made dump torrent create magnet links

examples/dump_torrent.cpp

@@ -39,6 +39,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/bencode.hpp"
 #include "libtorrent/torrent_info.hpp"
 #include "libtorrent/lazy_entry.hpp"
+#include "libtorrent/magnet_uri.hpp"
 #include <boost/filesystem/operations.hpp>
 
 
@@ -105,6 +106,7 @@ int main(int argc, char* argv[])
 		std::cout << "info hash: " << t.info_hash() << "\n";
 		std::cout << "comment: " << t.comment() << "\n";
 		std::cout << "created by: " << t.creator() << "\n";
+		std::cout << "magnet link: " << make_magnet_uri(t) << "\n";
 		std::cout << "files:\n";
 		int index = 0;
 		for (torrent_info::file_iterator i = t.begin_files();

include/libtorrent/magnet_uri.hpp

@@ -46,6 +46,7 @@ namespace libtorrent
 	struct torrent_handle;
 
 	std::string TORRENT_EXPORT make_magnet_uri(torrent_handle const& handle);
+	std::string TORRENT_EXPORT make_magnet_uri(torrent_info const& info);
 
 #ifndef TORRENT_NO_DEPRECATE
 	// deprecated in 0.14

src/magnet_uri.cpp

@@ -69,6 +69,26 @@ namespace libtorrent
 		return ret.str();
 	}
 
+	std::string make_magnet_uri(torrent_info const& info)
+	{
+		std::stringstream ret;
+		if (!info.is_valid()) return ret.str();
+
+		std::string name = info.name();
+
+		ret << "magnet:?xt=urn:btih:" << base32encode(
+			std::string((char*)info.info_hash().begin(), 20));
+		if (!name.empty())
+			ret << "&dn=" << escape_string(name.c_str(), name.length());
+		std::vector<announce_entry> const& tr = info.trackers();
+		if (!tr.empty())
+		{
+			ret << "&tr=" << escape_string(tr[0].url.c_str()
+				, tr[0].url.length());
+		}
+		return ret.str();
+	}
+
 #ifndef TORRENT_NO_DEPRECATE
 	torrent_handle add_magnet_uri(session& ses, std::string const& uri
 		, fs::path const& save_path