warp-runtime 1.4.1

//! The one WASI call warp programs make, `fd_write` (print), for a store of any state: the warp-runtime stub needs no WASI library
use wasmtime::{Caller, Extern, Linker, Result};

pub const WASI_LIBRARY: &str = "wasi_snapshot_preview1";
pub const FD_WRITE: &str = "fd_write";
const STDOUT: i32 = 1;
const STDERR: i32 = 2;
const ERRNO_SUCCESS: i32 = 0;
const ERRNO_BADF: i32 = 8;
const ERRNO_FAULT: i32 = 21;
const IOVEC_BYTES: usize = 8;

/// fd_write(fd, iovecs, count, written) to stdout or stderr
pub fn link_output<T: 'static>(linker: &mut Linker<T>) -> Result<()> {
	linker.func_wrap(
		WASI_LIBRARY,
		FD_WRITE,
		|mut caller: Caller<'_, T>, fd: i32, iovecs: i32, count: i32, written: i32| -> i32 {
			let Some(Extern::Memory(memory)) = caller.get_export("memory") else {
				return ERRNO_FAULT;
			};
			let bytes = memory.data(&caller);
			let word =
				|at: usize| bytes.get(at..at + 4).map(|word| u32::from_le_bytes(word.try_into().unwrap()) as usize);
			let mut text = Vec::new();
			for index in 0..count.max(0) as usize {
				let at = iovecs as usize + index * IOVEC_BYTES;
				let (Some(start), Some(length)) = (word(at), word(at + 4)) else {
					return ERRNO_FAULT;
				};
				let Some(part) = bytes.get(start..start + length) else {
					return ERRNO_FAULT;
				};
				text.extend_from_slice(part);
			}
			use std::io::Write;
			let outcome = match fd {
				STDOUT => std::io::stdout().write_all(&text),
				STDERR => std::io::stderr().write_all(&text),
				_ => return ERRNO_BADF,
			};
			if outcome.is_err() {
				return ERRNO_BADF;
			}
			match memory.write(&mut caller, written as usize, &(text.len() as u32).to_le_bytes()) {
				Ok(()) => ERRNO_SUCCESS,
				Err(_) => ERRNO_FAULT,
			}
		},
	)?;
	Ok(())
}