Keith points out that the cid/mid urls provide for private messages
that work as web pages. He points out that at some point the referred
to entities need to be reduced to filenames on the recipient's system.
That implies the main page, the text/html entity, must be edited to
convert the cid/mid to file names.
This is what I'd like to avoid. I don't think the MIME reader should
have to know about text/html (or any other body part) so it can convert
its internal references to another format. I'd far rather the helper
apps have some interface to map content-ids to filenames (which the
MIME reader has conveniently stored), but this requires making the
relevant helper apps smarter, which is difficult. Using content-disposition
filenames seems like the easiest hack which doesn't require substantial
changes to the helper apps.
However, it doesn't work to put arbitrary URLs in the Content-Disposition
field, because most file systems won't be able to store files using
a URL as a file name. The filenames used for this purpose need to be
very portable, say xxxxxxxx.yyy format using upper case letters or digits,
and maybe with certain names disallowed.
Keith