Check if device is opened before trying to create image handler.

Change-Id: I60f1f6890fdd73e489da4aab9928370163f55f58
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: aavit <eirik.aavitsland@digia.com>

src/gui/image/qimagewriter.cpp

@@ -245,6 +245,8 @@ class QImageWriterPrivate
 public:
     QImageWriterPrivate(QImageWriter *qq);
 
+    bool canWriteHelper();
+
     // device
     QByteArray format;
     QIODevice *device;
@@ -282,6 +284,31 @@ QImageWriterPrivate::QImageWriterPrivate(QImageWriter *qq)
     q = qq;
 }
 
+bool QImageWriterPrivate::canWriteHelper()
+{
+    if (!device) {
+        imageWriterError = QImageWriter::DeviceError;
+        errorString = QT_TRANSLATE_NOOP(QImageWriter,
+                                        QLatin1String("Device is not set"));
+        return false;
+    }
+    if (!device->isOpen())
+        device->open(QIODevice::WriteOnly);
+    if (!device->isWritable()) {
+        imageWriterError = QImageWriter::DeviceError;
+        errorString = QT_TRANSLATE_NOOP(QImageWriter,
+                                        QLatin1String("Device not writable"));
+        return false;
+    }
+    if (!handler && (handler = createWriteHandlerHelper(device, format)) == 0) {
+        imageWriterError = QImageWriter::UnsupportedFormatError;
+        errorString = QT_TRANSLATE_NOOP(QImageWriter,
+                                        QLatin1String("Unsupported image format"));
+        return false;
+    }
+    return true;
+}
+
 /*!
     Constructs an empty QImageWriter object. Before writing, you must
     call setFormat() to set an image format, then setDevice() or
@@ -561,21 +588,15 @@ void QImageWriter::setText(const QString &key, const QString &text)
 */
 bool QImageWriter::canWrite() const
 {
-    if (d->device && !d->handler && (d->handler = createWriteHandlerHelper(d->device, d->format)) == 0) {
-        d->imageWriterError = QImageWriter::UnsupportedFormatError;
-        d->errorString = QT_TRANSLATE_NOOP(QImageWriter,
-                                           QLatin1String("Unsupported image format"));
-        return false;
+    if (QFile *file = qobject_cast<QFile *>(d->device)) {
+        const bool remove = !file->isOpen() && !file->exists();
+        const bool result = d->canWriteHelper();
+        if (!result && remove)
+            file->remove();
+        return result;
     }
-    if (d->device && !d->device->isOpen())
-        d->device->open(QIODevice::WriteOnly);
-    if (!d->device || !d->device->isWritable()) {
-        d->imageWriterError = QImageWriter::DeviceError;
-        d->errorString = QT_TRANSLATE_NOOP(QImageWriter,
-                                           QLatin1String("Device not writable"));
-        return false;
-    }
-    return true;
+
+    return d->canWriteHelper();
 }
 
 /*!

tests/auto/gui/image/qimagewriter/tst_qimagewriter.cpp

@@ -50,6 +50,7 @@
 #include <QImageWriter>
 #include <QPainter>
 #include <QSet>
+#include <QTemporaryDir>
 
 #ifdef Q_OS_UNIX // for geteuid()
 # include <sys/types.h>
@@ -84,6 +85,7 @@ private slots:
     void supportedMimeTypes();
 
     void writeToInvalidDevice();
+    void testCanWrite();
 
     void supportsOption_data();
     void supportsOption();
@@ -402,6 +404,28 @@ void tst_QImageWriter::writeToInvalidDevice()
     }
 }
 
+void tst_QImageWriter::testCanWrite()
+{
+    {
+        // device is not set
+        QImageWriter writer;
+        QVERIFY(!writer.canWrite());
+        QCOMPARE(writer.error(), QImageWriter::DeviceError);
+    }
+
+    {
+        // check if canWrite won't leave an empty file
+        QTemporaryDir dir;
+        QVERIFY(dir.isValid());
+        QString fileName(dir.path() + QLatin1String("/001.garble"));
+        QVERIFY(!QFileInfo(fileName).exists());
+        QImageWriter writer(fileName);
+        QVERIFY(!writer.canWrite());
+        QCOMPARE(writer.error(), QImageWriter::UnsupportedFormatError);
+        QVERIFY(!QFileInfo(fileName).exists());
+    }
+}
+
 void tst_QImageWriter::supportsOption_data()
 {
     QTest::addColumn<QString>("fileName");