face: congestion detection in TCP, UDP, and Unix socket transports
refs #4362
Change-Id: Idaa5d65e1f33663d95bad56de42640183b2cda6d
diff --git a/daemon/face/socket-utils.hpp b/daemon/face/socket-utils.hpp
new file mode 100644
index 0000000..3929d8a
--- /dev/null
+++ b/daemon/face/socket-utils.hpp
@@ -0,0 +1,48 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2014-2018, Regents of the University of California,
+ * Arizona Board of Regents,
+ * Colorado State University,
+ * University Pierre & Marie Curie, Sorbonne University,
+ * Washington University in St. Louis,
+ * Beijing Institute of Technology,
+ * The University of Memphis.
+ *
+ * This file is part of NFD (Named Data Networking Forwarding Daemon).
+ * See AUTHORS.md for complete list of NFD authors and contributors.
+ *
+ * NFD is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * NFD, e.g., in COPYING.md file. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef NFD_DAEMON_FACE_SOCKET_UTILS_HPP
+#define NFD_DAEMON_FACE_SOCKET_UTILS_HPP
+
+#include "core/common.hpp"
+
+namespace nfd {
+namespace face {
+
+/** \brief obtain send queue length from a specified system socket
+ * \param fd file descriptor of the socket
+ * \retval QUEUE_UNSUPPORTED this operation is unsupported on the current platform
+ * \retval QUEUE_ERROR there was an error retrieving the send queue length
+ *
+ * On Linux, ioctl() is used to obtain the value of SIOCOUTQ from the socket.
+ * On macOS, getsockopt() is used to obtain the value of SO_NWRITE from the socket.
+ */
+ssize_t
+getTxQueueLength(int fd);
+
+} // namespace face
+} // namespace nfd
+
+#endif // NFD_DAEMON_FACE_SOCKET_UTILS_HPP