Detect OZF files by contents rather than by file extension

src/offlinemap.cpp

@@ -342,13 +342,7 @@ bool OfflineMap::getImageInfo(const QString &path)
 		return false;
 	}
 
-	QString suffix = ii.suffix().toLower();
+	if (OZF::isOZF(_imgPath)) {
-	if (suffix == "ozf4" || suffix == "ozfx4") {
-		_errorString = QString("%1: OZF4 image files not supported")
-		  .arg(QFileInfo(_imgPath).fileName());
-		return false;
-	} else if (suffix == "ozf2" || suffix == "ozfx2" || suffix == "ozf3"
-	  || suffix == "ozfx3") {
 		_ozf.load(_imgPath);
 		_size = _ozf.size();
 	} else {

src/ozf.cpp

@@ -232,3 +232,19 @@ QPixmap OZF::tile(int x, int y)
 
 	return QPixmap::fromImage(img.mirrored());
 }
+
+bool OZF::isOZF(const QString &path)
+{
+	QFile file(path);
+	quint16 magic;
+
+	if (!file.open(QIODevice::ReadOnly))
+		return false;
+	if (file.read((char*)&magic, sizeof(magic)) < (qint64)sizeof(magic))
+		return false;
+
+	if (magic == OZF2_MAGIC || magic == OZF3_MAGIC)
+		return true;
+
+	return false;
+}

src/ozf.h

@@ -22,6 +22,8 @@ public:
 	QSize tileSize() const {return QSize(64, 64);}
 	QPixmap tile(int x, int y);
 
+	static bool isOZF(const QString &path);
+
 private:
 	template<class T> bool readValue(T &val);
 	bool read(void *data, size_t size);