#include "tap-encode-decode.h"

#include <sys/wait.h>

#include <sys/stat.h>

#include <sys/socket.h>

#include <sys/un.h>

#include <sys/ioctl.h>

#include <net/ethernet.h>

#include <net/if.h>

#include <netinet/in.h>

#include <netpacket/packet.h>

#include <arpa/inet.h>

#include <errno.h>

#include <limits>

#include <stdlib.h>

#define TAP_MAGIC 95549

    m_ifIndex (0),

    m_mtu (0),

    m_sock (-1)

void

TapBridge::CreateTap (void)

{

  NS_LOG_FUNCTION_NOARGS ();

  //

  // We want to create a tap device on the host.  Unfortunately for us

  // you have to have root privileges to do that.  Instead of running the 

  // entire simulation as root, we decided to make a small program who's whole

  // reason for being is to run as suid root and do what it takes to create the

  // tap.  We're going to fork and exec that program soon, but we need to have 

  // a socket to talk to it with.  So we create a local interprocess (Unix) 

  // socket for that purpose.

  //

  int sock = socket (PF_UNIX, SOCK_DGRAM, 0);

  if (sock == -1)

    {

      NS_FATAL_ERROR ("TapBridge::CreateTap(): Unix socket creation error, errno = " << strerror (errno));

    }

  //

  // Bind to that socket and let the kernel allocate an endpoint

  //

  struct sockaddr_un un;

  memset (&un, 0, sizeof (un));

  un.sun_family = AF_UNIX;

  int status = bind (sock, (struct sockaddr*)&un, sizeof (sa_family_t));

  if (status == -1)

    {

      NS_FATAL_ERROR ("TapBridge::CreateTap(): Could not bind(): errno = " << strerror (errno));

    }

  NS_LOG_INFO ("Created Unix socket");

  NS_LOG_INFO ("sun_family = " << un.sun_family);

  NS_LOG_INFO ("sun_path = " << un.sun_path);

  //

  // We have a socket here, but we want to get it there -- to the program we're

  // going to exec.  What we'll do is to do a getsockname and then encode the

  // resulting address information as a string, and then send the string to the

  // program as an argument.  So we need to get the sock name.

  //

  socklen_t len = sizeof (un);

  status = getsockname (sock, (struct sockaddr*)&un, &len);

  if (status == -1)

    {

      NS_FATAL_ERROR ("TapBridge::CreateTap(): Could not getsockname(): errno = " << strerror (errno));

    }

  //

  // Now encode that socket name (family and path) as a string of hex digits

  //

  std::string path = TapBufferToString((uint8_t *)&un, len);

  NS_LOG_INFO ("Encoded Unix socket as \"" << path << "\"");

  //

  // Fork and exec the process to create our socket.  If we're us (the parent)

  // we wait for the child (the creator) to complete and read the  socket it created using the ancillary data mechanism.

  //

  pid_t pid = ::fork ();

  if (pid == 0)

    {

      NS_LOG_DEBUG ("Child process");

      //

      // build a command line argument from the encoded endpoint string that 

      // the socket creation process will use to figure out how to respond to

      // the (now) parent process.  We're going to have to give this program

      // quite a bit of information and we use program arguments to do so.

      //

      // -d<device-name> The name of the tap device we want to create;

      // -g<gateway-address> The IP address to use as the default gateway;

      // -i<IP-address> The IP address to assign to the new tap device;

      // -m<MAC-address> The MAC-48 address to assign to the new tap device;

      // -n<network-mask> The network mask to assign to the new tap device;

      // -p<path> the path to the unix socket described above.

      //

      // Example tap-sock-creator -dnewdev -g1.2.3.2 -i1.2.3.1 -m08:00:2e:00:01:23 -n255.255.255.0 -pblah

      //

      std::ostringstream oss;

      oss << "-d" << m_tapDeviceName << " -g" << m_tapGateway << " -i" << m_tapIp << " -m" << m_tapMac

          << " -n" << m_tapNetmask << " -p" << path;

      NS_LOG_INFO ("creator arguments set to \"" << oss.str () << "\"");

      //

      // Execute the socket creation process image.

      //

      status = ::execl (FindCreator ().c_str (), "tap-sock-creator", oss.str ().c_str (), (char *)NULL);

      //

      // If the execl successfully completes, it never returns.  If it returns it failed or the OS is

      // broken.  In either case, we bail.

      //

      NS_FATAL_ERROR ("TapBridge::CreateTap(): Back from execl(), errno = " << ::strerror (errno));

    }

  else

    {

      NS_LOG_DEBUG ("Parent process");

      //

      // We're the process running the emu net device.  We need to wait for the

      // socket creator process to finish its job.

