From d0b54cede8d8ea0b8431c64abb51d0cd1a71327b Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@theqtcompany.com>
Date: Fri, 27 Nov 2015 13:28:45 +0100
Subject: [PATCH] Ensure QTextStream doesn't modify the Text flag on the
 underlying iodevice

An empty read or a failed write on the underlying QIODevice of the text
stream would lead to an early return where we wouldn't correctly restore
the QIODevice::Text flag of the io device.

Change-Id: I5b632f45dea6ede3f408113556c3dad1b96574e2
Task-number: QTBUG-47176
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>
---
 src/corelib/io/qtextstream.cpp                | 21 ++++++++++---------
 .../io/qtextstream/tst_qtextstream.cpp        | 17 +++++++++++++++
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/corelib/io/qtextstream.cpp b/src/corelib/io/qtextstream.cpp
index a8fd2dd7ab..78dcbfe0e7 100644
--- a/src/corelib/io/qtextstream.cpp
+++ b/src/corelib/io/qtextstream.cpp
@@ -449,6 +449,10 @@ bool QTextStreamPrivate::fillReadBuffer(qint64 maxBytes)
             bytesRead = device->read(buf, sizeof(buf));
     }
 
+    // reset the Text flag.
+    if (textModeEnabled)
+        device->setTextModeEnabled(true);
+
     if (bytesRead <= 0)
         return false;
 
@@ -484,10 +488,6 @@ bool QTextStreamPrivate::fillReadBuffer(qint64 maxBytes)
     readBuffer += QString::fromLatin1(buf, bytesRead);
 #endif
 
-    // reset the Text flag.
-    if (textModeEnabled)
-        device->setTextModeEnabled(true);
-
     // remove all '\r\n' in the string.
     if (readBuffer.size() > oldReadBufferSize && textModeEnabled) {
         QChar CR = QLatin1Char('\r');
@@ -586,17 +586,18 @@ void QTextStreamPrivate::flushWriteBuffer()
     qDebug("QTextStreamPrivate::flushWriteBuffer(), device->write(\"%s\") == %d",
            qt_prettyDebug(data.constData(), qMin(data.size(),32), data.size()).constData(), int(bytesWritten));
 #endif
+
+#if defined (Q_OS_WIN)
+    // reset the text flag
+    if (textModeEnabled)
+        device->setTextModeEnabled(true);
+#endif
+
     if (bytesWritten <= 0) {
         status = QTextStream::WriteFailed;
         return;
     }
 
-#if defined (Q_OS_WIN)
-    // replace the text flag
-    if (textModeEnabled)
-        device->setTextModeEnabled(true);
-#endif
-
     // flush the file
 #ifndef QT_NO_QOBJECT
     QFileDevice *file = qobject_cast<QFileDevice *>(device);
diff --git a/tests/auto/corelib/io/qtextstream/tst_qtextstream.cpp b/tests/auto/corelib/io/qtextstream/tst_qtextstream.cpp
index 3ab53848d8..a0348f3c54 100644
--- a/tests/auto/corelib/io/qtextstream/tst_qtextstream.cpp
+++ b/tests/auto/corelib/io/qtextstream/tst_qtextstream.cpp
@@ -228,6 +228,8 @@ private slots:
     void alignAccountingStyle();
     void setCodec();
 
+    void textModeOnEmptyRead();
+
 private:
     void generateLineData(bool for_QString);
     void generateAllData(bool for_QString);
@@ -3045,6 +3047,21 @@ void tst_QTextStream::int_write_with_locale()
     QCOMPARE(result, output);
 }
 
+void tst_QTextStream::textModeOnEmptyRead()
+{
+    const QString filename("textmodetest.txt");
+    QFile::remove(filename); // Remove file if exists
+
+
+    QFile file(filename);
+    QVERIFY(file.open(QIODevice::ReadWrite | QIODevice::Text));
+    QTextStream stream(&file);
+    QVERIFY(file.isTextModeEnabled());
+    QString emptyLine = stream.readLine(); // Text mode flag cleared here
+    QVERIFY(file.isTextModeEnabled());
+}
+
+
 // ------------------------------------------------------------------------------
 
 QTEST_MAIN(tst_QTextStream)