/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#elif defined(_MSC_VER)
#include "config-msvc.h"
#endif

#include "syshead.h"

#if PORT_SHARE

#include "event.h"
#include "socket.h"
#include "fdmisc.h"
#include "crypto.h"
#include "ps.h"

#include "memdbg.h"

struct port_share *port_share = NULL; /* GLOBAL */

/* size of i/o buffers */
#define PROXY_CONNECTION_BUFFER_SIZE 1500

/* Command codes for foreground -> background communication */
#define COMMAND_REDIRECT 10
#define COMMAND_EXIT     11

/* Response codes for background -> foreground communication */
#define RESPONSE_INIT_SUCCEEDED   20
#define RESPONSE_INIT_FAILED      21

/*
 * Return values for proxy_connection_io functions
 */

#define IOSTAT_EAGAIN_ON_READ   0 /* recv returned EAGAIN */
#define IOSTAT_EAGAIN_ON_WRITE  1 /* send returned EAGAIN */
#define IOSTAT_READ_ERROR       2 /* the other end of our read socket (pc) was closed */
#define IOSTAT_WRITE_ERROR      3 /* the other end of our write socket (pc->counterpart) was closed */
#define IOSTAT_GOOD             4 /* nothing to report */

/*
 * A foreign (non-OpenVPN) connection we are proxying,
 * usually HTTPS
 */
struct proxy_connection {
  bool defined;
  struct proxy_connection *next;
  struct proxy_connection *counterpart;
  struct buffer buf;
  bool buffer_initial;
  int rwflags;
  int sd;
  char *jfn;
};

#if 0
static const char *
headc (const struct buffer *buf)
{
  static char foo[16];
  strncpy (foo, BSTR(buf), 15);
  foo[15] = 0;
  return foo;
}
#endif

static inline void
close_socket_if_defined (const socket_descriptor_t sd)
{
  if (socket_defined (sd))
    openvpn_close_socket (sd);
}

/*
 * Close most of parent's fds.
 * Keep stdin/stdout/stderr, plus one
 * other fd which is presumed to be
 * our pipe back to parent.
 * Admittedly, a bit of a kludge,
 * but posix doesn't give us a kind
 * of FD_CLOEXEC which will stop
 * fds from crossing a fork().
 */
static void
close_fds_except (int keep)
{
  socket_descriptor_t i;
  closelog ();
  for (i = 3; i <= 100; ++i)
    {
      if (i != keep)
	openvpn_close_socket (i);
    }
}

/*
 * Usually we ignore signals, because our parent will
 * deal with them.
 */
static void
set_signals (void)
{
  signal (SIGTERM, SIG_DFL);

  signal (SIGINT, SIG_IGN);
  signal (SIGHUP, SIG_IGN);
  signal (SIGUSR1, SIG_IGN);
  signal (SIGUSR2, SIG_IGN);
  signal (SIGPIPE, SIG_IGN);
}

/*
 * Socket read/write functions.
 */

static int
recv_control (const socket_descriptor_t fd)
{
  unsigned char c;
  const ssize_t size = read (fd, &c, sizeof (c));
  if (size == sizeof (c))
    return c;
  else
    {
      return -1;
    }
}

static int
send_control (const socket_descriptor_t fd, int code)
{
  unsigned char c = (unsigned char) code;
  const ssize_t size = write (fd, &c, sizeof (c));
  if (size == sizeof (c))
    return (int) size;
  else
    return -1;
}

static int
cmsg_size ()
{
  return CMSG_SPACE(sizeof(socket_descriptor_t));
}

/*
 * Send a command (char), data (head), and a file descriptor (sd_send) to a local process
 * over unix socket sd.  Unfortunately, there's no portable way to send file descriptors
 * to other processes, so this code, as well as its analog (control_message_from_parent below),
 * is Linux-specific. This function runs in the context of the main process and is used to
 * send commands, data, and file descriptors to the background process.
 */
static void
port_share_sendmsg (const socket_descriptor_t sd,
		    const char command,
		    const struct buffer *head,
		    const socket_descriptor_t sd_send)
{
  if (socket_defined (sd))
    {
      struct msghdr mesg;
      struct cmsghdr* h;
      struct iovec iov[2];
      socket_descriptor_t sd_null[2] = { SOCKET_UNDEFINED, SOCKET_UNDEFINED };
      char cmd;
      ssize_t status;

