The Input Method Protocol

Version 1.0

X Consortium Standard

X Version 11, Release 7

libX11 1.3.1
Masahiko Narita
FUJITSU Limited.
Hideki Hiura
SunSoft, Inc.
ABSTRACT

This specifies a protocol between IM library and
IM (Input Method) Server for internationalized
text input, which is independent from any specific
language, any specific input method and the
transport layer used in communication between the
IM library and the IM Server, and uses a
client-server model. This protocol allows user to
use his/her favorite input method for all
applications within the stand-alone distributed
environment.

X Window System is a trademark of X Consortium, Inc.

Copyright © 1993, 1994 by X Consortium, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.

Copyright © 1993, 1994 by FUJITSU LIMITED

Copyright © 1993, 1994 by Sun Microsystems, Inc.

Permission to use, copy, modify, and distribute this documentation for any purpose and without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. Fujitsu and Sun Microsystems make no representations about the suitability for any purpose of the information in this document. This documentation is provided as is without express or implied warranty.

1. Introduction

1.1. Scope

The internationalization in the X Window System Version 11, Release 5 (X11R5) provides a common API which application developers can use to create portable internationalized programs and to adapt them to the requirements of different native languages, local customs, and character string encodings (this is called ‘‘localization’’). As one of its internationalization mechanisms X11R5 has defined a functional interface for internationalized text input, called XIM (X Input Method).

When a client-server model is used with an IM (Input Method) implementation, a protocol must be established between the client and the server. However, the protocol used to interface Input Method Servers (IM Servers) with the Input Method libraries (IM libraries) to which applications are linked was not addressed in X11R5. This led application developers to depend on vendor-specific input methods, decreased the user’s choice of available input methods, and made it more difficult for developers to create portable applications. This paper describes the Input Method Protocol developed for X11R6 to resolve the above problems and to address the requirements of existing and future input methods.

The Input Method Protocol is independent from the transport layer used in communication between the IM library and the IM Server. Thus, the input method protocol can be built on any inter-process communication mechanism, such as TCP/IP or the X protocol.

In addition, the protocol provides for future extensions such as differing input model types.

1.2. Background

Text input is much more simple for some languages than others. English, for instance, uses an alphabet of a manageable size, and input consists of pressing the corresponding key on a keyboard, perhaps in combination with a shift key for capital letters or special characters.

Some languages have larger alphabets, or modifiers such as accents, which require the addition of special key combinations in order to enter text. These input methods may require ‘‘dead-keys’’ or ‘‘compose-keys’’ which, when followed by different combinations of key strokes, generate different characters.

Text input for ideographic languages is much less simple. In these languages, characters represent actual objects rather than phonetic sounds used in pronouncing a word, and the number of characters in these languages may continue to grow. In Japanese, for instance, most text input methods involve entering characters in a phonetic alphabet, after which the input method searches a dictionary for possible ideographic equivalents (of which there may be many). The input method then presents the candidate characters for the user to choose from.

In Japanese, either Kana (phonetic symbols) or Roman letters are typed and then a region is selected for conversion to Kanji. Several Kanji characters may have the same phonetic representation. If that is the case with the string entered, a menu of characters is presented and the user must choose the appropriate one. If no choice is necessary or a preference has been established, the input method does the substitution directly.

These complicated input methods must present state information (Status Area), text entry and edit space (Preedit Area), and menu/choice presentations (Auxiliary Area). Much of the protocol between the IM library and the IM Server involves managing these IM areas. Because of the size and complexity of these input methods, and because of how widely they vary from one language or locale to another, they are usually implemented as separate processes which can serve many client processes on the same computer or network.

1.3. Input Method Styles

X11 internationalization support includes the following four types of input method:

Client applications must choose from the available input methods supported by the IM Server and provide the display areas and callbacks required by the input method.

2. Architecture

2.1. Implementation Model

Within the X Window System environment, the following two typical architectural models can be used as an input method’s implementation model.

- Client/Server model:
A separate process, the IM Server, processes input and handles preediting, converting, and committing. The IM library within the application, acting as client to the IM Server, simply receives the committed string from the IM Server.

Most languages which need complex preediting, such as Asian languages, are implemented using the Client/Server IM model. Other languages which need only dead key or compose key processing, such as European languages, are implemented using the Library model.

In this paper, we discuss mainly the Client/Server IM model and the protocol used in communication between the IM library (client) and the IM Server.

2.2. Structure of IM

When the client connects or disconnects to the IM Server, an open or close operation occurs between the client and the IM Server.

The IM can be specified at the time of XOpenIM() by setting the locale of the client and a locale modifier. Since the IM remembers the locale at the time of creation XOpenIM() can be called multiple times (with the setting for the locale and the locale modifier changed) to support multiple languages.

In addition, the supported IM type can be obtained using XGetIMValues().

The client usually holds multiple input (text) fields. Xlib provides a value type called the ‘‘Input Context’’ (IC) to manage each individual input field. An IC can be created by specifying XIM using XCreateIC(), and it can be destroyed using XDestroyIC().

The IC can specify the type of IM which is supported by XIM for each input field, so each input field can handle a different type of IM.

Most importantly information such as the committed string sent from the IM Server to the client, is exchanged based on each IC.

Since each IC corresponds to an input field, the focused input field should be announced to the IM Server using XSetICFocus(). (XUnsetICFocus() can also be used to change the focus.)

2.3. Event Handling Model

Existing input methods support either the FrontEnd method, the BackEnd method, or both. This protocol specifically supports the BackEnd method as the default method, but also supports the FrontEnd method as an optional IM Server extension.

The difference between the FrontEnd and BackEnd methods is in how events are delivered to the IM Server. (Fig. 1)

2.3.1. BackEnd Method

In the BackEnd method, client window input events are always delivered to the IM library, which then passes them to the IM Server. Events are handled serially in the order delivered, and therefore there is no synchronization problem between the IM library and the IM Server.

Using this method, the IM library forwards all KeyPress and KeyRelease events to the IM Server (as required by the Event Flow Control model described in section 2.4. ‘‘Event Flow Control’’), and synchronizes with the IM Server (as described in section 4.16. ‘‘Filtering Events’’).

2.3.2. FrontEnd Method

In the FrontEnd method, client window input events are delivered by the X server directly to both the IM Server and the IM library. Therefore this method provides much better interactive performance while preediting (particularly in cases such as when the IM Server is running locally on the user’s workstation and the client application is running on another workstation over a relatively slow network).

However, the FrontEnd model may have synchronization problems between the key events handled in the IM Server and other events handled in the client, and these problems could possibly cause the loss or duplication of key events. For this reason, the BackEnd method is the core method supported, and the FrontEnd method is made available as an extension for performance purposes. (Refer to Appendix A for more information.)

