mirror of
https://github.com/idanoo/GoScrobble.git
synced 2024-11-24 09:25:15 +00:00
72 lines
2.7 KiB
JavaScript
72 lines
2.7 KiB
JavaScript
let crypto = require('crypto')
|
||
|
||
let { urlAlphabet } = require('../url-alphabet/index.cjs')
|
||
|
||
// `crypto.randomFill()` is a little faster than `crypto.randomBytes()`,
|
||
// because it is possible to use in combination with `Buffer.allocUnsafe()`.
|
||
let random = bytes =>
|
||
new Promise((resolve, reject) => {
|
||
// `Buffer.allocUnsafe()` is faster because it doesn’t flush the memory.
|
||
// Memory flushing is unnecessary since the buffer allocation itself resets
|
||
// the memory with the new bytes.
|
||
crypto.randomFill(Buffer.allocUnsafe(bytes), (err, buf) => {
|
||
if (err) {
|
||
reject(err)
|
||
} else {
|
||
resolve(buf)
|
||
}
|
||
})
|
||
})
|
||
|
||
let customAlphabet = (alphabet, size) => {
|
||
// 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)
|
||
|
||
let tick = id =>
|
||
random(step).then(bytes => {
|
||
// A compact alternative for `for (var 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
|
||
}
|
||
return tick(id)
|
||
})
|
||
|
||
return () => tick('')
|
||
}
|
||
|
||
let nanoid = (size = 21) =>
|
||
random(size).then(bytes => {
|
||
let id = ''
|
||
// A compact alternative for `for (var i = 0; i < step; 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, random }
|