static int xdmseen_cmp(void *a, void *b)
{
    struct XDMSeen *sa = a, *sb = b;
    return sa->time > sb->time ? 1 :
	   sa->time < sb->time ? -1 :
           memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
}

/* Do-nothing "plug" implementation, used by x11_setup_display() when it
 * creates a trial connection (and then immediately closes it).
 * XXX: bit out of place here, could in principle live in a platform-
 *      independent network.c or something */
static void dummy_plug_log(Plug p, int type, SockAddr addr, int port,
			   const char *error_msg, int error_code) { }
static int dummy_plug_closing
     (Plug p, const char *error_msg, int error_code, int calling_back)
{ return 1; }
static int dummy_plug_receive(Plug p, int urgent, char *data, int len)
{ return 1; }
static void dummy_plug_sent(Plug p, int bufsize) { }
static int dummy_plug_accepting(Plug p, OSSocket sock) { return 1; }
static const struct plug_function_table dummy_plug = {
    dummy_plug_log, dummy_plug_closing, dummy_plug_receive,
    dummy_plug_sent, dummy_plug_accepting
};

struct X11Display *x11_setup_display(char *display, int authtype,
				     const Config *cfg)
{
    struct X11Display *disp = snew(struct X11Display);
    char *localcopy;
    int i;

     */
    if (localcopy[0] == '/') {
	disp->unixsocketpath = localcopy;
	disp->unixdomain = TRUE;
	disp->hostname = NULL;
	disp->displaynum = -1;
	disp->screennum = 0;
	disp->addr = NULL;
    } else {
	char *colon, *dot, *slash;
	char *protocol, *hostname;

	colon = strrchr(localcopy, ':');
	if (!colon) {
	    sfree(disp);

	else
	    disp->unixdomain = FALSE;

	if (!disp->hostname && !disp->unixdomain)
	    disp->hostname = dupstr("localhost");

	disp->unixsocketpath = NULL;
	disp->addr = NULL;

	sfree(localcopy);
    }

    /*
     * Look up the display hostname, if we need to.
     */
    if (disp->unixdomain) {
    if (!disp->unixdomain) {
	disp->addr = platform_get_x11_unix_address(disp->unixsocketpath,
						   disp->displaynum);
	if (disp->unixsocketpath)
	    disp->realhost = dupstr(disp->unixsocketpath);
	else
	    disp->realhost = dupprintf("unix:%d", disp->displaynum);
	disp->port = 0;
    } else {
	const char *err;

	disp->port = 6000 + disp->displaynum;
	disp->addr = name_lookup(disp->hostname, disp->port,
				 &disp->realhost, cfg, ADDRTYPE_UNSPEC);
    
	if ((err = sk_addr_error(disp->addr)) != NULL) {
	    sk_addr_free(disp->addr);
	    sfree(disp->hostname);
	    sfree(disp->unixsocketpath);
	    return NULL;	       /* FIXME: report an error */
	}
    }

    /*
     * Try upgrading an IP-style localhost display to a Unix-socket
     * display (as the standard X connection libraries do).
     */
    if (!disp->unixdomain && sk_address_is_local(disp->addr)) {
	SockAddr ux = platform_get_x11_unix_address(NULL, disp->displaynum);
	const char *err = sk_addr_error(ux);
	if (!err) {
	    /* Create trial connection to see if there is a useful Unix-domain
	     * socket */
	    const struct plug_function_table *dummy = &dummy_plug;
	    Socket s = sk_new(sk_addr_dup(ux), 0, 0, 0, 0, 0, (Plug)&dummy);
	    err = sk_socket_error(s);
	    sk_close(s);
	}
	if (err) {
	    sk_addr_free(ux);
	} else {
	    sk_addr_free(disp->addr);
	    disp->unixdomain = TRUE;
	    disp->addr = ux;
	    /* Fill in the rest in a moment */
	}
    }

    if (disp->unixdomain) {
	if (!disp->addr)
	    disp->addr = platform_get_x11_unix_address(disp->unixsocketpath,
						       disp->displaynum);
	if (disp->unixsocketpath)
	    disp->realhost = dupstr(disp->unixsocketpath);
	else
	    disp->realhost = dupprintf("unix:%d", disp->displaynum);
	disp->port = 0;
    }

    /*
     * Invent the remote authorisation details.
     */
    if (authtype == X11_MIT) {
	disp->remoteauthproto = X11_MIT;

void x11_get_auth_from_authfile(struct X11Display *disp,
				const char *authfilename)
{
    FILE *authfp;
    char *buf, *ptr, *str[4];
    int len[4];
    int family, protocol;
    int ideal_match = FALSE;
    char *ourhostname = get_hostname();