1

X Input Method Protocol libX11 1.3.1
... 0.05 6.513 4.737 10.45 ... 0.000i 3.937i 4.687i 0.000i │ │ │ │ │ │ │ _______ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │____________________ │ │ │____________________ │ │ │ _____________________ │ │ │_____________________ │ │ │ _____________ │ │ │ _____________ │ │ │ ____________________ │ │ │ │ │ │ │ │ │____________________ │ │ │ │ │ │ │ │ │
FrontEnd Method (Extension)
BackEnd Method (Core)
X Server
IM Server
Library
Application

Fig.1 The Flow of Events

2.4. Event Flow Control

This protocol supports two event flow models for communication between the IM library and the IM Server (Static and Dynamic).

Static Event Flow requires that input events always be sent to the IM Server from the client.

Dynamic Event Flow, however, requires only that those input events which need to be processed (converted) be sent to the IM Server from the client.

For instance, in the case of inputing a combination of ASCII characters and Chinese characters, ASCII characters do not need to be processed in the IM Server, so their key events do not have to be sent to the IM Server. On the other hand, key events necessary for composing Chinese characters must be sent to the IM Server.

Thus, by adopting the Dynamic Event Flow, the number of requests among the X Server, the client, and the IM Server is significantly reduced, and the number of context switches is also reduced, resulting in improved performance. The IM Server can send XIM_REGISTER_TRIGGERKEYS message in order to switch the event flow in the Dynamic Event Flow.

The protocol for this process is described in section 4.5. ‘‘Event Flow Control’’.

3. Default Preconnection Convention

IM Servers are strongly encouraged to register their symbolic names as the ATOM names into the IM Server directory property, XIM_SERVERS, on the root window of the screen_number 0. This property can contain a list of ATOMs, and the each ATOM represents each possible IM Server. IM Server names are restricted to POSIX Portable Filename Character Set. To discover if the IM Server is active, see if there is an owner for the selection with that atom name. To learn the address of that IM Server, convert the selection target TRANSPORT, which will return a string form of the transport address(es). To learn the supported locales of that IM Server, convert the selection target LOCALES, which will return a set of names of the supported locales in the syntax X/Open defines.

The basic semantics to determine the IM Server if there are multiple ATOMs are found in XIM_SERVERS property, is first fit if the IM Server name is not given as a X modifier’s category im.

The address information retrievable from the TRANSPORT target is a transport-specific name. The preregistered formats for transport-specific names are listed in Appendix B. Additional transport-specific names may be registered with X Consortium.

For environments that lack X connections, or for IM Servers which do not use the X Window System, the preconnection convention with IM Server may be given outside the X Window system (e.g. using a Name Service).

4. Protocol

The protocol described below uses the bi-directional synchronous/asynchronous request/reply/error model and is specified using the same conventions outlined in Section 2 of the core X Window System protocol [1]:

4.1. Basic Requests Packet Format

This section describes the requests that may be exchanged between the client and the IM Server.

The basic request packet header format is as follows.

major-opcode: CARD8

The MAJOR-OPCODE specifies which core request or extension package this packet represents. If the MAJOR-OPCODE corresponds to a core request, the MINOR-OPCODE contains 8 bits of request-specific data. (If the MINOR-OPCODE is not used, it is 0.) Otherwise, the MAJOR-OPCODE and the MINOR-OPCODE are specified by XIM_QUERY_EXTENSION message. (Refer to 4.7. Query the supported extension protocol list.) The LENGTH field specifies the number of 4 bytes elements following the header. If no additional data is followed by the header, the LENGTH field will be 0.

4.2. Data Types

The following data types are used in the core X IM Server protocol:

BITMASK16

BITMASK32

PADDING FORMAT

LPCE

2

X Input Method Protocol libX11 1.3.1

The im-attribute argument specifies XIM values such as XNQueryInputStyle.

values data format
#0 Separator of NestedList ----- (*3)
#1 byte data CARD8
#2 word data CARD16
#3 long data CARD32
#4 char data STRING8
#5 Window CARD32
#10 XIMStyles 2 n number of XIMStyle list
2 unused
n CARD32 XIMStyle list
#11 XRectangle 2 INT16 X
2 INT16 Y
2 CARD16 width
2 CARD16 height
#12 XPoint 2 INT16 X
2 INT16 Y
#13 XFontSet 2 n length of Base font name
n STRING8 Base font name list
p unused, p = Pad(2+n)
#15 XIMHotKeyTriggers 4 n
number of XIMTRIGGERKEY
list (*4)
n XIMTRIGGERKEY XIMHotkeyTrigger list
#16 XIMHotKeyState XIMHOTKEYSTATE
HotKey processing state
#17 XIMStringConversion XIMSTRCONVTEXT
#18 XIMPreeditState XIMPREEDITSTATE
#19 XIMResetState XIMRESETSTATE

, which is registered in X Consortium and cannot be used for any other purpose.

A Type name of the form LISTof FOO means a counted list of elements of type FOO. The size of the length field may vary (it is not necessarily the same size as a FOO), and in some cases, it may be implicit.

XIMTRIGGERKEY

ENCODINGINFO

EXT

XIMATTRIBUTE

XICATTRIBUTE

3

X Input Method Protocol libX11 1.3.1

XIMFEEDBACK

XIMHOTKEYSTATE

XIMPREEDITSTATE

XIMRESETSTATE

4.3. Error Notification

Both the IM Server and the IM library return XIM_ERROR messages instead of the corresponding reply messages if any errors occur during data processing.

At most one error is generated per request. If more than one error condition is encountered in processing a request, the choice of which error is returned is implementation-dependent.

XIM_ERROR (IM Server ←→ IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 BITMASK16 flag (*1)
#0000 Both Input-Method-ID and Input-Context-ID are invalid
#0001 Input-Method-ID is valid
#0002 Input-Context-ID is valid
2 CARD16 Error Code
#1 BadAlloc
#2 BadStyle
#3 BadClientWindow
#4 BadFocusWindow
#5 BadArea
#6 BadSpotLocation
#7 BadColormap
#8 BadAtom
#9 BadPixel
#10 BadPixmap
#11 BadName
#12 BadCursor
#13 BadProtocol
#14 BadForeground
#15 BadBackground
#16 LocaleNotSupported
#999 BadSomething (*2)
2 n byte length of error detail.
2 CARD16 type of error detail (*3)
n STRING8 error detail (*4)
p unused, p = Pad(n)

4.4. Connection Establishment

XIM_CONNECT message requests to establish a connection over a mutually-understood virtual stream.

XIM_CONNECT (IM library → IM Server)
1 byte order
#x42 MSB first
#x6c LSB first
1 unused
2 CARD16 client-major-protocol-version (*1)
2 CARD16 client-minor-protocol-version (*1)
2 CARD16 number of client-auth-protocol-names
n LISTofSTRING client-auth-protocol-names

A client must send XIM_CONNECT message as the first message on the connection. The list specifies the names of authentication protocols the sending IM Server is willing to perform. (If the client need not authenticate, the list may be omited.)

