Hello, I have uploaded the simple-sendfile package to HackageDB. http://hackage.haskell.org/package/simple-sendfile This is a simple version of the sendfile package which use unnecessary system calls (stat() and lseek()). The simple-sendfile package provides native sendfile support for Linux, BSDs, and MacOS. For other OSes, a fallback function using read()/send () is provided. Since the limitation of sendfile on Linux, stat() is called if EntireFile is used. But we can use PartOfFile instead to send entire files. I modified Warp to make use of the simple-sendfile package. https://github.com/kazu-yamamoto/warp/commit/fd73ffb098475255756f7706f832851... And I confirmed that performance becomes much better. I'm very satisfied with the current performance. Since I don't know how T.Handle should be used, the commit above just ignores T.Handle at this moment. If necessary, I would love to modify the API of the simple-sendfile package. --Kazu