Update documentation and error messages

This allows users to get an actionable error message about this
particular problem. We also add detection for this problem.

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

src/error.rs

@@ -168,7 +168,7 @@ fn internal_desc(error: Error) -> Option<&'static str> {
         Error::WEB_CRYPTO => Some("Web Crypto API 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 CommonJS module is unavailable"),
+        Error::NODE_CRYPTO => Some("Node.js crypto CommonJS module is unavailable, see https://docs.rs/getrandom#nodejs-es6-module-support"),
         Error::NODE_RANDOM_FILL_SYNC => Some("Calling Node.js API crypto.randomFillSync failed"),
         _ => None,
     }

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 +91,17 @@
 //!
 //! This feature has no effect on targets other than `wasm32-unknown-unknown`.
 //!
+//! #### Node.js ES6 Module support
+//!
+//! Due to limitations in wasm-bindgen's [`module`] support, we cannot directly
+//! support Node.js running in an ESM context. 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 +165,12 @@
 //! [`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
 
 #![doc(
     html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",