86 行
3.3 KiB
JavaScript
86 行
3.3 KiB
JavaScript
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'use strict'
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const STANDARD_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
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const URL_SAFE_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'
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/**
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* 纯 JS Base64 编码，默认输出带填充的标准 Base64。
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* 协议调用方必须显式声明 URL-safe 与是否保留填充，避免现场字符串替换。
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*/
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function encodeBase64(value, options = {}) {
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if (!(value instanceof Uint8Array)) throw new TypeError('Base64 value must be Uint8Array')
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const alphabet = options.urlSafe ? URL_SAFE_ALPHABET : STANDARD_ALPHABET
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const padding = options.padding !== false
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let output = ''
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for (let offset = 0; offset < value.length; offset += 3) {
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const first = value[offset]
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const hasSecond = offset + 1 < value.length
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const hasThird = offset + 2 < value.length
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const second = hasSecond ? value[offset + 1] : 0
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const third = hasThird ? value[offset + 2] : 0
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output += alphabet[first >>> 2]
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output += alphabet[((first & 0x03) << 4) | (second >>> 4)]
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if (hasSecond) {
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output += alphabet[((second & 0x0f) << 2) | (third >>> 6)]
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} else if (padding) {
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output += '='
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}
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if (hasThird) {
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output += alphabet[third & 0x3f]
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} else if (padding) {
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output += '='
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}
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}
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return output
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}
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/**
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* 严格解码标准 Base64 或 Base64URL，不依赖浏览器/Hermes 的 atob。
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* 接受有填充或无填充形式，但拒绝混合字母表、非法长度、非法填充和非零尾随位。
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*/
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function decodeBase64(value) {
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if (typeof value !== 'string') throw new TypeError('Base64 value must be a string')
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if (value.length === 0) return new Uint8Array(0)
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if (/[^A-Za-z0-9+/_=-]/.test(value)) throw new Error('Base64 contains invalid characters')
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if (/[+\/]/.test(value) && /[-_]/.test(value)) {
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throw new Error('Base64 cannot mix standard and URL-safe alphabets')
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}
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const firstPadding = value.indexOf('=')
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const data = firstPadding === -1 ? value : value.slice(0, firstPadding)
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const padding = firstPadding === -1 ? '' : value.slice(firstPadding)
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if (padding !== '' && padding !== '=' && padding !== '==') {
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throw new Error('Base64 padding is invalid')
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}
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if (data.includes('=')) throw new Error('Base64 padding is invalid')
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const remainder = data.length % 4
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if (remainder === 1) throw new Error('Base64 length is invalid')
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const expectedPadding = remainder === 0 ? 0 : 4 - remainder
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if (padding.length !== 0 && padding.length !== expectedPadding) {
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throw new Error('Base64 padding length is invalid')
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}
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const normalized = data.replace(/-/g, '+').replace(/_/g, '/')
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const outputLength = Math.floor((normalized.length * 6) / 8)
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const output = new Uint8Array(outputLength)
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let accumulator = 0
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let bitCount = 0
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let outputIndex = 0
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for (const character of normalized) {
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const sextet = STANDARD_ALPHABET.indexOf(character)
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if (sextet < 0) throw new Error('Base64 contains invalid characters')
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accumulator = (accumulator << 6) | sextet
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bitCount += 6
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if (bitCount >= 8) {
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bitCount -= 8
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output[outputIndex] = (accumulator >>> bitCount) & 0xff
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outputIndex += 1
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accumulator &= (1 << bitCount) - 1
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}
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}
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if (accumulator !== 0) throw new Error('Base64 has non-zero trailing bits')
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return output
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}
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module.exports = { decodeBase64, encodeBase64 }
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