/*
 * Serve a program over a Unix domain socket.
 *
 * Dan Cross <net!gajendra!cross>
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

void
background(void)
{
	pid_t pid;

	if ((pid = fork()) < 0) {
		perror("fork");
		exit(EXIT_FAILURE);
	}
	if (pid != 0) {
		exit(EXIT_SUCCESS);
	}
}

/*  ARGSUSED  */
void
child(int signo)
{

	wait(NULL);
}

void
setsigs(void)
{
	struct sigaction sa;

	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = child;
	sigaction(SIGCHLD, &sa, NULL);
}

int
srvfile(char *file)
{
	int sd;
	struct sockaddr_un sock;

	unlink(file);
	memset(&sock, 0, sizeof(sock));
	sock.sun_family = AF_UNIX;
	strncpy(sock.sun_path, file, sizeof(sock.sun_path));
	if ((sd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
		perror("socket");
		exit(EXIT_FAILURE);
	}
	if (bind(sd, (struct sockaddr *)&sock, sizeof(sock)) < 0) {
		perror("bind");
		exit(EXIT_FAILURE);
	}
	if (listen(sd, 5) < 0) {
		perror("listen");
		exit(EXIT_FAILURE);
	}

	return(sd);
}

int
main(int argc, char *argv[])
{
	pid_t pid;
	int nsd, sd;
	struct sockaddr_un sock;
	socklen_t clen;

	if (argc < 3) {
		fprintf(stderr, "Usage: %s path prog [args].\n", argv[0]);
		return(EXIT_FAILURE);
	}
	background();
	setsigs();
	sd = srvfile(argv[1]);
	for ( ; ; ) {
		clen = sizeof(sock);
		if ((nsd = accept(sd, (struct sockaddr *)&sock, &clen)) < 0) {
			if (errno == EINTR) {
				/*  Probably got a SIGCHLD.  */
				continue;
			}
			perror("accept");
			exit(EXIT_FAILURE);
		}
		if ((pid = fork()) < 0) {
			perror("fork");
			close(nsd);
			continue;
		} else if (pid == 0) {
			close(sd);
			dup2(nsd, STDIN_FILENO);
			dup2(nsd, STDOUT_FILENO);
			dup2(nsd, STDERR_FILENO);
			execvp(argv[2], argv + 2);
		} else {
			close(nsd);
		}
	}

	return(EXIT_SUCCESS);
}