@waiting/base64/dist/lib/from_buffer.js

Base64 encoding/decoding in pure JS on both modern Browsers and Node.js. Also supports URL-safe base64

// rewrite from https://github.com/beatgammit/base64-js
import { lookup, ErrMsg } from './config'
export function fromUint8Array(input) {
    /* tslint:disable: no-bitwise */
    const len = input.length
    const extraBytes = len % 3 // if we have 1 byte left, pad 2 bytes
    const len2 = len - extraBytes
    const maxChunkLength = 12000 // must be multiple of 3
    const parts = new Array(Math.ceil(len2 / maxChunkLength) + (extraBytes ? 1 : 0))
    let curChunk = 0

    // go through the array every three bytes, we'll deal with trailing stuff later
    for (let i = 0, nextI = 0; i < len2; i = nextI) {
        nextI = i + maxChunkLength
        parts[curChunk] = encodeChunk(input, i, Math.min(nextI, len2))
        curChunk += 1
    }
    // pad the end with zeros, but make sure to not forget the extra bytes
    if (extraBytes === 1) {
        const tmp = input[len2] & 0xFF

        parts[curChunk] = lookup[tmp >> 2] + lookup[tmp << 4 & 0x3F] + '=='
    }
    else if (extraBytes === 2) {
        const tmp = (input[len2] & 0xFF) << 8 | (input[len2 + 1] & 0xFF)

        parts[curChunk] = lookup[tmp >> 10] +
            lookup[tmp >> 4 & 0x3F] +
            lookup[tmp << 2 & 0x3F] +
            '='
    }
    /* tslint:enable: no-bitwise */
    return parts.join('')
}
function encodeChunk(input, start, end) {
    if (start >= end) {
        throw new Error(ErrMsg.startMustGrossToEnd)
    }
    const arrLen = Math.ceil((end - start) / 3)
    const ret = new Array(arrLen)

    /* tslint:disable: no-bitwise */
    for (let i = start, curTriplet = 0; i < end; i += 3, curTriplet += 1) {
        ret[curTriplet] = tripletToBase64((input[i] & 0xFF) << 16 |
            (input[i + 1] & 0xFF) << 8 |
            (input[i + 2] & 0xFF))
    }
    /* tslint:enable: no-bitwise */
    return ret.join('')
}
function tripletToBase64(pos) {
    /* tslint:disable: no-bitwise */
    return lookup[pos >> 18 & 0x3F] +
        lookup[pos >> 12 & 0x3F] +
        lookup[pos >> 6 & 0x3F] +
        lookup[pos & 0x3F]
    /* tslint:enable: no-bitwise */
}