1 files changed, 113 insertions, 0 deletions
diff --git a/getrandom/src/wasm32_bindgen.rs b/getrandom/src/wasm32_bindgen.rs
new file mode 100644
index 0000000..86839a0
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+++ b/getrandom/src/wasm32_bindgen.rs
@@ -0,0 +1,113 @@
+// Copyright 2018 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementation for WASM via wasm-bindgen
+extern crate std;
+
+use core::cell::RefCell;
+use core::mem;
+use std::thread_local;
+
+use wasm_bindgen::prelude::*;
+
+use crate::error::{BINDGEN_CRYPTO_UNDEF, BINDGEN_GRV_UNDEF};
+use crate::Error;
+
+#[derive(Clone, Debug)]
+enum RngSource {
+    Node(NodeCrypto),
+    Browser(BrowserCrypto),
+}
+
+// JsValues are always per-thread, so we initialize RngSource for each thread.
+//   See: https://github.com/rustwasm/wasm-bindgen/pull/955
+thread_local!(
+    static RNG_SOURCE: RefCell<Option<RngSource>> = RefCell::new(None);
+);
+
+pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
+    assert_eq!(mem::size_of::<usize>(), 4);
+
+    RNG_SOURCE.with(|f| {
+        let mut source = f.borrow_mut();
+        if source.is_none() {
+            *source = Some(getrandom_init()?);
+        }
+
+        match source.as_ref().unwrap() {
+            RngSource::Node(n) => n.random_fill_sync(dest),
+            RngSource::Browser(n) => {
+                // see https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues
+                //
+                // where it says:
+                //
+                // > A QuotaExceededError DOMException is thrown if the
+                // > requested length is greater than 65536 bytes.
+                for chunk in dest.chunks_mut(65536) {
+                    n.get_random_values(chunk)
+                }
+            }
+        };
+        Ok(())
+    })
+}
+
+fn getrandom_init() -> Result<RngSource, Error> {
+    if let Ok(self_) = Global::get_self() {
+        // 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 = self_.crypto();
+        if crypto.is_undefined() {
+            return Err(BINDGEN_CRYPTO_UNDEF);
+        }
+
+        // Test if `crypto.getRandomValues` is undefined as well
+        let crypto: BrowserCrypto = crypto.into();
+        if crypto.get_random_values_fn().is_undefined() {
+            return Err(BINDGEN_GRV_UNDEF);
+        }
+
+        return Ok(RngSource::Browser(crypto));
+    }
+
+    return Ok(RngSource::Node(node_require("crypto")));
+}
+
+#[wasm_bindgen]
+extern "C" {
+    type Global;
+    #[wasm_bindgen(getter, catch, static_method_of = Global, js_class = self, js_name = self)]
+    fn get_self() -> Result<Self_, JsValue>;
+
+    type Self_;
+    #[wasm_bindgen(method, getter, structural)]
+    fn crypto(me: &Self_) -> JsValue;
+
+    #[derive(Clone, Debug)]
+    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)]
+    fn get_random_values_fn(me: &BrowserCrypto) -> JsValue;
+    #[wasm_bindgen(method, js_name = getRandomValues, structural)]
+    fn get_random_values(me: &BrowserCrypto, buf: &mut [u8]);
+
+    #[wasm_bindgen(js_name = require)]
+    fn node_require(s: &str) -> NodeCrypto;
+
+    #[derive(Clone, Debug)]
+    type NodeCrypto;
+
+    #[wasm_bindgen(method, js_name = randomFillSync, structural)]
+    fn random_fill_sync(me: &NodeCrypto, buf: &mut [u8]);
+}