@alagoutte, thanks for your PR! By analyzing the history of the files in this pull request, we identified @yangtse, @bagder and @jay to be potential reviewers.

Thanks!

May be also update the comment ?

So at this
* point returning a value different from sz*nmemb indicates failure. <=

I don't think we need to. I think the comment explains the logic fine why we return what we do, even if it doesn't match the code exactly. Changing the comment to look like the code makes the language in the comment harder to follow I think?

may be add different from sz*nmemb (ak sz && nmemb)

The comment is based on the explanation in the man page:

This callback function must return the number of bytes actually taken care of. If that amount differs from the amount passed in to your function, it'll signal an error to the library.

... and sz * nbmemb is the actual size...