# Using ToolTalk Messaging

Some code fragments shown in this chapter are taken from a ToolTalk demo program called `broadcast`. See the directory `/usr/dt/examples/tt` for the source code, `Makefile` and `README` file.

## Telling Your Application about ToolTalk Functionality

Before your application can use the inter-operability functionality provided by the ToolTalk service and the Messaging Toolkit, it needs to know where the ToolTalk libraries and toolkit reside.

### Using the Messaging Toolkit and Including ToolTalk Commands

To use the ToolTalk service, an application calls ToolTalk functions from the ToolTalk application programming interface (API). The Messaging Toolkit provides higher-level functions than the ToolTalk API, such as functions to register with the ToolTalk service, to create message patterns, to send messages, to receive messages, and to examine message information. To modify your application to use the ToolTalk service and toolkit, you must include the following header files:

    #include <Tt/tt_c.h>    /* ToolTalk Header File */
    #include <Tt/tttk.h>    /* Messaging Toolkit Header File */

### Using the ToolTalk Library

The ToolTalk library is located in the directory:

    /usr/dt/lib

The library name is platform-dependent (for example, on Solaris it is named `libtt.so` and on HP-UX is its named `libtt.sl`).

## Before You Start Coding

Before you can incorporate the Messaging Toolkit functionality into your application, you need to determine the way that your tool will work with other tools. There are several basic questions you need to ask:

- How will these tools work together?

- What kinds of operations can these tools perform?

- What kinds of operations can these tools ask other tools to perform?

- What events will these tools generate that may interest other tools? (What types of messages will these tools want to send?)

- What events generated by other tools will be of interest to these tools? (What types of messages will these tools want to receive?)

To best answer these questions, you need to understand the difference between events and operations, and how the ToolTalk service handles messages regarding each of these.

### What Is the Difference Between an Event and an Operation?

An event is an announcement that something has happened. An event is simply a news bulletin. The sending process has no formal expectations as to whether any other process will hear about the event, or whether an action is taken as a consequence of the event. When a process uses the ToolTalk service to inform interested processes that an event has occurred, it sends a notice. Since the sending process does not expect a reply, an event cannot fail.

An operation is an inquiry or an action. The requesting process makes an inquiry or requests that an operation be performed. The requesting process expects a result to be returned and needs to be informed of the status of the inquiry or action. When a process uses the ToolTalk service to ask another tool to perform an operation, it sends a request. The ToolTalk service delivers the request to interested processes and informs the sending process of the status of the request.

#### Sending Notices

When your application sends a ToolTalk notice, it will not receive a reply or be informed about whether or not any tool pays attention to the notice. It is important to make the notice an impartial report of the event as it happens. For example, if your tool sends the Desktop Services message `Modified`, it may expect any listening tools to react in a given way. Your tool, however, should not care, and does not need to be informed about whether any or no other tool reacts to the message; it only wants to report the event, THE_USER_HAS_MADE_CHANGES_TO_THIS.

#### Sending Requests

When your application sends a ToolTalk request, it expects one tool to perform the indicated operation, or to answer the inquiry, and return a reply message. For example, if your tool sends the Desktop Services message `Get_Modified`, it should expect notification that the message was delivered and the action performed. The ToolTalk service guarantees that either a reply will be returned by the receiving process or the sender will be informed of the request's failure.

You can identify requests in three ways:

- By identifying the operations requested by your tool that can fail.

- By identifying the operations your tool can perform for other tools.

- By identifying the operations your tool will want other tools to perform.

A good method to use to identify these operations is to develop a scenario that outlines the order of events and operations that you expect your tool to perform and have performed.

### Developing a Scenario

A scenario outlines the order of the events and operations that a tool will expect to perform and to have performed. For example, the following scenario outlines the events a generic editor could expect to perform and to have performed:

1. User double-clicks on a document icon in the File Manager. The file opens in the editor, which is started by the system if one is not already running. (If another tool has modifications to the text pending for the document, the user is asked whether the other tool should save the text changes or revert to the last saved version of the document.)

2. User inserts text.

3. User saves the document. (If another tool has modifications pending for the document, the user is asked whether to modify the document.)

