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Use Math.random when debugger is attached #8

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merged 4 commits into from
Apr 20, 2020
Merged

Use Math.random when debugger is attached #8

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1463ff3
Use Math.random when debugger is attached
TheAlmightyBob Apr 20, 2020
19b5fdf
Warn when using insecure random number generator
LinusU Apr 20, 2020
ffba939
Only fallback to insecure RNG when syncrounous calling is unavailable
LinusU Apr 20, 2020
8711ec0
Improve warning message
LinusU Apr 20, 2020
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24 changes: 24 additions & 0 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,21 @@ const base64Decode = require('fast-base64-decode')
class TypeMismatchError extends Error {}
class QuotaExceededError extends Error {}

let warned = false
function insecureRandomValues (array) {
if (!warned) {
console.warn('Using an insecure random number generator, this should only happen when running in a debugger without support for crypto.getRandomValues')
warned = true
}

for (let i = 0, r; i < array.length; i++) {
if ((i & 0x03) === 0) r = Math.random() * 0x100000000
array[i] = (r >>> ((i & 0x03) << 3)) & 0xff
}

return array
}

/**
* @param {Int8Array|Uint8Array|Int16Array|Uint16Array|Int32Array|Uint32Array|Uint8ClampedArray} array
*/
Expand All @@ -16,6 +31,15 @@ function getRandomValues (array) {
throw new QuotaExceededError('Can only request a maximum of 65536 bytes')
}

// Calling RNGetRandomValues.getRandomBase64 in debug mode leads to the error
// "Calling synchronous methods on native modules is not supported in Chrome".
// So in that specific case we fall back to just using Math.random.
if (__DEV__) {
if (typeof global.nativeCallSyncHook === 'undefined') {
return insecureRandomValues(array)
}
}

base64Decode(RNGetRandomValues.getRandomBase64(array.byteLength), new Uint8Array(array.buffer, array.byteOffset, array.byteLength))

return array
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