Интерфейс системы WebAssembly (WASI)

Исходный код: lib/wasi.js

API WASI предоставляет реализацию спецификации Интерфейса системы WebAssembly. WASI предоставляет доступ к основной операционной системе для защищённых приложений WebAssembly через набор функций, подобных POSIX.

MJS-модули

import { readFile } from 'fs/promises';
import { WASI } from 'wasi';
import { argv, env } from 'process';

const wasi = new WASI({
  args: argv,
  env,
  preopens: {
    '/sandbox': '/some/real/path/that/wasm/can/access'
  }
});

// Some WASI binaries require:
//   const importObject = { wasi_unstable: wasi.wasiImport };
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };

const wasm = await WebAssembly.compile(
  await readFile(new URL('./demo.wasm', import.meta.url))
);
const instance = await WebAssembly.instantiate(wasm, importObject);

wasi.start(instance);

CJS-модули

'use strict';
const { readFile } = require('fs/promises');
const { WASI } = require('wasi');
const { argv, env } = require('process');
const { join } = require('path');

const wasi = new WASI({
  args: argv,
  env,
  preopens: {
    '/sandbox': '/some/real/path/that/wasm/can/access'
  }
});

// Some WASI binaries require:
//   const importObject = { wasi_unstable: wasi.wasiImport };
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };

(async () => {
  const wasm = await WebAssembly.compile(
    await readFile(join(__dirname, 'demo.wasm'))
  );
  const instance = await WebAssembly.instantiate(wasm, importObject);

  wasi.start(instance);
})();

Для запуска вышеприведённого примера создайте новый файл WebAssembly в формате текста с именем demo.wat:

(module
    ;; Import the required fd_write WASI function which will write the given io vectors to stdout
    ;; The function signature for fd_write is:
    ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
    (import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))

    (memory 1)
    (export "memory" (memory 0))

    ;; Write 'hello world\n' to memory at an offset of 8 bytes
    ;; Note the trailing newline which is required for the text to appear
    (data (i32.const 8) "hello world\n")

    (func $main (export "_start")
        ;; Creating a new io vector within linear memory
        (i32.store (i32.const 0) (i32.const 8))  ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
        (i32.store (i32.const 4) (i32.const 12))  ;; iov.iov_len - The length of the 'hello world\n' string

        (call $fd_write
            (i32.const 1) ;; file_descriptor - 1 for stdout
            (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
            (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
            (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
        )
        drop ;; Discard the number of bytes written from the top of the stack
    )
)

Используйте wabt для компиляции .wat в .wasm

$ wat2wasm demo.wat

Для запуска этого примера необходим аргумент командной строки --experimental-wasi-unstable-preview1.