[libcalamares] Refactor request internals

- distinguish timeouts from other failures
 - git synchronousPing() a more detailed result, which is
   still bool-compatible.

src/libcalamares/network/Manager.cpp

@@ -107,7 +107,7 @@ Manager::setCheckHasInternetUrl( const QUrl& url )
  * On failure, returns nullptr (e.g. bad URL, timeout). The request
  * is marked for later automatic deletion, so don't store the pointer.
  */
-static QNetworkReply*
+static QPair< RequestStatus, QNetworkReply* >
 synchronousRun( const std::unique_ptr< QNetworkAccessManager >& nam, const QUrl& url, const RequestOptions& options )
 {
     QNetworkRequest request = QNetworkRequest( url );
@@ -119,7 +119,7 @@ synchronousRun( const std::unique_ptr< QNetworkAccessManager >& nam, const QUrl&
     if ( reply->error() )
     {
         reply->deleteLater();
-        return nullptr;
+        return qMakePair( RequestStatus( RequestStatus::Failed ), nullptr );
     }
 
     options.applyToRequest( &request );
@@ -135,23 +135,30 @@ synchronousRun( const std::unique_ptr< QNetworkAccessManager >& nam, const QUrl&
     if ( options.hasTimeout() && !timer.isActive() )
     {
         reply->deleteLater();
-        return nullptr;
+        return qMakePair( RequestStatus( RequestStatus::Timeout ), nullptr );
     }
 
     reply->deleteLater();
-    return reply;
+    return qMakePair( RequestStatus( RequestStatus::Ok ), reply );
 }
 
-bool
+RequestStatus
 Manager::synchronousPing( const QUrl& url, const RequestOptions& options )
 {
     if ( !url.isValid() )
     {
-        return false;
+        return RequestStatus::Failed;
     }
 
-    auto* reply = synchronousRun( d->m_nam, url, options );
-    return reply && reply->bytesAvailable();
+    auto reply = synchronousRun( d->m_nam, url, options );
+    if ( reply.first )
+    {
+        return reply.second->bytesAvailable() ? RequestStatus::Ok : RequestStatus::Empty;
+    }
+    else
+    {
+        return reply.first;
+    }
 }
 
 QByteArray
@@ -162,8 +169,8 @@ Manager::synchronousGet( const QUrl& url, const RequestOptions& options )
         return QByteArray();
     }
 
-    auto* reply = synchronousRun( d->m_nam, url, options );
-    return reply ? reply->readAll() : QByteArray();
+    auto reply = synchronousRun( d->m_nam, url, options );
+    return reply.first ? reply.second->readAll() : QByteArray();
 }
 
 }  // namespace Network

src/libcalamares/network/Manager.h

@@ -70,6 +70,22 @@ private:
 
 Q_DECLARE_OPERATORS_FOR_FLAGS( RequestOptions::Flags );
 
+struct RequestStatus
+{
+    enum State
+    {
+        Ok,
+        Timeout,  // Timeout exceeded
+        Failed,  // bad Url
+        Empty  // for ping(), response is empty
+    };
+
+    RequestStatus( State s = Ok );
+    operator bool() const { return m_s == Ok; }
+
+    State m_s;
+};
+
 class DLLEXPORT Manager : QObject
 {
     Q_OBJECT
@@ -87,15 +103,19 @@ public:
 
     /** @brief Checks if the given @p url returns data.
      *
-     * Returns @c true if it does; @c false means no data, typically
-     * because of an error or no network access.
+     * Returns a RequestStatus, which converts to @c true if the ping
+     * was successful. Other status reasons convert to @c false,
+     * typically because of no data, a Url error or no network access.
+     *
+     * May return Empty if the request was successful but returned
+     * no data at all.
      */
-    bool synchronousPing( const QUrl& url, const RequestOptions& options = RequestOptions() );
+    RequestStatus synchronousPing( const QUrl& url, const RequestOptions& options = RequestOptions() );
 
     /** @brief Downloads the data from a given @p url
      *
      * Returns the data as a QByteArray, or an empty
-     * array if any error occurred.
+     * array if any error occurred (or no data was returned).
      */
     QByteArray synchronousGet( const QUrl& url, const RequestOptions& options = RequestOptions() );