};

struct XDMSeen {
    unsigned int time;
    unsigned char clientid[6];
};

struct X11Auth {
    unsigned char fakedata[64], realdata[64];
    int fakeproto, realproto;
    int fakelen, reallen;
    tree234 *xdmseen;
};

struct X11Private {
    const struct plug_function_table *fn;
    /* the above variable absolutely *must* be the first in this structure */
    unsigned char firstpkt[12];	       /* first X data packet */
    struct X11Auth *auth;
    struct X11Display *disp;
    char *auth_protocol;
    unsigned char *auth_data;
    int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
    int verified;
    int throttled, throttle_override;
    unsigned long peer_ip;
    int peer_port;
    void *c;			       /* data used by ssh.c */
    Socket s;
};

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));
}

void *x11_invent_auth(char *proto, int protomaxlen,
		      char *data, int datamaxlen, int proto_id)
struct X11Display *x11_setup_display(char *display, int authtype,
				     const Config *cfg)
{
    struct X11Auth *auth = snew(struct X11Auth);
    char ourdata[64];
    struct X11Display *disp = snew(struct X11Display);
    char *localcopy;
    int i;

    if (!display || !*display) {
	localcopy = platform_get_x_display();
	if (!localcopy || !*localcopy) {
	    sfree(localcopy);
	    localcopy = dupstr(":0");  /* plausible default for any platform */
	}
    } else
	localcopy = dupstr(display);

    /*
     * Parse the display name.
     *
     * We expect this to have one of the following forms:
     * 
     *  - the standard X format which looks like
     *    [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ]
     *    (X11 also permits a double colon to indicate DECnet, but
     *    that's not our problem, thankfully!)
     *
     * 	- only seen in the wild on MacOS (so far): a pathname to a
     * 	  Unix-domain socket, which will typically and confusingly
     * 	  end in ":0", and which I'm currently distinguishing from
     * 	  the standard scheme by noting that it starts with '/'.
     */
    if (localcopy[0] == '/') {
	disp->unixsocketpath = localcopy;
	disp->unixdomain = TRUE;
	disp->hostname = NULL;
	disp->displaynum = -1;
	disp->screennum = 0;
    } else {
	char *colon, *dot, *slash;
	char *protocol, *hostname;

	colon = strrchr(localcopy, ':');
	if (!colon) {
	    sfree(disp);
	    sfree(localcopy);
	    return NULL;	       /* FIXME: report a specific error? */
	}

	*colon++ = '\0';
	dot = strchr(colon, '.');
	if (dot)
	    *dot++ = '\0';

	disp->displaynum = atoi(colon);
	if (dot)
	    disp->screennum = atoi(dot);
	else
	    disp->screennum = 0;

	protocol = NULL;
	hostname = localcopy;
	if (colon > localcopy) {
	    slash = strchr(localcopy, '/');
	    if (slash) {
		*slash++ = '\0';
		protocol = localcopy;
		hostname = slash;
	    }
	}

	disp->hostname = *hostname ? dupstr(hostname) : NULL;

    if (proto_id == X11_MIT) {
	auth->fakeproto = X11_MIT;
	if (protocol)
	    disp->unixdomain = (!strcmp(protocol, "local") ||
				!strcmp(protocol, "unix"));
	else
	    disp->unixdomain = platform_uses_x11_unix_by_default;

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

	disp->unixsocketpath = NULL;

	sfree(localcopy);
    }

    /*
     * Look up the display hostname, if we need to.
     */
    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 */
	}
    }

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

	/* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
	auth->fakelen = 16;
	disp->remoteauthdata = snewn(16, unsigned char);
	for (i = 0; i < 16; i++)
	    auth->fakedata[i] = random_byte();
	auth->xdmseen = NULL;
	    disp->remoteauthdata[i] = random_byte();
	disp->remoteauthdatalen = 16;

	disp->xdmseen = NULL;
    } else {
	assert(proto_id == X11_XDM);
	auth->fakeproto = X11_XDM;
	assert(authtype == X11_XDM);
	disp->remoteauthproto = X11_XDM;

	/* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
	auth->fakelen = 16;
	disp->remoteauthdata = snewn(16, unsigned char);
	for (i = 0; i < 16; i++)
	    auth->fakedata[i] = (i == 8 ? 0 : random_byte());
	auth->xdmseen = newtree234(xdmseen_cmp);
	    disp->remoteauthdata[i] = (i == 8 ? 0 : random_byte());
	disp->remoteauthdatalen = 16;

	disp->xdmseen = newtree234(xdmseen_cmp);
    }
    disp->remoteauthprotoname = dupstr(x11_authnames[disp->remoteauthproto]);
    disp->remoteauthdatastring = snewn(disp->remoteauthdatalen * 2 + 1, char);
    for (i = 0; i < disp->remoteauthdatalen; i++)
	sprintf(disp->remoteauthdatastring + i*2, "%02x",
		disp->remoteauthdata[i]);