XIM_AUTH_REQUIRED message is used to send the authentication protocol name and protocol-specific data.

XIM_AUTH_REQUIRED (IM library ←→ IM Server)
1 CARD8 auth-protocol-index
3 unused
2 n length of authentication data
2 unused
n <varies> data
p unused, p = Pad(n)

The auth-protocol is specified by an index into the list of names given in the XIM_CONNECT or XIM_AUTH_SETUP message. Any protocol-specific data that might be required is also sent.

The IM library sends XIM_AUTH_REPLY message as the reply to XIM_AUTH_REQUIRED message, if the IM Server is authenticated.

XIM_AUTH_REPLY (IM library → IM Server)
2 n length of authentication data
2 unused
2 n length of authentication data
2 unused
n <varies> data
p unused, p = Pad(n)

The auth data is specific to the authentication protocol in use.

XIM_AUTH_NEXT message requests to send more auth data.

XIM_AUTH_NEXT (IM library ←→ IM Server)
2 n length of authentication data
2 unused
n <varies> data
p unused, p = Pad(n)

The auth data is specific to the authentication protocol in use.

The IM Server sends XIM_AUTH_SETUP message to authenticate the client.

XIM_AUTH_SETUP (IM Server → IM library)
2 CARD16 number of client-auth-protocol-names
2 unused
n LISTofSTRING server-auth-protocol-names

The list specifies the names of authentication protocols the client is willing to perform.

XIM_AUTH_NG message requests to give up the connection.

XIM_AUTH_NG (IM library ←→ IM Server)

The IM Server sends XIM_CONNECT_REPLY message as the reply to XIM_CONNECT or XIM_AUTH_REQUIRED message.

XIM_CONNECT_REPLY (IM Server → IM library)
2 CARD16 server-major-protocol-version (*1)
2 CARD16 server-minor-protocol-version (*1)

Here are the state diagrams for the client and the IM Server.

State transitions for the client

init_status:

Use authorization function → client_ask
Not use authorization function → client_no_check

start:

Send XIM_CONNECT

If client_ask → client_wait1
If client_no_check, client-auth-protocol-names may be omited → client_wait2

client_wait1:

Receive XIM_AUTH_REQUIRED → client_check
Receive <other> → client_NG

client_check:

If no more auth needed, send XIM_AUTH_REPLY → client_wait2
If good auth data, send XIM_AUTH_NEXT → client_wait1
If bad auth data, send XIM_AUTH_NG → give up on this protocol

client_wait2:

Receive XIM_CONNECT_REPLY → connect
Receive XIM_AUTH_SETUP → client_more
Receive XIM_AUTH_NEXT → client_more
Receive XIM_AUTH_NG → give up on this protocol
Receive <other> → client_NG

client_more:

Send XIM_AUTH_REQUIRED → client_wait2

client_NG:

Send XIM_AUTH_NG → give up on this protocol

State transitions for the IM Server

init-status:

Use authorization function → server_ask
Not use authorization function → server_no_check

start:

Receive XIM_CONNECT → start2
Receive <other> → server_NG

start2:

If client_ask, send XIM_AUTH_REQUIRED → server_wait1
If client_no_check and server_ask, send XIM_AUTH_SETUP → server_wait2
If client_no_check and server_no_check, send XIM_CONNECT_REPLY → connect

server_wait1:

Receive XIM_AUTH_REPLY → server2
Receive XIM_AUTH_NEXT → server_more
Receive <other> → server_NG

server_more

Send XIM_AUTH_REQUIRED → server_wait1

server2

If server_ask, send XIM_AUTH_SETUP → server_wait2
If server_no_check, send XIM_CONNECT_REPLY → connect

server_wait2

Receive XIM_AUTH_REQUIRED → server_check
Receive <other> → server_NG

server_check

If no more auth data, send XIM_CONNECT_REPLY → connect
If bad auth data, send XIM_AUTH_NG → give up on this protocol
If good auth data, send XIM_AUTH_NEXT → server_wait2

server_NG

Send XIM_AUTH_NG → give up on this protocol

XIM_DISCONNECT message requests to shutdown the connection over a mutually-understood virtual stream.

XIM_DISCONNECT (IM library → IM Server)

XIM_DISCONNECT is a synchronous request. The IM library should wait until it receives either an XIM_DISCONNECT_REPLY packet or an XIM_ERROR packet.

XIM_DISCONNECT_REPLY (IM Server → IM library)

XIM_OPEN requests to establish a logical connection between the IM library and the IM Server.

XIM_OPEN (IM library → IM Server)
n STR locale name
p unused, p = Pad(n)

XIM_OPEN is a synchronous request. The IM library should wait until receiving either an XIM_OPEN_REPLY packet or an XIM_ERROR packet.

XIM_OPEN_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 n byte length of IM attributes supported
n LISTofXIMATTR IM attributes supported
2 m byte length of IC attributes supported
2 CARD16 unused
m LISTofXICATTR IC attributes supported

XIM_OPEN_REPLY message returns all supported IM and IC attributes in LISTofXIMATTR and LISTofXICATTR. These IM and IC attribute IDs are used to reduce the amount of data which must be transferred via the network. In addition, this indicates to the IM library what kinds of IM/IC attributes can be used in this session, and what types of data will be exchanged. This allows the IM Server provider and application writer to support IM system enhancements with new IM/IC attributes, without modifying Xlib. The IC value for the separator of NestedList must be included in the LISTofXICATTR.

XIM_CLOSE message requests to shutdown the logical connection between the IM library and the IM Server.

XIM_CLOSE (IM library → IM Server)
2 CARD16 input-method-ID
2 unused

XIM_CLOSE is a synchronous request. The IM library should wait until receiving either an XIM_CLOSE_REPLY packet or an XIM_ERROR packet.

XIM_CLOSE_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 unused

4.5. Event Flow Control

An IM Server must send XIM_SET_EVENT_MASK message to the IM library in order for events to be forwarded to the IM Server, since the IM library initially doesn’t forward any events to the IM Server. In the protocol, the IM Server will specify masks of X events to be forwarded and which need to be synchronized by the IM library.

XIM_SET_EVENT_MASK (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 EVENTMASK forward-event-mask (*1)
4 EVENTMASK synchronous-event-mask (*2)

XIM_SET_EVENT_MASK is an asynchronous request. The event masks are valid immediately after they are set until changed by another XIM_SET_EVENT_MASK message. If input-context-ID is set to zero, the default value of the input-method-ID will be changed to the event masks specified in the request. That value will be used for the IC’s which have no individual values.

Using the Dynamic Event Flow model, an IM Server sends XIM_REGISTER_TRIGGERKEYS message to the IM library before sending XIM_OPEN_REPLY message. Or the IM library may suppose that the IM Server uses the Static Event Flow model.

