qt: Add a function that extracts the suffix from a filter

Extract the 'Extract first suffix from filter pattern...'
functionality into a testable utility function

src/qt/guiutil.cpp

@@ -292,6 +292,16 @@ QString getDefaultDataDirectory()
     return PathToQString(GetDefaultDataDir());
 }
 
+QString ExtractFirstSuffixFromFilter(const QString& filter)
+{
+    QRegExp filter_re(".* \\(\\*\\.(.*)[ \\)]");
+    QString suffix;
+    if (filter_re.exactMatch(filter)) {
+        suffix = filter_re.cap(1);
+    }
+    return suffix;
+}
+
 QString getSaveFileName(QWidget *parent, const QString &caption, const QString &dir,
     const QString &filter,
     QString *selectedSuffixOut)
@@ -309,13 +319,7 @@ QString getSaveFileName(QWidget *parent, const QString &caption, const QString &
     /* Directly convert path to native OS path separators */
     QString result = QDir::toNativeSeparators(QFileDialog::getSaveFileName(parent, caption, myDir, filter, &selectedFilter));
 
-    /* Extract first suffix from filter pattern "Description (*.foo)" or "Description (*.foo *.bar ...) */
+    QString selectedSuffix = ExtractFirstSuffixFromFilter(selectedFilter);
-    QRegExp filter_re(".* \\(\\*\\.(.*)[ \\)]");
-    QString selectedSuffix;
-    if(filter_re.exactMatch(selectedFilter))
-    {
-        selectedSuffix = filter_re.cap(1);
-    }
 
     /* Add suffix if needed */
     QFileInfo info(result);
@@ -357,14 +361,8 @@ QString getOpenFileName(QWidget *parent, const QString &caption, const QString &
 
     if(selectedSuffixOut)
     {
-        /* Extract first suffix from filter pattern "Description (*.foo)" or "Description (*.foo *.bar ...) */
+        *selectedSuffixOut = ExtractFirstSuffixFromFilter(selectedFilter);
-        QRegExp filter_re(".* \\(\\*\\.(.*)[ \\)]");
+        ;
-        QString selectedSuffix;
-        if(filter_re.exactMatch(selectedFilter))
-        {
-            selectedSuffix = filter_re.cap(1);
-        }
-        *selectedSuffixOut = selectedSuffix;
     }
     return result;
 }

src/qt/guiutil.h

@@ -123,6 +123,14 @@ namespace GUIUtil
      */
     QString getDefaultDataDirectory();
 
+    /**
+     * Extract first suffix from filter pattern "Description (*.foo)" or "Description (*.foo *.bar ...).
+     *
+     * @param[in] filter Filter specification such as "Comma Separated Files (*.csv)"
+     * @return QString
+     */
+    QString ExtractFirstSuffixFromFilter(const QString& filter);
+
     /** Get save filename, mimics QFileDialog::getSaveFileName, except that it appends a default suffix
         when no suffix is provided by the user.