Hello Michael, Thank you for your reply.
ResponseIO enables to choose a function which sends files with minimum system calls for WAI users.
I have already implemented this both in wai and warp, and confirmed that this works well.
Obviously getting sendfile and Warp to be more efficient should be a goal here (which I know you're already following up on). My question is, barring issues with the sendfile package, is there any other use case for this constructor? I'm hesitant to add it, because it does not have a natural implementation for anything but a standalone server (i.e., CGI, FastCGI, wai-test will always have trouble with this). I just want to clarify the need before we make any changes.
If the sendfile library will be faster, this constructor is not necessary. I also agree that making the sendfile library faster is a right way to go. But I cannot contact the authors of the sendfile library. Do you have any advices on what I should do? --Kazu