[libcalamares] Expand the number of URLs to check for connectivity

- introduce a list of URLs instead of just one
- ping each of them, in turn, until one responds

src/libcalamares/network/Manager.cpp

@@ -27,7 +27,7 @@ namespace Network
 void
 RequestOptions::applyToRequest( QNetworkRequest* request ) const
 {
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)
+#if QT_VERSION < QT_VERSION_CHECK( 5, 15, 0 )
     constexpr const auto RedirectPolicyAttribute = QNetworkRequest::FollowRedirectsAttribute;
 #else
     constexpr const auto RedirectPolicyAttribute = QNetworkRequest::RedirectPolicyAttribute;
@@ -60,8 +60,9 @@ public slots:
     void cleanupNam();
 
 public:
-    QUrl m_hasInternetUrl;
-    bool m_hasInternet;
+    QVector< QUrl > m_hasInternetUrls;
+    bool m_hasInternet = false;
+    int m_lastCheckedUrlIndex = -1;
 
     Private();
 
@@ -155,8 +156,33 @@ Manager::hasInternet()
 bool
 Manager::checkHasInternet()
 {
+    if ( d->m_hasInternetUrls.empty() )
+    {
+        return false;
+    }
+    if ( d->m_lastCheckedUrlIndex < 0 )
+    {
+        d->m_lastCheckedUrlIndex = 0;
+    }
+    int attempts = 0;
+    do
+    {
+        // Start by pinging the same one as last time
+        d->m_hasInternet = synchronousPing( d->m_hasInternetUrls.at( d->m_lastCheckedUrlIndex ) );
+        // if it's not responding, **then** move on to the next one,
+        // and wrap around if needed
+        if ( !d->m_hasInternet )
+        {
+            if ( ++( d->m_lastCheckedUrlIndex ) >= d->m_hasInternetUrls.size() )
+            {
+                d->m_lastCheckedUrlIndex = 0;
+            }
+        }
+        // keep track of how often we've tried, because there's no point in
+        // going around more than once.
+        attempts++;
+    } while ( !d->m_hasInternet && ( attempts < d->m_hasInternetUrls.size() ) );
 
-    d->m_hasInternet = synchronousPing( d->m_hasInternetUrl );
 
 // For earlier Qt versions (< 5.15.0), set the accessibility flag to
 // NotAccessible if synchronous ping has failed, so that any module
@@ -177,7 +203,11 @@ Manager::checkHasInternet()
 void
 Manager::setCheckHasInternetUrl( const QUrl& url )
 {
-    d->m_hasInternetUrl = url;
+    if ( d->m_hasInternetUrls.empty() )
+    {
+        d->m_lastCheckedUrlIndex = -1;
+    }
+    d->m_hasInternetUrls.append( url );
 }
 
 /** @brief Does a request asynchronously, returns the (pending) reply