      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE: sendmsg sd=%d len=%d",
	    (int)sd_send,
	    head ? BLEN(head) : -1);

      CLEAR (mesg);

      cmd = command;

      iov[0].iov_base = &cmd;
      iov[0].iov_len = sizeof (cmd);
      mesg.msg_iovlen = 1;

      if (head)
	{
	  iov[1].iov_base = BPTR (head);
	  iov[1].iov_len = BLEN (head);
	  mesg.msg_iovlen = 2;
	}

      mesg.msg_iov = iov;

      mesg.msg_controllen = cmsg_size ();
      mesg.msg_control = (char *) malloc (mesg.msg_controllen);
      check_malloc_return (mesg.msg_control);
      mesg.msg_flags = 0;

      h = CMSG_FIRSTHDR(&mesg);
      h->cmsg_level = SOL_SOCKET;
      h->cmsg_type = SCM_RIGHTS;
      h->cmsg_len = CMSG_LEN(sizeof(socket_descriptor_t));

      if (socket_defined (sd_send))
	{
	  *((socket_descriptor_t*)CMSG_DATA(h)) = sd_send;
	}
      else
	{
	  socketpair (PF_UNIX, SOCK_DGRAM, 0, sd_null);
	  *((socket_descriptor_t*)CMSG_DATA(h)) = sd_null[0];
	}

      status = sendmsg (sd, &mesg, MSG_NOSIGNAL);
      if (status == -1)
	msg (M_WARN|M_ERRNO, "PORT SHARE: sendmsg failed -- unable to communicate with background process (%d,%d,%d,%d)",
	     sd, sd_send, sd_null[0], sd_null[1]
	     );

      close_socket_if_defined (sd_null[0]);
      close_socket_if_defined (sd_null[1]);
      free (mesg.msg_control);
    }
}

static void
proxy_entry_close_sd (struct proxy_connection *pc, struct event_set *es)
{
  if (pc->defined && socket_defined (pc->sd))
    {
      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: delete sd=%d", (int)pc->sd);
      if (es)
	event_del (es, pc->sd);
      openvpn_close_socket (pc->sd);
      pc->sd = SOCKET_UNDEFINED;
    }
}

/*
 * Mark a proxy entry and its counterpart for close.
 */
static void
proxy_entry_mark_for_close (struct proxy_connection *pc, struct event_set *es)
{
  if (pc->defined)
    {
      struct proxy_connection *cp = pc->counterpart;
      proxy_entry_close_sd (pc, es);
      free_buf (&pc->buf);
      pc->buffer_initial = false;
      pc->rwflags = 0;
      pc->defined = false;
      if (pc->jfn)
	{
	  unlink (pc->jfn);
	  free (pc->jfn);
	  pc->jfn = NULL;
	}
      if (cp && cp->defined && cp->counterpart == pc)
	proxy_entry_mark_for_close (cp, es);
    }
}

/*
 * Run through the proxy entry list and delete all entries marked
 * for close.
 */
static void
proxy_list_housekeeping (struct proxy_connection **list)
{
  if (list)
    {
      struct proxy_connection *prev = NULL;
      struct proxy_connection *pc = *list;

      while (pc)
	{
	  struct proxy_connection *next = pc->next;
	  if (!pc->defined)
	    {
	      free (pc);
	      if (prev)
		prev->next = next;
	      else
		*list = next;
	    }
	  else
	    prev = pc;
	  pc = next;
	}
    }
}

