1 files changed, 106 insertions, 0 deletions
diff --git a/src/js.rs b/src/js.rs
new file mode 100644
index 0000000..d48c7d3
--- /dev/null
+++ b/src/js.rs
@@ -0,0 +1,106 @@
+// 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.
+use crate::Error;
+
+extern crate std;
+use std::thread_local;
+
+use js_sys::Uint8Array;
+use wasm_bindgen::prelude::*;
+
+// Maximum is 65536 bytes see https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues
+const BROWSER_CRYPTO_BUFFER_SIZE: usize = 256;
+
+enum RngSource {
+    Node(NodeCrypto),
+    Browser(BrowserCrypto, Uint8Array),
+}
+
+// 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: Result<RngSource, Error> = getrandom_init();
+);
+
+pub(crate) fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
+    RNG_SOURCE.with(|result| {
+        let source = result.as_ref().map_err(|&e| e)?;
+
+        match source {
+            RngSource::Node(n) => {
+                if n.random_fill_sync(dest).is_err() {
+                    return Err(Error::NODE_RANDOM_FILL_SYNC);
+                }
+            }
+            RngSource::Browser(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) {
+                    // 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);
+                    }
+                    sub_buf.copy_to(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). We get `self.crypto` (called `msCrypto` on IE), so we
+        // can call `crypto.getRandomValues`. If `crypto` isn't defined, we
+        // assume we're in an older web browser and the OS RNG isn't available.
+
+        let crypto: BrowserCrypto = match (self_.crypto(), self_.ms_crypto()) {
+            (crypto, _) if !crypto.is_undefined() => crypto,
+            (_, crypto) if !crypto.is_undefined() => crypto,
+            _ => return Err(Error::WEB_CRYPTO),
+        };
+
+        let buf = Uint8Array::new_with_length(BROWSER_CRYPTO_BUFFER_SIZE as u32);
+        return Ok(RngSource::Browser(crypto, buf));
+    }
+
+    let crypto = MODULE.require("crypto").map_err(|_| Error::NODE_CRYPTO)?;
+    Ok(RngSource::Node(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, js_name = "msCrypto")]
+    fn ms_crypto(me: &Self_) -> BrowserCrypto;
+    #[wasm_bindgen(method, getter)]
+    fn crypto(me: &Self_) -> BrowserCrypto;
+
+    type BrowserCrypto;
+    #[wasm_bindgen(method, js_name = getRandomValues, catch)]
+    fn get_random_values(me: &BrowserCrypto, buf: &Uint8Array) -> Result<(), JsValue>;
+
+    #[wasm_bindgen(js_name = module)]
+    static MODULE: NodeModule;
+
+    type NodeModule;
+    #[wasm_bindgen(method, catch)]
+    fn require(this: &NodeModule, s: &str) -> Result<NodeCrypto, JsValue>;
+
+    type NodeCrypto;
+    #[wasm_bindgen(method, js_name = randomFillSync, catch)]
+    fn random_fill_sync(crypto: &NodeCrypto, buf: &mut [u8]) -> Result<(), JsValue>;
+}