      //

      int st;

      pid_t waited = waitpid (pid, &st, 0);

      if (waited == -1)

	{

	  NS_FATAL_ERROR ("TapBridge::CreateTap(): waitpid() fails, errno = " << strerror (errno));

	}

      NS_ASSERT_MSG (pid == waited, "TapBridge::CreateTap(): pid mismatch");

      //

      // Check to see if the socket creator exited normally and then take a 

      // look at the exit code.  If it bailed, so should we.  If it didn't

      // even exit normally, we bail too.

      //

      if (WIFEXITED (st))

	{

          int exitStatus = WEXITSTATUS (st);

          if (exitStatus != 0)

            {

              NS_FATAL_ERROR ("TapBridge::CreateTap(): socket creator exited normally with status " << exitStatus);

            }

	}

      else 

	{

          NS_FATAL_ERROR ("TapBridge::CreateTap(): socket creator exited abnormally");

	}

      //

      // At this point, the socket creator has run successfully and should 

      // have created our tap device, initialized it with the information we

      // passed and sent it back to the socket address we provided.  A socket

      // (fd) we can use to talk to this tap device should be waiting on the 

      // Unix socket we set up to receive information back from the creator

      // program.  We've got to do a bunch of grunt work to get at it, though.

      //

      // The struct iovec below is part of a scatter-gather list.  It describes a

      // buffer.  In this case, it describes a buffer (an integer) that will

      // get the data that comes back from the socket creator process.  It will

      // be a magic number that we use as a consistency/sanity check.

      // 

      struct iovec iov;

      uint32_t magic;

      iov.iov_base = &magic;

      iov.iov_len = sizeof(magic);

      //

      // The CMSG macros you'll see below are used to create and access control 

      // messages (which is another name for ancillary data).  The ancillary 

      // data is made up of pairs of struct cmsghdr structures and associated

      // data arrays.

      //

      // First, we're going to allocate a buffer on the stack to receive our 

      // data array (that contains the socket).  Sometimes you'll see this called

      // an "ancillary element" but the msghdr uses the control message termimology

      // so we call it "control."

      //

      size_t msg_size = sizeof(int);

      char control[CMSG_SPACE(msg_size)];

      //

      // There is a msghdr that is used to minimize the number of parameters

      // passed to recvmsg (which we will use to receive our ancillary data).  

      // This structure uses terminology corresponding to control messages, so

      // you'll see msg_control, which is the pointer to the ancillary data and 

      // controllen which is the size of the ancillary data array.

      //

      // So, initialize the message header that describes the ancillary/control

      // data we expect to receive and point it to buffer.

      //

      struct msghdr msg;

      msg.msg_name = 0;

      msg.msg_namelen = 0;

      msg.msg_iov = &iov;

      msg.msg_iovlen = 1;

      msg.msg_control = control;

      msg.msg_controllen = sizeof (control);

      msg.msg_flags = 0;

      //

      // Now we can actually receive the interesting bits from the tap

      // creator process.

      //

      ssize_t bytesRead = recvmsg (sock, &msg, 0);

      if (bytesRead != sizeof(int))

	{

          NS_FATAL_ERROR ("TapBridge::CreateTap(): Wrong byte count from socket creator");

	}

      //

      // There may be a number of message headers/ancillary data arrays coming in.

      // Let's look for the one with a type SCM_RIGHTS which indicates it' the

      // one we're interested in.

      //

      struct cmsghdr *cmsg;

      for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) 

	{

	  if (cmsg->cmsg_level == SOL_SOCKET &&

	      cmsg->cmsg_type == SCM_RIGHTS)

	    {

              //

              // This is the type of message we want.  Check to see if the magic 

              // number is correct and then pull out the socket we care about if

              // it matches

              //

              if (magic == TAP_MAGIC)

                {

                  NS_LOG_INFO ("Got SCM_RIGHTS with correct magic " << magic);

                  int *rawSocket = (int*)CMSG_DATA (cmsg);

                  NS_LOG_INFO ("Got the socket from the socket creator = " << *rawSocket);

                  m_sock = *rawSocket;

                  return;

                }

              else

                {

                  NS_LOG_INFO ("Got SCM_RIGHTS, but with bad magic " << magic);                  

                }

	    }

	}

      NS_FATAL_ERROR ("Did not get the raw socket from the socket creator");

    }

}

std::string

TapBridge::FindCreator (void)

{

  struct stat st;

  std::string debug = "./build/debug/src/devices/tap-bridge/tap-sock-creator";

  std::string optimized = "./build/optimized/src/devices/tap-bridge/tap-sock-creator";

  if (::stat (debug.c_str (), &st) == 0)

    {

      return debug;

    }

  if (::stat (optimized.c_str (), &st) == 0)

    {

      return optimized;

    }

  NS_FATAL_ERROR ("TapBridge::FindCreator(): Couldn't find creator");

  return ""; // quiet compiler

}