Rework JS feature detection

src/error.rs

@@ -43,16 +43,19 @@ impl Error {
     pub const FAILED_RDRAND: Error = internal_error(5);
     /// RDRAND instruction unsupported on this target.
     pub const NO_RDRAND: Error = internal_error(6);
-    /// The browser does not have support for `self.crypto`.
+    /// The environment does not support the Web Crypto API.
     pub const WEB_CRYPTO: Error = internal_error(7);
-    /// The browser does not have support for `crypto.getRandomValues`.
+    /// Calling Web Crypto API `crypto.getRandomValues` failed.
     pub const WEB_GET_RANDOM_VALUES: Error = internal_error(8);
     /// On VxWorks, call to `randSecure` failed (random number generator is not yet initialized).
     pub const VXWORKS_RAND_SECURE: Error = internal_error(11);
-    /// NodeJS does not have support for the `crypto` module.
+    /// Node.js does not have the `crypto` CommonJS module.
     pub const NODE_CRYPTO: Error = internal_error(12);
-    /// NodeJS does not have support for `crypto.randomFillSync`.
+    /// Calling Node.js function `crypto.randomFillSync` failed.
     pub const NODE_RANDOM_FILL_SYNC: Error = internal_error(13);
+    /// Called from an ES module on Node.js. This is unsupported, see:
+    /// https://docs.rs/getrandom#nodejs-es6-module-support.
+    pub const NODE_ES_MODULE: Error = internal_error(14);
 
     /// Codes below this point represent OS Errors (i.e. positive i32 values).
     /// Codes at or above this point, but below [`Error::CUSTOM_START`] are
@@ -166,10 +169,11 @@ fn internal_desc(error: Error) -> Option<&'static str> {
         Error::FAILED_RDRAND => Some("RDRAND: failed multiple times: CPU issue likely"),
         Error::NO_RDRAND => Some("RDRAND: instruction not supported"),
         Error::WEB_CRYPTO => Some("Web Crypto API is unavailable"),
-        Error::WEB_GET_RANDOM_VALUES => Some("Web API crypto.getRandomValues is unavailable"),
+        Error::WEB_GET_RANDOM_VALUES => Some("Calling Web API crypto.getRandomValues failed"),
         Error::VXWORKS_RAND_SECURE => Some("randSecure: VxWorks RNG module is not initialized"),
-        Error::NODE_CRYPTO => Some("Node.js crypto module is unavailable"),
-        Error::NODE_RANDOM_FILL_SYNC => Some("Node.js API crypto.randomFillSync is unavailable"),
+        Error::NODE_CRYPTO => Some("Node.js crypto CommonJS module is unavailable"),
+        Error::NODE_RANDOM_FILL_SYNC => Some("Calling Node.js API crypto.randomFillSync failed"),
+        Error::NODE_ES_MODULE => Some("Node.js ES modules are not directly supported, see https://docs.rs/getrandom#nodejs-es6-module-support"),
         _ => None,
     }
 }

src/js.rs

@@ -10,15 +10,16 @@ use crate::Error;
 extern crate std;
 use std::thread_local;
 
-use js_sys::{global, Uint8Array};
+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 BROWSER_CRYPTO_BUFFER_SIZE: usize = 256;
+const WEB_CRYPTO_BUFFER_SIZE: usize = 256;
 
 enum RngSource {
     Node(NodeCrypto),
-    Browser(BrowserCrypto, Uint8Array),
+    Web(WebCrypto, Uint8Array),
 }
 
 // JsValues are always per-thread, so we initialize RngSource for each thread.
@@ -37,10 +38,10 @@ pub(crate) fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
                     return Err(Error::NODE_RANDOM_FILL_SYNC);
                 }
             }
-            RngSource::Browser(crypto, buf) => {
+            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(BROWSER_CRYPTO_BUFFER_SIZE) {
+                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);
@@ -58,25 +59,33 @@ pub(crate) fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
 
 fn getrandom_init() -> Result<RngSource, Error> {
     let global: Global = global().unchecked_into();
-    if is_node(&global) {
-        let crypto = NODE_MODULE
-            .require("crypto")
-            .map_err(|_| Error::NODE_CRYPTO)?;
-        return Ok(RngSource::Node(crypto));
-    }
 
-    // Assume we are in some Web environment (browser or web worker). We get
-    // `self.crypto` (called `msCrypto` on IE), so we can call
-    // `crypto.getRandomValues`. If `crypto` isn't defined, we assume that
-    // we are in an older web browser and the OS RNG isn't available.
-    let crypto = match (global.crypto(), global.ms_crypto()) {
-        (c, _) if c.is_object() => c,
-        (_, c) if c.is_object() => c,
-        _ => return Err(Error::WEB_CRYPTO),
+    // 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 require isn't a valid function, we are in an ES module.
+            match Module::require_fn().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(BROWSER_CRYPTO_BUFFER_SIZE as u32);
-    Ok(RngSource::Browser(crypto, buf))
+    let buf = Uint8Array::new_with_length(WEB_CRYPTO_BUFFER_SIZE as u32);
+    Ok(RngSource::Web(crypto, buf))
 }
 
