.cpp
index 35b0130afc..90c8fcec1e 100644
--- a/src/network/socket/qlocalsocket_win.cpp
+++ b/src/network/socket/qlocalsocket_win.cpp
@@ -200,6 +200,9 @@ qint64 QLocalSocket::readData(char *data, qint64 maxSize)
 {
     Q_D(QLocalSocket);
 
+    if (!maxSize)
+        return 0;
+
     return d->pipeReader->read(data, maxSize);
 }