on-demand.c

/* -*- mode: C; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <errno.h>
#include <sys/un.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/select.h>

int main(int ac, char* av[])
{
    char buf[128];
    int fd;
    fd_set socks;
    char listen_pid[64];
    char* listen_fds="LISTEN_FDS=1";

    struct sockaddr_un xsockaddr;

    if (ac < 3) {
        fprintf(stderr, "Usage:\n  on-demand <socket> <command>\n");
        exit(1);
    }
    snprintf(listen_pid, sizeof(listen_pid), "LISTEN_PID=%d", getpid());
    putenv(listen_fds);
    putenv(listen_pid);

    memset(buf, 0, sizeof(buf));

    fd=socket(AF_UNIX, SOCK_STREAM, 0);
    if (fd < 0) {
        perror("socket");
        exit(1);
    }

    printf("socket: %d\n", fd);

    memset(&xsockaddr, 0, sizeof(xsockaddr));
    xsockaddr.sun_family = AF_UNIX;
    snprintf(xsockaddr.sun_path,
             sizeof(xsockaddr.sun_path),
             "%s", av[1]);

    unlink(xsockaddr.sun_path);
    if (bind(fd, (struct sockaddr *) &xsockaddr, sizeof(xsockaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if (listen(fd, 16) == -1) {
        perror("listen");
        exit(1);
    }
    
    FD_ZERO(&socks);
    FD_SET(fd, &socks);
    select(fd+1, &socks, NULL, NULL, NULL);
    execvp(av[2], av+2);

    return 0;
}