loop.c

#include "apue.h"

#define	BUFFSIZE	512

static void sig_term (int);
static volatile sig_atomic_t sigcaught;	/* set by signal handler */

void
loop (int ptym, int ignoreeof)
{
  pid_t child;
  int nread;
  char buf[BUFFSIZE];

  if ((child = fork ()) < 0)
    {
      err_sys ("fork error");
    }
  else if (child == 0)
    {				/* child copies stdin to ptym */
      for (;;)
	{
	  if ((nread = read (STDIN_FILENO, buf, BUFFSIZE)) < 0)
	    err_sys ("read error from stdin");
	  else if (nread == 0)
	    break;		/* EOF on stdin means we're done */
	  if (writen (ptym, buf, nread) != nread)
	    err_sys ("writen error to master pty");
	}

      /*
       * We always terminate when we encounter an EOF on stdin,
       * but we notify the parent only if ignoreeof is 0.
       */
      if (ignoreeof == 0)
	kill (getppid (), SIGTERM);	/* notify parent */
      exit (0);			/* and terminate; child can't return */
    }

  /*
   * Parent copies ptym to stdout.
   */
  if (signal_intr (SIGTERM, sig_term) == SIG_ERR)
    err_sys ("signal_intr error for SIGTERM");

  for (;;)
    {
      if ((nread = read (ptym, buf, BUFFSIZE)) <= 0)
	break;			/* signal caught, error, or EOF */
      if (writen (STDOUT_FILENO, buf, nread) != nread)
	err_sys ("writen error to stdout");
    }

  /*
   * There are three ways to get here: sig_term() below caught the
   * SIGTERM from the child, we read an EOF on the pty master (which
   * means we have to signal the child to stop), or an error.
   */
  if (sigcaught == 0)		/* tell child if it didn't send us the signal */
    kill (child, SIGTERM);

  /*
   * Parent returns to caller.
   */
}

/*
 * The child sends us SIGTERM when it gets EOF on the pty slave or
 * when read() fails.  We probably interrupted the read() of ptym.
 */
static void
sig_term (int signo)
{
  sigcaught = 1;		/* just set flag and return */
}