//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program 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 Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// Add routes on Linux using AF_NETLINK socket

#ifndef OPENVPN_NETCONF_LINUX_ROUTE_H
#define OPENVPN_NETCONF_LINUX_ROUTE_H

#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <net/if.h>
#include <errno.h>

#include <string>

#include <openvpn/common/exception.hpp>
#include <openvpn/common/scoped_fd.hpp>
#include <openvpn/common/strerror.hpp>
#include <openvpn/addr/route.hpp>

namespace openvpn {

  class LinuxRoute
  {
  public:
    OPENVPN_EXCEPTION(linux_route_error);

    LinuxRoute()
    {
      fd.reset(::socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE));
      if (!fd.defined())
	throw linux_route_error("creating AF_NETLINK socket");

      struct sockaddr_nl local;
      ::memset(&local, 0, sizeof(local));
      local.nl_family = AF_NETLINK;
      local.nl_pad = 0;
      local.nl_pid = 0; // only use getpid() if unique instantiation per process
      local.nl_groups = 0;
      if (::bind(fd(), (struct sockaddr*)&local, sizeof(local)) < 0)
	throw linux_route_error("binding to AF_NETLINK socket");
    }

    void add_delete(const bool add,
		    const IP::Route& route,
		    const int if_index,
		    const int table=RT_TABLE_MAIN)
    {
      typedef struct {
	struct nlmsghdr  nlmsg_info;
	struct rtmsg	 rtmsg_info;
	char		 buffer[64];  // must be large enough to contain request
      } netlink_req_t;

      struct rtattr *rtattr_ptr;
      int rtmsg_len;
      struct sockaddr_nl peer;
      struct msghdr msg_info;
      struct iovec iov_info;
      netlink_req_t netlink_req;

      ::memset(&peer, 0, sizeof(peer));
      peer.nl_family = AF_NETLINK;
      peer.nl_pad = 0;
      peer.nl_pid = 0;
      peer.nl_groups = 0;

      ::memset(&msg_info, 0, sizeof(msg_info));
      msg_info.msg_name = (void *) &peer;
      msg_info.msg_namelen = sizeof(peer);

      ::memset(&netlink_req, 0, sizeof(netlink_req));

      rtmsg_len = sizeof(struct rtmsg);

      // add destination addr
      rtattr_ptr = (struct rtattr *) netlink_req.buffer;
      rtattr_ptr->rta_type = RTA_DST;
      rtattr_ptr->rta_len = sizeof(struct rtattr) + route.addr.size_bytes();
      route.addr.to_byte_string_variable(((unsigned char *)rtattr_ptr) + sizeof(struct rtattr));
      rtmsg_len += rtattr_ptr->rta_len;

      // add if_index
      rtattr_ptr = (struct rtattr *) (((unsigned char *)rtattr_ptr) + rtattr_ptr->rta_len);
      rtattr_ptr->rta_type = RTA_OIF;
      rtattr_ptr->rta_len = sizeof(struct rtattr) + 4;
      ::memcpy(((unsigned char *)rtattr_ptr) + sizeof(struct rtattr), &if_index, 4);
      rtmsg_len += rtattr_ptr->rta_len;

      netlink_req.nlmsg_info.nlmsg_len = NLMSG_LENGTH(rtmsg_len);

      if (add)
	{
	  netlink_req.nlmsg_info.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE;
	  netlink_req.nlmsg_info.nlmsg_type = RTM_NEWROUTE;
	}
      else // delete
	{
	  netlink_req.nlmsg_info.nlmsg_flags = NLM_F_REQUEST;
	  netlink_req.nlmsg_info.nlmsg_type = RTM_DELROUTE;
	}

      netlink_req.rtmsg_info.rtm_family = route.addr.family();
      netlink_req.rtmsg_info.rtm_table = table;
      netlink_req.rtmsg_info.rtm_dst_len = route.prefix_len; // add prefix

      netlink_req.rtmsg_info.rtm_protocol = RTPROT_STATIC;
      netlink_req.rtmsg_info.rtm_scope = RT_SCOPE_UNIVERSE;
      netlink_req.rtmsg_info.rtm_type = RTN_UNICAST;

      iov_info.iov_base = (void *) &netlink_req.nlmsg_info;
      iov_info.iov_len = netlink_req.nlmsg_info.nlmsg_len;
      msg_info.msg_iov = &iov_info;
      msg_info.msg_iovlen = 1;

      const ssize_t status = ::sendmsg(fd(), &msg_info, 0);
      if (status < 0)
	{
	  const int eno = errno;
	  OPENVPN_THROW(linux_route_error, "add_delete: sendmsg failed: " << strerror_str(eno));
	}
    }

    static int if_index(const std::string& iface)
    {
      const unsigned int ret = ::if_nametoindex(iface.c_str());
      if (!ret)
	OPENVPN_THROW(linux_route_error, "if_index: no such interface: " << iface);
      return ret;
    }

  private:
    ScopedFD fd;
  };

}

#endif