XIM_REGISTER_TRIGGERKEYS (IM Server → IM library)
2 CARD16 input-method-ID
2 unused
4 n byte length of on-keys
n LISTofXIMTRIGGERKEY on-keys list
4 m byte length of off-keys
m LISTofXIMTRIGGERKEY off-keys list

XIM_REGISTER_TRIGGERKEYS is an asynchronous request. The IM Server notifys the IM library of on-keys and off-keys lists with this message.

The IM library notifys the IM Server with XIM_TRIGGER_NOTIFY message that a key event matching either on-keys or off-keys has been occurred.

XIM_TRIGGER_NOTIFY (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 CARD32 flag
#0 on-keys list
#1 off-keys list
4 CARD32 index of keys list
4 EVENTMASK client-select-event-mask (*1)

XIM_TRIGGER_NOTIFY is a synchronous request. The IM library should wait until receiving either an XIM_TRIGGER_NOTIFY_REPLY packet or an XIM_ERROR packet.

XIM_TRIGGER_NOTIFY_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

4.6. Encoding Negotiation

XIM_ENCODING_NEGOTIATION message requests to decide which encoding to be sent across the wire. When the negotiation fails, the fallback default encoding is Portable Character Encoding.

XIM_ENCODING_NEGOTIATION (IM library → IM Server).sp 6p
2 CARD16 input-method-ID
2 n byte length of encodings listed by name
n LISTofSTR list of encodings supported in the IM library.
p unused, p = Pad(n)
2 m byte length of encodings listed by detailed data
2 unused
m LISTofENCODINGINFO list of encordings supported in the IM library

The IM Server must choose one encoding from the list sent by the IM library. If index of the encording determined is -1 to indicate that the negotiation is failed, the fallback default encoding is used. The message must be issued after sending XIM_OPEN message via XOpenIM(). The name of encoding may be registered with X Consortium.

XIM_ENCODING_NEGOTIATION is a synchronous request. The IM library should wait until receiving either an XIM_ENCODING_NEGOTIATION_REPLY packet or an XIM_ERROR packet.

XIM_ENCODING_NEGOTIATION_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 category of the encoding determined.
#0 name
#1 detailed data
2 INT16 index of the encoding determinated.
2 unused

4.7. Query the supported extension protocol list

XIM_QUERY_EXTENSION message requests to query the IM extensions supported by the IM Server to which the client is being connected.

XIM_QUERY_EXTENSION (IM library → IM Server)
2 CARD16 input-method-ID
2 n
byte length of extensions supported by
the IM library
n LISTofSTR extensions supported by the IM library
p unused, p = Pad(n)

An example of a supported extension is FrontEnd. The message must be issued after sending XIM_OPEN message via XOpenIM().

If n is 0, the IM library queries the IM Server for all extensions.

If n is not 0, the IM library queries whether the IM Server supports the contents specified in the list.

If a client uses an extension request without previously having issued a XIM_QUERY_EXTENSION message for that extension, the IM Server responds with a BadProtocol error. If the IM Server encounters a request with an unknown MAJOR-OPCODE or MINOR-OPCODE, it responds with a BadProtocol error.

XIM_QUERY_EXTENSION is a synchronous request. The IM library should wait until receiving either an XIM_QUERY_EXTENSION_REPLY packet or an XIM_ERROR packet.

XIM_QUERY_EXTENSION_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 n
byte length of extensions supported
by both the IM library and the IM
Server
n LISTofEXT
list of extensions supported by
both the IM library and the IM
Server

XIM_QUERY_EXTENSION_REPLY message returns the list of extensions supported by both the IM library and the IM Server. If the list passed in XIM_QUERY_EXTENSION message is NULL, the IM Server returns the full list of extensions supported by the IM Server. If the list is not NULL, the IM Server returns the extensions in the list that are supported by the IM Server.

A zero-length string is not a valid extension name. The IM library should disregard any zero-length strings that are returned in the extension list. The IM library does not use the requests which are not supported by the IM Server.

4.8. Setting IM Values

XIM_SET_IM_VALUES requests to set attributes to the IM.

XIM_SET_IM_VALUES (IM library → IM Server)
2 CARD16 input-method-ID
2 n byte length of im-attribute
n LISTofXIMATTRIBUTE im-attributes

The im-attributes in XIM_SET_IM_VALUES message are specified as a LISTofXIMATTRIBUTE, specifying the attributes to be set. Attributes other than the ones returned by XIM_OPEN_REPLY message should not be specified.

XIM_SET_IM_VALUES is a synchronous request. The IM library should wait until receiving either an XIM_SET_IM_VALUES_REPLY packet or an XIM_ERROR packet, because it must receive the error attribute if XIM_ERROR message is returned.

XIM_SET_IM_VALUES_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 unused

XIM_SET_IM_VALUES_REPLY message returns the input-method-ID to distinguish replies from multiple IMs.

4.9. Getting IM Values

XIM_GET_IM_VALUES requests to query IM values supported by the IM Server currently being connected.

XIM_GET_IM_VALUES (IM library → IM Server)
2 CARD16 input-method-ID
2 n byte length of im-attribute-id
n LISTofCARD16 im-attribute-id
p unused, p=Pad(n)

XIM_GET_IM_VALUES is a synchronous request. The IM library should wait until it receives either an XIM_GET_IM_VALUES_REPLY packet or an XIM_ERROR packet.

XIM_GET_IM_VALUES_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 n byte length of im-attributes returned
n LISTofXIMATTRIBUTE im-attributes returned

The IM Server returns IM values with XIM_GET_IM_VALUES_REPLY message. The order of the returned im-attribute values corresponds directly to that of the list passed with the XIM_GET_IM_VALUES message.

4.10. Creating an IC

XIM_CREATE_IC message requests to create an IC.

XIM_CREATE_IC (IM library → IM Server)
2 CARD16 input-method-ID
2 n byte length of ic-attributes
n LISTofXICATTRIBUTE ic-attributes

The input-context-id is specified by the IM Server to identify the client (IC). (It is not specified by the client in XIM_CREATE_IC message.), and it should not be set to zero.

XIM_CREATE_IC is a synchronous request which returns the input-context-ID. The IM library should wait until it receives either an XIM_CREATE_IC_REPLY packet or an XIM_ERROR packet.

XIM_CREATE_IC_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

4.11. Destroying the IC

XIM_DESTROY_IC message requests to destroy the IC.

XIM_DESTROY_IC (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

XIM_DESTROY_IC is a synchronous request. The IM library should not free its resources until it receives an XIM_DESTROY_IC_REPLY message because XIM_DESTROY_IC message may result in Callback packets such as XIM_PREEDIT_DRAW and XIM_PREEDIT_DONE.

XIM_DESTROY_IC_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

4.12. Setting IC Values

XIM_SET_IC_VALUES messages requests to set attributes to the IC.

