The structure typed as TransportSW contains the list of the transport layer the specific implementations supports.

typedef struct {
      char *transport_name;
      Bool (*config);
} TransportSW;

A sample entry for the Xlib supporting transporters is shown below:

TransportSW _XimTransportRec[] = {
/*     char *:
 *     transport_name,     Bool (*config)()
 */
      "X",             _XimXConf,
      "tcp",           _XimTransConf,
      "local",         _XimTransConf,
      "decnet",        _XimTransConf,
      "streams",       _XimTransConf,
      (char *)NULL,    (Bool (*)())NULL,
};

The following function will be called once when Xlib configures the transporter functions.

This function must setup the transporter function pointers.

The actual config function will be chosen by IM Server at the pre-connection time, matching by the transport_name specified in the _XimTransportRec array; The specific members of XimProto structure listed below must be initialized so that point they appropriate transporter functions.

If the specified transporter has been configured successfully, this function returns True. There is no Alternative Entry for config function itself.

The structure XimProto contains the following function pointers:

Bool (*connect)();               /* Open connection */
Bool (*shutdown)();              /* Close connection */
Bool (*write)();                 /* Write data */
Bool (*read)();                  /* Read data */
Bool (*flush)();                 /* Flush data buffer */
Bool (*register_dispatcher)();   /* Register asynchronous data handler */
Bool (*call_dispatcher)();       /* Call dispatcher */

These functions are called when Xlib needs to communicate the IM Server. These functions must process the appropriate procedure described below.

When XOpenIM is called, the following function is called to connect with the IM Server.

This function must establishes the connection to the IM Server. If the connection is established successfully, this function returns True. The Alternative Entry for this function is:

When XCloseIM is called, the following function is called to disconnect the connection with the IM Server. The Alternative Entry for this function is:

This function must close connection with the IM Server. If the connection is closed successfully, this function returns True. The Alternative Entry for this function is:

The following function is called, when Xlib needs to write data to the IM Server.

This function writes the data to the IM Server, regardless of the contents. The number of bytes is passed to len. The writing data is passed to data. If data is sent successfully, the function returns True. Refer to "The Input Method Protocol" for the contents of the writing data. The Alternative Entry for this function is:

The following function is called when Xlib waits for response from IM server synchronously.

This function stores the read data in read_buf, which size is specified as buf_len. The size of data is set to ret_len. This function return True, if the data is read normally or reading data is completed.

The Alternative Entry for this function is:

The predicate procedure indicates whether the data is for the XIM or not. len This function stores the read data in buf, which size is specified as buf_len. The size of data is set to ret_len. If preedicate() returns True, this function returns True. If not, it calls the registered callback function.

The procedure and its arguments are:

The following function is called when Xlib needs to flush the data.

This function must flush the data stored in internal buffer on the transport layer. If data transfer is completed, the function returns True. The Alternative Entry for this function is:

Xlib needs to handle asynchronous response from IM Server. This is because some of the XIM data occur asynchronously to X events.

Those data will be handled in the Filter, and the Filter will call asynchronous data handler in the protocol layer. Then it calls dispatchers in the transport layer. The dispatchers are implemented by the protocol layer. This function must store the information and prepare for later call of the dispatchers using _XimCallDispatcher.

When multiple dispatchers are registered, they will be called sequentially in order of registration, on arrival of asynchronous data. The register_dispatcher is declared as following:

The dispatcher is a function of the following type:

The dispatcher is provided by the protocol layer. They are called once for every asynchronous data, in order of registration. If the data is used, it must return True. otherwise, it must return False.

If the dispatcher function returns True, the Transport Layer assume that the data has been processed by the upper layer. The Alternative Entry for this function is:

The following function is used to call the registered dispatcher function, when the asynchronous response from IM Server has arrived.

The call_dispatcher must call the dispatcher function, in order of their registration. len and data are the data passed to register_dispatcher.

The return values are checked at each invocation, and if it finds True, it immediately return with true for its return value.

It is depend on the upper layer whether the read data is XIM Protocol packet unit or not. The Alternative Entry for this function is:

At the beginning of the X Transport connection for the XIM transport mechanism, two different windows must be created either in an Xlib XIM or in an IM Server, with which the Xlib and the IM Server exchange the XIM transports by using the ClientMessage events and Window Properties. In the following, the window created by the Xlib is referred as the "client communication window", and on the other hand, the window created by the IM Server is referred as the "IMS communication window".

only-CM            :    data is sent via a ClientMessage
multi-CM           :    data is sent via multiple ClientMessages
Property-with-CM   :    data is written in Property, and its Atom
                        is send via ClientMessage
PropertyNotify     :    data is written in Property, and its Atom
                        is send via PropertyNotify