    /*
     * Normally we should look for precisely the details specified in
     * `disp'. However, there's an oddity when the display is local:
     * displays like "localhost:0" usually have their details stored
     * in a Unix-domain-socket record (even if there isn't actually a
     * real Unix-domain socket available, as with OpenSSH's proxy X11
     * server).
     *
     * This is apparently a fudge to get round the meaninglessness of
     * "localhost" in a shared-home-directory context -- xauth entries
     * for Unix-domain sockets already disambiguate this by storing
     * the *local* hostname in the conveniently-blank hostname field,
     * but IP "localhost" records couldn't do this. So, typically, an
     * IP "localhost" entry in the auth database isn't present and if
     * it were it would be ignored.
     *
     * However, we don't entirely trust that (say) Windows X servers
     * won't rely on a straight "localhost" entry, bad idea though
     * that is; so if we can't find a Unix-domain-socket entry we'll
     * fall back to an IP-based entry if we can find one.
     */
    int localhost = !disp->unixdomain && sk_address_is_local(disp->addr);

    authfp = fopen(authfilename, "rb");
    if (!authfp)
	return;

    /* Records in .Xauthority contain four strings of up to 64K each */
    buf = snewn(65537 * 4, char);

    while (1) {
	int c, i, j;
    while (!ideal_match) {
	int c, i, j, match = FALSE;
	
#define GET do { c = fgetc(authfp); if (c == EOF) goto done; c = (unsigned char)c; } while (0)
	/* Expect a big-endian 2-byte number giving address family */
	GET; family = c;
	GET; family = (family << 8) | c;
	/* Then expect four strings, each composed of a big-endian 2-byte
	 * length field followed by that many bytes of data */

	for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
	    if (!strcmp(str[2], x11_authnames[protocol]))
		break;
	if (protocol == lenof(x11_authnames))
	    continue;  /* don't recognise this protocol, look for another */

	switch (family) {
	  case 0:
	  case 0:   /* IPv4 */
	    if (!disp->unixdomain &&
		sk_addrtype(disp->addr) == ADDRTYPE_IPV4) {
		char buf[4];
		sk_addrcopy(disp->addr, buf);
		if (len[0] == 4 && !memcmp(str[0], buf, 4))
		    goto found;
	    }
		if (len[0] == 4 && !memcmp(str[0], buf, 4)) {
		    match = TRUE;
		    /* If this is a "localhost" entry, note it down
		     * but carry on looking for a Unix-domain entry. */
		    ideal_match = !localhost;
		}
	    }
	    break;
	  case 6:
	  case 6:   /* IPv6 */
	    if (!disp->unixdomain &&
		sk_addrtype(disp->addr) == ADDRTYPE_IPV6) {
		char buf[16];
		sk_addrcopy(disp->addr, buf);
		if (len[0] == 16 && !memcmp(str[0], buf, 16))
		if (len[0] == 16 && !memcmp(str[0], buf, 16)) {
		    goto found;
	    }
		    match = TRUE;
		    ideal_match = !localhost;
		}
	    }
	    break;
	  case 256:
	    if (disp->unixdomain && !strcmp(disp->hostname, str[0]))
	  case 256: /* Unix-domain / localhost */
	    if ((disp->unixdomain || localhost)
		goto found;
	       	&& ourhostname && !strcmp(ourhostname, str[0]))
		/* A matching Unix-domain socket is always the best
		 * match. */
		match = ideal_match = TRUE;
	    break;
	}
    }


	if (match) {
    found:
    disp->localauthproto = protocol;
    disp->localauthdata = snewn(len[3], unsigned char);
    memcpy(disp->localauthdata, str[3], len[3]);
    disp->localauthdatalen = len[3];
	    /* Current best guess -- may be overridden if !ideal_match */
	    disp->localauthproto = protocol;
	    sfree(disp->localauthdata); /* free previous guess, if any */
	    disp->localauthdata = snewn(len[3], unsigned char);
	    memcpy(disp->localauthdata, str[3], len[3]);
	    disp->localauthdatalen = len[3];
	}
    }

    done:
    fclose(authfp);
    memset(buf, 0, 65537 * 4);
    sfree(buf);
    sfree(ourhostname);
}

static void x11_log(Plug p, int type, SockAddr addr, int port,
		    const char *error_msg, int error_code)
{
    /* We have no interface to the logging module here, so we drop these. */
}