blob: 8e7c979a2232858227391d515769eadd5389ae18 [file] [log] [blame]
// Copyright 2018 Developers of the Rand project.
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
//> or the MIT license
// <LICENSE-MIT or>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Implementation for WASM via wasm-bindgen
use rand_core::{Error, ErrorKind};
use super::OsRngImpl;
use wasm_bindgen::prelude::*;
extern "C" {
pub type Function;
pub fn new(s: &str) -> Function;
pub fn call(this: &Function, self_: &JsValue) -> JsValue;
pub type This;
#[wasm_bindgen(method, getter, structural, js_name = self)]
pub fn self_(me: &This) -> JsValue;
#[wasm_bindgen(method, getter, structural)]
pub fn crypto(me: &This) -> JsValue;
#[derive(Clone, Debug)]
pub type BrowserCrypto;
// TODO: these `structural` annotations here ideally wouldn't be here to
// avoid a JS shim, but for now with feature detection they're
// unavoidable.
#[wasm_bindgen(method, js_name = getRandomValues, structural, getter)]
pub fn get_random_values_fn(me: &BrowserCrypto) -> JsValue;
#[wasm_bindgen(method, js_name = getRandomValues, structural)]
pub fn get_random_values(me: &BrowserCrypto, buf: &mut [u8]);
#[wasm_bindgen(js_name = require)]
pub fn node_require(s: &str) -> NodeCrypto;
#[derive(Clone, Debug)]
pub type NodeCrypto;
#[wasm_bindgen(method, js_name = randomFillSync, structural)]
pub fn random_fill_sync(me: &NodeCrypto, buf: &mut [u8]);
#[derive(Clone, Debug)]
pub enum OsRng {
impl OsRngImpl for OsRng {
fn new() -> Result<OsRng, Error> {
// First up we need to detect if we're running in node.js or a
// browser. To do this we get ahold of the `this` object (in a bit
// of a roundabout fashion).
// Once we have `this` we look at its `self` property, which is
// only defined on the web (either a main window or web worker).
let this = Function::new("return this").call(&JsValue::undefined());
assert!(this != JsValue::undefined());
let this = This::from(this);
let is_browser = this.self_() != JsValue::undefined();
if !is_browser {
return Ok(OsRng::Node(node_require("crypto")))
// If `self` is defined then we're in a browser somehow (main window
// or web worker). Here we want to try to use
// `crypto.getRandomValues`, but if `crypto` isn't defined we assume
// we're in an older web browser and the OS RNG isn't available.
let crypto = this.crypto();
if crypto.is_undefined() {
let msg = "self.crypto is undefined";
return Err(Error::new(ErrorKind::Unavailable, msg))
// Test if `crypto.getRandomValues` is undefined as well
let crypto: BrowserCrypto = crypto.into();
if crypto.get_random_values_fn().is_undefined() {
let msg = "crypto.getRandomValues is undefined";
return Err(Error::new(ErrorKind::Unavailable, msg))
// Ok! `self.crypto.getRandomValues` is a defined value, so let's
// assume we can do browser crypto.
fn fill_chunk(&mut self, dest: &mut [u8]) -> Result<(), Error> {
match *self {
OsRng::Node(ref n) => n.random_fill_sync(dest),
OsRng::Browser(ref n) => n.get_random_values(dest),
fn max_chunk_size(&self) -> usize {
match *self {
OsRng::Node(_) => usize::max_value(),
OsRng::Browser(_) => {
// see
// where it says:
// > A QuotaExceededError DOMException is thrown if the
// > requested length is greater than 65536 bytes.
fn method_str(&self) -> &'static str {
match *self {
OsRng::Node(_) => "crypto.randomFillSync",
OsRng::Browser(_) => "crypto.getRandomValues",