RE: [Libevent-users] Dynamic changes of read water mark

["Gilad Benjamini" <gilad@xxxxxxxxxxxxxxxxx>]

> > It seems that this can be done with a buffered event which keeps
> changing
> > the read low watermark (twice per message).

Your sample code did not include the watermark part.
May I assume that at the end of the code snippet you would set the low
watermark ?
If I set the low watermark to X, am I guaranteed that the next time I reach
the callback at least X bytes are available ?
Is that also true if I leave some bytes in the buffer at the end of my
processing ?

> > Is this a "proper" way to use buffered events ?
> >
> 
> Yes, bufferevents are fine for this, this abstracts some of the hard
> work. I do the same thing in one of my applications. Something along
> the lines of:
> 
> struct frame {
> 	uint16_t something;
>   uint16_t length;
> };
> 
> size_t frame_length = 4;
> 
> buf = bufferevent_get_input(bev);
> 
> while (evbuffer_get_length(buf) > 0) {
>   unsigned char *data;
> 	unsigned char *payload;
> 	struct frame   frame;
> 
> 	data = evbuffer_pullup(buf, frame_length);


Is there a good reason to do the pullup before checking the length, or was
that just placed here while you quickly came up with a sample code ?

> 
> 	if (evbuffer_get_length(data) < frame_length) {
> 	  /* we don't have enough data yet to fill in our frame, return
> and wait for more */
> 		break;
> 	}
> 
> 	memcpy((char *)&frame.something, data, sizeof(uint16_t));
>   memcpy((char *)&frame.length, &data[sizeof(uint16_t)],
> sizeof(uint16_t))/
> 
> 	if ((evbuffer_get_length(buf) - frame_length) < frame.length) {
> 		/* whole payload hasn't been seen */
> 		break;
> 	}
> 
> 	/* drain the header portion from the evbuffer */
> 	evbuffer_drain(buf, frame_length);
> 
> 	if (!(payload = malloc(frame.length))) {
> 		perror("malloc");
> 		return;
> 	}
> 
> 	evbuffer_remove_buffer(buf, payload, frame.length);
> }
> 


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