Add WebAPI for downloading torrent metadata

Signed-off-by: Thomas Piccirello <thomas@piccirello.com>

src/base/bittorrent/torrentdescriptor.cpp

@@ -141,6 +141,22 @@ catch (const lt::system_error &err)
     return nonstd::make_unexpected(QString::fromLocal8Bit(err.what()));
 }
 
+nonstd::expected<QByteArray, QString> BitTorrent::TorrentDescriptor::saveToBuffer() const
+try
+{
+    const lt::entry torrentEntry = lt::write_torrent_file(m_ltAddTorrentParams);
+    // usually torrent size should be smaller than 1 MB,
+    // however there are >100 MB v2/hybrid torrent files out in the wild
+    QByteArray buffer;
+    buffer.reserve(1024 * 1024);
+    lt::bencode(std::back_inserter(buffer), torrentEntry);
+    return buffer;
+}
+catch (const lt::system_error &err)
+{
+    return nonstd::make_unexpected(QString::fromLocal8Bit(err.what()));
+}
+
 BitTorrent::TorrentDescriptor::TorrentDescriptor(lt::add_torrent_params ltAddTorrentParams)
     : m_ltAddTorrentParams {std::move(ltAddTorrentParams)}
 {

src/base/bittorrent/torrentdescriptor.h

@@ -69,6 +69,7 @@ namespace BitTorrent
         static nonstd::expected<TorrentDescriptor, QString> loadFromFile(const Path &path) noexcept;
         static nonstd::expected<TorrentDescriptor, QString> parse(const QString &str) noexcept;
         nonstd::expected<void, QString> saveToFile(const Path &path) const;
+        nonstd::expected<QByteArray, QString> saveToBuffer() const;
 
         const lt::add_torrent_params &ltAddTorrentParams() const;
 

src/webui/api/torrentscontroller.cpp

@@ -997,9 +997,9 @@ void TorrentsController::addAction()
     if (!filePrioritiesParam.isEmpty())
     {
         if (urls.size() > 1)
-            throw APIError(APIErrorType::BadParams, tr("You cannot specify filePriorities when adding multiple torrents"));
+            throw APIError(APIErrorType::BadParams, tr("Cannot specify filePriorities when adding multiple torrents"));
         if (!torrents.isEmpty())
-            throw APIError(APIErrorType::BadParams, tr("You cannot specify filePriorities when uploading torrent files"));
+            throw APIError(APIErrorType::BadParams, tr("Cannot specify filePriorities when uploading torrent files"));
 
         filePriorities.reserve(filePrioritiesParam.size());
         for (const QString &priorityStr : filePrioritiesParam)
@@ -2035,6 +2035,36 @@ void TorrentsController::parseMetadataAction()
     setResult(result);
 }
 
+void TorrentsController::saveMetadataAction()
+{
+    requireParams({u"source"_s});
+
+    const QString sourceParam = params()[u"source"_s].trimmed();
+    if (sourceParam.isEmpty())
+        throw APIError(APIErrorType::BadParams, tr("Must specify URI or hash"));
+
+    const QString source = QUrl::fromPercentEncoding(sourceParam.toLatin1());
+
+    BitTorrent::InfoHash infoHash;
+    if (const auto iter = m_torrentSourceCache.constFind(source); iter != m_torrentSourceCache.constEnd())
+        infoHash = iter.value();
+    else if (const auto sourceTorrentDescr = BitTorrent::TorrentDescriptor::parse(source))
+        infoHash = sourceTorrentDescr.value().infoHash();
+
+    if (!infoHash.isValid())
+        throw APIError(APIErrorType::NotFound);
+
+    const BitTorrent::TorrentDescriptor &torrentDescr = m_torrentMetadataCache.value(infoHash);
+    if (!torrentDescr.info().has_value())
+        throw APIError(APIErrorType::Conflict, tr("Metadata is not yet available"));
+
+    const nonstd::expected<QByteArray, QString> result = torrentDescr.saveToBuffer();
+    if (!result)
+        throw APIError(APIErrorType::Conflict, tr("Unable to export torrent metadata. Error: %1").arg(result.error()));
+
+    setResult(result.value(), u"application/x-bittorrent"_s, (infoHash.toTorrentID().toString() + u".torrent"));
+}
+
 void TorrentsController::onDownloadFinished(const Net::DownloadResult &result)
 {
     const QString source = result.url;

src/webui/api/torrentscontroller.h

@@ -112,6 +112,7 @@ private slots:
     void setSSLParametersAction();
     void fetchMetadataAction();
     void parseMetadataAction();
+    void saveMetadataAction();
 
 private:
     void onDownloadFinished(const Net::DownloadResult &result);