Fix QTextStream::pos() causes buffer offset issues on large text files.

 When reading large files that are greater in size than the
TEXTSTREAM_BUFFERSIZE buffer, calling pos() caused erroneous buffer
positioning. The cause of this was QTextStreamPrivate::readBufferOffset
value being updated, but QTextStreamPrivate::readConverterSavedStateOffset
was not.  Usually, if pos() is called, it is called multiple times. Since
QTextStreamPrivate::readConverterSavedStateOffset was never reset,
QTextStreamPrivate::readBufferOffset would accumulate the wrong position
and QTextStreamPrivate::consume() will 'discard' the wrong number of
bytes from the buffer.

Task-number: QTBUG-9814
Merge-request: 2569
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>

2 files changed, 37 insertions, 0 deletions

diff --git a/src/corelib/io/qtextstream.cpp b/src/corelib/io/qtextstream.cpp
index b630502616..a5837cbeb5 100644
--- a/src/corelib/io/qtextstream.cpp
+++ b/src/corelib/io/qtextstream.cpp
@@ -1264,6 +1264,7 @@ qint64 QTextStream::pos() const
                 return qint64(-1);
         }
         thatd->readBufferOffset = oldReadBufferOffset;
+        thatd->readConverterSavedStateOffset = 0;
 
         // Return the device position.
         return d->device->pos();
diff --git a/tests/auto/qtextstream/tst_qtextstream.cpp b/tests/auto/qtextstream/tst_qtextstream.cpp
index 99f25563b7..2d7c24d238 100644
--- a/tests/auto/qtextstream/tst_qtextstream.cpp
+++ b/tests/auto/qtextstream/tst_qtextstream.cpp
@@ -208,6 +208,7 @@ private slots:
     void seek();
     void pos();
     void pos2();
+    void pos3LargeFile();
     void readStdin();
     void readAllFromStdin();
     void readLineFromStdin();
@@ -1502,6 +1503,41 @@ void tst_QTextStream::pos2()
 }
 
 // ------------------------------------------------------------------------------
+void tst_QTextStream::pos3LargeFile()
+{
+    {
+        QFile file(TestFileName);
+        file.open(QIODevice::WriteOnly | QIODevice::Text);
+        QTextStream out( &file );
+        // NOTE: The unusual spacing is to ensure non-1-character whitespace.
+        QString lineString = " 0  1  2\t3  4\t \t5  6  7  8   9 \n";
+        // Approximate 50kb text file
+        const int NbLines = (50*1024) / lineString.length() + 1;
+        for (int line = 0; line < NbLines; ++line)
+            out << lineString;
+        // File is automatically flushed and closed on destruction.
+    }
+    QFile file(TestFileName);
+    file.open(QIODevice::ReadOnly | QIODevice::Text);
+    QTextStream in( &file );
+    const int testValues[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+    int value;
+    while (true) {
+        in.pos();
+        for ( int i = 0; i < 10; ++i ) {
+            in >> value;
+            if (in.status() != QTextStream::Ok) {
+                // End case, i == 0 && eof reached.
+                QCOMPARE(i, 0);
+                QCOMPARE(in.status(), QTextStream::ReadPastEnd);
+                return;
+            }
+            QCOMPARE(value, testValues[i]);
+        }
+    }
+}
+
+// ------------------------------------------------------------------------------
 void tst_QTextStream::readStdin()
 {
 #if defined(Q_OS_WINCE) || defined(Q_OS_SYMBIAN)