XIM_SET_IC_VALUES (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 n byte length of ic-attributes
2 unused
n LISTofXICATTRIBUTE ic-attributes

The ic-attributes in XIM_SET_IC_VALUES message are specified as a LISTofXICATTRIBUTE, specifying the attributes to be set. Attributes other than the ones returned by XIM_OPEN_REPLY message should not be specified.

XIM_SET_IC_VALUES is a synchronous request. The IM library should wait until receiving either an XIM_SET_IC_VALUES_REPLY packet or an XIM_ERROR packet, because it must receive the error attribute if XIM_ERROR message is returned.

XIM_SET_IC_VALUES_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

4.13. Getting IC Values

XIM_GET_IC_VALUES message requests to query IC values supported by the IM Server currently being connected.

XIM_GET_IC_VALUES (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 n byte length of ic-attribute-id
n LISTofCARD16 ic-attribute-id
p unused, p=Pad(2+n)

In LISTofCARD16, the appearance of the ic-attribute-id for the separator of NestedList shows the end of the heading nested list.

XIM_GET_IC_VALUES is a synchronous request and returns each attribute with its values to show the correspondence. The IM library should wait until receiving either an XIM_GET_IC_VALUES_REPLY packet or an XIM_ERROR packet.

XIM_GET_IC_VALUES_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 n byte length of ic-attribute
2 unused
n LISTofXICATTRIBUTE ic-attribute

4.14. Setting IC Focus

XIM_SET_IC_FOCUS message requests to set the focus to the IC.

XIM_SET_IC_FOCUS (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

XIM_SET_IC_FOCUS is an asynchronous request.

4.15. Unsetting IC Focus

XIM_UNSET_IC_FOCUS message requests to unset the focus to the focused IC.

XIM_UNSET_IC_FOCUS (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

XIM_UNSET_IC_FOCUS is an asynchronous request.

4.16. Filtering Events

Event filtering is mainly provided for BackEnd method to allow input method to capture X events transparently to clients.

X Events are forwarded by XIM_FORWARD_EVENT message. This message can be operated both synchronously and asynchronously. If the requester sets the synchronous flag, the receiver must send XIM_SYNC_REPLY message back to the requester when all the data processing is done.

Protocol flow of BackEnd model

With BackEnd method, the protocol flow can be classified into two methods in terms of synchronization, depending on the synchronous-eventmask of XIM_SET_EVENT_MASK message. One can be called on-demand-synchronous method and another can be called as full-synchronous method.

In on-demand-synchronous method, the IM library always receives XIM_FORWARD_EVENT or XIM_COMMIT message as a synchronous request. Also, the IM Server needs to synchronously process the correspondent reply from the IM library and the following XIM_FORWARD_EVENT message sent from the IM library when any of the event causes the IM Server to send XIM_FORWARD_EVENT or XIM_COMMIT message to the IM library, so that the input service is consistent. If the IM library gets the control back from the application after receiving the synchronous request, the IM library replies for the synchronous request before processing any of the events. In this time, the IM Server blocks XIM_FORWARD_EVENT message which is sent by the IM library, and handles it after receiving the reply. However, the IM Server handles the other protocols at any time.

In full-synchronous method, the IM library always sends XIM_FORWARD_EVENT message to the IM Server as a synchronous request. Therefore, the reply to it from the IM Server will be put between the XIM_FORWARD_EVENT message and its XIM_SYNC_REPLY message. In case of sending XIM_FORWARD_EVENT or XIM_COMMIT message, the IM Server should set the synchronous flag off. Because the synchronization can be done by the following XIM_SYNC_REPLY message.

Sample Protocol flow chart 1

Following chart shows one of the simplest protocol flow which only deals with keyevents for preediting operation.

... 0.425 6.888 6.3 10.296 ... 0.000i 3.408i 5.875i 0.000i _____ ____ ____ ___ │ │ │ │ │ │ │ │ │ │ │ │ _________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________________ _________________
XNextEvent
XFilterEvent
XNextEvent
XFilterEvent
XNextEvent
XmbLookupString
IM Server
IM library
XFilterEvent (returns False)
the focus
Xlib API
Application moves
XIM_FORWARD_EVENT
XIM_FORWARD_EVENT
XIM_FORWARD_EVENT
or XIM_COMMIT
synchronous
request
Key event
Key event
(synchronous)
Pending
processed
(The focused
IC is changed)
processed
XSetICFocus
XIM_SYNC_REPLY as a reply
of the XIM_FORWARD_EVENT
XNextEvent
XIM_SET_IC_FOCUS
XIM_SYNC
XIM_SYNC_REPLY
processed

Fig.2 Sample Protocol Flow

Sample Protocol flow chart 2

Following chart shows one of the complex protocol flow, which deals with multiple focus windows and button press event as well as keyevent, and the focus is moved by the application triggered by both of keyevent and button press event.

4

X Input Method Protocol libX11 1.3.1
... 0.425 5.575 6.3 10.296 ... 0.000i 4.721i 5.875i 0.000i ____
XNextEvent
XFilterEvent
XIM_FORWARD_EVENT
Key event ____ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ ___ _____ ___ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________ ____ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │
XNextEvent
XFilterEvent
IM Server
IM library
Xlib API
XIM_FORWARD_EVENT
synchronous
request
Key event
(synchronous)
Button press causes
focus change
XSetICFocus
or XIM_COMMIT
XIM_FORWARD_EVENT
XIM_SYNC
XIM_SYNC_REPLY
XNextEvent
XmbLookupString
XFilterEvent (returns False)
the focus
Application moves
processed
(The focused
IC is changed)
processed
XIM_SYNC_REPLY as a reply
of the XIM_FORWARD_EVENT
XNextEvent
processed
Pending
processed
XSetICFocus
is started by XIM_COMMIT
XIM_SET_IC_FOCUS is
pend because another sync cycle
sync cycle is done
Pending until
Key event
XFilterEvent
XIM_FORWARD_EVENT
XIM_SET_IC_FOCUS
XIM_SET_IC_FOCUS

Fig.3 Sample Protocol Flow chart

XIM_FORWARD_EVENT (IM library ←→ IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 BITMASK16 flag
#0001 synchronous
#0002 request filtering (*1)
#0004 request lookupstring (*2)
2 CARD16 serial number
XEVENT X event

(*1) Indicate the receiver should filter events and possible preedit may be invoked.

(*2) Indicate the receiver should only do lookup string. The IM Server is expected to just do a conversion of the key event to the best candidate. This bit may affect the state of the preedit state (e.g. compose of dead key sequences).

XEVENT format is same as the X Protocol event format(xEvent). As the value of xEvent’s sequenceNumber is the bottom of 16 bit of XEvent’s xany.serial, the top of 16 bit is sent by serial number(INT16).

