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Node.js v15.0.0-test20200430ccd18343cb Documentation
Table of Contents
WebAssembly System Interface (WASI)#
The WASI API provides an implementation of the WebAssembly System Interface specification. WASI gives sandboxed WebAssembly applications access to the underlying operating system via a collection of POSIX-like functions.
'use strict';
const fs = require('fs');
const { WASI } = require('wasi');
const wasi = new WASI({
args: process.argv,
env: process.env,
preopens: {
'/sandbox': '/some/real/path/that/wasm/can/access'
}
});
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };
(async () => {
const wasm = await WebAssembly.compile(fs.readFileSync('./binary.wasm'));
const instance = await WebAssembly.instantiate(wasm, importObject);
wasi.start(instance);
})();
The --experimental-wasi-unstable-preview1
and --experimental-wasm-bigint
CLI arguments are needed for the previous example to run.
Class: WASI
#
The WASI
class provides the WASI system call API and additional convenience
methods for working with WASI-based applications. Each WASI
instance
represents a distinct sandbox environment. For security purposes, each WASI
instance must have its command line arguments, environment variables, and
sandbox directory structure configured explicitly.
new WASI([options])
#
-
options
<Object>args
<Array> An array of strings that the WebAssembly application will see as command line arguments. The first argument is the virtual path to the WASI command itself. Default:[]
.env
<Object> An object similar toprocess.env
that the WebAssembly application will see as its environment. Default:{}
.preopens
<Object> This object represents the WebAssembly application's sandbox directory structure. The string keys ofpreopens
are treated as directories within the sandbox. The corresponding values inpreopens
are the real paths to those directories on the host machine.returnOnExit
<boolean> By default, WASI applications terminate the Node.js process via the__wasi_proc_exit()
function. Setting this option totrue
causeswasi.start()
to return the exit code rather than terminate the process. Default:false
.
wasi.start(instance)
#
instance
<WebAssembly.Instance>
Attempt to begin execution of instance
as a WASI command by invoking its
_start()
export. If instance
does not contain a _start()
export, or if
instance
contains an _initialize()
export, then an exception is thrown.
start()
requires that instance
exports a WebAssembly.Memory
named
memory
. If instance
does not have a memory
export an exception is thrown.
If start()
is called more than once, an exception is thrown.
wasi.wasiImport
#
wasiImport
is an object that implements the WASI system call API. This object
should be passed as the wasi_snapshot_preview1
import during the instantiation
of a WebAssembly.Instance
.