The XIM Transport Specification
Revision 0.1
X Version 11, Release 6.4
Takashi Fujiwara
FUJITSU LIMITED
ABSTRACT
This specification describes the transport layer
interfaces between Xlib and IM Server, which makes
various channels usable such as X protocol or,
TCP/IP, DECnet and etc.
Copyright (C) 1994 by FUJITSU LIMITED
Permission to use, copy, modify, and distribute this docu-
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provided that the above copyright notice and this permission
notice appear in all copies. Fujitsu makes no representa-
tions about the suitability for any purpose of the informa-
tion in this document. This documentation is provided as is
without express or implied warranty.
Copyright (C) 1994 X Consortium
Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documenta-
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X Window System is a trademark of X Consortium, Inc.
1. Introduction
The Xlib XIM implementation is layered into three functions,
a protocol layer, an interface layer and a transport layer.
The purpose of this layering is to make the protocol inde-
pendent of transport implementation. Each function of these
layers are:
The protocol layer
implements overall function of XIM and calls the
interface layer functions when it needs to commu-
nicate to IM Server.
The interface layer
separates the implementation of the transport
layer from the protocol layer, in other words, it
provides implementation independent hook for the
transport layer functions.
The transport layer
handles actual data communication with IM Server.
It is done by a set of several functions named
transporters.
This specification describes the interface layer and the
transport layer, which makes various communication channels
usable such as X protocol or, TCP/IP, DECnet, STREAM, etc.,
and provides the information needed for adding another new
transport layer. In addition, sample implementations for
the transporter using the X connection is described in sec-
tion 4.
2. Initialization
2.1. Registering structure to initialize
The structure typed as TransportSW contains the list of the
transport layer the specific implementations supports.
typedef struct {
char *transport_name;
Bool (*config);
} TransportSW;
transport_name name of transport(*1)
config initial configuration function
-----------
(*1) Refer to "The Input Method Protocol: Appendix
B"
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XIM Transport Specification X11, Release 6.4
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,
};
2.2. Initialization function
The following function will be called once when Xlib config-
ures the transporter functions.
Bool (*config)(im, transport_data)
XIM im;
char *transport_data;
im Specifies XIM structure address.
transport_data
Specifies the data specific to the transporter, in
IM Server address. (*1)
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 mem-
bers of XimProto structure listed below must be initialized
so that point they appropriate transporter functions.
If the specified transporter has been configured success-
fully, this function returns True. There is no Alternative
Entry for config function itself.
The structure XimProto contains the following function
pointers:
-----------
(*1) Refer to "The Input Method Protocol: Appendix
B"
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XIM Transport Specification X11, Release 6.4
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.
3. The interface/transport layer functions
Following functions are used for the transport interface.
Table 3-1; The Transport Layer Functions.
+-----------------------+---------------------+----------+
| Alternative Entry | XimProto member | Section |
| (Interface Layer) | (Transport Layer) | |
+-----------------------+---------------------+----------+
|_XimConnect | connect | 3.1 |
+-----------------------+---------------------+----------+
|_XimShutdown | shutdown | 3.2 |
+-----------------------+---------------------+----------+
|_XimWrite | write | 3.3 |
+-----------------------+---------------------+----------+
|_XimRead | read | 3.4 |
+-----------------------+---------------------+----------+
|_XimFlush | flush | 3.5 |
+-----------------------+---------------------+----------+
|_XimRegisterDispatcher | register_dispatcher | 3.6 |
+-----------------------+---------------------+----------+
|_XimCallDispatcher | call_dispatcher | 3.7 |
+-----------------------+---------------------+----------+
The Protocol layer calls the above functions using the
Alternative Entry in the left column. The transport imple-
mentation defines XimProto member function in the right col-
umn. The Alternative Entry is provided so as to make easier
to implement the Protocol Layer.
3.1. Opening connection
When XOpenIM is called, the following function is called to
connect with the IM Server.
Bool (*connect)(im)
XIM im;
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XIM Transport Specification X11, Release 6.4
im Specifies XIM structure address.
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 func-
tion is:
Bool _XimConnect(im)
XIM im;
im Specifies XIM structure address.