/*
 * Record IP/port of client in filesystem, so that server receiving
 * the proxy can determine true client origin.
 */
static void
journal_add (const char *journal_dir, struct proxy_connection *pc, struct proxy_connection *cp)
{
  struct gc_arena gc = gc_new ();
  struct openvpn_sockaddr from, to;
  socklen_t slen, dlen;
  int fnlen;
  char *jfn;
  int fd;

  slen = sizeof(from.addr.sa);
  dlen = sizeof(to.addr.sa);
  if (!getpeername (pc->sd, (struct sockaddr *) &from.addr.sa, &slen)
      && !getsockname (cp->sd, (struct sockaddr *) &to.addr.sa, &dlen))
    {
      const char *f = print_sockaddr_ex (&from, ":", PS_SHOW_PORT, &gc);
      const char *t = print_sockaddr_ex (&to, ":", PS_SHOW_PORT, &gc);
      fnlen =  strlen(journal_dir) + strlen(t) + 2;
      jfn = (char *) malloc(fnlen);
      check_malloc_return (jfn);
      openvpn_snprintf (jfn, fnlen, "%s/%s", journal_dir, t);
      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: client origin %s -> %s", jfn, f);
      fd = platform_open (jfn, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP);
      if (fd != -1)
	{
	  write(fd, f, strlen(f));
	  close (fd);
	  cp->jfn = jfn;
	}
      else
	{
	  msg (M_WARN|M_ERRNO, "PORT SHARE: unable to write journal file in %s", jfn);
	  free (jfn);
	}
    }
  gc_free (&gc);
}

/*
 * Cleanup function, on proxy process exit.
 */
static void
proxy_list_close (struct proxy_connection **list)
{
  if (list)
    {
      struct proxy_connection *pc = *list;
      while (pc)
	{
	  proxy_entry_mark_for_close (pc, NULL);
	  pc = pc->next;
	}
      proxy_list_housekeeping (list);
    }
}

static void
sock_addr_set (struct openvpn_sockaddr *osaddr,
	       const in_addr_t addr,
	       const int port)
{
  CLEAR (*osaddr);
  osaddr->addr.in4.sin_family = AF_INET;
  osaddr->addr.in4.sin_addr.s_addr = htonl (addr);
  osaddr->addr.in4.sin_port = htons (port);
}

static inline void
proxy_connection_io_requeue (struct proxy_connection *pc, const int rwflags_new, struct event_set *es)
{
  if (socket_defined (pc->sd) && pc->rwflags != rwflags_new)
    {
      /*dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: requeue[%d] rwflags=%d", (int)pc->sd, rwflags_new);*/
      event_ctl (es, pc->sd, rwflags_new, (void*)pc);
      pc->rwflags = rwflags_new;
    }
}

/*
 * Create a new pair of proxy_connection entries, one for each
 * socket file descriptor involved in the proxy.  We are given
 * the client fd, and we should derive our own server fd by connecting
 * to the server given by server_addr/server_port.  Return true
 * on success and false on failure to connect to server.
 */
static bool
proxy_entry_new (struct proxy_connection **list,
		 struct event_set *es,
		 const in_addr_t server_addr,
		 const int server_port,
		 const socket_descriptor_t sd_client,
		 struct buffer *initial_data,
		 const char *journal_dir)
{
  struct openvpn_sockaddr osaddr;
  socket_descriptor_t sd_server;
  int status;
  struct proxy_connection *pc;
  struct proxy_connection *cp;

  /* connect to port share server */
  sock_addr_set (&osaddr, server_addr, server_port);
  if ((sd_server = socket (PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
    {
      msg (M_WARN|M_ERRNO, "PORT SHARE PROXY: cannot create socket");
      return false;
    }
  status = openvpn_connect (sd_server, &osaddr, 5, NULL);
  if (status)
    {
      msg (M_WARN, "PORT SHARE PROXY: connect to port-share server failed");
      openvpn_close_socket (sd_server);
      return false;
    }
  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: connect to port-share server succeeded");

  set_nonblock (sd_client);
  set_nonblock (sd_server);

