/*

  Copyright 2008 Nathan Phillip Brink, Ethan Zonca

  This file is a part of DistRen.

  DistRen is free software: you can redistribute it and/or modify

  it under the terms of the GNU Affero General Public License as published by

  the Free Software Foundation, either version 3 of the License, or

  (at your option) any later version.

  DistRen 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 DistRen.  If not, see <http://www.gnu.org/licenses/>.

*/

#include "execio.h"

#include <unistd.h>

#include <sys/types.h>

#include <sys/wait.h>

#include <signal.h>

#include <malloc.h>

#include <fcntl.h>

#include <stdio.h>

#include <errno.h>

int execio_open(struct execio **rem, const char *progname, char *const argv[])

{

  /* pipe used to write to child */

  int pipe_write[2];

  /* pipe used to read from child */

  int pipe_read[2];

  pid_t child;

  /* for wait(2) if needed */

  int childstatus;

  int counter;

  int counter2;

  int maxfds;

  /* create two pipes to facilitate communication with child */

  if(pipe(pipe_write))

    return 1;

  if(pipe(pipe_read))

    {

      close(pipe_write[0]);

      close(pipe_write[1]);

      return 1;

    }

  /* parent */

  child = fork();

  if(child == -1)

    {

      close(pipe_write[0]);

      close(pipe_write[1]);

      close(pipe_read[0]);

      close(pipe_read[1]);

      return 1;

    }

  if(child)

    /* the parent proc: */

    {

      /* close sides of pipe we won't use */

      close(pipe_write[0]);

      close(pipe_read[1]);

      /* setup execio struct */

      (*rem) = malloc(sizeof(struct execio));

      if(!(*rem))

	{

	  /* we should tell the child we're dead - use wait and close our end of the pipes! */

	  close(pipe_write[1]);

	  close(pipe_read[0]);

	  /* we should probably pass of the wait() call to a thread that just does boring things like that. Especially for when the server tries to connect to other servers... */

	  kill(child, SIGTERM);

	  /* the waitpid(2) seems to indicate that only when the child is terminated will this wait return. */

	  waitpid(child, &childstatus, 0); 

	}

      (*rem)->pipe_write = pipe_write[1];

      (*rem)->pipe_read = pipe_read[0];

      (*rem)->state = 0;

      (*rem)->child = child;

      return 0;

    }

  /* child */

  else

    {

      /* close unused pipes */

      close(pipe_write[1]);

      close(pipe_read[0]);

      /*

	reset stdin, stdout, and stderr to the appropriate files. OK, not stderr :-) 

      */

      dup2(pipe_read[1], STDOUT_FILENO);

      dup2(pipe_write[0], STDIN_FILENO);

      /*

	close the fds that were dup'd

       */

      close(pipe_read[1]);

      close(pipe_write[0]);

      /* 

	 close all other file descriptors. We want to keep 0, 1, and 2 open. We don't know that the last open() or pipe() always gives the highest fd number. However, I will assume that it does. Maybe this is a bad idea:

       */

      counter = pipe_write[0];

      if(counter < pipe_write[1])

	counter = pipe_write[1];

      if(counter < pipe_read[0])

	counter = pipe_read[0];

      if(counter < pipe_read[1])

	counter = pipe_read[1];

      counter2 = 0;

      maxfds = counter;

      while(counter > 2)

	{

	  if(!close(counter))

	    counter2 ++; /* record how many descriptors we still had open :-) */

	  counter --;

	}

      /* stderr is the only stream we haven't confiscated atm - just for fun - I will confiscate it later, though, to support parsing error messages */

      fprintf(stderr, "closed %d/%d fds before execing \"%s\"\n", counter2, maxfds, progname);

      /*

	now exec: execvp uses interpreter to find the file to exec

       */

      execvp(progname, argv);

      return 1; /* this line should never be reached because we exec -- unless if the exec returns something bad. Then we'd have to tell execio over the pipe about that somehow... */

      /* in fact, maybe we should abort() here because if we returned, a monster of a distren client would exist! */

    }

}

/*

  returns 1 if child has exited, 

  returns 0 if child is still alive

 */

int _execio_checkpid(struct execio *eio)

{

  int childstatus;

  waitpid(eio->child, &childstatus, WNOHANG);

  /* perror()? */

  return WIFEXITED(childstatus);

}

int execio_read(struct execio *eio, void *buf, size_t len, size_t *bytesread)

{

  /*

    TODO: detect NULL eio? 

    TODO: errno?

    update status of eio for execio_status/to be able to cleanup subproc??

    whenever read() returns 0, it means EOF

   */

  (*bytesread) = read(eio->pipe_read, buf, len);

  if(!*bytesread)

    {

      /* should also be able to figure out if is bad fd and should set EXECIO_STATE_ERROR instead of _EOF */

      eio->state = EXECIO_STATE_EOF;

      return 1;

    }

  return 0;

}

int execio_write(struct execio *eio, void *buf, size_t len, size_t *bytesread)

{

  errno = 0;

  (*bytesread) = write(eio->pipe_write, buf, len);

  if(!*bytesread)

    {

      switch(errno)

	{

	case EPIPE:

	  /* 

	     the program closed the pipe (died)

	  */

	fprintf(stderr, "execio_write: the child program closed its stdin pipe\n");

	eio->state = EXECIO_STATE_EOF;

	break;

	default:

	  fprintf(stderr, "execio_write: unhandled error writing to an fd: \n");

	  perror("write");

	  eio->state = EXECIO_STATE_ERROR;

	  break;

	}

      return 1;

    }

  return 0;

}

enum execio_state execio_state(struct execio *eio)

{

  return eio->state;

}

int execio_close(struct execio *eio)

{

  int childstatus;

  close(eio->pipe_read);

  close(eio->pipe_write);

  kill(eio->child, SIGTERM);

  /* 

     the waitpid(2) seems to indicate that only when the child is terminated will this wait return. 

     This are of code will probably need improving - the ability to seng SIGKILL after a timeout? So we'll output a debug line before running waitpid

  */

  fprintf(stderr, "execio_close: running waitpid\n");

  waitpid(eio->child, &childstatus, 0);

  return 0;

}