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Modify random_get to use crypto.getRandomValues #75

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merged 8 commits into from
May 3, 2024
Merged

Modify random_get to use crypto.getRandomValues #75

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6729ef8
switch random_get to use crypto.getRandomValues
May 1, 2024
d9d1b48
globalThis.crypto to crypto
May 1, 2024
741e185
fallback to Math.random if crypto not found
May 1, 2024
eb77211
fixing crypto detection
May 1, 2024
1d69adc
fix usage of this instead of self
May 1, 2024
fab1ef3
fixed bug
May 1, 2024
2140456
refactor to more succinct code
May 1, 2024
6c3da50
switch to `"crypto" in globalThis`
May 3, 2024
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18 changes: 16 additions & 2 deletions src/wasi.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ export default class WASI {
inst: { exports: { memory: WebAssembly.Memory } };
// eslint-disable-next-line @typescript-eslint/no-explicit-any
wasiImport: { [key: string]: (...args: Array<any>) => unknown };
private readonly hasCrypto: boolean = "crypto" in Function("return this")();

/// Start a WASI command
start(instance: {
Expand Down Expand Up @@ -826,8 +827,21 @@ export default class WASI {
sched_yield() {},
random_get(buf: number, buf_len: number) {
const buffer8 = new Uint8Array(self.inst.exports.memory.buffer);
for (let i = 0; i < buf_len; i++) {
buffer8[buf + i] = (Math.random() * 256) | 0;
const end = buf + buf_len;

if (self.hasCrypto) {
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Can you check "crypto" in globalThis instead and not cache it in an instance variable?

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@Aandreba Aandreba May 1, 2024 •
edited
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I tried, but it didn't pass the tests. Looks like globalThis doesn't exist on all environments 😞

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Also, caching it is most probably faster than checking every time random_get gets called

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Did it fail in node.js? Maybe the node.js version that was used is too old? globalThis is supposed to work in all environments. It was introduced as way to unify window, self and global across the various javascript environments.

As for performance, if random_get is called rarely a tiny slowdown shouldn't matter and if it is called frequently, I would expect the JIT to optimize it down to a couple instructions max, which is much less than even the overhead of making a native call, let alone actually running the PRNG.

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I remembered it failing on some test, but it seems I was mistaken. I've pushed the uncached "crypto" in globalThis version.

let i = buf;
for (; i < end; ) {
const next_i = i + 65_536;
crypto.getRandomValues(
buffer8.subarray(i, next_i > end ? end : next_i),
);
i = next_i;
}
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} else {
for (let i = buf; i < end; i++) {
buffer8[i] = (Math.random() * 256) | 0;
}
}
},
// eslint-disable-next-line @typescript-eslint/no-unused-vars
Expand Down
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