Attribute Macro host_function 

#[host_function]

Generate a host-function wrapper that issues a guest→host RPC.

use nub_host_guest_macro::host_function;

#[host_function(fn_id = 10)]
pub fn read_block(block_id: &[u8]) -> Vec<u8>;

Expands the foreign-item-function declaration into a real function whose body calls nub_arch_guestbin::host_comm::call_host_raw(fn_id, payload). Like #[guest_function], the signature must be fn(&[u8]) -> Vec<u8> — typed encode/decode is the caller’s job.