if (bufchain_size(&p->pending_input_data) < 2)
		return 1;	       /* not got anything yet */

	    /* get the response */
	    bufchain_fetch(&p->pending_input_data, data, 2);

	    if (data[0] != 1) {
		plug_closing(p->plug, "Proxy error: SOCKS password "
			     "subnegotiation contained wrong version number",
			     PROXY_ERROR_GENERAL, 0);
		return 1;
	    }

	    if (data[1] != 0) {

		plug_closing(p->plug, "Proxy error: SOCKS proxy refused"
			     " password authentication",
			     PROXY_ERROR_GENERAL, 0);
		return 1;
	    }

	    bufchain_consume(&p->pending_input_data, 2);
	    p->state = 2;	       /* now proceed as authenticated */
	}

	if (p->state == 2) {

	    /* request format:
	     *  version number (1 byte) = 5
	     *  command code (1 byte)
	     *    1 = CONNECT
	     *    2 = BIND
	     *    3 = UDP ASSOCIATE
	     *  reserved (1 byte) = 0x00
	     *  address type (1 byte)
	     *    1 = IPv4
	     *    3 = domainname (first byte has length, no terminating null)
	     *    4 = IPv6
	     *  dest. address (variable)
	     *  dest. port (2 bytes) [network order]
	     */

	    char command[512];
	    int len;
	    int type;

	    type = sk_addrtype(p->remote_addr);
	    if (type == ADDRTYPE_IPV4) {
		len = 10;	       /* 4 hdr + 4 addr + 2 trailer */
		command[3] = 1; /* IPv4 */
		sk_addrcopy(p->remote_addr, command+4);
	    } else if (type == ADDRTYPE_IPV6) {
		len = 22;	       /* 4 hdr + 16 addr + 2 trailer */
		command[3] = 4; /* IPv6 */
		sk_addrcopy(p->remote_addr, command+4);
	    } else {
		assert(type == ADDRTYPE_NAME);
		command[3] = 3;
		sk_getaddr(p->remote_addr, command+5, 256);
		command[4] = strlen(command+5);
		len = 7 + command[4];  /* 4 hdr, 1 len, N addr, 2 trailer */
	    }

	    command[0] = 5; /* version 5 */
	    command[1] = 1; /* CONNECT command */
	    command[2] = 0x00;

	    /* port */
	    command[len-2] = (char) (p->remote_port >> 8) & 0xff;
	    command[len-1] = (char) p->remote_port & 0xff;

	    sk_write(p->sub_socket, command, len);

	    p->state = 3;
	    return 1;
	}

	if (p->state == 3) {

	    /* reply format:
	     *  version number (1 bytes) = 5
	     *  reply code (1 byte)
	     *    0 = succeeded
	     *    1 = general SOCKS server failure
	     *    2 = connection not allowed by ruleset
	     *    3 = network unreachable
	     *    4 = host unreachable
	     *    5 = connection refused
	     *    6 = TTL expired
	     *    7 = command not supported
	     *    8 = address type not supported
	     * reserved (1 byte) = x00
	     * address type (1 byte)
	     *    1 = IPv4
	     *    3 = domainname (first byte has length, no terminating null)
	     *    4 = IPv6
	     * server bound address (variable)
	     * server bound port (2 bytes) [network order]
	     */
	    char data[5];
	    int len;

	    /* First 5 bytes of packet are enough to tell its length. */ 
	    if (bufchain_size(&p->pending_input_data) < 5)
		return 1;	       /* not got anything yet */

	    /* get the response */
	    bufchain_fetch(&p->pending_input_data, data, 5);

	    if (data[0] != 5) {
		plug_closing(p->plug, "Proxy error: SOCKS proxy returned wrong version number",
			     PROXY_ERROR_GENERAL, 0);
		return 1;
	    }

	    if (data[1] != 0) {
		char buf[256];

		strcpy(buf, "Proxy error: ");

		switch (data[1]) {
		  case 1: strcat(buf, "General SOCKS server failure"); break;
		  case 2: strcat(buf, "Connection not allowed by ruleset"); break;
		  case 3: strcat(buf, "Network unreachable"); break;
		  case 4: strcat(buf, "Host unreachable"); break;
		  case 5: strcat(buf, "Connection refused"); break;
		  case 6: strcat(buf, "TTL expired"); break;
		  case 7: strcat(buf, "Command not supported"); break;
		  case 8: strcat(buf, "Address type not supported"); break;
		  default: sprintf(buf+strlen(buf),
				   "Unrecognised SOCKS error code %d",
				   data[1]);
		    break;
		}
		plug_closing(p->plug, buf, PROXY_ERROR_GENERAL, 0);

		return 1;
	    }

	    /*
	     * Eat the rest of the reply packet.
	     */
	    len = 6;		       /* first 4 bytes, last 2 */
	    switch (data[3]) {
	      case 1: len += 4; break; /* IPv4 address */
	      case 4: len += 16; break;/* IPv6 address */
	      case 3: len += (unsigned char)data[4]; break; /* domain name */
	      default:
		plug_closing(p->plug, "Proxy error: SOCKS proxy returned "
			     "unrecognised address format",
			     PROXY_ERROR_GENERAL, 0);
		return 1;
	    }
	    if (bufchain_size(&p->pending_input_data) < len)
		return 1;	       /* not got whole reply yet */
	    bufchain_consume(&p->pending_input_data, len);

