mirror of
https://github.com/idanoo/GoScrobble.git
synced 2024-11-22 16:35:14 +00:00
81 lines
3.0 KiB
JavaScript
81 lines
3.0 KiB
JavaScript
let crypto = require('crypto')
|
|
|
|
let { urlAlphabet } = require('./url-alphabet/index.cjs')
|
|
|
|
// It is best to make fewer, larger requests to the crypto module to
|
|
// avoid system call overhead. So, random numbers are generated in a
|
|
// pool. The pool is a Buffer that is larger than the initial random
|
|
// request size by this multiplier. The pool is enlarged if subsequent
|
|
// requests exceed the maximum buffer size.
|
|
const POOL_SIZE_MULTIPLIER = 32
|
|
let pool, poolOffset
|
|
|
|
let random = bytes => {
|
|
if (!pool || pool.length < bytes) {
|
|
pool = Buffer.allocUnsafe(bytes * POOL_SIZE_MULTIPLIER)
|
|
crypto.randomFillSync(pool)
|
|
poolOffset = 0
|
|
} else if (poolOffset + bytes > pool.length) {
|
|
crypto.randomFillSync(pool)
|
|
poolOffset = 0
|
|
}
|
|
|
|
let res = pool.subarray(poolOffset, poolOffset + bytes)
|
|
poolOffset += bytes
|
|
return res
|
|
}
|
|
|
|
let customRandom = (alphabet, size, getRandom) => {
|
|
// First, a bitmask is necessary to generate the ID. The bitmask makes bytes
|
|
// values closer to the alphabet size. The bitmask calculates the closest
|
|
// `2^31 - 1` number, which exceeds the alphabet size.
|
|
// For example, the bitmask for the alphabet size 30 is 31 (00011111).
|
|
let mask = (2 << (31 - Math.clz32((alphabet.length - 1) | 1))) - 1
|
|
// Though, the bitmask solution is not perfect since the bytes exceeding
|
|
// the alphabet size are refused. Therefore, to reliably generate the ID,
|
|
// the random bytes redundancy has to be satisfied.
|
|
|
|
// Note: every hardware random generator call is performance expensive,
|
|
// because the system call for entropy collection takes a lot of time.
|
|
// So, to avoid additional system calls, extra bytes are requested in advance.
|
|
|
|
// Next, a step determines how many random bytes to generate.
|
|
// The number of random bytes gets decided upon the ID size, mask,
|
|
// alphabet size, and magic number 1.6 (using 1.6 peaks at performance
|
|
// according to benchmarks).
|
|
let step = Math.ceil((1.6 * mask * size) / alphabet.length)
|
|
|
|
return () => {
|
|
let id = ''
|
|
while (true) {
|
|
let bytes = getRandom(step)
|
|
// A compact alternative for `for (let i = 0; i < step; i++)`.
|
|
let i = step
|
|
while (i--) {
|
|
// Adding `|| ''` refuses a random byte that exceeds the alphabet size.
|
|
id += alphabet[bytes[i] & mask] || ''
|
|
if (id.length === size) return id
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
let customAlphabet = (alphabet, size) => customRandom(alphabet, size, random)
|
|
|
|
let nanoid = (size = 21) => {
|
|
let bytes = random(size)
|
|
let id = ''
|
|
// A compact alternative for `for (let i = 0; i < size; i++)`.
|
|
while (size--) {
|
|
// It is incorrect to use bytes exceeding the alphabet size.
|
|
// The following mask reduces the random byte in the 0-255 value
|
|
// range to the 0-63 value range. Therefore, adding hacks, such
|
|
// as empty string fallback or magic numbers, is unneccessary because
|
|
// the bitmask trims bytes down to the alphabet size.
|
|
id += urlAlphabet[bytes[size] & 63]
|
|
}
|
|
return id
|
|
}
|
|
|
|
module.exports = { nanoid, customAlphabet, customRandom, urlAlphabet, random }
|