  /* allocate 2 new proxy_connection objects */
  ALLOC_OBJ_CLEAR (pc, struct proxy_connection);
  ALLOC_OBJ_CLEAR (cp, struct proxy_connection);

  /* client object */
  pc->defined = true;
  pc->next = cp;
  pc->counterpart = cp;
  pc->buf = *initial_data;
  pc->buffer_initial = true;
  pc->rwflags = EVENT_UNDEF;
  pc->sd = sd_client;

  /* server object */
  cp->defined = true;
  cp->next = *list;
  cp->counterpart = pc;
  cp->buf = alloc_buf (PROXY_CONNECTION_BUFFER_SIZE);
  cp->buffer_initial = false;
  cp->rwflags = EVENT_UNDEF;
  cp->sd = sd_server;

  /* add to list */
  *list = pc;

  /* add journal entry */
  if (journal_dir)
    journal_add (journal_dir, pc, cp);
  
  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: NEW CONNECTION [c=%d s=%d]", (int)sd_client, (int)sd_server);

  /* set initial i/o states */
  proxy_connection_io_requeue (pc, EVENT_READ, es);
  proxy_connection_io_requeue (cp, EVENT_READ|EVENT_WRITE, es);
  
  return true;
}

/*
 * This function runs in the context of the background proxy process.
 * Receive a control message from the parent (sent by the port_share_sendmsg
 * function above) and act on it.  Return false if the proxy process should
 * exit, true otherwise.
 */
static bool
control_message_from_parent (const socket_descriptor_t sd_control,
			     struct proxy_connection **list,
			     struct event_set *es,
			     const in_addr_t server_addr,
			     const int server_port,
			     const int max_initial_buf,
			     const char *journal_dir)
{
  /* this buffer needs to be large enough to handle the largest buffer
     that might be returned by the link_socket_read call in read_incoming_link. */
  struct buffer buf = alloc_buf (max_initial_buf);

  struct msghdr mesg;
  struct cmsghdr* h;
  struct iovec iov[2];
  char command = 0;
  ssize_t status;
  int ret = true;

  CLEAR (mesg);

  iov[0].iov_base = &command;
  iov[0].iov_len = sizeof (command);
  iov[1].iov_base = BPTR (&buf);
  iov[1].iov_len = BCAP (&buf);
  mesg.msg_iov = iov;
  mesg.msg_iovlen = 2;

  mesg.msg_controllen = cmsg_size ();
  mesg.msg_control = (char *) malloc (mesg.msg_controllen);
  check_malloc_return (mesg.msg_control);
  mesg.msg_flags = 0;

  h = CMSG_FIRSTHDR(&mesg);
  h->cmsg_len = CMSG_LEN(sizeof(socket_descriptor_t));
  h->cmsg_level = SOL_SOCKET;
  h->cmsg_type = SCM_RIGHTS;
  *((socket_descriptor_t*)CMSG_DATA(h)) = SOCKET_UNDEFINED;

  status = recvmsg (sd_control, &mesg, MSG_NOSIGNAL);
  if (status != -1)
    {
      if (   h == NULL
	  || h->cmsg_len    != CMSG_LEN(sizeof(socket_descriptor_t))
	  || h->cmsg_level  != SOL_SOCKET
	  || h->cmsg_type   != SCM_RIGHTS )
	{
	  msg (M_WARN, "PORT SHARE PROXY: received unknown message");
	}
      else
	{
	  const socket_descriptor_t received_fd = *((socket_descriptor_t*)CMSG_DATA(h));
	  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: RECEIVED sd=%d", (int)received_fd);

	  if (status >= 2 && command == COMMAND_REDIRECT)
	    {
	      buf.len = status - 1;
	      if (proxy_entry_new (list,
				   es,
				   server_addr,
				   server_port,
				   received_fd,
				   &buf,
				   journal_dir))
		{
		  CLEAR (buf); /* we gave the buffer to proxy_entry_new */
		}
	      else
		{
		  openvpn_close_socket (received_fd);
		}
	    }
	  else if (status >= 1 && command == COMMAND_EXIT)
	    {
	      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: RECEIVED COMMAND_EXIT");
	      openvpn_close_socket (received_fd); /* null socket */
	      ret = false;
	    }
	}
    }
  free (mesg.msg_control);
  free_buf (&buf);
  return ret;
}