4. User exits the editor. (If text has unsaved changes, the user is asked whether to save or discard the changes before quitting the file.)

Once the scenario is done, you can answer your basic questions.

#### How Will the Tools Work Together?

- The File Manager requests that an editor open a document for editing.

- Each instance of the editor notifies other interested instances of changes it makes to the state of the document.

#### What Kinds of Operations Do the Tools Perform?

- Each instance of the editor can answer questions about itself and its state, such as “What is your status?”

- Each instance of the editor has the capability of performing operations such as:

  - Iconifying and de-iconifying

  - Raising to front and lowering to back

  - Editing a document

  - Displaying a document (read-only)

  - Quitting

#### What Kinds of Operations Can the Tools Ask Other Tools to Perform?

- The File Manager must request that the editor open a document for editing.

- An instance of the editor can ask another instance of the editor to save changes to the open document.

- An instance of the editor can ask another instance of the editor to revert to the last saved version of the open document.

#### What Events Will the Tools Generate that May Interest Other Tools?

- The document has been opened.

- The document has been modified.

- The document has been reverted to last saved version.

- The document has been saved.

- An instance of the editor has been exited.

#### What Events Generated by Other Tools Will Be of Interest to This Tool?

- The document has been opened.

- The document has been modified.

- The document has been reverted to last saved version.

- The document has been saved.

- An instance of the editor has been exited.

## Preparing Your Application for Communication

The ToolTalk service provides you with a complete set of functions for application integration. Using the functionality provided with the ToolTalk Messaging Toolkit, your applications can be made to “speak” to other applications that are ToolTalk-compliant. This section describes how to add the kinds of ToolTalk functions you need to include in your application so that it can communicate with other ToolTalk-aware applications that follow the same protocols.

### Creating a Ptype File

The ToolTalk types mechanism is designed to help the ToolTalk service route messages. When your tool declares a ptype (process type), the message patterns listed in it are automatically registered. The ToolTalk service then matches messages it receives to these registered patterns. These static message patterns remain in effect until the tool closes communication with the ToolTalk service.

The ToolTalk Types Database already has installed ptypes for tools bundled with this release. You can extract a list of the installed ptypes from the ToolTalk Types Database, as follows:

    % tt_type_comp -d user | system | network -P

The names of the ptypes are printed out in source format.

To generate a list of the installed ptypes including their signatures:

    % tt_type_comp -d user | system | network -p

For all other tools (that is, tools that are not included in this release), you need to first create a ptype file to define the ptype for your application, and then compile the ptype with the ToolTalk type compiler, `tt_type_comp`. To define a ptype, you need to include the following information in a file:

- A process-type identifier (`ptid`).

- An optional start string — The ToolTalk service executes this command, if necessary, to start a process running the program.

- Signatures — Describes the TT_PROCEDURE-addressed messages that the program wants to receive. Messages to be observed are described separately from messages to be handled.

To create a ptype file, you can use any text editor (such as `vi`, `emacs`, or `dtpad`).

After you have created a ptype file, you need to install the ptype by running the ToolTalk type compiler. On the command line, type:

    % tt_type_comp file_name.ptype

where file_name.ptype is the name of the ptype file.

#### Testing for Existing Ptypes in Current Session

The ToolTalk service provides the following function to test if a given ptype is already registered in the current session:

    tt_ptype_exists(const char *ptype_id)

where ptype_id is the identifier of the session to test for registration.

#### Merging a Compiled Ptype File into a Currently Running ttsession

The ToolTalk service provides the following function to merge a compiled ToolTalk type file into the currently running `ttsession`:

    tt_session_types_load (
                const char  *session,
                const char  *compile_types_file)

where session is the current default ToolTalk session and compiled_types_file is the name of the compiled ToolTalk types file. This function adds new types and replaces existing types of the same name; other existing types remain unchanged.

### Tasks Every ToolTalk-aware Application Needs to Perform

There are a number of tasks every ToolTalk-aware application needs to perform, including:

- Initializing the toolkit.

- Joining a ToolTalk session and registering patterns.

- Adding the ToolTalk service to its event loop.

This section provides examples of the ToolTalk code you need to include in your application so that it can perform these tasks.

