Re: [Libevent-users] evbuffer_add_file() completion callback

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Mon, Nov 21, 2011 at 7:52 AM,  <aaron@xxxxxxxxx> wrote:
> Hey all, I'm using evbuffer_add_file() to add a bunch of open file
> descriptors to a buffer event. It works good, until there are many connected
> clients requesting many different files. I'm using a technique similar to
> HTTP pipelining (not using HTTP though) so a workaround would be to have a
> queue of files to send, and once one has finished sending, send the next one
> in the queue. I've had a look around for a callback mechanism to work with
> evbuffer_add_file(), but can't figure it out. Is there a way I can provide a
> callback for after evbuffer_add_file() finishes sending the whole file?

You can't do this directly, but there are two plausible ways to fake
it with the current Libevent 2 APIs.  You can either add a callback to
the evbuffer, or set a watermark on the bufferevent.

The evbuffer callback will get notified when _any_ data is added or
drained from the evbuffer, so you could keep track of how much data
had been drained, and decide that the file as a whole was sent when
all the data was gone.

More realistically, you can just set a write low-watermark for the
bufferevent, so that you get a write callback once the amount of data
pending to be written gets low enough.

cheers,
-- 
Nick
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