    /* Now format for the recipient. */
    strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
    ourdata[0] = '\0';
    for (i = 0; i < auth->fakelen; i++)
    /*
     * Fetch the local authorisation details.
     */
    disp->localauthproto = X11_NO_AUTH;
    disp->localauthdata = NULL;
    disp->localauthdatalen = 0;
	sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
    strncpy(data, ourdata, datamaxlen);
    platform_get_x11_auth(disp, cfg);

    return auth;
    return disp;
}

void x11_free_auth(void *authv)
void x11_free_display(struct X11Display *disp)
{
    struct X11Auth *auth = (struct X11Auth *)authv;
    struct XDMSeen *seen;
    if (disp->xdmseen != NULL) {
	struct XDMSeen *seen;

    if (auth->xdmseen != NULL) {
	while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
	while ((seen = delpos234(disp->xdmseen, 0)) != NULL)
	    sfree(seen);
	freetree234(auth->xdmseen);
	freetree234(disp->xdmseen);
    }
    sfree(auth);
    sfree(disp->hostname);
}

    sfree(disp->unixsocketpath);
/*
 * Fetch the real auth data for a given display string, and store
 * it in an X11Auth structure. Returns NULL on success, or an error
 * string.
    if (disp->localauthdata)
	memset(disp->localauthdata, 0, disp->localauthdatalen);
    sfree(disp->localauthdata);
    if (disp->remoteauthdata)
	memset(disp->remoteauthdata, 0, disp->remoteauthdatalen);
 */
void x11_get_real_auth(void *authv, char *display)
    sfree(disp->remoteauthdata);
{
    struct X11Auth *auth = (struct X11Auth *)authv;

    sfree(disp->remoteauthprotoname);
    sfree(disp->remoteauthdatastring);
    auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */

    sk_addr_free(disp->addr);
    auth->reallen = sizeof(auth->realdata);
    platform_get_x11_auth(display, &auth->realproto,
    sfree(disp);
                          auth->realdata, &auth->reallen);
}

#define XDM_MAXSKEW 20*60      /* 20 minute clock skew should be OK */

static char *x11_verify(unsigned long peer_ip, int peer_port,
			struct X11Auth *auth, char *proto,
			struct X11Display *disp, char *proto,
			unsigned char *data, int dlen)
{
    if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
	return "wrong authentication protocol attempted";
    if (auth->fakeproto == X11_MIT) {
        if (dlen != auth->fakelen)
    if (strcmp(proto, x11_authnames[disp->remoteauthproto]) != 0)
	return "wrong authorisation protocol attempted";
    if (disp->remoteauthproto == X11_MIT) {
        if (dlen != disp->remoteauthdatalen)
            return "MIT-MAGIC-COOKIE-1 data was wrong length";
        if (memcmp(auth->fakedata, data, dlen) != 0)
        if (memcmp(disp->remoteauthdata, data, dlen) != 0)
            return "MIT-MAGIC-COOKIE-1 data did not match";
    }
    if (auth->fakeproto == X11_XDM) {
    if (disp->remoteauthproto == X11_XDM) {
	unsigned long t;
	time_t tim;
	int i;
	struct XDMSeen *seen, *ret;

        if (dlen != 24)
            return "XDM-AUTHORIZATION-1 data was wrong length";
	if (peer_port == -1)
            return "cannot do XDM-AUTHORIZATION-1 without remote address data";
	des_decrypt_xdmauth(auth->fakedata+9, data, 24);
        if (memcmp(auth->fakedata, data, 8) != 0)
	des_decrypt_xdmauth(disp->remoteauthdata+9, data, 24);
        if (memcmp(disp->remoteauthdata, data, 8) != 0)
            return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
	if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
            return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
	if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
            return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
	t = GET_32BIT_MSB_FIRST(data+14);
	for (i = 18; i < 24; i++)
	    if (data[i] != 0)	       /* zero padding wrong */
		return "XDM-AUTHORIZATION-1 data failed check";
	tim = time(NULL);
	if (abs(t - tim) > XDM_MAXSKEW)
	    return "XDM-AUTHORIZATION-1 time stamp was too far out";
	seen = snew(struct XDMSeen);
	seen->time = t;
	memcpy(seen->clientid, data+8, 6);
	assert(auth->xdmseen != NULL);
	ret = add234(auth->xdmseen, seen);
	assert(disp->xdmseen != NULL);
	ret = add234(disp->xdmseen, seen);
	if (ret != seen) {
	    sfree(seen);
	    return "XDM-AUTHORIZATION-1 data replayed";
	}
	/* While we're here, purge entries too old to be replayed. */
	for (;;) {
	    seen = index234(auth->xdmseen, 0);
	    seen = index234(disp->xdmseen, 0);
	    assert(seen != NULL);
	    if (t - seen->time <= XDM_MAXSKEW)
		break;
	    sfree(delpos234(auth->xdmseen, 0));
	    sfree(delpos234(disp->xdmseen, 0));
	}
    }
    /* implement other protocols here if ever required */
    return NULL;
}

