wasm_greeter.rs

//Based on https://github.com/wasmerio/php-ext-wasm/blob/master/examples/greet.rs
//Javascript that uses this: https://pastebin.com/Pz9ZMgEm

#![no_std]

use core::panic::PanicInfo;

//RLS complains about this being a "duplicate lang item",
//perhaps because my RLS is stable and I'm compiling with nightly?
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

const SIZE: usize=20;
static mut IN_BUF : [u8;SIZE]=[0;SIZE];
static mut OUT_BUF: [u8;SIZE]=[0;SIZE];

#[no_mangle]
pub fn get_input_ptr() -> *const u8 {
    unsafe {IN_BUF}.as_ptr()
}

#[no_mangle]
pub fn greet(input_ptr: *const u8) -> *const u8 {
    //input_ptr and get_input_ptr() should both point to IN_BUF,
    //so why does only the first version work properly?
    //JS logs "Hello, テスト!"
    let input: &[u8]=unsafe {core::slice::from_raw_parts(input_ptr,SIZE)};

    //JS logs "Hello, "
    // let input: &[u8]=unsafe {core::slice::from_raw_parts(get_input_ptr(),SIZE)};

    //JS logs "Hello, !"
    // let input: &[u8]=unsafe {&IN_BUF};

    let output: &mut [u8]=unsafe {&mut OUT_BUF};

    b"Hello, ".iter()
        .chain(input.iter().take_while(|&&chr| chr!=0))
        .chain(b"!\0")
        .enumerate().for_each(|(i,&chr)| {
            let elem=unsafe {output.get_unchecked_mut(i)};
            *elem=chr;
        });

    output.as_ptr()

    //JS logs input instead?!
    // unsafe {OUT_BUF}.as_ptr()
}