Don't write byte-order-mark after seek()

Ideally, we should write a BOM after seek(0) if setGenerateByteOrderMark
has been called, but we don't store that information. This commit is an
improvement for the default case when generateByteOrderMark is false, and
also when seeking to any other position than 0.

Task-number: QTBUG-6295
Reviewed-by: Olivier
(cherry picked from commit 7837de27309c958dc5a5985afc55492ec3054ee0)

2 files changed, 60 insertions, 1 deletions

diff --git a/src/corelib/io/qtextstream.cpp b/src/corelib/io/qtextstream.cpp
index ac0d08b..139eb89 100644
--- a/src/corelib/io/qtextstream.cpp
+++ b/src/corelib/io/qtextstream.cpp
@@ -70,7 +70,7 @@ static const int QTEXTSTREAM_BUFFERSIZE = 16384;
     have reached the end of the data stream, with stdin. The reason for this is
     that as long as stdin doesn't give any input to the QTextStream, \c atEnd()
     will return true even if the stdin is open and waiting for more characters.
-    
+
     Besides using QTextStream's constructors, you can also set the
     device or string QTextStream operates on by calling setDevice() or
     setString(). You can seek to a position by calling seek(), and
@@ -1196,6 +1196,7 @@ bool QTextStream::seek(qint64 pos)
         resetCodecConverterStateHelper(&d->writeConverterState);
         delete d->readConverterSavedState;
         d->readConverterSavedState = 0;
+        d->writeConverterState.flags |= QTextCodec::IgnoreHeader;
 #endif
         return true;
     }
diff --git a/tests/auto/qtextstream/tst_qtextstream.cpp b/tests/auto/qtextstream/tst_qtextstream.cpp
index 7c72fb7..d9ee460 100644
--- a/tests/auto/qtextstream/tst_qtextstream.cpp
+++ b/tests/auto/qtextstream/tst_qtextstream.cpp
@@ -221,6 +221,7 @@ private slots:
     void nanInf();
     void utf8IncompleteAtBufferBoundary_data();
     void utf8IncompleteAtBufferBoundary();
+    void writeSeekWriteNoBOM();
 
     // status
     void status_real_read_data();
@@ -1847,6 +1848,63 @@ void tst_QTextStream::utf8IncompleteAtBufferBoundary()
 }
 
 // ------------------------------------------------------------------------------
+
+// Make sure we don't write a BOM after seek()ing
+
+void tst_QTextStream::writeSeekWriteNoBOM()
+{
+
+    //First with the default codec (normally either latin-1 or UTF-8)
+
+    QBuffer out;
+    out.open(QIODevice::WriteOnly);
+    QTextStream stream(&out);
+
+    int number = 0;
+    QString sizeStr = QLatin1String("Size=")
+        + QString::number(number).rightJustified(10, QLatin1Char('0'));
+    stream << sizeStr << endl;
+    stream << "Version=" << QString::number(14) << endl;
+    stream << "blah blah blah" << endl;
+    stream.flush();
+
+    QCOMPARE(out.buffer().constData(), "Size=0000000000\nVersion=14\nblah blah blah\n");
+
+    // Now overwrite the size header item
+    number = 42;
+    stream.seek(0);
+    sizeStr = QLatin1String("Size=")
+        + QString::number(number).rightJustified(10, QLatin1Char('0'));
+    stream << sizeStr << endl;
+    stream.flush();
+
+    // Check buffer is still OK
+    QCOMPARE(out.buffer().constData(), "Size=0000000042\nVersion=14\nblah blah blah\n");
+
+
+    //Then UTF-16
+
+    QBuffer out16;
+    out16.open(QIODevice::WriteOnly);
+    QTextStream stream16(&out16);
+    stream16.setCodec("UTF-16");
+
+    stream16 << "one" << "two" << QLatin1String("three");
+    stream16.flush();
+
+    // save that output
+    QByteArray first = out16.buffer();
+
+    stream16.seek(0);
+    stream16 << "one";
+    stream16.flush();
+
+    QCOMPARE(out16.buffer(), first);
+}
+
+
+
+// ------------------------------------------------------------------------------
 void tst_QTextStream::generateOperatorCharData(bool for_QString)
 {
     QTest::addColumn<QByteArray>("input");