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//! Implementation for WASM based on Web and Node.js
use crate::Error;
extern crate std;
use std::{mem::MaybeUninit, thread_local};
use js_sys::{global, Function, Uint8Array};
use wasm_bindgen::{prelude::wasm_bindgen, JsCast, JsValue};
// Size of our temporary Uint8Array buffer used with WebCrypto methods
// Maximum is 65536 bytes see https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues
const WEB_CRYPTO_BUFFER_SIZE: usize = 256;
// Node.js's crypto.randomFillSync requires the size to be less than 2**31.
const NODE_MAX_BUFFER_SIZE: usize = (1 << 31) - 1;
enum RngSource {
Node(NodeCrypto),
Web(WebCrypto, Uint8Array),
}
// JsValues are always per-thread, so we initialize RngSource for each thread.
thread_local!(
static RNG_SOURCE: Result<RngSource, Error> = getrandom_init();
);
pub(crate) fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
RNG_SOURCE.with(|result| {
let source = result.as_ref().map_err(|&e| e)?;
match source {
RngSource::Node(n) => {
for chunk in dest.chunks_mut(NODE_MAX_BUFFER_SIZE) {
// SAFETY: chunk is never used directly, the memory is only
// modified via the Uint8Array view, which is passed
// directly to JavaScript. Also, crypto.randomFillSync does
// not resize the buffer. We know the length is less than
// u32::MAX because of the chunking above.
// Note that this uses the fact that JavaScript doesn't
// have a notion of "uninitialized memory", this is purely
// a Rust/C/C++ concept.
let res = n.random_fill_sync(unsafe {
Uint8Array::view_mut_raw(chunk.as_mut_ptr() as *mut u8, chunk.len())
});
if res.is_err() {
return Err(Error::NODE_RANDOM_FILL_SYNC);
}
}
}
RngSource::Web(crypto, buf) => {
// getRandomValues does not work with all types of WASM memory,
// so we initially write to browser memory to avoid exceptions.
for chunk in dest.chunks_mut(WEB_CRYPTO_BUFFER_SIZE) {
// The chunk can be smaller than buf's length, so we call to
// JS to create a smaller view of buf without allocation.
let sub_buf = buf.subarray(0, chunk.len() as u32);
if crypto.get_random_values(&sub_buf).is_err() {
return Err(Error::WEB_GET_RANDOM_VALUES);
}
// SAFETY: `sub_buf`'s length is the same length as `chunk`
unsafe { sub_buf.raw_copy_to_ptr(chunk.as_mut_ptr() as *mut u8) };
}
}
};
Ok(())
})
}
fn getrandom_init() -> Result<RngSource, Error> {
let global: Global = global().unchecked_into();
// Get the Web Crypto interface if we are in a browser, Web Worker, Deno,
// or another environment that supports the Web Cryptography API. This
// also allows for user-provided polyfills in unsupported environments.
let crypto = match global.crypto() {
// Standard Web Crypto interface
c if c.is_object() => c,
// Node.js CommonJS Crypto module
_ if is_node(&global) => {
// If module.require isn't a valid function, we are in an ES module.
match Module::require_fn().and_then(JsCast::dyn_into::<Function>) {
Ok(require_fn) => match require_fn.call1(&global, &JsValue::from_str("crypto")) {
Ok(n) => return Ok(RngSource::Node(n.unchecked_into())),
Err(_) => return Err(Error::NODE_CRYPTO),
},
Err(_) => return Err(Error::NODE_ES_MODULE),
}
}
// IE 11 Workaround
_ => match global.ms_crypto() {
c if c.is_object() => c,
_ => return Err(Error::WEB_CRYPTO),
},
};
let buf = Uint8Array::new_with_length(WEB_CRYPTO_BUFFER_SIZE as u32);
Ok(RngSource::Web(crypto, buf))
}
fn is_node(global: &Global) -> bool {
let process = global.process();
if process.is_object() {
let versions = process.versions();
if versions.is_object() {
return versions.node().is_string();
}
}
false
}
#[wasm_bindgen]
extern "C" {
// Return type of js_sys::global()
type Global;
type WebCrypto;
// Getters for the WebCrypto API
#[wasm_bindgen(method, getter)]
fn crypto(this: &Global) -> WebCrypto;
#[wasm_bindgen(method, getter, js_name = msCrypto)]
fn ms_crypto(this: &Global) -> WebCrypto;
// Crypto.getRandomValues()
#[wasm_bindgen(method, js_name = getRandomValues, catch)]
fn get_random_values(this: &WebCrypto, buf: &Uint8Array) -> Result<(), JsValue>;
type NodeCrypto;
// crypto.randomFillSync()
#[wasm_bindgen(method, js_name = randomFillSync, catch)]
fn random_fill_sync(this: &NodeCrypto, buf: Uint8Array) -> Result<(), JsValue>;
// Ideally, we would just use `fn require(s: &str)` here. However, doing
// this causes a Webpack warning. So we instead return the function itself
// and manually invoke it using call1. This also lets us to check that the
// function actually exists, allowing for better error messages. See:
type Module;
#[wasm_bindgen(getter, static_method_of = Module, js_class = module, js_name = require, catch)]
fn require_fn() -> Result<JsValue, JsValue>;
#[wasm_bindgen(method, getter)]
fn process(this: &Global) -> Process;
type Process;
#[wasm_bindgen(method, getter)]
fn versions(this: &Process) -> Versions;
type Versions;
#[wasm_bindgen(method, getter)]
fn node(this: &Versions) -> JsValue;
}