util: split platform-specific NetworkMonitor backends into separate files

In preparation for a major overhaul of the rtnetlink implementation.

Change-Id: Iab660ab4bceb0f06db01a31f264cdfe0b7cdf077
Refs: #3353
diff --git a/src/util/detail/network-monitor-impl-rtnl.cpp b/src/util/detail/network-monitor-impl-rtnl.cpp
new file mode 100644
index 0000000..36c9190
--- /dev/null
+++ b/src/util/detail/network-monitor-impl-rtnl.cpp
@@ -0,0 +1,90 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2016 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library 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 Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#include "ndn-cxx-config.hpp"
+
+#ifdef NDN_CXX_HAVE_RTNETLINK
+
+#include "network-monitor-impl-rtnl.hpp"
+
+#include <netinet/in.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <net/if.h>
+
+#include <cerrno>
+#include <cstring>
+
+namespace ndn {
+namespace util {
+
+NetworkMonitor::Impl::Impl(NetworkMonitor& nm, boost::asio::io_service& io)
+  : m_nm(nm)
+  , m_socket(io)
+{
+  int fd = ::socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+  if (fd < 0)
+    BOOST_THROW_EXCEPTION(Error(std::string("Cannot create netlink socket (") +
+                                std::strerror(errno) + ")"));
+
+  sockaddr_nl addr{};
+  addr.nl_family = AF_NETLINK;
+  addr.nl_groups = RTMGRP_LINK |
+                   RTMGRP_IPV4_IFADDR | RTMGRP_IPV4_ROUTE |
+                   RTMGRP_IPV6_IFADDR | RTMGRP_IPV6_ROUTE;
+
+  if (::bind(fd, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)) == -1) {
+    BOOST_THROW_EXCEPTION(Error(std::string("Cannot bind on netlink socket (") +
+                                std::strerror(errno) + ")"));
+  }
+
+  m_socket.assign(fd);
+
+  m_socket.async_read_some(boost::asio::buffer(m_buffer, NETLINK_BUFFER_SIZE),
+                           bind(&Impl::onReceiveRtNetlink, this, _1, _2));
+}
+
+void
+NetworkMonitor::Impl::onReceiveRtNetlink(const boost::system::error_code& error, size_t nBytesReceived)
+{
+  if (error) {
+    return;
+  }
+
+  const nlmsghdr* nlh = reinterpret_cast<const nlmsghdr*>(m_buffer);
+  while ((NLMSG_OK(nlh, nBytesReceived)) && (nlh->nlmsg_type != NLMSG_DONE)) {
+    if (nlh->nlmsg_type == RTM_NEWADDR || nlh->nlmsg_type == RTM_DELADDR ||
+        nlh->nlmsg_type == RTM_NEWLINK || nlh->nlmsg_type == RTM_DELLINK ||
+        nlh->nlmsg_type == RTM_NEWROUTE || nlh->nlmsg_type == RTM_DELROUTE) {
+      m_nm.onNetworkStateChanged();
+      break;
+    }
+    nlh = NLMSG_NEXT(nlh, nBytesReceived);
+  }
+
+  m_socket.async_read_some(boost::asio::buffer(m_buffer, NETLINK_BUFFER_SIZE),
+                           bind(&Impl::onReceiveRtNetlink, this, _1, _2));
+}
+
+} // namespace util
+} // namespace ndn
+
+#endif // NDN_CXX_HAVE_RTNETLINK