Add support for exporting .torrent from WebUI

PR #16968.

src/webui/api/apicontroller.cpp

@@ -91,3 +91,8 @@ void APIController::setResult(const QJsonObject &result)
 {
     m_result = QJsonDocument(result);
 }
+
+void APIController::setResult(const QByteArray &result)
+{
+    m_result = result;
+}

src/webui/api/apicontroller.h

@@ -55,6 +55,7 @@ protected:
     void setResult(const QString &result);
     void setResult(const QJsonArray &result);
     void setResult(const QJsonObject &result);
+    void setResult(const QByteArray &result);
 
 private:
     StringMap m_params;

src/webui/api/torrentscontroller.cpp

@@ -1414,3 +1414,19 @@ void TorrentsController::renameFolderAction()
         throw APIError(APIErrorType::Conflict, error.message());
     }
 }
+
+void TorrentsController::exportAction()
+{
+    requireParams({u"hash"_qs});
+
+    const auto id = BitTorrent::TorrentID::fromString(params()[u"hash"_qs]);
+    const BitTorrent::Torrent *const torrent = BitTorrent::Session::instance()->findTorrent(id);
+    if (!torrent)
+        throw APIError(APIErrorType::NotFound);
+
+    const nonstd::expected<QByteArray, QString> result = torrent->exportToBuffer();
+    if (!result)
+        throw APIError(APIErrorType::Conflict, tr("Unable to export torrent file. Error: %1").arg(result.error()));
+
+    setResult(result.value());
+}

src/webui/api/torrentscontroller.h

@@ -87,4 +87,5 @@ private slots:
     void toggleFirstLastPiecePrioAction();
     void renameFileAction();
     void renameFolderAction();
+    void exportAction();
 };