create a unix socket on X11 display in C

xsock.c

#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>

#define _PATH_UNIX_X "/tmp/.X11-unix/X%d"
#define DISPLAY_PORT 0

int
main(void) {
    int rc,sock;
    struct sockaddr_un addr;

    sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock<0) return -1;

    memset(&addr, 0, sizeof(addr));
    addr.sun_family = AF_UNIX;
    snprintf(addr.sun_path, sizeof(addr.sun_path), _PATH_UNIX_X, DISPLAY_PORT);
    rc = connect(sock, (struct sockaddr *) &addr, sizeof(addr));

    sleep(10);

    close(sock);

    return 0;
}

Connection can be tested using ss(8) on Linux:

% ss -x -p -f unix -r | grep xsock
u_str ESTAB 0 0 * 1701647 * 0 users:(("xsock",2066,3))

Transmitted data can be sniffed using strace(1):

% export XORG_FD=$(sudo lsof 2>&1 |grep X0 | awk '{print $4}')
% export XORG_PID=$(sudo lsof 2>&1 |grep X0|awk '{print $2}')
% sudo strace -e trace=read,write -e read=${XORG_FD} -e write=${XORG_FD} -p ${XORG_PID}

I'm doing the same im Assembly, you did a great job!