bc518174
 王天杨
提交两个项目文件
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let random = async bytes => crypto.getRandomValues(new Uint8Array(bytes))
let customAlphabet = (alphabet, defaultSize = 21) => {
// 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).
// `Math.clz32` is not used, because it is not available in browsers.
let mask = (2 << (Math.log(alphabet.length - 1) / Math.LN2)) - 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).
// `-~f => Math.ceil(f)` if f is a float
// `-~i => i + 1` if i is an integer
let step = -~((1.6 * mask * defaultSize) / alphabet.length)
return async (size = defaultSize) => {
let id = ''
while (true) {
let bytes = crypto.getRandomValues(new Uint8Array(step))
// A compact alternative for `for (var i = 0; i < step; i++)`.
let i = step | 0
while (i--) {
// Adding `|| ''` refuses a random byte that exceeds the alphabet size.
id += alphabet[bytes[i] & mask] || ''
if (id.length === size) return id
}
}
}
}
let nanoid = async (size = 21) => {
let id = ''
let bytes = crypto.getRandomValues(new Uint8Array((size |= 0)))
// 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.
let byte = bytes[size] & 63
if (byte < 36) {
// `0-9a-z`
id += byte.toString(36)
} else if (byte < 62) {
// `A-Z`
id += (byte - 26).toString(36).toUpperCase()
} else if (byte < 63) {
id += '_'
} else {
id += '-'
}
}
return id
}
module.exports = { nanoid, customAlphabet, random }
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