ttmedia_ptype_declare(library call) ttmedia_ptype_declare(library call)
NAMEttmedia_ptype_declare — declare the ptype of a Media Exchange media
editor
SYNOPSIS
#include <Tt/tttk.h>
Tt_status ttmedia_ptype_declare(
const char *ptype,
int base_opnum,
Ttmedia_load_pat_cb cb,
void *clientdata,
int declare);
DESCRIPTION
The ttmedia_ptype_declare function is used to initialize an editor that
implements the Media Exchange message interface for a particular media
type. The ttmedia_ptype_declare function notifies the ToolTalk service
that the cb callback is to be called when the editor is asked to edit a
document of the kind supported by ptype. The ttmedia_ptype_declare
function installs an implementation-specific opnum callback on a series
of signatures that ptype is assumed to contain. These signatures are
listed below, with their corresponding opnum offsets. Opnums in ptype
for these signatures start at base_opnum, which must be zero or a mul‐
tiple of 1000. The implementation-specific opnum callback will pass
clientdata to cb when a request is received that matches one of these
signatures.
If declare is True, ttmedia_ptype_declare calls tt_ptype_declare with
the ptype argument. If ptype implements Media Exchange for several
different media types, then ttmedia_ptype_declare can be called multi‐
ple times, with a different base_opnum each time, and with declare
being True only once.
The Ttmedia_load_pat_cb argument is a callback defined as:
Tt_message (*Ttmedia_load_pat_cb)(Tt_message msg,
void *clientdata,
Tttk_op op,
Tt_status diagnosis,
unsigned char *contents,
int len,
char *file,
char *docname);
The msg argument is a TT_REQUEST in Tt_state TT_SENT. The client pro‐
gram becomes responsible for either failing, rejecting or replying to
it. This can either be done inside the callback, or the message can be
saved and dismissed later (that is, after the callback returns). Usu‐
ally, the callback will either immediately reject/fail the request, or
it will start processing the request, perhaps by associating it with a
new window. When the request is finally dismissed, it should be
destroyed, for example, using tt_message_destroy.
If the callback knows it will handle the request (either fail or reply
to it, but not reject it), then it should call ttdt_message_accept(3).
But if the return value of tt_message_status(3) of msg is
TT_WRN_START_MESSAGE, then the callback should probably do ttdt_ses‐
sion_join, and perhaps a ttdt_file_join, before accepting the message.
The op argument is the op of the incoming request, one of TTME_COMPOSE,
TTME_EDIT or TTME_DISPLAY. The diagnosis argument is the recommended
error code; if the ToolTalk service detects a problem with the request
(for example, TT_DESKTOP_ENODATA), then it passes in the error code
that it recommends the request should be failed with. If diagnosis was
not TT_OK and the Ttmedia_load_pat_cb returns msg, then the ToolTalk
service will fail and destroy msg.
The ToolTalk service does not simply fail the request transparently,
because the request may be the reason that the client process was
started by ToolTalk in the first place. So if diagnosis is not TT_OK
and the tt_message_status of msg is TT_WRN_START_MESSAGE, then many
applications will decide that they have no reason to continue running.
If such an application chooses to exit in the callback, then it should
first dismiss the request. Otherwise, it can set some global flag,
return msg (thus allowing the ToolTalk service to dismiss the message),
and then have main check the flag and exit before even entering the
event loop. (Exiting without dismissing the request would fail it with
status TT_ERR_PROCID, instead of with diagnostic.)
The contents, len, and file arguments represent the contents of the
arriving document. If len is zero, then the document is contained in
file. If contents or file are non- NULL, they can be freed using
tt_free.
The docname argument is the name of the document, if any. The client‐
data argument is the clientdata passed to ttmedia_ptype_declare.
A Ttmedia_load_pat_cb should return zero if it processes msg success‐
fully, or a tt_error_pointer cast to Tt_message if processing results
in an error. It should return the msg if it does not consume it. If
diagnosis is not TT_OK and msg is returned, then the ToolTalk service
will consume (namely, fail and destroy) it. If diagnosis is TT_OK and
msg is returned, then the ToolTalk service will pass TT_CALLBACK_CON‐
TINUE down the call stack, so that msg will be offered to other call‐
backs or (more likely) be returned from tt_message_receive(3). Applica‐
tions will rarely want msg to get processed by other callbacks or in
the main event loop.
RETURN VALUE
Upon successful completion, the ttmedia_ptype_declare function returns
the status of the operation. The application can use tt_ptr_error(3)
to extract one of the following Tt_status values from the returned han‐
dle:
TT_OK The operation completed successfully.
TT_ERR_NOMP
The ttsession(1) process is not running and the ToolTalk ser‐
vice cannot restart it.
TT_ERR_POINTER
The pointer passed does not point to an object of the correct
type for this operation.