static int
proxy_connection_io_recv (struct proxy_connection *pc)
{
  /* recv data from socket */
  const int status = recv (pc->sd, BPTR(&pc->buf), BCAP(&pc->buf), MSG_NOSIGNAL);
  if (status < 0)
    {
      return (errno == EAGAIN) ? IOSTAT_EAGAIN_ON_READ : IOSTAT_READ_ERROR;
    }
  else
    {
      if (!status)
	return IOSTAT_READ_ERROR;
      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: read[%d] %d", (int)pc->sd, status);
      pc->buf.len = status;
    }
  return IOSTAT_GOOD;
}

static int
proxy_connection_io_send (struct proxy_connection *pc, int *bytes_sent)
{
  const socket_descriptor_t sd = pc->counterpart->sd;
  const int status = send (sd, BPTR(&pc->buf), BLEN(&pc->buf), MSG_NOSIGNAL);

  if (status < 0)
    {
      const int e = errno;
      return (e == EAGAIN) ? IOSTAT_EAGAIN_ON_WRITE : IOSTAT_WRITE_ERROR;
    }
  else
    {
      *bytes_sent += status;
      if (status != pc->buf.len)
	{
	  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: partial write[%d], tried=%d got=%d", (int)sd, pc->buf.len, status);
	  buf_advance (&pc->buf, status);
	  return IOSTAT_EAGAIN_ON_WRITE;
	}
      else
	{
	  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: wrote[%d] %d", (int)sd, status);
	  pc->buf.len = 0;
	  pc->buf.offset = 0;
	}
    }

  /* realloc send buffer after initial send */
  if (pc->buffer_initial)
    {
      free_buf (&pc->buf);
      pc->buf = alloc_buf (PROXY_CONNECTION_BUFFER_SIZE);
      pc->buffer_initial = false;
    }
  return IOSTAT_GOOD;
}

/*
 * Forward data from pc to pc->counterpart.
 */

static int
proxy_connection_io_xfer (struct proxy_connection *pc, const int max_transfer)
{
  int transferred = 0;
  while (transferred < max_transfer)
    {
      if (!BLEN (&pc->buf))
	{
	  const int status = proxy_connection_io_recv (pc);
	  if (status != IOSTAT_GOOD)
	    return status;
	}

      if (BLEN (&pc->buf))
	{
	  const int status = proxy_connection_io_send (pc, &transferred);
	  if (status != IOSTAT_GOOD)
	    return status;
	}
    }
  return IOSTAT_EAGAIN_ON_READ;
}

/*
 * Decide how the receipt of an EAGAIN status should affect our next IO queueing.
 */
static bool
proxy_connection_io_status (const int status, int *rwflags_pc, int *rwflags_cp)
{
  switch (status)
    {
    case IOSTAT_EAGAIN_ON_READ:
      *rwflags_pc |= EVENT_READ;
      *rwflags_cp &= ~EVENT_WRITE;
      return true;
    case IOSTAT_EAGAIN_ON_WRITE:
      *rwflags_pc &= ~EVENT_READ;
      *rwflags_cp |= EVENT_WRITE;
      return true;
    case IOSTAT_READ_ERROR:
      return false;
    case IOSTAT_WRITE_ERROR:
      return false;
    default:
      msg (M_FATAL, "PORT SHARE PROXY: unexpected status=%d", status);
    }
  return false; /* NOTREACHED */
}

/*
 * Dispatch function for forwarding data between the two socket fds involved
 * in the proxied connection.
 */
static int
proxy_connection_io_dispatch (struct proxy_connection *pc,
			      const int rwflags,
			      struct event_set *es)
{
  const int max_transfer_per_iteration = 10000;
  struct proxy_connection *cp = pc->counterpart;
  int rwflags_pc = pc->rwflags;
  int rwflags_cp = cp->rwflags;

