Qt 5.11 | Qt Network | Network Download Example | main.cpp Example File

Qt 5.11.3 Reference Documentation

# main.cpp Example File

download/main.cpp

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      #include <QtCore>
      #include <QtNetwork>

      #include <cstdio>

      class QSslError;

      using namespace std;

      class DownloadManager: public QObject
      {
          Q_OBJECT
          QNetworkAccessManager manager;
          QVector<QNetworkReply *> currentDownloads;

      public:
          DownloadManager();
          void doDownload(const QUrl &url);
          static QString saveFileName(const QUrl &url);
          bool saveToDisk(const QString &filename, QIODevice *data);
          static bool isHttpRedirect(QNetworkReply *reply);

      public slots:
          void execute();
          void downloadFinished(QNetworkReply *reply);
          void sslErrors(const QList<QSslError> &errors);
      };

      DownloadManager::DownloadManager()
      {
          connect(&manager, SIGNAL(finished(QNetworkReply*)),
                  SLOT(downloadFinished(QNetworkReply*)));
      }

      void DownloadManager::doDownload(const QUrl &url)
      {
          QNetworkRequest request(url);
          QNetworkReply *reply = manager.get(request);

      #if QT_CONFIG(ssl)
          connect(reply, SIGNAL(sslErrors(QList<QSslError>)),
                  SLOT(sslErrors(QList<QSslError>)));
      #endif

          currentDownloads.append(reply);
      }

      QString DownloadManager::saveFileName(const QUrl &url)
      {
          QString path = url.path();
          QString basename = QFileInfo(path).fileName();

          if (basename.isEmpty())
              basename = "download";

          if (QFile::exists(basename)) {
              // already exists, don't overwrite
              int i = 0;
              basename += '.';
              while (QFile::exists(basename + QString::number(i)))
                  ++i;

              basename += QString::number(i);
          }

          return basename;
      }

      bool DownloadManager::saveToDisk(const QString &filename, QIODevice *data)
      {
          QFile file(filename);
          if (!file.open(QIODevice::WriteOnly)) {
              fprintf(stderr, "Could not open %s for writing: %s\n",
                      qPrintable(filename),
                      qPrintable(file.errorString()));
              return false;
          }

          file.write(data->readAll());
          file.close();

          return true;
      }

      bool DownloadManager::isHttpRedirect(QNetworkReply *reply)
      {
          int statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
          return statusCode == 301 || statusCode == 302 || statusCode == 303
                 || statusCode == 305 || statusCode == 307 || statusCode == 308;
      }

      void DownloadManager::execute()
      {
          QStringList args = QCoreApplication::instance()->arguments();
          args.takeFirst();           // skip the first argument, which is the program's name
          if (args.isEmpty()) {
              printf("Qt Download example - downloads all URLs in parallel\n"
                     "Usage: download url1 [url2... urlN]\n"
                     "\n"
                     "Downloads the URLs passed in the command-line to the local directory\n"
                     "If the target file already exists, a .0, .1, .2, etc. is appended to\n"
                     "differentiate.\n");
              QCoreApplication::instance()->quit();
              return;
          }

          for (const QString &arg : qAsConst(args)) {
              QUrl url = QUrl::fromEncoded(arg.toLocal8Bit());
              doDownload(url);
          }
      }

      void DownloadManager::sslErrors(const QList<QSslError> &sslErrors)
      {
      #if QT_CONFIG(ssl)
          for (const QSslError &error : sslErrors)
              fprintf(stderr, "SSL error: %s\n", qPrintable(error.errorString()));
      #else
          Q_UNUSED(sslErrors);
      #endif
      }

      void DownloadManager::downloadFinished(QNetworkReply *reply)
      {
          QUrl url = reply->url();
          if (reply->error()) {
              fprintf(stderr, "Download of %s failed: %s\n",
                      url.toEncoded().constData(),
                      qPrintable(reply->errorString()));
          } else {
              if (isHttpRedirect(reply)) {
                  fputs("Request was redirected.\n", stderr);
              } else {
                  QString filename = saveFileName(url);
                  if (saveToDisk(filename, reply)) {
                      printf("Download of %s succeeded (saved to %s)\n",
                             url.toEncoded().constData(), qPrintable(filename));
                  }
              }
          }

          currentDownloads.removeAll(reply);
          reply->deleteLater();

          if (currentDownloads.isEmpty()) {
              // all downloads finished
              QCoreApplication::instance()->quit();
          }
      }

      int main(int argc, char **argv)
      {
          QCoreApplication app(argc, argv);

          DownloadManager manager;
          QTimer::singleShot(0, &manager, SLOT(execute()));

          app.exec();
      }

      #include "main.moc"