Pasted

Cargo.toml
 [dependencies]
libc = "0.2"
 [lib]
name = ""
crate-type = ["dylib"]
 ---
 lib.rs
 extern crate libc;
use std::ffi::{CStr, CString};
 #[no_mangle]
pub extern fn lib_fn(name: *const libc::c_char) {
	let name = unsafe { CStr::from_ptr(name) };
	// implementation
}
 ---
 test.rb
 require 'ffi'
 module Test
	extend FFI::Library
	ffi_lib 'path/to/lib'
	attach_function :lib_fn, [:string], :void
end
 Test.lib_fn(str)