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Emacs Tooltalk API Summary

The Emacs Lisp interface to Tooltalk is similar, at least in spirit,
to the standard C Tootalk API.  Only the message and pattern parts
of the API are supported at present, more of the API could be added
if needed.  The Lisp interface departs from the C API in a few ways:

- Tooltalk is initialized automatically at emacs startup-time.  Messages
can only be sent other Tooltalk applications connected to the same
X11 server that emacs is running on.

- There are fewer entry points, polymorphic functions with keyword
arguments are used instead.

- The callback interface is simpler and marginally less functional.
A single callback may be associated with a message or a pattern,
the callback is specified with a Lisp symbol (the symbol should
have a function binding).

- The session attribute for messages and patterns is always
initialized to the default session.

- Anywhere a Tooltalk enum constant, e.g. TT_SESSION, is valid one
can substitute the corresponding symbol, e.g. 'TT_SESSION.  This
simplifies building lists that represent messages and patterns.


* Example: Receiving Messages

Here's a simple example of a handler for a message that tells
emacs to display a string in the mini-buffer area.  The message
operation is called "emacs-display-string", its first (0th) argument
is the string to display:

(defun tooltalk-display-string-handler (msg)
  (message (get-tooltalk-message-attribute msg 'arg_val 0)))

(defvar display-string-pattern
  '(category TT_HANDLE
       scope TT_SESSION
          op "emacs-display-string"
    callback tooltalk-display-string-handler))

(let ((p (make-tooltalk-pattern display-string-pattern)))
  (register-tooltalk-pattern p))


* Example: Sending Messages

Here's a simple example that sends a query to another application
and then displays its reply.  Both the query and the reply are
stored in the first argument of the message.

(defun tooltalk-random-query-handler (msg)
  (let ((state (get-tooltalk-message-attribute msg 'state)))
    (cond
      ((eq state 'TT_HANDLED)
       (message (get-tooltalk-message-attribute msg arg_val 0)))
      ((memq state '(TT_FAILED TT_REJECTED))
       (message "Random query turns up nothing")))))

(defvar random-query-message
  '(   class TT_REQUEST
       scope TT_SESSION
     address TT_PROCEDURE
          op "random-query"
        args '((TT_INOUT "?" "string"))
    callback tooltalk-random-query-handler))

(let ((m (make-tooltalk-message random-query-message)))
  (send-tooltalk-message m))


* Emacs Lisp Tooltalk API

** Sending Messages:

(make-tooltalk-message attributes)

Create a tooltalk message and initialize its attributes.
The value of attributes must be a list of alternating keyword/values,
where keywords are symbols that name valid message attributes.
For example:

  (make-tooltalk-message
    '(class TT_NOTICE
      scope TT_SESSION
      address TT_PROCEDURE
      op "do-something"
      args ("arg1" 12345 (TT_INOUT "arg3" "string"))))

Values must always be strings, integers, or symbols that
represent Tooltalk constants.  Attribute names are the same as
those supported by set-tooltalk-message-attribute, plus 'args.

The value of args should be a list of message arguments where
each message argument has the following form:

   (mode [value [type]]) or just value

Where mode is one of TT_IN, TT_OUT, TT_INOUT and type is a string.
If type isn't specified then "int" is used if the value is a
number otherwise "string" is used.  If type is "string" then value is
converted to a string (if it isn't a string already) with
prin1-to-string.  If only a value is specified then mode defaults
to TT_IN.  If mode is TT_OUT then value and type don't need
to be specified.  You can find out more about the semantics and
uses of ToolTalk message arguments in chapter 4 of the Tooltalk
Programmers Guide.


(send-tooltalk-message msg)

Send the message on its way.  Once the message has been sent it's
almost always a good idea to get rid of it with destroy-tooltalk-message.


(return-tooltalk-message msg &optional mode)

Send a reply to this message.  The second argument can be
'reply, 'reject or 'fail, the default is 'reply.  Before sending
a reply all message arguments whose mode is TT_INOUT or TT_OUT should
have been filled in - see set-tooltalk-message-attribute."


(get-tooltalk-message-attribute msg attribute &optional argn)

Returns the indicated Tooltalk message attribute.  Attributes are
identified by symbols with the same name (underscores and all) as the
suffix of the Tooltalk tt_message_<attribute> function that extracts the value.
String attribute values are copied, enumerated type values (except disposition)
are converted to symbols - e.g. TT_HANDLER is 'TT_HANDLER, uid and gid are
represented by fixnums (small integers), opnum is converted to a string,
and disposition is converted to a fixnum.  We convert opnum (a C int) to a
string, e.g. 123 => \"123\" because there's no guarantee that opnums will fit
within the range of Emacs Lisp integers.

[TBD] Use the 'plist attribute instead of C API 'user attribute
for user defined message data.  To retrieve the value of a message property
specify the indicator for argn.  For example to get the value of a property
called 'rflagg, use
   (get-tooltalk-message-attribute msg 'plist 'rflag)


To get the value of a message argument use one of the 'arg_val (strings),
'arg_ival (integers), or 'arg_bval (strings with embedded nulls), attributes.
Because integer valued arguments can be larger than Emacs Lisp integers
'arg_ival yields a string.  If the value is will fit within 24 bits then
convert it to an integer with string-to-int.  For example to get the integer
value of the third argument:

   (string-to-int (get-tooltalk-message-attribute msg 'arg_ival 2))

As you can see, argument numbers are zero based.  The type of each arguments
can be retrieved, with the 'arg_type attribute, however Tooltalk doesn't
define any semantics for the string value of 'arg_type.  Conventionally
"string" is used for strings and "int" for 32 bit integers.  Note that
Emacs Lisp stores the lengths of strings explicitly (unlike C) so treating the
value returned by 'arg_bval like a string is fine.