  ASSERT(pc->defined && cp->defined && cp->counterpart == pc);

  if (rwflags & EVENT_READ)
    {
      const int status = proxy_connection_io_xfer (pc, max_transfer_per_iteration);
      if (!proxy_connection_io_status (status, &rwflags_pc, &rwflags_cp))
	goto bad;
    }
  if (rwflags & EVENT_WRITE)
    {
      const int status = proxy_connection_io_xfer (cp, max_transfer_per_iteration);
      if (!proxy_connection_io_status (status, &rwflags_cp, &rwflags_pc))
	goto bad;
    }
  proxy_connection_io_requeue (pc, rwflags_pc, es);
  proxy_connection_io_requeue (cp, rwflags_cp, es);

  return true;

 bad:
  proxy_entry_mark_for_close (pc, es);
  return false;
}

/*
 * This is the main function for the port share proxy background process.
 */
static void
port_share_proxy (const in_addr_t hostaddr,
		  const int port,
		  const socket_descriptor_t sd_control,
		  const int max_initial_buf,
		  const char *journal_dir)
{
  if (send_control (sd_control, RESPONSE_INIT_SUCCEEDED) >= 0)
    {
      void *sd_control_marker = (void *)1;
      int maxevents = 256;
      struct event_set *es;
      struct event_set_return esr[64];
      struct proxy_connection *list = NULL;
      time_t last_housekeeping = 0;

      msg (D_PS_PROXY, "PORT SHARE PROXY: proxy starting");

      es = event_set_init (&maxevents, 0);
      event_ctl (es, sd_control, EVENT_READ, sd_control_marker);
      while (true)
	{
	  int n_events;
	  struct timeval tv;
	  time_t current;

	  tv.tv_sec = 10;
	  tv.tv_usec = 0;
	  n_events = event_wait (es, &tv, esr, SIZE(esr));
	  /*dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: event_wait returned %d", n_events);*/
	  current = time(NULL);
	  if (n_events > 0)
	    {
	      int i;
	      for (i = 0; i < n_events; ++i)
		{
		  const struct event_set_return *e = &esr[i];
		  if (e->arg == sd_control_marker)
		    {
		      if (!control_message_from_parent (sd_control, &list, es, hostaddr, port, max_initial_buf, journal_dir))
			goto done;
		    }
		  else
		    {
		      struct proxy_connection *pc = (struct proxy_connection *)e->arg;
		      if (pc->defined)
			proxy_connection_io_dispatch (pc, e->rwflags, es);
		    }
		}
	    }
	  else if (n_events < 0)
	    {
	      dmsg (D_PS_PROXY_DEBUG, "PORT SHARE PROXY: event_wait failed");
	    }
	  if (current > last_housekeeping)
	    {
	      proxy_list_housekeeping (&list);
	      last_housekeeping = current;
	    }
	}

    done:
      proxy_list_close (&list);
      event_free (es);
    }
  msg (M_INFO, "PORT SHARE PROXY: proxy exiting");
}

/*
 * Called from the main OpenVPN process to enable the port
 * share proxy.
 */
struct port_share *
port_share_open (const char *host,
		 const int port,
		 const int max_initial_buf,
		 const char *journal_dir)
{
  pid_t pid;
  socket_descriptor_t fd[2];
  in_addr_t hostaddr;
  struct port_share *ps;

  ALLOC_OBJ_CLEAR (ps, struct port_share);
  ps->foreground_fd = -1;
  ps->background_pid = -1;

  /*
   * Get host's IP address
   */
  hostaddr = getaddr (GETADDR_RESOLVE|GETADDR_HOST_ORDER|GETADDR_FATAL, host, 0, NULL, NULL);

