127 lines
3.0 KiB
JavaScript
127 lines
3.0 KiB
JavaScript
'use strict';
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/*
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Decode functions adapted from:
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Version 1.0 12/25/99 Copyright (C) 1999 Masanao Izumo <iz@onicos.co.jp>
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http://www.onicos.com/staff/iz/amuse/javascript/expert/base64.txt
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*/
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const Stream = require('stream');
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const internals = {
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decodeChars: [
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
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52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
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-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
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15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
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-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
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41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1
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]
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};
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exports.decode = function (buffer) {
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const decodeChars = internals.decodeChars;
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const len = buffer.length;
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const allocated = Math.ceil(len / 4) * 3;
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const result = Buffer.alloc(allocated);
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let c1;
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let c2;
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let c3;
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let c4;
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let j = 0;
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for (let i = 0; i < len; ) {
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do {
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c1 = decodeChars[buffer[i++] & 0xff];
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}
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while (i < len && c1 === -1);
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if (c1 === -1) {
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break;
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}
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do {
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c2 = decodeChars[buffer[i++] & 0xff];
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}
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while (i < len && c2 === -1);
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if (c2 === -1) {
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break;
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}
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result[j++] = (c1 << 2) | ((c2 & 0x30) >> 4);
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do {
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c3 = buffer[i++] & 0xff;
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if (c3 === 61) { // =
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return result.slice(0, j);
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}
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c3 = decodeChars[c3];
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}
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while (i < len && c3 === -1);
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if (c3 === -1) {
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break;
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}
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result[j++] = ((c2 & 0x0f) << 4) | ((c3 & 0x3c) >> 2);
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do {
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c4 = buffer[i++] & 0xff;
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if (c4 === 61) { // =
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return result.slice(0, j);
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}
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c4 = decodeChars[c4];
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}
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while (i < len && c4 === -1);
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if (c4 !== -1) {
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result[j++] = ((c3 & 0x03) << 6) | c4;
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}
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}
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return (j === allocated ? result : result.slice(0, j));
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};
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exports.Decoder = class Decoder extends Stream.Transform {
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constructor() {
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super();
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this._reminder = null;
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}
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_transform(chunk, encoding, callback) {
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let part = this._reminder ? Buffer.concat([this._reminder, chunk]) : chunk;
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const remaining = part.length % 4;
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if (remaining) {
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this._reminder = part.slice(part.length - remaining);
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part = part.slice(0, part.length - remaining);
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}
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else {
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this._reminder = null;
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}
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this.push(exports.decode(part));
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return callback();
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}
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_flush(callback) {
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if (this._reminder) {
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this.push(exports.decode(this._reminder));
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}
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return callback();
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}
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};
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