XIM_FORWARD_EVENT message is used for forwarding the events from the IM library to the IM Server in order for IM to be able to filter the event. On the other hand, this message is also used for forwarding the events from the IM Server to the IM library if the event forwarded from the IM library is not filtered. The IM Server, which receives XIM_FORWARD_EVENT message without synchronous bit, should set synchronous bit. If both ‘‘request event filtering’’ and ‘‘request lookupstring’’ flag are set, then both filtering and lookup should be done for the same event.

4.17. Synchronizing with the IM Server

XIM_SYNC message requests to synchronize the IM library and the IM Server.

XIM_SYNC (IM library ←→ IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

This synchronization can be started either on the IM library side or on the IM Server side. The side which receives XIM_SYNC message should process all XIM requests before replying. The input-context-ID is necessary to distinguish the IC with which the IM library and the IM Server are synchronized.

XIM_SYNC_REPLY (IM Server ←→ IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

The side which receives XIM_FORWARD_EVENT, XIM_COMMIT or any other message with synchronous bit, should process all XIM request before replying, and send XIM_SYNC_REPLY message as the reply to the previous message.

4.18. Sending a committed string

When the IM Server commits a string, the IM Server sends either the committed string or list of KeySym, or both, by XIM_COMMIT message.

XIM_COMMIT (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 BITMASK16 flag
#0001 synchronous
#0002 XLookupChars
#0004 XLookupKeySym
#0006 XLookupBoth = XLookupChars | XLookupKeySym

If flag is XLookupKeySym, the arguments continue as follows:
2 unused
4 KEYSYM KeySym

If flag is XLookupChars, the arguments continue as follows:
2 m byte length of committed string
m LISTofBYTE committed string
p unused, p = Pad(m)

If flag is XLookupBoth, the arguments continue as follows:
2 unused
4 KEYSYM KeySym
2 n byte length of committed string
n LISTofBYTE committed string
p unused, p = Pad(2+n)

The IM Server which receives XIM_COMMIT message without synchronous bit should set synchronous bit.

4.19. Reset IC

XIM_RESET_IC message requests to reset the status of IC in the IM Server.

XIM_RESET_IC (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

XIM_RESET_IC is a synchronous request. The IM library should wait until receiving either an XIM_RESET_IC_REPLY packet or an XIM_ERROR packet.

XIM_RESET_IC_REPLY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 n byte length of preedit string
n LISTofBYTE preedit string
p unused, p = Pad(2+n)

XIM_RESET_IC_REPLY message returns the input-context-ID to distinguish replies from multiple ICs.

4.20. Callbacks

If XIMStyle has XIMPreeditArea or XIMStatusArea set, XIMGeometryCallback may be used, and if XIMPreeditCallback and/or XIMStatusCallback are set, corresponding callbacks may be used.

Any callback request may be sent from an IM Server to an IM client asynchronously in response to any request previously sent by the IM client to the IM Server.

When an IM Server needs to send a callback request synchronously with the request previously sent by an IM client, the IM Server sends it before replying to the previous request.

4.20.1. Negotiating geometry

The IM Server sends XIM_GEOMETRY message to start geometry negotiation, if XIMStyle has XIMPreeditArea or XIMStatusArea set.

XIM_GEOMETRY (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

There is always a single Focus Window, even if some input fields have only one IC.

4.20.2. Converting a string

XIM_STR_CONVERSION (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 CARD16 XIMStringConversionPosition
2 unused
4 CARD32 XIMCaretDirection
#0 XIMForwardChar
#1 XIMBackwardChar
#2 XIMForwardWord
#3 XIMBackwardWord
#4 XIMCaretUp
#5 XIMCaretDown
#6 XIMNextLine
#7 XIMCPreviousLine
#8 XIMLineStart
#9 XIMLineEnd
#10 XIMAbsolutePosition
#11 XIMDontChange
2 CARD16 factor
2 CARD16 XIMStringConversionOperation
#0001 XIMStringConversionSubstitution
#0002 XIMStringConversionRetrieval
2 INT16
byte length to multiply the
XIMStringConversionType

XIM_STR_CONVERSION message may be used to start the string conversion from the IM Server.

XIM_STR_CONVERSION_REPLY (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 CARD32 XIMStringConversionFeedback
XIMSTRCONVTEXT XIMStringConversionText

XIM_STR_CONVERSION_REPLY message returns the string to be converted and the feedback information array.

4.20.3. Preedit Callbacks

The IM Server sends XIM_PREEDIT_START message to call the XIMPreeditStartCallback function.

XIM_PREEDIT_START (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

The reply to this message must be sent synchronously. The reply forwards the return value from the callback function to the IM Server.

XIM_PREEDIT_START_REPLY (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 INT32 return value

XIM_PREEDIT_START_REPLY message returns the input-context-ID to distinguish replies from multiple IC’s. The return value contains the return value of the function XIMPreeditStartCallback.

The IM Server sends XIM_PREEDIT_DRAW message to call the XIMPreeditDrawCallback function.

XIM_PREEDIT_DRAW (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 INT32 caret
4 INT32 chg_first
4 INT32 chg_length
4 BITMASK32 status
#x0000001 no string
#x0000002 no feedback
2 n length of preedit string
n STRING8 preedit string
p unused, p = Pad(2+n)
2 m byte length of feedback array
2 unused
m LISTofXIMFEEDBACK feedback array

The fields ‘‘caret’’, ‘‘chg_first’’ and ‘‘chg_length’’ correspond to the fields of XIMPreeditDrawCallbackStruct. When the ‘‘no string’’ bit of the status field is set, the text field of XIMPreeditDrawCallbackStruct is NULL. When the ‘‘no feedback’’ bit of the status field is set, the text feedback field of XIMPreeditDrawCallbackStruct is NULL. When the above bits are not set, ‘‘preedit string’’ contains the preedit string to be displayed, and the feedback array contains feedback information.

The IM Server sends XIM_PREEDIT_CARET message to call the PreeditCaretCallback function.

XIM_PREEDIT_CARET (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 INT32 position
4 CARD32 direction
#0 XIMForwardChar
#1 XIMBackwardChar
#2 XIMForwardWord
#3 XIMBackwardWord
#4 XIMCaretUp
#5 XIMCaretDown
#6 XIMNextLine
#7 XIMCPreviousLine
#8 XIMLineStart
#9 XIMLineEnd
#10 XIMAbsolutePosition
#11 XIMDontChange
4 CARD32 style
#0 XIMInvisible
#1 XIMCPrimary
#2 XIMSecondary

Each entry corresponds to a field of XIMPreeditCaretCallbackStruct. Since this callback sets the caret position, its reply must be sent synchronously.

XIM_PREEDIT_CARET_REPLY (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 CARD32 position

The position is the value returned by the callback function after it has been called.

The IM Server sends XIM_PREEDIT_DONE message to call the XIMPreeditDoneCallback function.

XIM_PREEDIT_DONE (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

4.20.4. Preedit state notify

XIM_PREEDITSTATE (IM Server → IM Library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 BITMASK32 XIMPreeditState
#x0000000 XIMPreeditUnknown
#x0000001 XIMPreeditEnable
#x0000002 XIMPreeditDisable

XIM_PREEDITSTATE message is used to call the XIMPreeditStateNotifyCallback function.

