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NAME
ttmedia_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 inter-
face for a particular media type. The
ttmedia_ptype_declare() function notifies the ToolTalk ser-
vice 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 signa-
tures 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 multiple 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 imple-
ments Media Exchange for several different media types, then
ttmedia_ptype_declare() can be called multiple 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 program 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). Usually, 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_session_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 ser-
vice 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 diag-
nosis 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 tran-
sparently, 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 clientdata argument is the clientdata passed to
ttmedia_ptype_declare().
A Ttmedia_load_pat_cb should return zero if it processes msg
successfully, 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_CONTINUE down the call stack, so that msg will
be offered to other callbacks or (more likely) be returned
from tt_message_receive(3). Applications 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 applica-
tion can use tt_ptr_error(3) to extract one of the following
Tt_status values from the returned handle:
TT_OK The operation completed successfully.
TT_ERR_NOMP
The ttsession(1) process is not running and the
ToolTalk service 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;
}
/* We should only operate on files we own. */
if (tt_message_uid() != getuid() || tt_message_gid() != getgid()) {
tttk_message_fail(msg, TT_DESKTOP_EACCES, 0, 1);
/* tt_free as appropriate... */
return 0;
}
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 that ptype should conform to:
ptype Acme_Calc {
start "acalc";
handle:
/*
* 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
tttk(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).
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