Beware, there are versions of go where sendfile is broken and only sends the first 4k of a file on macos.

A good reminder. It is surprising first time you encounter it.

Same for Rust. As https://doc.rust-lang.org/stable/std/io/fn.copy.html says, std::io::copy can use copy_file_range(2), sendfile(2), or splice(2).

How is the byte counting reader supposed to work in user space without putting the buffer in user space? The article claims there is a way but I want to see what is meant by counting bytes in that case.

Zero-Copy in Go: Why magic is an antipattern, and: performance is observable behavior.

This is almost like the expression problem. Copy is a new operation, and you introduced a new type, thus creating a new grid cell nobody from either side could have reasonably known about - except for the fact Copy is in the standard library so you could have known about it but not done anything.

Ugh, AI slop writing.

Interesting premise for a post, but I had to stop midway due to the AI slop writing adding meaningless information.