ttmedia_load(3)

NAME
ttmedia_load - send a Display, Edit or Compose request

SYNOPSIS
#include <Tt/tttk.h>

Tt_message ttmedia_load(Tt_message context,
	Ttmedia_load_msg_cb cb,
	void *clientdata,
	Tttk_op op,
	const char *media_type,
	const unsigned char *contents,
	int len,
	const char *file,
	const char *docname,
	int send);

DESCRIPTION
The ttmedia_load() function is used to create and optionally send a Media Exchange request to display, edit or compose a document.

The cb argument will be passed clientdata when the reply is received, or when intermediate versions of the document are checkpointed through Deposit requests. The op argument must be one of TTME_DISPLAY, TTME_EDIT or TTME_COMPOSE. The media_type argument names the data format of the document, and is usually the primary determinant of which application will be chosen to handle the request. The contents and len arguments specify the document; if they are NULL and zero, respectively, and file is not NULL, then the document is assumed to be contained in file. If docname is not NULL, then ttmedia_load() uses it as the title of the document. If send is True, the message is sent before being returned.

The context argument describes the environment to use. If context is not zero, messages created by ttmedia_load() inherit from context all contexts whose slotname begins with the characters ENV_.

The Ttmedia_load_msg_cb argument is a callback defined as:

    Tt_message (*Ttmedia_load_msg_cb)(Tt_message msg,
    	void *clientdata),
    	Tttk_op op,
    	unsigned char *contents,
    	int len,
    	char *file);

The msg argument is the reply to the load request, or a Deposit request with a messageID argument naming the identifier (see tt_message_id(3)) of the load request. In the latter case, the client program becomes responsible for either failing or replying to the request. In either case, msg should be destroyed after being processed.

The op argument is the op of msg. It must be either TTME_DEPOSIT or the op passed to ttmedia_load(3).

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 clientdata argument is the clientdata passed to ttmedia_load().

RETURN VALUE
Upon successful completion, the ttmedia_load() function returns the request it was asked to build; otherwise, it returns an error pointer. The application can use tt_ptr_error(3) to extract one of the following Tt_status values from the returned handle:

    There is insufficient memory available to perform the function.
    The ttsession(1) process is not running and the ToolTalk service cannot restart it.
    The ToolTalk service has more active messages than it can handle. (The maximum number of active messages is implementation specific, but is at least 2000.)
    The specified process identifier is out of date or invalid.

APPLICATION USAGE
After the request created by ttmedia_load() is sent, the application will probably want to use ttdt_subcontract_manage() immediately afterwards to manage the standard interactions with the handler of the request.

A Ttmedia_load_msg_cb callback should return NULL 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, in which case 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.

EXAMPLES
This is the typical algorithm of a Ttmedia_load_msg_cb:

    Tt_message
    myLoadMsgCB(Tt_message  msg,
            void           *clientData,
            Tttk_op         op,
            unsigned char  *contents,
            int             len,
            char           *file)
    {
            if (len > 0) {
                    /* Replace data with len bytes in contents */
            } else if (file != 0) {
                    /* Replace data with data read from file */
            }
            if (op == TTME_DEPOSIT) {
                    tt_message_reply(msg);
            }
            tttk_message_destroy(msg);
            return 0;
    }

SEE ALSO
Tttttk(5), ttmedia_load_reply(3), ttmedia_ptype_declare(3), ttmedia_Deposit(3), tt_free(3), tt_message_receive(3).