/* mailif.c   by Michael Thorpe   2014-09-29 */

/*
 * THIS_IS_A_SANE_SYSTEM should be 1 for Linux and 0 * for OpenBSD.
 *
 * For other systems, test whether poll() on a closed fd says that fd is
 * ready to read; if if does, it's stupid like OpenBSD and
 * THIS_IS_A_SANE_SYSTEM needs to be 0.  If it says the fd isn't ready to
 * read then THIS_IS_A_SANE_SYSTEM should be 1.
 *
 * If you're not sure, set it to 0.
 */
#define THIS_IS_A_SANE_SYSTEM 0

#if THIS_IS_A_SANE_SYSTEM

#include <unistd.h>
#include <sys/poll.h>

int main(int argc,char **argv) {
	struct pollfd u;

	u.fd=0;
	u.events=POLLIN|POLLERR|POLLHUP|POLLNVAL;
	u.revents=0;
	poll(&u,1,-1);
	if(!(u.revents&POLLIN))
		return(0);
	execvp("mail",argv);
	execvp("sendmail",argv);
	execv("/usr/sbin/sendmail",argv);
	execv("/usr/lib/sendmail",argv);
	return(-1);
}

#else

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

static pid_t child=0;
static FILE *out;

static void stop_child() {
	pid_t p;
	int status;

	p=waitpid(child,&status,0);
	if(-1==p) {
		perror("waitpid");
		exit(-1);
	}
	if(p != child) {
		fprintf(stderr,"Got exit value for non-child %d?!?\n",p);
		exit(-1);
	}
	if(WIFEXITED(status))
		exit(WEXITSTATUS(status));
	fputs("Child died\n",stderr);
	exit(-1);
}

static void start_child(char **argv) {
	int fds[2];

	if(pipe(fds)) {
		perror("pipe");
		exit(-1);
	}
	child=fork();
	if(-1==child) {
		perror("fork");
		exit(-1);
	}
	if(child) {
		close(fds[0]);
		out=fdopen(fds[1],"wb");
		if(!out) {
			perror("fdopen");
			exit(-1);
		}
	} else {
		close(fds[1]);
		if(fds[0]) {
			if(dup2(fds[0],0)) {
				perror("dup2");
				exit(-1);
			}
			close(fds[0]);
		}
		execvp("mail",argv);
		execvp("sendmail",argv);
		execv("/usr/sbin/sendmail",argv);
		execv("/usr/lib/sendmail",argv);
		exit(-1);
	}
}

int main(int argc,char **argv) {
	int c;

	while(EOF != (c=fgetc(stdin))) {
		if(!child)
			start_child(argv);
		fputc(c,out);
	}
	if(child) {
		fclose(out);
		stop_child();
	}
	return(0);
}

#endif