 // Taken from https://www.npmjs.com/package/browser-or-node
@@ -93,30 +102,33 @@ fn is_node(global: &Global) -> bool {
 
 #[wasm_bindgen]
 extern "C" {
-    type Global; // Return type of js_sys::global()
+    // Return type of js_sys::global()
+    type Global;
 
-    // Web Crypto API (https://www.w3.org/TR/WebCryptoAPI/)
-    #[wasm_bindgen(method, getter, js_name = "msCrypto")]
-    fn ms_crypto(this: &Global) -> BrowserCrypto;
+    // Web Crypto API: Crypto interface (https://www.w3.org/TR/WebCryptoAPI/)
+    type WebCrypto;
+    // Getters for the WebCrypto API
     #[wasm_bindgen(method, getter)]
-    fn crypto(this: &Global) -> BrowserCrypto;
-    type BrowserCrypto;
+    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: &BrowserCrypto, buf: &Uint8Array) -> Result<(), JsValue>;
+    fn get_random_values(this: &WebCrypto, buf: &Uint8Array) -> Result<(), JsValue>;
 
-    // We use a "module" object here instead of just annotating require() with
-    // js_name = "module.require", so that Webpack doesn't give a warning. See:
-    //   https://github.com/rust-random/getrandom/issues/224
-    type NodeModule;
-    #[wasm_bindgen(js_name = module)]
-    static NODE_MODULE: NodeModule;
     // Node JS crypto module (https://nodejs.org/api/crypto.html)
-    #[wasm_bindgen(method, catch)]
-    fn require(this: &NodeModule, s: &str) -> Result<NodeCrypto, JsValue>;
     type NodeCrypto;
+    // crypto.randomFillSync()
     #[wasm_bindgen(method, js_name = randomFillSync, catch)]
     fn random_fill_sync(this: &NodeCrypto, buf: &mut [u8]) -> Result<(), JsValue>;
 
+    // We use a "module" object here instead of just annotating require() with
+    // js_name = "module.require", so that Webpack doesn't give a warning. See:
+    //   https://github.com/rust-random/getrandom/issues/224
+    type Module;
+    #[wasm_bindgen(getter, static_method_of = Module, js_class = module, js_name = require)]
+    fn require_fn() -> JsValue;
+
     // Node JS process Object (https://nodejs.org/api/process.html)
     #[wasm_bindgen(method, getter)]
     fn process(this: &Global) -> Process;

src/lib.rs

@@ -31,7 +31,7 @@
 //! | Emscripten        | `*‑emscripten`     | `/dev/random` (identical to `/dev/urandom`)
 //! | WASI              | `wasm32‑wasi`      | [`random_get`]
 //! | Web Browser       | `wasm32‑*‑unknown` | [`Crypto.getRandomValues`], see [WebAssembly support]
-//! | Node.js           | `wasm32‑*‑unknown` | [`crypto.randomBytes`], see [WebAssembly support]
+//! | Node.js           | `wasm32‑*‑unknown` | [`crypto.randomFillSync`], see [WebAssembly support]
 //! | SOLID             | `*-kmc-solid_*`    | `SOLID_RNG_SampleRandomBytes`
 //! | Nintendo 3DS      | `armv6k-nintendo-3ds` | [`getrandom`][1]
 //!
@@ -91,6 +91,18 @@
 //!
 //! This feature has no effect on targets other than `wasm32-unknown-unknown`.
 //!
+//! #### Node.js ES module support
+//!
+//! Node.js supports both [CommonJS modules] and [ES modules]. Due to
+//! limitations in wasm-bindgen's [`module`] support, we cannot directly
+//! support ES Modules running on Node.js. However, on Node v15 and later, the
+//! module author can add a simple shim to support the Web Cryptography API:
+//! ```js
+//! import { webcrypto } from 'node:crypto'
+//! globalThis.crypto = webcrypto
+//! ```
+//! This crate will then use the provided `webcrypto` implementation.
+//!
 //! ### Custom implementations
 //!
 //! The [`register_custom_getrandom!`] macro allows a user to mark their own
@@ -154,11 +166,14 @@
 //! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
 //! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
 //! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
-//! [`crypto.randomBytes`]: https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
+//! [`crypto.randomFillSync`]: https://nodejs.org/api/crypto.html#cryptorandomfillsyncbuffer-offset-size
 //! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
 //! [`random_get`]: https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#-random_getbuf-pointeru8-buf_len-size---errno
 //! [WebAssembly support]: #webassembly-support
 //! [`wasm-bindgen`]: https://github.com/rustwasm/wasm-bindgen
+//! [`module`]: https://rustwasm.github.io/wasm-bindgen/reference/attributes/on-js-imports/module.html
+//! [CommonJS modules]: https://nodejs.org/api/modules.html
+//! [ES modules]: https://nodejs.org/api/esm.html
 
 #![doc(
     html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",