sendfile() on BSD/OSX is complicated by the headers/trailers args. You'll have to take that into account in the retry logic, adding unnecessary complexity. Since sendfile() may already return fewer bytes than requested (e.g. non-blocking sockets or big files) it's just easier to return the bytes sent thus far (if any). I can work on a patch once I find some time.

> Wasn't the point of PEP475 that all EINTR returns would be explicitly handled by retrying rather than forcing the user to handle it?

From PEP475: <<[...] to relieve application code from the burden of doing so>>