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From: Daniel Stenberg <>
Date: Thu, 18 Sep 2014 09:21:28 +0200 (CEST)

On Thu, 18 Sep 2014, Pashupati Kumar wrote:

> I am new to libcurI and still learning my ways around it. I have few
> questions on it. I discovered that user needs to copy the data in write
> call-back function and also the way our application behave, it will end up
> doing copy during read call back function as well. This will be a big
> draw-back as the application is data intensive.

Will it really? Some people have claimed this over the years but I've never
seen any real numbers proving this. On the contrary I think this is a common
belief and suspicion that rarely actually turns out to be an actual problem.

Have you measured how much CPU - in your case - that would be "wasted" on this
extra copy? Or perhaps if that waste even makes a difference to the total
performance of your application.

> I came across an old mail thread on avoiding copy for CURLOPT_WRITEFUNCTION.
> I don't know what was the final outcome of it.

We discuss this topic every once in a while and it always ends up getting
burried again when the work to implement something like this ends up being
more than the gains in having the feature. But maybe it is different this

> For read callback function, application data is available in scatter list of
> buffers. This brings me to my next question. Can libcurl use scatter-gather
> buffers?


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Received on 2014-09-18