3.2. Closing connection
When XCloseIM is called, the following function is called to
disconnect the connection with the IM Server. The Alterna-
tive Entry for this function is:
Bool (*shutdown)(im)
XIM im;
im Specifies XIM structure address.
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:
Bool _XimShutdown(im)
XIM im;
im Specifies XIM structure address.
3.3. Writing data
The following function is called, when Xlib needs to write
data to the IM Server.
Bool (*write)(im, len, data)
XIM im;
INT16 len;
XPointer data;
im Specifies XIM structure address.
len Specifies the length of writing data.
data Specifies the writing data.
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XIM Transport Specification X11, Release 6.4
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 success-
fully, the function returns True. Refer to "The Input Method
Protocol" for the contents of the writing data. The Alterna-
tive Entry for this function is:
Bool _XimWrite(im, len, data)
XIM im;
INT16 len;
XPointer data;
im Specifies XIM structure address.
len Specifies the length of writing data.
data Specifies the writing data.
3.4. Reading data
The following function is called when Xlib waits for
response from IM server synchronously.
Bool (*read)(im, read_buf, buf_len, ret_len)
XIM im;
XPointer read_buf;
int buf_len;
int *ret_len;
im Specifies XIM structure address.
read_buf Specifies the buffer to store data.
buf_len Specifies the size of the buffer
ret_len Specifies the length of stored data.
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:
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XIM Transport Specification X11, Release 6.4
Bool _XimRead(im, ret_len, buf, buf_len, predicate, predicate_arg)
XIM im;
INT16 *ret_len;
XPointer buf;
int buf_len;
Bool (*predicate)();
XPointer predicate_arg;
im Specifies XIM structure address.
ret_len Specifies the size of the data buffer.
buf Specifies the buffer to store data.
buf_len Specifies the length of buffer.
predicate Specifies the predicate for the XIM data.
predicate_arg
Specifies the predicate specific data.
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:
Bool (*predicate)(im, len, data, predicate_arg)
XIM im;
INT16 len;
XPointer data;
XPointer predicate_arg;
im Specifies XIM structure address.
len Specifies the size of the data buffer.
data Specifies the buffer to store data.
predicate_arg
Specifies the predicate specific data.
3.5. Flushing buffer
The following function is called when Xlib needs to flush
the data.
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XIM Transport Specification X11, Release 6.4
void (*flush)(im)
XIM im;
im Specifies XIM structure address.
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 func-
tion is:
void _XimFlush(im)
XIM im;
im Specifies XIM structure address.
3.6. Registering asynchronous data handler
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 dis-
patchers are implemented by the protocol layer. This func-
tion 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:
Bool (*register_dispatcher)(im, dispatcher, call_data)
XIM im;
Bool (*dispatcher)();
XPointer call_data;
im Specifies XIM structure address.
dispatcher
Specifies the dispatcher function to register.
call_data Specifies a parameter for the dispatcher.
The dispatcher is a function of the following type:
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XIM Transport Specification X11, Release 6.4
Bool (*dispatcher)(im, len, data, call_data)
XIM im;
INT16 len;
XPointer data;
XPointer call_data;
im Specifies XIM structure address.
len Specifies the size of the data buffer.
data Specifies the buffer to store data.
call_data Specifies a parameter passed to the register_dis-
patcher.
The dispatcher is provided by the protocol layer. They are
called once for every asynchronous data, in order of regis-
tration. If the data is used, it must return True. other-
wise, 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:
Bool _XimRegisterDispatcher(im, dispatcher, call_data)
XIM im;
Bool (*dispatcher)();
XPointer call_data;
im Specifies XIM structure address.
dispatcher
Specifies the dispatcher function to register.
call_data Specifies a parameter for the dispatcher.
3.7. Calling dispatcher
The following function is used to call the registered dis-
patcher function, when the asynchronous response from IM
Server has arrived.
Bool (*call_dispatcher)(im, len, data)
XIM im;
INT16 len;
XPointer data;
im Specifies XIM structure address.
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XIM Transport Specification X11, Release 6.4
len Specifies the size of data buffer.
data Specifies the buffer to store data.
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:
Bool _XimCallDispatcher(im, len, data)
XIM im;
INT16 len;
XPointer call_data;
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XIM Transport Specification X11, Release 6.4
4. Sample implementations for the Transport Layer
Sample implementations for the transporter using the X con-
nection is described here.
