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

int main(void)
{
    int sv[2];
    assert(0 == socketpair(AF_UNIX, SOCK_STREAM, 0, sv));
    int sock1 = sv[0];
    int sock2 = sv[1];

    struct msghdr msg = {0};

    char buf[] = "Hello world!";
    struct iovec iov = {
        .iov_base = buf,
        .iov_len = sizeof(buf) - 1,
    };
    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    int fds[] = {1};
    //int fds[] = {1, 2};

    msg.msg_controllen = CMSG_LEN(sizeof(fds));
    msg.msg_control = calloc(1, msg.msg_controllen);
    assert(msg.msg_control != NULL);

    struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    cmsg->cmsg_len = CMSG_LEN(sizeof(fds));
    memcpy(CMSG_DATA(cmsg), &fds, sizeof(fds));

    assert(sendmsg(sock1, &msg, 0) >= 0);
    assert(recvmsg(sock2, &msg, 0) == sizeof(buf) - 1);
}