(set-tooltalk-message-attribute value msg attribute &optional argn)

Initialize one ToolTalk message attribute.

Attribue names and values are the same as for get-tooltalk-message-attribute.
A property list is provided for user data (instead of the 'user message
attribute), see get-tooltalk-message-attribute.

Callbacks are handled slightly differently than in the C Tooltalk API.
The value of callback should be the name of a function of one argument.
It will be called each time the state of the message changes.  This
is usually used to notice when the messages state has
changed to TT_HANDLED (or TT_FAILED), so that reply argument values
can be used.

If one of the argument attributes is specified, 'arg_val, 'arg_ival, or
'arg_bval then argn must be the number of an already created argument.
Arguments can be added to a message with add-tooltalk-message-arg.


(add-tooltalk-message-arg msg mode type &optional value)

Append one new argument to the message.  Mode must be one of: TT_IN,
TT_INOUT, or TT_OUT, type must be a string, and value can
be a string or an integer.   Tooltalk doesn't
define any semantics for type, so only the participants in the
protocol you're using need to agree what types mean (if anything).
Conventionally "string" is used for strings and "int" for 32 bit integers.
Arguments can initialized by providing a value or with
set-tooltalk-message-attribute, the latter is necessary if you
want to initialize the argument with a string that can contain
embedded nulls (use 'arg_bval).


(create-tooltalk-message)

Create a new tooltalk message.  The messages session attribute is
initialized to the default session.  Other attributes can be initialized
with set-tooltalk-message-attribute.  Make-tooltalk-message is the
preferred to create and initialize a message.


(destroy-tooltalk-message msg)

Apply tt_message_destroy to the message.  It's not necessary
to destroy messages after they've been processed by a message or
pattern callback, the Lisp/Tooltalk callback machinery does this
for you.


** Receiving Messages:


(make-tooltalk-pattern attributes)

Create a tooltalk pattern and initialize its attributes.
The value of attributes must be a list of alternating keyword/values,
where keywords are symbols that name valid pattern attributes
or lists of valid attributes.  For example:

  (make-tooltalk-pattern
    '(category TT_OBSERVE
         scope TT_SESSION
            op ("operation1" "operation2")
          args ("arg1" 12345 (TT_INOUT "arg3" "string"))))

Attribute names are the same as those supported by
add-tooltalk-pattern-attribute, plus 'args.

Values must always be strings, integers, or symbols that
represent Tooltalk constants or lists of same.  When a list
of values is provided all of the list elements are added to
the attribute.  In the example above, messages whose op
attribute is "operation1" or "operation2" would match the pattern.

The value of args should be a list of pattern arguments where
each pattern argument has the following form:

   (mode [value [type]]) or just value

Where mode is one of TT_IN, TT_OUT, TT_INOUT and type is a string.
If type isn't specified then "int" is used if the value is a
number otherwise "string" is used.  If type is "string" then value is
converted to a string (if it isn't a string already) with
prin1-to-string.  If only a value is specified then mode defaults
to TT_IN.  If mode is TT_OUT then value and type don't need
to be specified.  You can find out more about the semantics and
uses of ToolTalk pattern arguments in chapter 3 of the Tooltalk
Programmers Guide.


(register-tooltalk-pattern pat)

Emacs will begin receiving messages that match this pattern.


(unregister-tooltalk-pattern pat)

Emacs will stop receiving messages that match this pattern.


(add-tooltalk-pattern-attribute value pat indicator)

Add one value to the indicated pattern attribute. The names of attributes
are the same as the Tooltalk accessors used to set them less the
"tooltalk_pattern_" prefix and the "_add" suffix).  For example
the name of the attribute for tt_pattern_disposition_add attribute
is 'disposition.  The 'category attribute is handled specially,
since a pattern can only be a member of one category (TT_OBSERVE
or TT_HANDLE.

Callbacks are handled slightly differently than in the C Tooltalk API.
The value of callback should be the name of a function of one argument.
It will be called each time the pattern matches an incoming message.


(add-tooltalk-pattern-arg pat mode type value)

Add one, fully specified, argument to a tooltalk pattern.  Mode must
be one of TT_IN, TT_INOUT, or TT_OUT, type must be a string.
Value can be an integer, string or nil.  If value is an integer then
an integer argument (tt_pattern_iarg_add) added otherwise a string argument
is added.  At present there's no way to add a binary data argument.


(create-tooltalk-pattern)

Create a new Tooltalk pattern and initialize its session attribute to
be the default session.


(destroy-tooltalk-pattern pat)

Apply tt_pattern_destroy to the pattern.  This effecticely unregisters
the pattern.


(describe-tooltalk-message msg &optional stream)

Print the messages attributes and arguments to stream.  This is often
useful for debugging.


* Things to be Done

- At the moment there is almost no support for detecting and
handling ToolTalk errors.  This should be added.

- Message and patterns should support a plist attribute.  This
would be based on one more Tooltalk user data key.  This would also make
it useful to apply the message and pattern callbacks to
both the message and the matching pattern.
author	Ben Wing <ben@xemacs.org>
date	Fri, 19 Feb 2010 22:39:19 -0600
parents	576fb035e263
children	365bc8cb5894