Rust and WebAssembly error

index.js

const rust = require('rustify');
const wasm = rust`
  use std::ffi::{CString};
  use std::os::raw::{c_char};

  #[no_mangle]
  pub extern "C" fn str_len(ptr: *mut c_char) -> usize {
      unsafe {
          let string = CString::from_raw(ptr);
          string.to_bytes().len()
      }
  }

  #[no_mangle]
  pub extern "C" fn hello_world() -> *mut i8 {
    CString::new("Hello World!").unwrap().into_raw()
  }
`

function ptrToString(buffer, ptr, length) {
  const bytes = new Uint8Array(buffer, ptr, length);
  return new TextDecoder('utf8').decode(bytes);
}

WebAssembly.instantiate(wasm, {})
  .then(res => {
    const {str_len, hello_world, memory} = res.instance.exports;
    const hello_ptr = hello_world();
    const hello_len = str_len(hello_ptr);

    console.log(ptrToString(memory.buffer, hello_ptr, hello_len));
    // expected "Hello World!" got "ello World!"
  }).catch(e => {
    console.error('Creating WASM module failed', e)
  })