libmime Content Type Handler
Plugins
by Richard H. Pizzarro <rhp@netscape.com>
Contents
Overview
The libmime module implements a general-purpose
MIME parser and one of the primary methods provided by the parser is the
ability to emit an HTML representation of an input stream. The primary
use of libmime is to parse and render RFC822 messages for use by
the Messenger component of Seamonkey.
A necessary capability of this module is to dynamically add the ability
to decode and render various content types. This functionality will be
accomplished via Content Type Handler Plugins for libmime. libmime
has a homegrown object system written in C, and since the content type
handler plugins need to exist in this module, a description
of the libmime object system should be reviewed and understood.
API's
Content Type Handler Plugins are dynamically loaded and need to access
internal pointers, functions that are part of the C based object system.
The following XP-COM interface is implemented by libmime and is necessary
for Content Type Handler Plugin development.
#ifndef nsIMimeObjectClassAccess_h_
#define nsIMimeObjectClassAccess_h_
#include "prtypes.h"
// {C09EDB23-B7AF-11d2-B35E-525400E2D63A}
#define NS_IMIME_OBJECT_CLASS_ACCESS_IID \
{ 0xc09edb23, 0xb7af, 0x11d2,
\
{ 0xb3, 0x5e, 0x52, 0x54, 0x0, 0xe2,
0xd6, 0x3a } };
class nsIMimeObjectClassAccess : public nsISupports {
public:
// These methods are all implemented by libmime to be used
by
// content type handler plugins for processing stream data.
// This is the write call for outputting processed stream
data.
NS_IMETHOD MimeObjectWrite(void *mimeObject,
char *data,
PRInt32 length,
PRBool user_visible_p) = 0;
// The following group of calls expose the pointers for the
object
// system within libmime.
NS_IMETHOD GetmimeInlineTextClass(void
**ptr) = 0;
NS_IMETHOD GetmimeLeafClass(void **ptr)
= 0;
NS_IMETHOD GetmimeObjectClass(void **ptr)
= 0;
NS_IMETHOD GetmimeContainerClass(void
**ptr) = 0;
NS_IMETHOD GetmimeMultipartClass(void
**ptr) = 0;
NS_IMETHOD GetmimeMultipartSignedClass(void
**ptr) = 0;
};
#endif /* nsIMimeObjectClassAccess_h_ */
On the other side, are are the functions that need to be implemented
by the Content Type Handler Plugin:
/*
* MIME_GetContentType() is called by libmime to identify
the content
* type handled by this plugin.
*/
char
*MIME_GetContentType(void);
/*
* This will create the MimeObjectClass object to be used
by the libmime
* object system.
*/
MimeObjectClass *MIME_CreateContentTypeHandlerClass(const char
*content_type,
contentTypeHandlerInitStruct *initStruct);
Note: these may migrate to another XP-COM interface, but this would
require an additional registry to match content type's to content type
handler plugins. For now, this work is being postponed.
Plugin
Installation/Location
The installation of these modules will be similar to the that of Navigator
plugins. A folder/directory called mimeplugins will be created in
the binary release location of the libmime module. libmime will locate
the plugins by using this directory and looking for modules prefixed with
the string "mimect-".
Sample Content
Type Handler Plugin
To see an example of a Content Type Handler Plugin, the source for
the handler of the content type "text/calendar" can be viewed at the following
link: Calendar
plugin Note: This plugin simply creates a blue table in the output
stream to identify the fact that it is operational, but the basic constructs
of what is needed to build a functional content type handler can be seen.
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