Re: [Libevent-users] Bufferevent filter with greedy sender

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Sat, Apr 27, 2013 at 1:52 PM, kgardenia42 <kgardenia42@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> I have a bufferevent_filter to parse some protocol data from the "src"
> evbuffer and unwrap it into the "dst" evbuffer.
>
> This all works fine.  The problem I have, however, is that when there
> is a greedy sender sending a lot of data the input_filter just keeps
> getting called hundreds or thousands of times, massively bloating the
> dst buffer.
>
> What I would *like* to happen is for the lower level read callback (on
> the bev which is wrapped by the filter) to be called so that dst gets
> drained and I don't get the bloat.
>
> I've read the docs and I can't seem to grock this part of it and
> couldn't find a relevant example.  Can someone please advise how to
> accomplish this?
>
> I see that the filter callback has a "enum bufferevent_flush_mode
> state" parameter.  Is this relevant here?
>

I think you want to look into watermarks: it's a way to tell Libevent
"Don't let this buffer get more full than X" or "don't bother me
unless this buffer has at least X bytes".

I'm too distracted to post good code for using watermarks together
with filters tonight, but the idea should be pretty straightforward
from the documentation and the reference manual.  (If somebody _can_
write a good example, possibly nice and terse for inclusion in the
manual, that would rock.)  Let us know if it still doesn't make sense
or doesn't work for you though.

peace,
-- 
Nick
***********************************************************************
To unsubscribe, send an e-mail to majordomo@xxxxxxxxxxxxx with
unsubscribe libevent-users    in the body.