1 files changed, 48 insertions, 0 deletions
diff --git a/tests/auto/corelib/io/qbuffer/tst_qbuffer.cpp b/tests/auto/corelib/io/qbuffer/tst_qbuffer.cpp
index 4968742110..b02400e349 100644
--- a/tests/auto/corelib/io/qbuffer/tst_qbuffer.cpp
+++ b/tests/auto/corelib/io/qbuffer/tst_qbuffer.cpp
@@ -36,12 +36,14 @@ class tst_QBuffer : public QObject
     Q_OBJECT
 private slots:
     void open();
+    void openWriteOnlyDoesNotTruncate();
     void getSetCheck();
     void readBlock();
     void readBlockPastEnd();
     void writeBlock_data();
     void writeBlock();
     void seek();
+    void invalidSeeks();
     void seekTest_data();
     void seekTest();
     void read_rawdata();
@@ -130,6 +132,29 @@ void tst_QBuffer::open()
     b.close();
 }
 
+void tst_QBuffer::openWriteOnlyDoesNotTruncate()
+{
+    QBuffer b;
+    const auto data = QByteArrayLiteral("Hey, presto!");
+
+    {
+        QVERIFY(b.open(QIODevice::WriteOnly));
+        b.write(data);
+        b.close();
+    }
+    {
+        QVERIFY(b.open(QIODevice::ReadOnly));
+        QCOMPARE(b.readAll(), data);
+        b.close();
+    }
+    {
+        QVERIFY(b.open(QIODevice::WriteOnly));
+        QCOMPARE(b.size(), data.size());
+        QCOMPARE(b.pos(), 0);
+        b.close();
+    }
+}
+
 // some status() tests, too
 void tst_QBuffer::readBlock()
 {
@@ -286,6 +311,29 @@ void tst_QBuffer::seek()
     QCOMPARE(buffer.size(), pos);
 }
 
+void tst_QBuffer::invalidSeeks()
+{
+    if (sizeof(qsizetype) == sizeof(qint64)) {
+        // sizeof(qsizetype) == sizeof(qint64), so +1 would overflow
+        QSKIP("This is a 32-bit-only test.");
+    } else {
+        QBuffer buffer;
+        buffer.open(QIODevice::WriteOnly);
+        QCOMPARE(buffer.buffer().size(), qsizetype(0));
+        QCOMPARE(buffer.pos(), qint64(0));
+        constexpr qint64 MaxQByteArrayCapacity = (std::numeric_limits<qsizetype>::max)();
+        // this should fail fast, not after trying to allocate nearly 2 GiB of data,
+        // potentially crashing in the process:
+        QVERIFY(!buffer.seek(2 * MaxQByteArrayCapacity - 1));
+        QCOMPARE(buffer.buffer().size(), qsizetype(0));
+        QCOMPARE(buffer.pos(), qint64(0));
+        // ditto:
+        QVERIFY(!buffer.seek(MaxQByteArrayCapacity + 1));
+        QCOMPARE(buffer.buffer().size(), qsizetype(0));
+        QCOMPARE(buffer.pos(), qint64(0));
+    }
+}
+
 void tst_QBuffer::seekTest_data()
 {
     writeBlock_data();