[blaenk]

I hadn't considered this before but it seems to make sense. If I have nginx configured with ssl and sendfile (X-Accel-Redirect) and my app sends an X-Accel-Redirect response to nginx, you're saying that it's not actually using sendfile under the hood?

[inimino]

Sendfile is just a kernel feature for directly sending a file to a socket. If you are doing literally anything other than just sending the raw bytes of the file over the network, it can't be used.

[blaenk]

Yeah I'm aware that it's a system call that only knows about file descriptors. It's just that it just now hit me that a consequence of that is that a web server configured to use ssl _and_ sendfile isn't really using sendfile, short of some hairy hack of writing/encrypting the response into a file (maybe in-memory with something like memfd_create) and using sendfile on that, which would defeat the purpose of avoiding user-space entirely.