QIODevice: do not change the 'pos' member for sequential devices

Concept of 'current position' exists only for random-access devices.
As documented, for sequential devices QIODevice::pos() must always
return 0. Prevent a modification of the internal 'pos' member in
QIODevice::readAll() method to follow this rule.

Change-Id: Ida2ee6a629ccfc3068d62f95ab1064ada13fdda5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qiodevice.cpp

@@ -972,6 +972,7 @@ QByteArray QIODevice::readAll()
 
     QByteArray result;
     qint64 readBytes = 0;
+    const bool sequential = d->isSequential();
 
     // flush internal read buffer
     if (!(d->openMode & Text) && !d->buffer.isEmpty()) {
@@ -979,11 +980,12 @@ QByteArray QIODevice::readAll()
             return QByteArray();
         result = d->buffer.readAll();
         readBytes = result.size();
-        d->pos += readBytes;
+        if (!sequential)
+            d->pos += readBytes;
     }
 
     qint64 theSize;
-    if (d->isSequential() || (theSize = size()) == 0) {
+    if (sequential || (theSize = size()) == 0) {
         // Size is unknown, read incrementally.
         qint64 readResult;
         do {

tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp

@@ -58,6 +58,7 @@ private slots:
     void readLine2();
 
     void peekBug();
+    void readAllKeepPosition();
 };
 
 void tst_QIODevice::initTestCase()
@@ -584,5 +585,48 @@ void tst_QIODevice::peekBug()
 
 }
 
+class SequentialReadBuffer : public QIODevice
+{
+public:
+    SequentialReadBuffer(const char *data) : QIODevice(), buf(data), offset(0) { }
+
+    bool isSequential() const Q_DECL_OVERRIDE { return true; }
+    const QByteArray &buffer() const { return buf; }
+
+protected:
+    qint64 readData(char *data, qint64 maxSize) Q_DECL_OVERRIDE
+    {
+        maxSize = qMin(maxSize, qint64(buf.size() - offset));
+        memcpy(data, buf.constData() + offset, maxSize);
+        offset += maxSize;
+        return maxSize;
+    }
+    qint64 writeData(const char * /* data */, qint64 /* maxSize */) Q_DECL_OVERRIDE
+    {
+        return -1;
+    }
+
+private:
+    QByteArray buf;
+    int offset;
+};
+
+// Test readAll() on position change for sequential device
+void tst_QIODevice::readAllKeepPosition()
+{
+    SequentialReadBuffer buffer("Hello world!");
+    buffer.open(QIODevice::ReadOnly);
+    char c;
+
+    QVERIFY(buffer.getChar(&c));
+    QCOMPARE(buffer.pos(), qint64(0));
+    buffer.ungetChar(c);
+    QCOMPARE(buffer.pos(), qint64(0));
+
+    QByteArray resultArray = buffer.readAll();
+    QCOMPARE(buffer.pos(), qint64(0));
+    QCOMPARE(resultArray, buffer.buffer());
+}
+
 QTEST_MAIN(tst_QIODevice)
 #include "tst_qiodevice.moc"