4.20.5. Status Callbacks

The IM Server sends XIM_STATUS_START message to call the XIMStatusStartCallback function.

XIM_STATUS_START (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

The IM Server sends XIM_STATUS_DRAW message to call the XIMStatusDrawCallback function.

XIM_STATUS_DRAW (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 CARD32 type
#0 XIMTextType
#1 XIMBitmapType

If type is XIMTextType, the arguments continue as follows.
4 BITMASK32 status
#x0000001 no string
#x0000002 no feedback
2 n length of status string
n STRING8 status string
p unused, p = Pad(2+n)
2 m byte length of feedback array
2 unused
m LISTofXIMFEEDBACK feedback array

If type is XIMBitmapType, the arguments continue as follows.
4 PIXMAP pixmap data

The field ‘‘type’’ corresponds to the field in XIMStatusDrawCallbackStruct.

The IM Server sends XIM_STATUS_DONE message to call the XIMStatusDoneCallback function.

XIM_STATUS_DONE (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID

5

X Input Method Protocol libX11 1.3.1
5. Acknowledgements

This document represents the culmination of several years of debate and experiments done under the auspices of the MIT X Consortium i18n working group. Although this was a group effort, the author remains responsible for any errors or omissions.

We would like to thank to all members of this group. And we would like to make special thanks to the following people (in alphabetical order) for their participation in the IM Protocol design, Hector Chan, Takashi Fujiwara, Yoshio Horiuchi, Makoto Inada, Hiromu Inukai, Mickael Kung, Seiji Kuwari, Franky Ling, Hiroyuki Machida, Hiroyuki Miyamoto, Frank Rojas, Bob Scheifler, Makiko Shimamura, Shoji Sugiyama, Hidetoshi Tajima, Masaki Takeuchi, Makoto Wakamatsu, Masaki Wakao, Nobuyuki Tanaka, Shigeru Yamada, Katsuhisa Yano, Jinsoo Yoon.

6. References

All of the following documents are X Consortium standards available from MIT:

[1] Scheifler, Robert W., ‘‘X Window System Protocol Version 11’’

[2] Scheifler, Robert W. etc., ‘‘Xlib − C Language X Interface’’

6

X Input Method Protocol libX11 1.3.1

Appendix A

Common Extensions

Extension opcodes and packet names (e.g. XIM_EXT_SET_EVENT_MASK ) for additional extensions may be registered with X Consortium. The following is a commonly well-known extended packet.

XIM_EXT_SET_EVENT_MASK message specifies the set of event masks that the IM library should manipulate.

XIM_EXT_SET_EVENT_MASK (IM Server → IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
4 EVENTMASK filter-event-mask (*1)
4 EVENTMASK intercept-event-mask (*2)
4 EVENTMASK select-event-mask (*3)
4 EVENTMASK forward-event-mask (*4)
4 EVENTMASK synchronous-event-mask (*5)

The IM library must reply XIM_SYNC_REPLY message to the IM Server. This request is valid after the ic is created.

The following requests may be used for improvement of performance.

XIM_EXT_FORWARD_KEYEVENT message may be used instead of XIM_FORWARD_EVENT message.

XIM_EXT_FORWARD_KEYEVENT (IM Server ←→ IM library)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 BITMASK16 flag
#0001 synchronous
2 CARD16 sequence number
1 BYTE xEvent.u.u.type
1 BYTE keycode
2 CARD16 state
4 CARD32 time
4 CARD32 window

7

X Input Method Protocol libX11 1.3.1
XIM_EXT_MOVE message may be used to change the spot location instead of XIM_SET_IC_VALUES message. It is effective only if the client specified XIMPreeditPosition.

XIM_EXT_MOVE (IM library → IM Server)
2 CARD16 input-method-ID
2 CARD16 input-context-ID
2 INT16 X
2 INT16 Y

XIM_EXT_MOVE message is a asynchronous request.

8

X Input Method Protocol libX11 1.3.1

Appendix B

The list of transport specific IM Server address format registered

The following format represents the ATOM contained in XIM_SERVERS property and the string returned from the request converting selection target LOCALES and TRANSPORT.

The following categories are currently registered.

server : IM Server name (used for XIM_SERVERS)
locale : XPG4 locale name (LOCALES)
transport : transport-specific name (TRANSPORT)

The preregistered formats for transport-specific names are as follows:

TCP/IP Names

The following syntax should be used for system internal domain names:

<local name> ::= ‘‘local/’’<hostname>‘‘:’’<pathname>

Where <pathname> is a path name of socket address.

IM Server’s name should be set to <pathname> to run multiple IM Server at the same time

The following syntax should be used for Internet domain names:

<TCP name> ::= ‘‘tcp/’’<hostname>‘‘:’’<ipportnumber>

where <hostname> is either symbolic (such as expo.lcs.mit.edu) or numeric decimal (such as 18.30.0.212). The <ipportnumber> is the port on which the IM Server is listening for connections. For example:

tcp/expo.lcs.mit.edu:8012
tcp/18.30.0.212:7890

DECnet Names

The following syntax should be used for DECnet names:

<DECnet name> ::= ‘‘decnet/’’<nodename>‘‘::IMSERVER$’’<objname>

where <nodename> is either symbolic (such as SRVNOD) or the numeric decimal form of the DECnet address (such as 44.70). The <objname> is normal, case-insensitive DECnet object name. For example:

DECNET/SRVNOD::IMSERVER$DEFAULT
decnet/44.70::IMSERVER$other

X Names

The following syntax should be used for X names:

<X name> ::= ‘‘X/’’

If a given category has multiple values, the value is evaluated in order of setting.

