#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>

/**
 * Sends given file descriptior via given socket
 *
 * @param socket to be used for fd sending
 * @param fd to be sent
 * @return sendmsg result
 *
 * @note socket should be (PF_UNIX, SOCK_DGRAM)
 */
int send_fd(int sock, int fd){
    // This function does the arcane magic for sending
    // file descriptors over unix domain sockets
    struct msghdr msg;
    struct iovec iov[1];
    struct cmsghdr *cmsg = NULL;
    char ctrl_buf[CMSG_SPACE(sizeof(int))];
    char data[1];

    memset(&msg, 0, sizeof(struct msghdr));
    memset(ctrl_buf, 0, CMSG_SPACE(sizeof(int)));

    data[0] = ' ';
    iov[0].iov_base = data;
    iov[0].iov_len = sizeof(data);

    msg.msg_name = NULL;
    msg.msg_namelen = 0;
    msg.msg_iov = iov;
    msg.msg_iovlen = 1;
    msg.msg_controllen =  CMSG_SPACE(sizeof(int));
    msg.msg_control = ctrl_buf;

    cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    cmsg->cmsg_len = CMSG_LEN(sizeof(int));

    *((int *) CMSG_DATA(cmsg)) = fd;

    return sendmsg(sock, &msg, 0);
}

main(argc, argv)
    int argc;
    char *argv[];
{
    int fd, sock;
    struct sockaddr_un server;
    char buf[1024];

    if (argc < 3) {
        printf("usage:%s <sock path> <file name>", argv[0]);
        exit(1);
    }

    sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock < 0) {
        perror("opening stream socket");
        exit(1);
    }
    server.sun_family = AF_UNIX;
    strcpy(server.sun_path, argv[1]);

    if (connect(sock, (struct sockaddr *) &server, sizeof(struct sockaddr_un)) < 0) {
        close(sock);
        perror("connecting stream socket");
        exit(1);
    }

    // Open the file descriptor we want to send
    fd = open(argv[2], 0);

    send_fd(sock, fd);
    close(sock);
}