  /*
   * Make a socket for foreground and background processes
   * to communicate.
   */
  if (socketpair (PF_UNIX, SOCK_DGRAM, 0, fd) == -1)
    {
      msg (M_WARN, "PORT SHARE: socketpair call failed");
      goto error;
    }

  /*
   * Fork off background proxy process.
   */
  pid = fork ();

  if (pid)
    {
      int status;

      /*
       * Foreground Process
       */

      ps->background_pid = pid;

      /* close our copy of child's socket */
      openvpn_close_socket (fd[1]);

      /* don't let future subprocesses inherit child socket */
      set_cloexec (fd[0]);

      /* wait for background child process to initialize */
      status = recv_control (fd[0]);
      if (status == RESPONSE_INIT_SUCCEEDED)
	{
	  /* note that this will cause possible EAGAIN when writing to
	     control socket if proxy process is backlogged */
	  set_nonblock (fd[0]);

	  ps->foreground_fd = fd[0];
	  return ps;
	}
      else
	{
	  msg (M_ERR, "PORT SHARE: unexpected init recv_control status=%d", status);
	}
    }
  else
    {
      /*
       * Background Process
       */

      /* Ignore most signals (the parent will receive them) */
      set_signals ();

      /* Let msg know that we forked */
      msg_forked ();

#ifdef ENABLE_MANAGEMENT
      /* Don't interact with management interface */
      management = NULL;
#endif

      /* close all parent fds except our socket back to parent */
      close_fds_except (fd[1]);

      /* no blocking on control channel back to parent */
      set_nonblock (fd[1]);

      /* initialize prng */
      prng_init (NULL, 0);

      /* execute the event loop */
      port_share_proxy (hostaddr, port, fd[1], max_initial_buf, journal_dir);

      openvpn_close_socket (fd[1]);

      exit (0);
      return 0; /* NOTREACHED */
    }

 error:
  port_share_close (ps);
  return NULL;
}

void
port_share_close (struct port_share *ps)
{
  if (ps)
    {
      if (ps->foreground_fd >= 0)
	{
	  /* tell background process to exit */
	  port_share_sendmsg (ps->foreground_fd, COMMAND_EXIT, NULL, SOCKET_UNDEFINED);

	  /* wait for background process to exit */
	  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE: waiting for background process to exit");
	  if (ps->background_pid > 0)
	    waitpid (ps->background_pid, NULL, 0);
	  dmsg (D_PS_PROXY_DEBUG, "PORT SHARE: background process exited");

	  openvpn_close_socket (ps->foreground_fd);
	  ps->foreground_fd = -1;
	}

      free (ps);
    }
}

void
port_share_abort (struct port_share *ps)
{
  if (ps)
    {
      /* tell background process to exit */
      if (ps->foreground_fd >= 0)
	{
	  send_control (ps->foreground_fd, COMMAND_EXIT);
	  openvpn_close_socket (ps->foreground_fd);
	  ps->foreground_fd = -1;
	}
    }
}

/*
 * Given either the first 2 or 3 bytes of an initial client -> server
 * data payload, return true if the protocol is that of an OpenVPN
 * client attempting to connect with an OpenVPN server.
 */
bool
is_openvpn_protocol (const struct buffer *buf)
{
  const unsigned char *p = (const unsigned char *) BSTR (buf);
  const int len = BLEN (buf);
  if (len >= 3)
    {
      return p[0] == 0
	&& p[1] >= 14
	&& p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2<<P_OPCODE_SHIFT);
    }
  else if (len >= 2)
    {
      return p[0] == 0 && p[1] >= 14;
    }
  else
    return true;
}

/*
 * Called from the foreground process.  Send a message to the background process that it
 * should proxy the TCP client on sd to the host/port defined in the initial port_share_open
 * call.
 */
void
port_share_redirect (struct port_share *ps, const struct buffer *head, socket_descriptor_t sd)
{
  if (ps)
    {
      port_share_sendmsg (ps->foreground_fd, COMMAND_REDIRECT, head, sd);
    }
}

#endif
