struct sockaddr sa;
    struct sockaddr_in sa4;
    struct sockaddr_in6 sa6;
    struct sockaddr_storage sas;
} address;

/*
 * This structure describes per-instance state of a tcp-based channel.
 */

typedef struct TcpState TcpState;

typedef struct TcpFdList {
    TcpState *statePtr;
    int fd;
    struct TcpFdList *next;
} TcpFdList;

struct TcpState {
    Tcl_Channel channel;	/* Channel associated with this file. */
    int flags;			/* OR'ed combination of the bitfields defined
				 * below. */
    TcpFdList fds;		/* The file descriptors of the sockets. */
    int interest;		/* Event types of interest */

    /*
     * Only needed for server sockets
     */

    int filehandlers;           /* Caches FileHandlers that get set up while
                                 * an async socket is not yet connected. */
    int connectError;           /* Cache SO_ERROR of async socket. */
    int cachedBlocking;         /* Cache blocking mode of async socket. */
};

/*
 * These bits may be OR'ed together into the "flags" field of a TcpState
 * structure.
 */

#define TCP_NONBLOCKING		(1<<0)	/* Socket with non-blocking I/O */
#define TCP_ASYNC_CONNECT	(1<<1)	/* Async connect in progress. */
#define TCP_ASYNC_PENDING	(1<<4)	/* TcpConnect was called to
					 * process an async connect. This

/*
 * ----------------------------------------------------------------------
 *
 * WaitForConnect --
 *
 *	Check the state of an async connect process. If a connection attempt
 *	terminated, process it, which may finalize it or may start the next
 *	attempt. If a connect error occurs, it is saved in
 *	statePtr->connectError to be reported by 'fconfigure -error'.
 *
 *	There are two modes of operation, defined by errorCodePtr:
 *	 *  non-NULL: Called by explicit read/write command. Blocks if the
 *	    socket is blocking.
 *	    May return two error codes:
 *	     *	EWOULDBLOCK: if connect is still in progress
 *	     *	ENOTCONN: if connect failed. This would be the error message
 *		of a recv or sendto syscall so this is emulated here.
 *	 *  NULL: Called by a background operation. Do not block and do not
 *	    return any error code.
 *
 * Results:
 * 	0 if the connection has completed, -1 if still in progress or there is
 * 	an error.
 *
 * Side effects:

    if (errorCodePtr != NULL && GOT_BITS(statePtr->flags, TCP_ASYNC_FAILED)) {
	*errorCodePtr = ENOTCONN;
	return -1;
    }

    /*
     * Check if an async connect is running. If not return ok.
     */

    if (!GOT_BITS(statePtr->flags, TCP_ASYNC_PENDING)) {
	return 0;
    }

    /*

	/*
	 * Whether it is a bug or feature or otherwise, it is a fact of life
	 * that on at least some Linux kernels select() fails to report that a
	 * socket file descriptor is writable when the other end of the socket
	 * is closed.  This is in contrast to the guarantees Tcl makes that
	 * its channels become writable and fire writable events on an error
	 * condition.  This has caused a leak of file descriptors in a state of
	 * background flushing.  See Tcl ticket 1758a0b603.
	 *
	 * As a workaround, when our caller indicates an interest in writable
	 * notifications, we must tell the notifier built around select() that
	 * we are interested in the readable state of the file descriptor as
	 * well, as that is the only reliable means to get notified of error
	 * conditions.  Then it is the task of WrapNotify() above to untangle

 *
 *----------------------------------------------------------------------
 */

void *
TclpMakeTcpClientChannelMode(
    void *sock,		/* The socket to wrap up into a channel. */
    int mode)			/* OR'ed combination of TCL_READABLE and
				 * TCL_WRITABLE to indicate file mode. */
{
    TcpState *statePtr;
    char channelName[SOCK_CHAN_LENGTH];

    statePtr = (TcpState *)ckalloc(sizeof(TcpState));
    memset(statePtr, 0, sizeof(TcpState));