Re: downloading attachments on demand

[Jouni K Seppanen <jks@iki.fi>]

Sam Steingold <sds@podval.org> writes:

>> * Lars Magne Ingebrigtsen <ynefv@tahf.bet> [2006-04-11 08:13:26 +0200]:
>> Sam Steingold <sds@podval.org> writes:
>>> Is there a way to open a message without downloading all the attachments?
>>
>> If it's a multipart/mixed message, for instance, then there's
>> probably no way to query the storage back ends for just the textual
>> bits.  At least nntp or pop doesn't support anything like that...
>
> All I care about is IMAP (and it appears that Evolution and Mozilla can
> download just the text parts and the list of attachments, not the
> attachments themselves).

Yes, you can do that with IMAP. I just sent myself a message
containing the word "foo", an attachment consisting of the word "bar",
and my signature. Here's me querying the IMAP server about the
message:

a fetch 3475 bodystructure
* 3475 FETCH (BODYSTRUCTURE (("text" "plain" NIL NIL NIL "8bit" 5 1 NIL NIL NIL)("text" "plain" NIL NIL NIL "8bit" 3 0 NIL ("attachment" NIL) NIL)("text" "plain" NIL NIL NIL "8bit" 12 2 NIL NIL NIL) "mixed" ("boundary" "=-=-=") NIL NIL))
a OK FETCH completed.

You could almost use the Lisp reader on that... Here's how to get the
first part:

a fetch 3475 body[1]
* 3475 FETCH (BODY[1] {5}
foo
)
* 3475 FETCH (FLAGS (\Seen \Recent))
a OK FETCH completed.

Here's the attachment:

a fetch 3475 body[2]
* 3475 FETCH (BODY[2] {3}
bar)
a OK FETCH completed.

And the final part:

a fetch 3475 body[3]
* 3475 FETCH (BODY[3] {12}
-- 
Jouni
)
a OK FETCH completed.

(This is all documented in RFC 2060.)

From what I understand about the internal workings of Gnus, you'd have
to alter the backend protocol to make use of this. Instead of getting
a buffer filled with a message that it can parse for MIME structure,
the frontend would ask for some sort of a pre-parsed message object,
with stubs for the attachments, and only if the user wants to do
anything with them, would the frontend query the backend for their
contents.

-- 
Jouni