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69 lines
2.6 KiB
69 lines
2.6 KiB
let random = async bytes => crypto.getRandomValues(new Uint8Array(bytes)) |
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let customAlphabet = (alphabet, defaultSize = 21) => { |
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// First, a bitmask is necessary to generate the ID. The bitmask makes bytes |
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// values closer to the alphabet size. The bitmask calculates the closest |
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// `2^31 - 1` number, which exceeds the alphabet size. |
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// For example, the bitmask for the alphabet size 30 is 31 (00011111). |
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// `Math.clz32` is not used, because it is not available in browsers. |
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let mask = (2 << (Math.log(alphabet.length - 1) / Math.LN2)) - 1 |
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// Though, the bitmask solution is not perfect since the bytes exceeding |
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// the alphabet size are refused. Therefore, to reliably generate the ID, |
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// the random bytes redundancy has to be satisfied. |
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// Note: every hardware random generator call is performance expensive, |
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// because the system call for entropy collection takes a lot of time. |
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// So, to avoid additional system calls, extra bytes are requested in advance. |
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// Next, a step determines how many random bytes to generate. |
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// The number of random bytes gets decided upon the ID size, mask, |
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// alphabet size, and magic number 1.6 (using 1.6 peaks at performance |
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// according to benchmarks). |
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// `-~f => Math.ceil(f)` if f is a float |
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// `-~i => i + 1` if i is an integer |
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let step = -~((1.6 * mask * defaultSize) / alphabet.length) |
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return async (size = defaultSize) => { |
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let id = '' |
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while (true) { |
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let bytes = crypto.getRandomValues(new Uint8Array(step)) |
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// A compact alternative for `for (var i = 0; i < step; i++)`. |
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let i = step | 0 |
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while (i--) { |
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// Adding `|| ''` refuses a random byte that exceeds the alphabet size. |
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id += alphabet[bytes[i] & mask] || '' |
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if (id.length === size) return id |
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} |
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} |
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} |
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} |
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let nanoid = async (size = 21) => { |
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let id = '' |
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let bytes = crypto.getRandomValues(new Uint8Array((size |= 0))) |
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// A compact alternative for `for (var i = 0; i < step; i++)`. |
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while (size--) { |
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// It is incorrect to use bytes exceeding the alphabet size. |
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// The following mask reduces the random byte in the 0-255 value |
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// range to the 0-63 value range. Therefore, adding hacks, such |
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// as empty string fallback or magic numbers, is unneccessary because |
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// the bitmask trims bytes down to the alphabet size. |
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let byte = bytes[size] & 63 |
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if (byte < 36) { |
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// `0-9a-z` |
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id += byte.toString(36) |
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} else if (byte < 62) { |
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// `A-Z` |
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id += (byte - 26).toString(36).toUpperCase() |
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} else if (byte < 63) { |
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id += '_' |
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} else { |
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id += '-' |
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} |
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} |
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return id |
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} |
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module.exports = { nanoid, customAlphabet, random }
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