From 27b560373d2919d68ccea79f5a0b928f4a14c9cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20L=C3=B6hning?= <robert.loehning@qt.io>
Date: Wed, 12 Jan 2022 23:19:16 +0100
Subject: [PATCH] QImageReader: Check for existing handler in initHandler

Some calling code did this beforehand, other didn't. Now, the function
itself checks for an existing handler before doing anything else.

Change-Id: I8fc43fb8788c9dfe825b15ffa2fa69ee43915cd6
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
---
 src/gui/image/qimagereader.cpp                |  9 ++++---
 .../image/qimagereader/tst_qimagereader.cpp   | 26 +++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/src/gui/image/qimagereader.cpp b/src/gui/image/qimagereader.cpp
index dbfcb4ee8c..940f87af9a 100644
--- a/src/gui/image/qimagereader.cpp
+++ b/src/gui/image/qimagereader.cpp
@@ -529,6 +529,9 @@ QImageReaderPrivate::~QImageReaderPrivate()
 */
 bool QImageReaderPrivate::initHandler()
 {
+    if (handler)
+        return true;
+
     // check some preconditions
     if (!device || (!deleteDevice && !device->isOpen() && !device->open(QIODevice::ReadOnly))) {
         imageReaderError = QImageReader::DeviceError;
@@ -575,7 +578,7 @@ bool QImageReaderPrivate::initHandler()
     }
 
     // assign a handler
-    if (!handler && (handler = createReadHandlerHelper(device, format, autoDetectImageFormat, ignoresFormatAndExtension)) == nullptr) {
+    if ((handler = createReadHandlerHelper(device, format, autoDetectImageFormat, ignoresFormatAndExtension)) == nullptr) {
         imageReaderError = QImageReader::UnsupportedFormatError;
         errorString = QImageReader::tr("Unsupported image format");
         return false;
@@ -588,7 +591,7 @@ bool QImageReaderPrivate::initHandler()
 */
 void QImageReaderPrivate::getText()
 {
-    if (text.isEmpty() && (handler || initHandler()) && handler->supportsOption(QImageIOHandler::Description))
+    if (text.isEmpty() && initHandler() && handler->supportsOption(QImageIOHandler::Description))
         text = qt_getImageTextFromDescription(handler->option(QImageIOHandler::Description).toString());
 }
 
@@ -1223,7 +1226,7 @@ bool QImageReader::read(QImage *image)
         return false;
     }
 
-    if (!d->handler && !d->initHandler())
+    if (!d->initHandler())
         return false;
 
     // set the handler specific options.
diff --git a/tests/auto/gui/image/qimagereader/tst_qimagereader.cpp b/tests/auto/gui/image/qimagereader/tst_qimagereader.cpp
index 3191f9f06b..bf281f8d61 100644
--- a/tests/auto/gui/image/qimagereader/tst_qimagereader.cpp
+++ b/tests/auto/gui/image/qimagereader/tst_qimagereader.cpp
@@ -94,6 +94,8 @@ private slots:
     void setScaledClipRect_data();
     void setScaledClipRect();
 
+    void setFormat();
+
     void imageFormat_data();
     void imageFormat();
 
@@ -513,6 +515,30 @@ void tst_QImageReader::setScaledClipRect()
     QCOMPARE(originalImage.copy(newRect), image);
 }
 
+void tst_QImageReader::setFormat()
+{
+    QByteArray ppmImage = "P1 2 2\n1 0\n0 1";
+    QBuffer buf(&ppmImage);
+    QImageReader reader(&buf);
+
+    // read image in autodetected format
+    QCOMPARE(reader.size(), QSize(2,2));
+    buf.close();
+
+    // try reading with non-matching format, must not succeed
+    reader.setDecideFormatFromContent(false);
+    reader.setFormat("bmp");
+    reader.setDevice(&buf);
+    QCOMPARE(reader.size(), QSize());
+    buf.close();
+
+    // read with manually set matching format
+    reader.setFormat("ppm");
+    reader.setDevice(&buf);
+    QCOMPARE(reader.size(), QSize(2,2));
+    buf.close();
+}
+
 void tst_QImageReader::imageFormat_data()
 {
     QTest::addColumn<QString>("fileName");