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;

    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;
	
#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 */
	ptr = buf;
	for (i = 0; i < 4; i++) {
	    GET; len[i] = c;
	    GET; len[i] = (len[i] << 8) | c;
	    str[i] = ptr;
	    for (j = 0; j < len[i]; j++) {
		GET; *ptr++ = c;
	    }
	    *ptr++ = '\0';
	}
#undef GET

	/*
	 * Now we have a full X authority record in memory. See
	 * whether it matches the display we're trying to
	 * authenticate to.
	 *
	 * The details we've just read should be interpreted as
	 * follows:
	 * 
	 *  - 'family' is the network address family used to
	 *    connect to the display. 0 means IPv4; 6 means IPv6;
	 *    256 means Unix-domain sockets.
	 * 
	 *  - str[0] is the network address itself. For IPv4 and
	 *    IPv6, this is a string of binary data of the
	 *    appropriate length (respectively 4 and 16 bytes)
	 *    representing the address in big-endian format, e.g.
	 *    7F 00 00 01 means IPv4 localhost. For Unix-domain
	 *    sockets, this is the host name of the machine on
	 *    which the Unix-domain display resides (so that an
	 *    .Xauthority file on a shared file system can contain
	 *    authority entries for Unix-domain displays on
	 *    several machines without them clashing).
	 * 
	 *  - str[1] is the display number. I've no idea why
	 *    .Xauthority stores this as a string when it has a
	 *    perfectly good integer format, but there we go.
	 * 
	 *  - str[2] is the authorisation method, encoded as its
	 *    canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
	 *    "XDM-AUTHORIZATION-1" or something we don't
	 *    recognise).
	 * 
	 *  - str[3] is the actual authorisation data, stored in
	 *    binary form.
	 */

	if (disp->displaynum < 0 || disp->displaynum != atoi(str[1]))
	    continue;		       /* not the one */

	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:
	    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;
	    }
	    break;
	  case 6:
	    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))
		    goto found;
	    }
	    break;
	  case 256:
	    if (disp->unixdomain && !strcmp(disp->hostname, str[0]))
		goto found;
	    break;
	}
    }

    found:
    disp->localauthproto = protocol;
    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);
}

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. */
}

	return 0;
    n = strcspn(display, ".");
    if (!display[n])
	return 0;
    return atoi(display + n + 1);
}

/* Find the right display, returns an allocated string */
char *x11_display(const char *display) {
    char *ret;
    if(!display || !*display) {
	/* try to find platform-specific local display */
	if((ret = platform_get_x_display())==0 || !*ret)
	    /* plausible default for all platforms */
	    ret = dupstr(":0");
    } else
	ret = dupstr(display);
    if(ret[0] == ':') {
	/* no transport specified, use whatever we think is best */
	char *s = dupcat(platform_x11_best_transport, ret, (char *)0);
	sfree(ret);
	return s;
    } else
	return ret;
}

/*
 * Called to set up the raw connection.
 * 
 * Returns an error message, or NULL on success.
 * also, fills the SocketsStructure
 */
const char *x11_init(Socket * s, char *display, void *c, void *auth,
		     const char *peeraddr, int peerport, const Config *cfg)
extern const char *x11_init(Socket *s, struct X11Display *disp, void *c,
			    const char *peeraddr, int peerport,
			    const Config *cfg)
{
    static const struct plug_function_table fn_table = {
	x11_log,
	x11_closing,
	x11_receive,
	x11_sent,
	NULL
    };

    SockAddr addr;
    int port;
    const char *err;
    char *dummy_realhost;
    char host[128];
    int n, displaynum;
    struct X11Private *pr;

    /* default display */
    display = x11_display(display);
    /*
     * Split up display name into host and display-number parts.
     */
    n = strcspn(display, ":");
    assert(n != 0);		/* x11_display() promises this */
    if (display[n])
	displaynum = atoi(display + n + 1);
    else
	displaynum = 0;		       /* sensible default */
    if (n > sizeof(host) - 1)
	n = sizeof(host) - 1;
    strncpy(host, display, n);
    host[n] = '\0';
    sfree(display);
    
    if(!strcmp(host, "unix") || host[0] == '/') {
	/* use AF_UNIX sockets (doesn't make sense on all platforms) */
	addr = platform_get_x11_unix_address(display, displaynum,
					     &dummy_realhost);
	port = 0;		/* to show we are not confused */
    } else {
	port = 6000 + displaynum;
	