9

X Input Method Protocol libX11 1.3.1

Appendix C

Protocol number

Major Protocol number

XIM_CONNECT #001
XIM_CONNECT_REPLY #002
XIM_DISCONNECT #003
XIM_DISCONNECT_REPLY #004
XIM_AUTH_REQUIRED #010
XIM_AUTH_REPLY #011
XIM_AUTH_NEXT #012
XIM_AUTH_SETUP #013
XIM_AUTH_NG #014
XIM_ERROR #020
XIM_OPEN #030
XIM_OPEN_REPLY #031
XIM_CLOSE #032
XIM_CLOSE_REPLY #033
XIM_REGISTER_TRIGGERKEYS #034
XIM_TRIGGER_NOTIFY #035
XIM_TRIGGER_NOTIFY_REPLY #036
XIM_SET_EVENT_MASK #037
XIM_ENCODING_NEGOTIATION #038
XIM_ENCODING_NEGOTIATION_REPLY #039
XIM_QUERY_EXTENSION #040
XIM_QUERY_EXTENSION_REPLY #041
XIM_SET_IM_VALUES #042
XIM_SET_IM_VALUES_REPLY #043
XIM_GET_IM_VALUES #044
XIM_GET_IM_VALUES_REPLY #045
XIM_CREATE_IC #050
XIM_CREATE_IC_REPLY #051
XIM_DESTROY_IC #052
XIM_DESTROY_IC_REPLY #053
XIM_SET_IC_VALUES #054
XIM_SET_IC_VALUES_REPLY #055
XIM_GET_IC_VALUES #056
XIM_GET_IC_VALUES_REPLY #057
XIM_SET_IC_FOCUS #058
XIM_UNSET_IC_FOCUS #059
XIM_FORWARD_EVENT #060
XIM_SYNC #061
XIM_SYNC_REPLY #062
XIM_COMMIT #063
XIM_RESET_IC #064
XIM_RESET_IC_REPLY #065
XIM_GEOMETRY #070
XIM_STR_CONVERSION #071
XIM_STR_CONVERSION_REPLY #072
XIM_PREEDIT_START #073
XIM_PREEDIT_START_REPLY #074
XIM_PREEDIT_DRAW #075
XIM_PREEDIT_CARET #076
XIM_PREEDIT_CARET_REPLY #077
XIM_PREEDIT_DONE #078
XIM_STATUS_START #079
XIM_STATUS_DRAW #080
XIM_STATUS_DONE #081
XIM_PREEDITSTATE #082

(*) The IM Server’s extension protocol number should be more than #128.

10

X Input Method Protocol libX11 1.3.1

Appendix D

Implementation Tips

FrontEnd method is recognized as a performance acceleration by the trade off of the variety of the reliability.

In order to use the FrontEnd method, the IM library must query the IM Server to see if the FrontEnd extension is available. The query is made by using the XIM_QUERY_EXTENSION message. The IM Server may send XIM_EXT_SET_EVENT_MASK message with intercept-event-mask, forward-event-mask, and synchronous-event-mask values set after replying XIM_QUERY_EXTENSION_REPLY message.

FrontEnd method can be implemented in a couple of ways depending on how the IM Server utilize XIM_EXT_SET_EVENT_MASK message.

One approach is to update both of the input mask and the filter-event-mask depending on the preeidting state. The sample protocol sequence using the static event flow is as follows:

... 1.675 6.888 6.237 10.296 ... 0.000i 3.408i 4.562i 0.000i │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _______
IM Server
event mask is changed
to select the event
event mask is changed
to deselect the event
X events directly come
to the IM Server.
when preediting is turning off _________ _________________ _________________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________________
XIM_EXT_SET_EVENT_MASK
intercept-event-mask is set
XIM_EXT_SET_EVENT_MASK
select-event-mask is set
IM library
Keys in the on-key-list
event mask is changed
to select the event
to deselect the event
event mask is changed
XIM_FORWARD_EVENT

To pursuit a maximum performance regardless of the preediting mode, the IM Server may use the dynamic event flow with the following sample protocol sequence.

11

X Input Method Protocol libX11 1.3.1
... 1.675 6.888 6.237 10.296 ... 0.000i 3.408i 4.562i 0.000i │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _______
IM Server
event mask is changed
to select the event
event mask is changed
to deselect the event
X events directly come
to the IM Server.
when preediting is turning off _________ _________________ _________________ _________________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________________
XIM_TRIGGER_NOTIFY
XIM_TRIGGER_NOTIFY_REPLY
XIM_EXT_SET_EVENT_MASK
intercept-event-mask is set
XIM_EXT_SET_EVENT_MASK
select-event-mask is set
IM library
Keys in the on-key-list
event mask is changed
to select the event
to deselect the event
event mask is changed

This method can reduce the XIM protocol traffic dramatically by updating intercept-event-mask and select-event-mask accordingly. The tradeoff of this performance improvement is that the key events may be lost or disordered in some particular situation, such as when the user types the keyboard in following sequence really fast:

<preediting on key>‘‘some strings’’<preediting off key>‘‘another string’’

Since this method requires the input mask updates to the both the IM Server and Xlib when turning on and off the preediting, and there is a time lag till the requests take effect when two client issues the input mask updates simultaneously.

Another approach of the FrontEnd method is to update the filter-event-mask depending on the preediting state and not to update the input mask. The IM Server must register both of the preediting on key list and off key list by XIM_REGISTER_TRIGGERKEYS message. In this method, Both the IM Server and the IM client select the same events on the same client’s window, so that the events are delivered to both of the IM Server and the client. The preediting on and off states are expressed by whether the key events are filtered or not. The sample protocol sequence are as follows:

12

X Input Method Protocol libX11 1.3.1
<<Using static event flow>>

... 1.488 7.325 6.487 10.358 ... 0.000i 3.033i 4.999i 0.000i __________ __________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │
IM Server
the specified events
are being processed
the specified events
are being discarded
Keys in the off-key-list
Keys in the on-key-list_________ _________________│ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________________ _________ _________________
XIM_EXT_SET_EVENT_MASK
Keys in the on-key-list
filter-event-mask is set
the specified events
are being filtered
XIM_EXT_SET_EVENT_MASK
filter-event-mask is set
Keys in the off-key-list
IM library
the specified events
are being processed
XIM_FORWARD_EVENT

<<Using the dynamic event flow>>

... 1.488 7.325 6.487 10.358 ... 0.000i 3.033i 4.999i 0.000i __________ __________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │
IM Server
the specified events
are being processed
the specified events
are being discarded
Keys in the off-key-list
Keys in the on-key-list_________ _________________ _________________ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ _________________ _________ _________________
XIM_TRIGGER_NOTIFY
XIM_TRIGGER_NOTIFY_REPLY
XIM_EXT_SET_EVENT_MASK
Keys in the on-key-list
filter-event-mask is set
the specified events
are being filtered
XIM_EXT_SET_EVENT_MASK
filter-event-mask is set
Keys in the off-key-list
IM library
the specified events
are being processed

This method does not have the problem of the time lag when going across the preediting on and off mode, however, the amount of the performance acceleration is not as good as the method described above.

In general, the FrontEnd method requires some synchronization to some of the X protocols, such as the ChangeWindowAttribute protocol for the event mask change or the GrabKey protocol, since it relies on the X’s principal event dispatching mechanism. Any X protocol bindings do not consider the synchronization might cause some mis-synchronization between the IM clients and the IM Server.

13

X Input Method Protocol libX11 1.3.1

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 independent 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 communicate 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.

The interface layer and the transport layer make various communication channels usable such as X Protocol, TCP/IP, DECnet or STREAM. The following is a sample implementation for the transporter using the X connection. Refer to "xtrans" for the transporter using Socket 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 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".

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 D-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.

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X Input Method Protocol libX11 1.3.1

Table D-2; The ClientMessage sent by IM Server.

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)

The read/write method is decided by the combination of major/minor-transport-version, as follows:

Table D-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: