face: congestion detection in TCP, UDP, and Unix socket transports

refs #4362

Change-Id: Idaa5d65e1f33663d95bad56de42640183b2cda6d
diff --git a/daemon/face/socket-utils.cpp b/daemon/face/socket-utils.cpp
new file mode 100644
index 0000000..5b38e40
--- /dev/null
+++ b/daemon/face/socket-utils.cpp
@@ -0,0 +1,57 @@
+/* -*- 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/>.
+ */
+
+#include "socket-utils.hpp"
+#include "transport.hpp"
+
+#if defined(__linux__)
+#include <linux/sockios.h>
+#include <sys/ioctl.h>
+#elif defined(__APPLE__)
+#include <sys/socket.h>
+#endif
+
+namespace nfd {
+namespace face {
+
+ssize_t
+getTxQueueLength(int fd)
+{
+  int queueLength = QUEUE_UNSUPPORTED;
+#if defined(__linux__)
+  if (ioctl(fd, SIOCOUTQ, &queueLength) < 0) {
+    queueLength = QUEUE_ERROR;
+  }
+#elif defined(__APPLE__)
+  socklen_t queueLengthSize = sizeof(queueLength);
+  if (getsockopt(fd, SOL_SOCKET, SO_NWRITE, &queueLength, &queueLengthSize) < 0) {
+    queueLength = QUEUE_ERROR;
+  }
+#endif
+  return queueLength;
+}
+
+} // namespace face
+} // namespace nfd