/*
 *  server.c  Set up and handle communications with a server process.
 *
 *  Server Handling copyright 1992-1999 The Free Software Foundation
 *
 *  Server Handling is free software.
 *  You may redistribute it and/or modify it under the terms of the
 *  GNU General Public License, as published by the Free Software
 *  Foundation; either version 2, or (at your option) any later version.
 *
 *  Server Handling 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 Server Handling.  See the file "COPYING".  If not,
 *  write to:  The Free Software Foundation, Inc.,
 *             59 Temple Place - Suite 330,
 *             Boston,  MA  02111-1307, USA.
 *
 * As a special exception, The Free Software Foundation gives
 * permission for additional uses of the text contained in his release
 * of ServerHandler.
 *
 * The exception is that, if you link the ServerHandler library with other
 * files to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the ServerHandler library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by The Free
 * Software Foundation under the name ServerHandler.  If you copy code
 * from other sources under the General Public License into a copy of
 * ServerHandler, as the General Public License permits, the exception
 * does not apply to the code that you add in this way.  To avoid
 * misleading anyone as to the status of such modified files, you must
 * delete this exception notice from them.
 *
 * If you write modifications of your own for ServerHandler, it is your
 * choice whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.
 */
#include "auto-host.h"
#include "gansidecl.h"
#include "system.h"

#include "server.h"

/* If this particular system's header files define the macro `MAXPATHLEN',
   we happily take advantage of it; otherwise we use a value which ought
   to be large enough.  */
#ifndef MAXPATHLEN
# define MAXPATHLEN     4096
#endif

#ifndef STDIN_FILENO
# define STDIN_FILENO	0
#endif
#ifndef STDOUT_FILENO
# define STDOUT_FILENO	1
#endif

#ifdef DEBUG
#define STATIC
#else
#define STATIC static
#endif
#ifndef tSCC
#define tSCC static const char
#endif
#ifndef NUL
#define NUL '\0'
#endif

STATIC t_pchar def_args[] =
{ (char *) NULL, (char *) NULL };

/*
 *  chain_open
 *
 *  Given an FD for an inferior process to use as stdin,
 *  start that process and return a NEW FD that that process
 *  will use for its stdout.  Requires the argument vector
 *  for the new process and, optionally, a pointer to a place
 *  to store the child's process id.
 */
int
chain_open (stdin_fd, pp_args, p_child)
     int stdin_fd;
     t_pchar *pp_args;
     pid_t *p_child;
{
  t_fd_pair stdout_pair;
  pid_t ch_id;
  char *pz_cmd;

  stdout_pair.read_fd = stdout_pair.write_fd = -1;

  /*
   *  Create a pipe it will be the child process' stdout,
   *  and the parent will read from it.
   */
  if (pipe ((int *) &stdout_pair) < 0)
    {
      if (p_child != (pid_t *) NULL)
        *p_child = NOPROCESS;
      return -1;
    }

  /*
   *  If we did not get an arg list, use the default
   */
  if (pp_args == (t_pchar *) NULL)
    pp_args = def_args;

  /*
   *  If the arg list does not have a program,
   *  assume the "SHELL" from the environment, or, failing
   *  that, then sh.  Set argv[0] to whatever we decided on.
   */
  if (pz_cmd = *pp_args,
      (pz_cmd == (char *) NULL) || (*pz_cmd == '\0'))
    {

      pz_cmd = getenv ("SHELL");
      if (pz_cmd == (char *) NULL)
        pz_cmd = "sh";
    }

#ifdef DEBUG_PRINT
  printf ("START:  %s\n", pz_cmd);
  {
    int idx = 0;
    
    while (pp_args[++idx] != (char *) NULL)
      printf ("  ARG %2d:  %s\n", idx, pp_args[idx]);
  }
#endif

  /*
   *  Call fork() and see which process we become
   */
  ch_id = fork ();
  switch (ch_id)
    {
    case NOPROCESS:             /* parent - error in call */
      close (stdout_pair.read_fd);
      close (stdout_pair.write_fd);
      if (p_child != (pid_t *) NULL)
        *p_child = NOPROCESS;
      return -1;

    default:                    /* parent - return opposite FD's */
      if (p_child != (pid_t *) NULL)
        *p_child = ch_id;
#ifdef DEBUG_PRINT
      printf ("for pid %d:  stdin from %d, stdout to %d\n"
              "for parent:  read from %d\n",
              ch_id, stdin_fd, stdout_pair.write_fd, stdout_pair.read_fd);
#endif
      close (stdin_fd);
      close (stdout_pair.write_fd);
      return stdout_pair.read_fd;

    case NULLPROCESS:           /* child - continue processing */
      break;
    }

  /*
   *  Close the pipe end handed back to the parent process
   */
  close (stdout_pair.read_fd);

  /*
   *  Close our current stdin and stdout
   */
  close (STDIN_FILENO);
  close (STDOUT_FILENO);

  /*
   *  Make the fd passed in the stdin, and the write end of
   *  the new pipe become the stdout.
   */
  fcntl (stdout_pair.write_fd, F_DUPFD, STDOUT_FILENO);
  fcntl (stdin_fd, F_DUPFD, STDIN_FILENO);

  if (*pp_args == (char *) NULL)
    *pp_args = pz_cmd;

  execvp (pz_cmd, pp_args);
  fprintf (stderr, "Error %d:  Could not execvp( '%s', ... ):  %s\n",
           errno, pz_cmd, strerror (errno));
  exit (EXIT_PANIC);
}


/*
 *  proc2_open
 *
 *  Given a pointer to an argument vector, start a process and
 *  place its stdin and stdout file descriptors into an fd pair
 *  structure.  The "write_fd" connects to the inferior process
 *  stdin, and the "read_fd" connects to its stdout.  The calling
 *  process should write to "write_fd" and read from "read_fd".
 *  The return value is the process id of the created process.
 */
pid_t
proc2_open (p_pair, pp_args)
     t_fd_pair *p_pair;
     t_pchar *pp_args;
{
  pid_t ch_id;

  /*  Create a bi-directional pipe.  Writes on 0 arrive on 1 and vice
     versa, so the parent and child processes will read and write to
     opposite FD's.  */
  if (pipe ((int *) p_pair) < 0)
    return NOPROCESS;

  p_pair->read_fd = chain_open (p_pair->read_fd, pp_args, &ch_id);
  if (ch_id == NOPROCESS)
    close (p_pair->write_fd);

  return ch_id;
}


/*
 *  proc2_fopen
 *
 *  Identical to "proc2_open()", except that the "fd"'s are
 *  "fdopen(3)"-ed into file pointers instead.
 */
pid_t
proc2_fopen (pf_pair, pp_args)
     t_pf_pair *pf_pair;
     t_pchar *pp_args;
{
  t_fd_pair fd_pair;
  pid_t ch_id = proc2_open (&fd_pair, pp_args);

  if (ch_id == NOPROCESS)
    return ch_id;

  pf_pair->pf_read = fdopen (fd_pair.read_fd, "r");
  pf_pair->pf_write = fdopen (fd_pair.write_fd, "w");
  return ch_id;
}