	    /* we're done */
	    proxy_activate(p);
	    return 1;
	}

	if (p->state == 4) {
	    /* TODO: Handle GSSAPI authentication */
	    plug_closing(p->plug, "Proxy error: We don't support GSSAPI authentication",
			 PROXY_ERROR_GENERAL, 0);
	    return 1;
	}

	if (p->state == 5) {
	    if (p->cfg.proxy_username[0] || p->cfg.proxy_password[0]) {
		char userpwbuf[514];
		int ulen, plen;
		ulen = strlen(p->cfg.proxy_username);
		if (ulen > 255) ulen = 255; if (ulen < 1) ulen = 1;
		plen = strlen(p->cfg.proxy_password);
		if (plen > 255) plen = 255; if (plen < 1) plen = 1;
		userpwbuf[0] = 1;      /* version number of subnegotiation */
		userpwbuf[1] = ulen;
		memcpy(userpwbuf+2, p->cfg.proxy_username, ulen);
		userpwbuf[ulen+2] = plen;
		memcpy(userpwbuf+ulen+3, p->cfg.proxy_password, plen);
		sk_write(p->sub_socket, userpwbuf, ulen + plen + 3);
		p->state = 7;
	    } else 
		plug_closing(p->plug, "Proxy error: Server chose "
			     "username/password authentication but we "
			     "didn't offer it!",
			 PROXY_ERROR_GENERAL, 0);
	    return 1;
	}

	if (p->state == 6) {
	    /* TODO: Handle CHAP authentication */
	    plug_closing(p->plug, "Proxy error: We don't support CHAP authentication",
			 PROXY_ERROR_GENERAL, 0);
	    return 1;
	}

    }

    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
		 PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}

/* ----------------------------------------------------------------------
 * `Telnet' proxy type.
 *
 * (This is for ad-hoc proxies where you connect to the proxy's
 * telnet port and send a command such as `connect host port'. The
 * command is configurable, since this proxy type is typically not
 * standardised or at all well-defined.)
 */

char *format_telnet_command(SockAddr addr, int port, const Config *cfg)
{
    char *ret = NULL;
    int retlen = 0, retsize = 0;
    int so = 0, eo = 0;
#define ENSURE(n) do { \
    if (retsize < retlen + n) { \
	retsize = retlen + n + 512; \
	ret = sresize(ret, retsize, char); \
    } \
} while (0)

    /* we need to escape \\, \%, \r, \n, \t, \x??, \0???, 
     * %%, %host, %port, %user, and %pass
     */

    while (cfg->proxy_telnet_command[eo] != 0) {

	/* scan forward until we hit end-of-line,
	 * or an escape character (\ or %) */
	while (cfg->proxy_telnet_command[eo] != 0 &&
	       cfg->proxy_telnet_command[eo] != '%' &&
	       cfg->proxy_telnet_command[eo] != '\\') eo++;

	/* if we hit eol, break out of our escaping loop */
	if (cfg->proxy_telnet_command[eo] == 0) break;

	/* if there was any unescaped text before the escape
	 * character, send that now */
	if (eo != so) {
	    ENSURE(eo - so);
	    memcpy(ret + retlen, cfg->proxy_telnet_command + so, eo - so);
	    retlen += eo - so;
	}

	so = eo++;

	/* if the escape character was the last character of
	 * the line, we'll just stop and send it. */
	if (cfg->proxy_telnet_command[eo] == 0) break;

	if (cfg->proxy_telnet_command[so] == '\\') {

	    /* we recognize \\, \%, \r, \n, \t, \x??.
	     * anything else, we just send unescaped (including the \).
	     */

	    switch (cfg->proxy_telnet_command[eo]) {

	      case '\\':
		ENSURE(1);
		ret[retlen++] = '\\';
		eo++;
		break;

	      case '%':
		ENSURE(1);
		ret[retlen++] = '%';
		eo++;
		break;

	      case 'r':
		ENSURE(1);
		ret[retlen++] = '\r';
		eo++;
		break;

	      case 'n':
		ENSURE(1);
		ret[retlen++] = '\n';
		eo++;
		break;

	      case 't':
		ENSURE(1);
		ret[retlen++] = '\t';
		eo++;
		break;

	      case 'x':
	      case 'X':
		{
		    /* escaped hexadecimal value (ie. \xff) */
		    unsigned char v = 0;
		    int i = 0;

		    for (;;) {
			eo++;
			if (cfg->proxy_telnet_command[eo] >= '0' &&
			    cfg->proxy_telnet_command[eo] <= '9')
			    v += cfg->proxy_telnet_command[eo] - '0';
			else if (cfg->proxy_telnet_command[eo] >= 'a' &&
				 cfg->proxy_telnet_command[eo] <= 'f')
			    v += cfg->proxy_telnet_command[eo] - 'a' + 10;
			else if (cfg->proxy_telnet_command[eo] >= 'A' &&
				 cfg->proxy_telnet_command[eo] <= 'F')
			    v += cfg->proxy_telnet_command[eo] - 'A' + 10;
			else {
			    /* non hex character, so we abort and just
			     * send the whole thing unescaped (including \x)
			     */
			    ENSURE(1);
			    ret[retlen++] = '\\';
			    eo = so + 1;
			    break;
			}