4.1. X Transport
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 fol-
lowing, 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 com-
munication window".
4.1.1. Connection
In order to establish a connection, a communication window
is created. A ClientMessage in the following event's format
is sent to the owner window of XIM_SERVER selection, which
the IM Server has created.
Refer to "The Input Method Protocol" for the XIM_SERVER
atom.
Table 4-1; The ClientMessage sent to the IMS window.
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | IMS Window ID
Atom message_type | XInternAtom(display, ``_XIM_XCONNECT'', False)
int format | 32
long data.l[0] | client communication window ID
long data.l[1] | client-major-transport-version (*1)
long data.l[2] | client-major-transport-version (*1)
-----------------------+------------------------------------------------
In order to establish the connection (to notify the IM
Server communication window), the IM Server sends a
ClientMessage in the following event's format to the client
communication window.
Table 4-2; The ClientMessage sent by IM Server.
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XIM Transport Specification X11, Release 6.4
-----------------------+-------------------------------------------------------
Structure Member | Contents
-----------------------+-------------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | client communication window ID
Atom message_type | XInternAtom(display, ``_XIM_XCONNECT'', False)
int format | 32
long data.l[0] | IMS communication window ID
long data.l[1] | server-major-transport-version (*1)
long data.l[2] | server-minor-transport-version (*1)
long data.l[3] | dividing size between ClientMessage and Property (*2)
-----------------------+-------------------------------------------------------
(*1) major/minor-transport-version
The read/write method is decided by the combina-
tion of major/minor-transport-version, as follows:
Table 4-3; The read/write method and the major/minor-transport-version
+------------------+---------------------------------------+
|Transport-version | read/write |
+--------+---------+---------------------------------------+
| major | minor | |
+--------+---------+---------------------------------------+
| 0 | 0 | only-CM & Property-with-CM |
| | 1 | only-CM & multi-CM |
| | 2 | only-CM & multi-CM & Property-with-CM |
+--------+---------+---------------------------------------+
| 1 | 0 | PropertyNotify |
+--------+---------+---------------------------------------+
| 2 | 0 | only-CM & PropertyNotify |
| | 1 | only-CM & multi-CM & PropertyNotify |
+--------+---------+---------------------------------------+
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
The method to decide major/minor-transport-version is
as follows:
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XIM Transport Specification X11, Release 6.4
(1) The client sends 0 as major/minor-transport-ver-
sion to the IM Server. The client must support
all methods in Table 4-3. The client may send
another number as major/minor-transport-version to
use other method than the above in the future.
(2) The IM Server sends its major/minor-transport-ver-
sion number to the client. The client sends data
using the method specified by the IM Server.
(3) If major/minor-transport-version number is not
available, it is regarded as 0.
(*2) dividing size between ClientMessage and Property
If data is sent via both of multi-CM and Property,
specify the dividing size between ClientMessage
and Property. The data, which is smaller than this
size, is sent via multi-CM (or only-CM), and the
data, which is lager than this size, is sent via
Property.
4.1.2. read/write
The data is transferred via either ClientMessage or Window
Property in the X Window System.
4.1.2.1. Format for the data from the Client to the IM
Server
ClientMessage
If data is sent via ClientMessage event, the format is
as follows:
Table 4-4; The ClientMessage event's format (first or middle)
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | IMS communication window ID
Atom message_type | XInternAtom(display, ``_XIM_MOREDATA'', False)
int format | 8
char data.b[20] | (read/write DATA : 20 byte)
-----------------------+------------------------------------------------
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XIM Transport Specification X11, Release 6.4
Table 4-5; The ClientMessage event's format (only or last)
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | IMS communication window ID
Atom message_type | XInternAtom(display, ``_XIM_PROTOCOL'', False)
int format | 8
char data.b[20] | (read/write DATA : MAX 20 byte) (*1)
-----------------------+------------------------------------------------
(*1) If the data is smaller than 20 byte, all data
other than available data must be 0.
Property
In the case of large data, data will be sent via the
Window Property for the efficiency. There are the fol-
lowing two methods to notify Property, and transport-
version is decided which method is used.
