QImageReader: Pass up information about resource errors on open

If a system runs out of FDs, there is no sense in trying to autodetect
the format - as the real problem is the lack of FDs, not the
non-existent file.

Change-Id: I3302340859c3cc62995ac1b7b3c7b6e6326cb43e
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/gui/image/qimagereader.cpp b/src/gui/image/qimagereader.cpp
index 2f25f4dcbc..55c3a4704a 100644
--- a/src/gui/image/qimagereader.cpp
+++ b/src/gui/image/qimagereader.cpp
@@ -564,6 +564,16 @@ bool QImageReaderPrivate::initHandler()
 
     // probe the file extension
     if (deleteDevice && !device->isOpen() && !device->open(QIODevice::ReadOnly) && autoDetectImageFormat) {
+        Q_ASSERT(qobject_cast<QFile*>(device) != 0); // future-proofing; for now this should always be the case, so...
+        QFile *file = static_cast<QFile *>(device);
+
+        if (file->error() == QFileDevice::ResourceError) {
+            // this is bad. we should abort the open attempt and note the failure.
+            imageReaderError = QImageReader::DeviceError;
+            errorString = file->errorString();
+            return false;
+        }
+
         QList<QByteArray> extensions = QImageReader::supportedImageFormats();
         if (!format.isEmpty()) {
             // Try the most probable extension first
@@ -574,7 +584,6 @@ bool QImageReaderPrivate::initHandler()
 
         int currentExtension = 0;
 
-        QFile *file = static_cast<QFile *>(device);
         QString fileName = file->fileName();
 
         do {