#### Initializing the Toolkit

Your application needs to initialize and register with the initial ToolTalk session. To do so, it first needs to obtain a process identifier (procid). The following code fragment shows how to obtain a procid and how to initialize the toolkit.

    char *procid = ttdt_open(
                int        *tt_fd,
                const char *ptype_name,
                const char *vendor_name,
                const char *version,
                int        send_started)

Your application must call `ttdt_open` before any other ToolTalk calls are made; otherwise, errors may occur.

#### Joining the ToolTalk Session and Registering Message Patterns

Before your application can receive messages, it must join a ToolTalk session and register the message patterns that are to be matched. The ttdt_session_join function registers patterns and default callbacks for many standard desktop message interfaces.

    Tt_pattern *sess_patt = ttdt_session_join(
                const char        *session_id,
                Ttdt_contract_cb  cb,
                Widget            shell,
                void              *client_data,
                int               join)

Note that if an application has ptypes installed, it will normally call the function `ttmedia_ptype_declare` before calling `ttdt_session_join`.

#### Adding the ToolTalk Service to Event Loop

Your application also needs to add the ToolTalk service to its event loop. If the application is an Xt client, it would use `XtAppAddInput` as follows:

    XtAppAddInput (app_context,
                tt_fd(),
                (XtPointer) XtInputReadMask,
                tttk_Xt_input_handler,
                client_data)

### Tasks ToolTalk-aware Editor Applications Need to Perform

In addition to the duties described in the section “Tasks Every ToolTalk-aware Application Needs to Perform” in this chapter, ToolTalk-aware editor applications may also need to perform other tasks, including:

- Declaring a ptype.

- Writing a media load callback.

- Accepting a contract to handle a message.

- Replying when a request has been completed.

This section provides examples of the ToolTalk code you need to include in your editor application so that it can perform these additional tasks.

#### Declaring a Ptype

If an application has a ptype file that has been installed, the ptypes need to be associated with the application. The convenience function for declaring this association is ttmedia_ptype_declare:

    Tt_status status = ttmedia_ptype_declare(
                char                 *ptype_name,
                int                  base_opnum,
                Ttmedia_load_pat_cb  cb,
                void                 *client_data,
                int                  declare)

The callback `cb` is invoked when the application is asked to service a request supported by the ptype ptype_name.

#### Writing a Media Load Pattern Callback

Before coding an editor application to include any ToolTalk functions, you need to write a media load callback routine. This callback is invoked when another application responds to your application's `ttmedia_load` call.

#### Accepting a Contract to Handle a Message

When an application receives a message in its `ttmedia_ptype_declare` handler, it should call the following function to accept a contract to handle the request.

    Tt_pattern *desktop_patts = ttdt_message_accept (
                Tt_message        contract,
                Ttdt_contract_cb  cb,
                Widget            shell,
                void              *client_data,
                int               accept,
                int               send_status)

#### Replying When Request Is Completed

After your application has completed the operation requested (for example to edit a document), it must reply to the sending application. The following function can be used to do the reply and to return the edited contents of the text to the sender.

    Tt_message msg = ttmedia_load_reply (
                Tt_message           contract,
                const unsigned char  *new_contents,
                int                  new_length,
                int                  reply_and_destroy)

### Optional Tasks ToolTalk-aware Editor Applications Can Perform

In addition to the tasks described in the section “Tasks ToolTalk-aware Editor Applications Need to Perform” in this chapter, editor applications can also perform other optional tasks such as tasks that use desktop file interfaces to coordinate with other editors. This section mentions some of the ToolTalk functions you need to include in your editor application so that it can perform these optional tasks.

#### Requesting Modify, Revert, or Save Operations

The following functions can be used to request modify, revert, or save operations:

- `ttdt_Get_Modified`

- `ttdt_Revert`

- `ttdt_Save`

#### Notifying When a File Is Modified, Reverted, or Saved

The function `ttdt_file_event` can be used to notify other ToolTalk applications that your application's file has been modified, has reverted, or has been saved.

#### Quitting a File

The function `ttdt_file_quit` unregisters interest in ToolTalk events about a file and destroys the associated pattern.