//    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/>.

// Get IPv4 gateway info on Mac OS X.

#ifndef OPENVPN_TUN_MAC_GWV4_H
#define OPENVPN_TUN_MAC_GWV4_H

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/route.h>
#include <net/if.h>
#include <net/if_dl.h>

#include <cstring>
#include <string>
#include <sstream>
#include <algorithm> // for std::max
#include <cstdint>   // for std::uint32_t
#include <memory>

#include <openvpn/common/exception.hpp>
#include <openvpn/common/hexstr.hpp>
#include <openvpn/common/scoped_fd.hpp>
#include <openvpn/common/socktypes.hpp>
#include <openvpn/common/string.hpp>
#include <openvpn/addr/ip.hpp>
#include <openvpn/addr/addrpair.hpp>
#include <openvpn/addr/macaddr.hpp>

namespace openvpn {
  class MacGatewayInfoV4
  {
    struct rtmsg {
      struct rt_msghdr m_rtm;
      char m_space[512];
    };

#   define OPENVPN_ROUNDUP(a)			\
      ((a) > 0 ? (1 + (((a) - 1) | (sizeof(std::uint32_t) - 1))) : sizeof(std::uint32_t))

#   define OPENVPN_NEXTADDR(w, u)		\
      if (rtm_addrs & (w)) {			\
        l = OPENVPN_ROUNDUP(u.sa_len);		\
        std::memmove(cp, &(u), l);		\
        cp += l;				\
      }

#   define OPENVPN_ADVANCE(x, n)		\
      (x += OPENVPN_ROUNDUP((n)->sa_len))

  public:
    OPENVPN_EXCEPTION(route_gateway_error);

    enum {
      ADDR_DEFINED     = (1<<0), /* set if gateway.addr defined */
      NETMASK_DEFINED  = (1<<1), /* set if gateway.netmask defined */
      HWADDR_DEFINED   = (1<<2), /* set if hwaddr is defined */
      IFACE_DEFINED    = (1<<3), /* set if iface is defined */
    };

    MacGatewayInfoV4()
      : flags_(0)
    {
      struct rtmsg m_rtmsg;
      ScopedFD sockfd;
      int seq, l, pid, rtm_addrs, i;
      struct sockaddr so_dst, so_mask;
      char *cp = m_rtmsg.m_space; 
      struct sockaddr *gate = nullptr, *ifp = nullptr, *sa;
      struct rt_msghdr *rtm_aux;

      /* setup data to send to routing socket */
      pid = ::getpid();
      seq = 0;
      rtm_addrs = RTA_DST | RTA_NETMASK | RTA_IFP;

      std::memset(&m_rtmsg, 0, sizeof(m_rtmsg));
      std::memset(&so_dst, 0, sizeof(so_dst));
      std::memset(&so_mask, 0, sizeof(so_mask));
      std::memset(&m_rtmsg.m_rtm, 0, sizeof(struct rt_msghdr));

      m_rtmsg.m_rtm.rtm_type = RTM_GET;
      m_rtmsg.m_rtm.rtm_flags = RTF_UP | RTF_GATEWAY;
      m_rtmsg.m_rtm.rtm_version = RTM_VERSION;
      m_rtmsg.m_rtm.rtm_seq = ++seq;
      m_rtmsg.m_rtm.rtm_addrs = rtm_addrs; 

      so_dst.sa_family = AF_INET;
      so_dst.sa_len = sizeof(struct sockaddr_in);
      so_mask.sa_family = AF_INET;
      so_mask.sa_len = sizeof(struct sockaddr_in);

      OPENVPN_NEXTADDR(RTA_DST, so_dst);
      OPENVPN_NEXTADDR(RTA_NETMASK, so_mask);

      m_rtmsg.m_rtm.rtm_msglen = l = cp - (char *)&m_rtmsg;

      /* transact with routing socket */
      sockfd.reset(socket(PF_ROUTE, SOCK_RAW, 0));
      if (!sockfd.defined())
	throw route_gateway_error("GDG: socket #1 failed");
      if (::write(sockfd(), (char *)&m_rtmsg, l) < 0)
	throw route_gateway_error("GDG: problem writing to routing socket");
      do {
	l = ::read(sockfd(), (char *)&m_rtmsg, sizeof(m_rtmsg));
      } while (l > 0 && (m_rtmsg.m_rtm.rtm_seq != seq || m_rtmsg.m_rtm.rtm_pid != pid));                   
      sockfd.close();

      /* extract return data from routing socket */
      rtm_aux = &m_rtmsg.m_rtm;
      cp = ((char *)(rtm_aux + 1));
      if (rtm_aux->rtm_addrs)
	{
	  for (i = 1; i; i <<= 1)
	    {
	      if (i & rtm_aux->rtm_addrs)
		{
		  sa = (struct sockaddr *)cp;
		  if (i == RTA_GATEWAY )
		    gate = sa;
		  else if (i == RTA_IFP)
		    ifp = sa;
		  OPENVPN_ADVANCE(cp, sa);
		}
	    }
	}
      else
	return;

      /* get gateway addr and interface name */
      if (gate != nullptr )
	{
	  /* get default gateway addr */
	  gateway_.addr.reset_ipv4_from_uint32(ntohl(((struct sockaddr_in *)gate)->sin_addr.s_addr));
	  if (!gateway_.addr.unspecified())
	    flags_ |= ADDR_DEFINED;

	  if (ifp)
	    {
	      /* get interface name */
	      const struct sockaddr_dl *adl = (struct sockaddr_dl *) ifp;
	      const size_t len = adl->sdl_nlen;
	      if (len && len < sizeof(iface_))
		{
		  std::memcpy (iface_, adl->sdl_data, len);
		  iface_[len] = '\0';
		  flags_ |= IFACE_DEFINED;
		}
	    }
	}

      /* get netmask of interface that owns default gateway */
      if (flags_ & IFACE_DEFINED) {
	struct ifreq ifr;

	sockfd.reset(socket(AF_INET, SOCK_DGRAM, 0));
	if (!sockfd.defined())
	  throw route_gateway_error("GDG: socket #2 failed");

	std::memset(&ifr, 0, sizeof(ifr));
	ifr.ifr_addr.sa_family = AF_INET;
	string::strncpynt(ifr.ifr_name, iface_, IFNAMSIZ);

	if (::ioctl(sockfd(), SIOCGIFNETMASK, (char *)&ifr) < 0)
	  throw route_gateway_error("GDG: ioctl #1 failed");
	sockfd.close();

	gateway_.netmask.reset_ipv4_from_uint32(ntohl(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr));
	flags_ |= NETMASK_DEFINED;
      }

      /* try to read MAC addr associated with interface that owns default gateway */
      if (flags_ & IFACE_DEFINED)
	{
	  struct ifconf ifc;
	  struct ifreq *ifr;
	  const int bufsize = 4096;

	  std::unique_ptr<char[]> buffer(new char[bufsize]);
	  std::memset(buffer.get(), 0, bufsize);
	  sockfd.reset(socket(AF_INET, SOCK_DGRAM, 0));
	  if (!sockfd.defined())
	    throw route_gateway_error("GDG: socket #3 failed");

	  ifc.ifc_len = bufsize;
	  ifc.ifc_buf = buffer.get();

	  if (::ioctl(sockfd(), SIOCGIFCONF, (char *)&ifc) < 0)
	    throw route_gateway_error("GDG: ioctl #2 failed");
	  sockfd.close();

	  for (cp = buffer.get(); cp <= buffer.get() + ifc.ifc_len - sizeof(struct ifreq); )
	    {
	      ifr = (struct ifreq *)cp;
	      const size_t len = sizeof(ifr->ifr_name) + std::max(sizeof(ifr->ifr_addr), size_t(ifr->ifr_addr.sa_len));
	      if (!ifr->ifr_addr.sa_family)
		break;
	      if (!::strncmp(ifr->ifr_name, iface_, IFNAMSIZ))
		{
		  if (ifr->ifr_addr.sa_family == AF_LINK)
		    {
		      struct sockaddr_dl *sdl = (struct sockaddr_dl *)&ifr->ifr_addr;
		      hwaddr_.reset((const unsigned char *)LLADDR(sdl));
		      flags_ |= HWADDR_DEFINED;
		    }
		}
	      cp += len;
	    }
	}
    }
#   undef OPENVPN_ROUNDUP
#   undef OPENVPN_NEXTADDR
#   undef OPENVPN_ADVANCE

    std::string info() const
    {
      std::ostringstream os;
      os << "GATEWAY";
      if (flags_ & ADDR_DEFINED)
	{
	  os << " ADDR=" << gateway_.addr;
	  if (flags_ & NETMASK_DEFINED)
	    {
	      os << '/' << gateway_.netmask;
	    }
	}
      if (flags_ & IFACE_DEFINED)
	os << " IFACE=" << iface_;
      if (flags_ & HWADDR_DEFINED)
	os << " HWADDR=" << hwaddr_;
      return os.str();
    }

    unsigned int flags() const { return flags_; }
    const IP::Addr& gateway_addr() const { return gateway_.addr; }
    std::string gateway_addr_str() const { return gateway_addr().to_string(); }
    const IP::Addr& gateway_netmask() const { return gateway_.netmask; }
    std::string gateway_netmask_str() const { return gateway_netmask().to_string(); }
    std::string iface() const { return iface_; }
    const MACAddr& hwaddr() const { return hwaddr_; }

    bool iface_addr_defined() const
    {
      return (flags_ & (ADDR_DEFINED|IFACE_DEFINED)) == (ADDR_DEFINED|IFACE_DEFINED);
    }

    bool hwaddr_defined() const
    {
      return flags_ & HWADDR_DEFINED;
    }

  private:
    unsigned int flags_;
    IP::AddrMaskPair gateway_;
    char iface_[16];
    MACAddr hwaddr_;
  };

}

#endif