	/*
	 * Try to find host.
	 */
	addr = name_lookup(host, port, &dummy_realhost, cfg, ADDRTYPE_UNSPEC);
	if ((err = sk_addr_error(addr)) != NULL) {
	    sk_addr_free(addr);
	    return err;
	}
    }

    /*
     * Open socket.
     */
    pr = snew(struct X11Private);
    pr->fn = &fn_table;
    pr->auth_protocol = NULL;
    pr->auth = (struct X11Auth *)auth;
    pr->disp = disp;
    pr->verified = 0;
    pr->data_read = 0;
    pr->throttled = pr->throttle_override = 0;
    pr->c = c;

    pr->s = *s = new_connection(addr, dummy_realhost, port,
    pr->s = *s = new_connection(sk_addr_dup(disp->addr),
				disp->realhost, disp->port,
				0, 1, 0, 0, (Plug) pr, cfg);
    if ((err = sk_socket_error(*s)) != NULL) {
	sfree(pr);
	return err;
    }

    /*

    while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
	pr->auth_data[pr->data_read++ - 12 -
		      pr->auth_psize] = (unsigned char) (len--, *data++);
    if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
	return 0;

    /*
     * If we haven't verified the authentication, do so now.
     * If we haven't verified the authorisation, do so now.
     */
    if (!pr->verified) {
	char *err;

	pr->auth_protocol[pr->auth_plen] = '\0';	/* ASCIZ */
	err = x11_verify(pr->peer_ip, pr->peer_port,
			 pr->auth, pr->auth_protocol,
			 pr->disp, pr->auth_protocol,
			 pr->auth_data, pr->auth_dlen);

	/*
	 * If authentication failed, construct and send an error
	 * If authorisation failed, construct and send an error
	 * packet, then terminate the connection.
	 */
	if (err) {
	    char *message;
	    int msglen, msgsize;
	    unsigned char *reply;

	 * Now we know we're going to accept the connection. Strip
	 * the fake auth data, and optionally put real auth data in
	 * instead.
	 */
        {
            char realauthdata[64];
            int realauthlen = 0;
            int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
            int authstrlen = strlen(x11_authnames[pr->disp->localauthproto]);
	    int buflen = 0;	       /* initialise to placate optimiser */
            static const char zeroes[4] = { 0,0,0,0 };
	    void *buf;

            if (pr->auth->realproto == X11_MIT) {
                assert(pr->auth->reallen <= lenof(realauthdata));
                realauthlen = pr->auth->reallen;
                memcpy(realauthdata, pr->auth->realdata, realauthlen);
            } else if (pr->auth->realproto == X11_XDM &&
		       pr->auth->reallen == 16 &&
            if (pr->disp->localauthproto == X11_MIT) {
                assert(pr->disp->localauthdatalen <= lenof(realauthdata));
                realauthlen = pr->disp->localauthdatalen;
                memcpy(realauthdata, pr->disp->localauthdata, realauthlen);
            } else if (pr->disp->localauthproto == X11_XDM &&
		       pr->disp->localauthdatalen == 16 &&
		       ((buf = sk_getxdmdata(s, &buflen))!=0)) {
		time_t t;
                realauthlen = (buflen+12+7) & ~7;
		assert(realauthlen <= lenof(realauthdata));
		memset(realauthdata, 0, realauthlen);
		memcpy(realauthdata, pr->auth->realdata, 8);
		memcpy(realauthdata, pr->disp->localauthdata, 8);
		memcpy(realauthdata+8, buf, buflen);
		t = time(NULL);
		PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
		des_encrypt_xdmauth(pr->auth->realdata+9,
		des_encrypt_xdmauth(pr->disp->localauthdata+9,
				    (unsigned char *)realauthdata,
				    realauthlen);
		sfree(buf);
	    }
            /* implement other auth methods here if required */

            PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
            PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
        
            sk_write(s, (char *)pr->firstpkt, 12);

            if (authstrlen) {
                sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
                sk_write(s, x11_authnames[pr->disp->localauthproto],
			 authstrlen);
                sk_write(s, zeroes, 3 & (-authstrlen));
            }
            if (realauthlen) {
                sk_write(s, realauthdata, realauthlen);
                sk_write(s, zeroes, 3 & (-realauthlen));
            }
        }