Looks like the only unsafe parts are the parts which interop with the rest of the nginx codebase (marshalling pointers, calling various functions in nginx_sys,

Looks like the only unsafe parts are the parts which interop with the rest of the nginx codebase (marshalling pointers, calling various functions in nginx_sys, etc.) Rust cannot guarantee this external C stuff adheres to the necessary invariants, hence it must be marked unsafe. I don't see a way to integrate rust as a plugin into a C codebase without some level of unsafe usage like this.