			/* we only extract two hex characters */
			if (i == 1) {
			    ENSURE(1);
			    ret[retlen++] = v;
			    eo++;
			    break;
			}

			i++;
			v <<= 4;
		    }
		}
		break;

	      default:
		ENSURE(2);
		memcpy(ret+retlen, cfg->proxy_telnet_command + so, 2);
		retlen += 2;
		eo++;
		break;
	    }
	} else {

	    /* % escape. we recognize %%, %host, %port, %user, %pass.
	     * anything else, we just send unescaped (including the %).
	     */

	    if (cfg->proxy_telnet_command[eo] == '%') {
		ENSURE(1);
		ret[retlen++] = '%';
		eo++;
	    }
	    else if (strnicmp(cfg->proxy_telnet_command + eo,
			      "host", 4) == 0) {
		char dest[512];
		int destlen;
		sk_getaddr(addr, dest, lenof(dest));
		destlen = strlen(dest);
		ENSURE(destlen);
		memcpy(ret+retlen, dest, destlen);
		retlen += destlen;
		eo += 4;
	    }
	    else if (strnicmp(cfg->proxy_telnet_command + eo,
			      "port", 4) == 0) {
		char portstr[8], portlen;
		portlen = sprintf(portstr, "%i", port);
		ENSURE(portlen);
		memcpy(ret + retlen, portstr, portlen);
		retlen += portlen;
		eo += 4;
	    }
	    else if (strnicmp(cfg->proxy_telnet_command + eo,
			      "user", 4) == 0) {
		int userlen = strlen(cfg->proxy_username);
		ENSURE(userlen);
		memcpy(ret+retlen, cfg->proxy_username, userlen);
		retlen += userlen;
		eo += 4;
	    }
	    else if (strnicmp(cfg->proxy_telnet_command + eo,
			      "pass", 4) == 0) {
		int passlen = strlen(cfg->proxy_password);
		ENSURE(passlen);
		memcpy(ret+retlen, cfg->proxy_password, passlen);
		retlen += passlen;
		eo += 4;
	    }
	    else {
		/* we don't escape this, so send the % now, and
		 * don't advance eo, so that we'll consider the
		 * text immediately following the % as unescaped.
		 */
		ENSURE(1);
		ret[retlen++] = '%';
	    }
	}

	/* resume scanning for additional escapes after this one. */
	so = eo;
    }

    /* if there is any unescaped text at the end of the line, send it */
    if (eo != so) {
	ENSURE(eo - so);
	memcpy(ret + retlen, cfg->proxy_telnet_command + so, eo - so);
	retlen += eo - so;
    }

    ENSURE(1);
    ret[retlen] = '\0';
    return ret;

#undef ENSURE
}

int proxy_telnet_negotiate (Proxy_Socket p, int change)
{
    if (p->state == PROXY_CHANGE_NEW) {
	char *formatted_cmd;

	formatted_cmd = format_telnet_command(p->remote_addr, p->remote_port,
					      &p->cfg);

	sk_write(p->sub_socket, formatted_cmd, strlen(formatted_cmd));
	sfree(formatted_cmd);

	p->state = 1;
	return 0;
    }

    if (change == PROXY_CHANGE_CLOSING) {
	/* if our proxy negotiation process involves closing and opening
	 * new sockets, then we would want to intercept this closing
	 * callback when we were expecting it. if we aren't anticipating
	 * a socket close, then some error must have occurred. we'll
	 * just pass those errors up to the backend.
	 */
	return plug_closing(p->plug, p->closing_error_msg,
			    p->closing_error_code,
			    p->closing_calling_back);
    }

    if (change == PROXY_CHANGE_SENT) {
	/* some (or all) of what we wrote to the proxy was sent.
	 * we don't do anything new, however, until we receive the
	 * proxy's response. we might want to set a timer so we can
	 * timeout the proxy negotiation after a while...
	 */
	return 0;
    }

    if (change == PROXY_CHANGE_ACCEPTING) {
	/* we should _never_ see this, as we are using our socket to
	 * connect to a proxy, not accepting inbound connections.
	 * what should we do? close the socket with an appropriate
	 * error message?
	 */
	return plug_accepting(p->plug, p->accepting_sock);
    }

    if (change == PROXY_CHANGE_RECEIVE) {
	/* we have received data from the underlying socket, which
	 * we'll need to parse, process, and respond to appropriately.
	 */

	/* we're done */
	proxy_activate(p);
	/* proxy activate will have dealt with
	 * whatever is left of the buffer */
	return 1;
    }

    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
		 PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}