73 lines
2.8 KiB
JavaScript
73 lines
2.8 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] || ''
|
|||
|
|
// `id.length + 1 === size` is a more compact option.
|
|||
|
|
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 }
|