fix bug in udp tracker announce messages

src/udp_tracker_connection.cpp

@@ -709,9 +709,9 @@ namespace libtorrent
 		aux::write_int32(action_t::announce, out); // action (announce)
 		aux::write_int32(m_transaction_id, out); // transaction_id
 		std::copy(req.info_hash.begin(), req.info_hash.end(), out.data()); // info_hash
-		out.subspan(20);
+		out = out.subspan(20);
 		std::copy(req.pid.begin(), req.pid.end(), out.data()); // peer_id
-		out.subspan(20);
+		out = out.subspan(20);
 		aux::write_int64(req.downloaded, out); // downloaded
 		aux::write_int64(req.left, out); // left
 		aux::write_int64(req.uploaded, out); // uploaded

test/udp_tracker.cpp

@@ -94,6 +94,12 @@ struct udp_tracker
 		{
 			case 0: // connect
 
+				if (bytes_transferred < 16)
+				{
+					std::printf("invalid connect message: %d Bytes, expected 16 Bytes\n"
+						, int(bytes_transferred));
+					return;
+				}
 				std::printf("%s: UDP connect from %s\n", time_now_string()
 					, print_endpoint(*from).c_str());
 				ptr = buffer;
@@ -109,6 +115,13 @@ struct udp_tracker
 
 			case 1: // announce
 
+				if (bytes_transferred < 84)
+				{
+					std::printf("invalid announce message: %d Bytes, expected 84 Bytes\n"
+						, int(bytes_transferred));
+					return;
+				}
+
 				++m_udp_announces;
 				std::printf("%s: UDP announce [%d]\n", time_now_string()
 					, int(m_udp_announces));