(1) The XChangeProperty function is used to store data
in the client communication window, and Atom of
the stored data is notified to the IM Server via
ClientMessage event.
(2) The XChangeProperty function is used to store data
in the client communication window, and Atom of
the stored data is notified to the IM Server via
PropertyNotify event.
The arguments of the XChangeProperty are as follows:
Table 4-6; The XChangeProperty event's format
--------------------+--------------------------------
Argument | Contents
--------------------+--------------------------------
Display *display | The display to which connects
Window window | IMS communication window ID
Atom property | read/write property Atom (*1)
Atom type | XA_STRING
int format | 8
int mode | PropModeAppend
u_char *data | read/write DATA
int nelements | length of DATA
--------------------+--------------------------------
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XIM Transport Specification X11, Release 6.4
(*1) The read/write property ATOM allocates the follow-
ing strings by XInternAtom.
``_clientXXX''
The client changes the property with the mode of Prop-
ModeAppend and the IM Server will read it with the
delete mode i.e. (delete = True).
If Atom is notified via ClientMessage event, the format
of the ClientMessage is as follows:
Table 4-7; The ClientMessage event's format to send
Atom of property
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | IMS communication window ID
Atom message_type | XInternAtom(display, ``_XIM_PROTOCOL'', False)
int format | 32
long data.l[0] | length of read/write property Atom
long data.l[1] | read/write property Atom
-----------------------+------------------------------------------------
4.1.2.2. Format for the data from the IM Server to the
Client
ClientMessage
The format of the ClientMessage is as follows:
Table 4-8; The ClientMessage event's format (first or middle)
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | client communication window ID
Atom message_type | XInternAtom(display, ``_XIM_MOREDATA'', False)
int format | 8
char data.b[20] | (read/write DATA : 20 byte)
-----------------------+------------------------------------------------
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XIM Transport Specification X11, Release 6.4
Table 4-9; The ClientMessage event's format (only or last)
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | client communication window ID
Atom message_type | XInternAtom(display, ``_XIM_PROTOCOL'', False)
int format | 8
char data.b[20] | (read/write DATA : MAX 20 byte) (*1)
-----------------------+------------------------------------------------
(*1) If the data size is smaller than 20 bytes, all
data other than available data must be 0.
Property
In the case of large data, data will be sent via the
Window Property for the efficiency. There are the fol-
lowing two methods to notify Property, and transport-
version is decided which method is used.
(1) The XChangeProperty function is used to store data
in the IMS communication window, and Atom of the
property is sent via the ClientMessage event.
(2) The XChangeProperty function is used to store data
in the IMS communication window, and Atom of the
property is sent via PropertyNotify event.
The arguments of the XChangeProperty are as follows:
Table 4-10; The XChangeProperty event's format
--------------------+----------------------------------
Argument | Contents
--------------------+----------------------------------
Display *display | The display which to connects
Window window | client communication window ID
Atom property | read/write property Atom (*1)
Atom type | XA_STRING
int format | 8
int mode | PropModeAppend
u_char *data | read/write DATA
int nelements | length of DATA
--------------------+----------------------------------
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XIM Transport Specification X11, Release 6.4
(*1) The read/write property ATOM allocates some
strings, which are not allocated by the client, by
XInternAtom.
The IM Server changes the property with the mode of
PropModeAppend and the client reads it with the delete
mode, i.e. (delete = True).
If Atom is notified via ClientMessage event, the format
of the ClientMessage is as follows:
Table 4-11; The ClientMessage event's format to send
Atom of property
-----------------------+------------------------------------------------
Structure Member | Contents
-----------------------+------------------------------------------------
int type | ClientMessage
u_long serial | Set by the X Window System
Bool send_event | Set by the X Window System
Display *display | The display to which connects
Window window | client communication window ID
Atom message_type | XInternAtom(display, ``_XIM_PROTOCOL'', False)
int format | 32
long data.l[0] | length of read/write property ATOM
long data.l[1] | read/write property ATOM
-----------------------+------------------------------------------------
4.1.3. Closing Connection
If the client disconnect with the IM Server, shutdown func-
tion should free the communication window properties and
etc..
5. References
[1] Masahiko Narita and Hideki Hiura, ``The Input Method
Protocol''
16