TT_ERR_PROCID
The specified process identifier is out of date or invalid.
TT_ERR_PTYPE
The specified process type is not the name of an installed
process type.
EXAMPLES
This is the typical algorithm of a Ttmedia_load_pat_cb:
Tt_message
myAcmeSheetLoadCB(
Tt_message msg,
void *client_data,
Tttk_op op,
Tt_status diagnosis,
unsigned char *contents,
int len,
char *file,
char *docname
)
{
Tt_status status = TT_OK;
if (diagnosis != TT_OK) {
/* toolkit detected an error */
if (tt_message_status(msg) == TT_WRN_START_MESSAGE) {
/*
* Error is in start message! We now have no
* reason to live, so tell main() to exit().
*/
myAbortCode = 2;
}
/* let toolkit handle the error */
return msg;
}
if ((op == TTME_COMPOSE)&&(file == 0)) {
/* open empty new buffer */
} else if (len > 0) {
/* load contents into new buffer */
} else if (file != 0) {
if (ttdt_Get_Modified(msg, file, TT_BOTH, myCntxt, 5000)) {
switch(myUserChoice("Save, Revert, Ignore?")) {
case 0:
ttdt_Save(msg, file, TT_BOTH, myCntxt, 5000);
break;
case 1:
ttdt_Revert(msg, file, TT_BOTH, myCntxt, 5000);
break;
}
}
/* load file into new buffer */
} else {
tttk_message_fail(msg, TT_DESKTOP_ENODATA, 0, 1);
tt_free(contents); tt_free(file); tt_free(docname);
return 0;
}
int w, h, x, y = INT_MAX;
ttdt_sender_imprint_on(0, msg, 0, &w, &h, &x, &y, myCntxt, 5000);
positionMyWindowRelativeTo(w, h, x, y);
if (maxBuffersAreNowOpen) {
/* Un-volunteer to handle future requests until less busy */
tt_ptype_undeclare("Acme_Calc");
}
if (tt_message_status(msg) == TT_WRN_START_MESSAGE) {
/*
* Join session before accepting start message,
* to prevent unnecessary starts of our ptype
*/
ttdt_session_join(0, myContractCB, myShell, 0, 1);
}
ttdt_message_accept(msg, myContractCB, myShell, 0, 1, 1);
tt_free(contents); tt_free(file); tt_free(docname);
return 0;
}
This is the signature layout to which ptype should conform:
ptype Acme_Calc {
start "acalc";
handle:
/*
* Instantiate Acme_Sheet
* Include in tool's ptype if tool can be a document factory.
*/
session Instantiate(in Acme_Sheet template) => start opnum = 401;
/*
* Display Acme_Sheet
* Include in tool's ptype if tool can display a document.
*/
session Display( in Acme_Sheet contents) => start opnum = 1;
session Display( in Acme_Sheet contents,
in messageID counterfoil) => start opnum = 2;
session Display( in Acme_Sheet contents,
in title docName) => start opnum = 3;
session Display( in Acme_Sheet contents,
in messageID counterfoil,
in title docName) => start opnum = 4;
/*
* Edit Acme_Sheet
* Include in tool's ptype if tool can edit a document.
*/
session Edit( inout Acme_Sheet contents) => start opnum = 101;
session Edit( inout Acme_Sheet contents,
in messageID counterfoil) => start opnum = 102;
session Edit( inout Acme_Sheet contents,
in title docName) => start opnum = 103;
session Edit( inout Acme_Sheet contents,
in messageID counterfoil,
in title docName) => start opnum = 104;
/*
* Compose Acme_Sheet
* Include in tool's ptype if tool can compose a document from scratch.
*/
session Edit( out Acme_Sheet contents) => start opnum = 201;
session Edit( out Acme_Sheet contents,
in messageID counterfoil) => start opnum = 202;
session Edit( out Acme_Sheet contents,
in title docName) => start opnum = 203;
session Edit( out Acme_Sheet contents,
in messageID counterfoil,
in title docName) => start opnum = 204;
/*
* Mail Acme_Sheet
* Include in tool's ptype if tool can mail a document.
*/
session Mail( in Acme_Sheet contents) => start opnum = 301;
session Mail( inout Acme_Sheet contents) => start opnum = 311;
session Mail( inout Acme_Sheet contents,
in title docName) => start opnum = 313;
session Mail( out Acme_Sheet contents) => start opnum = 321;
session Mail( out Acme_Sheet contents,
in messageID counterfoil) => start opnum = 323;
};
SEE ALSO
Tt/tttk.h - Tttttk(5), tt_ptype_declare(3), tt_ptype_undeclare(3),
ttdt_message_accept(3), ttdt_session_join(3), ttdt_file_join(3),
tt_free(3), tt_message_receive(3).
ttmedia_ptype_declare(library call)
