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143 lines
3.7 KiB
143 lines
3.7 KiB
'use strict';
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const Transform = require('stream').Transform;
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/**
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* Encodes a Buffer into a base64 encoded string
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*
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* @param {Buffer} buffer Buffer to convert
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* @returns {String} base64 encoded string
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*/
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function encode(buffer) {
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if (typeof buffer === 'string') {
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buffer = Buffer.from(buffer, 'utf-8');
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}
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return buffer.toString('base64');
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}
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/**
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* Adds soft line breaks to a base64 string
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*
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* @param {String} str base64 encoded string that might need line wrapping
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* @param {Number} [lineLength=76] Maximum allowed length for a line
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* @returns {String} Soft-wrapped base64 encoded string
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*/
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function wrap(str, lineLength) {
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str = (str || '').toString();
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lineLength = lineLength || 76;
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if (str.length <= lineLength) {
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return str;
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}
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let result = [];
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let pos = 0;
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let chunkLength = lineLength * 1024;
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while (pos < str.length) {
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let wrappedLines = str
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.substr(pos, chunkLength)
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.replace(new RegExp('.{' + lineLength + '}', 'g'), '$&\r\n')
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.trim();
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result.push(wrappedLines);
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pos += chunkLength;
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}
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return result.join('\r\n').trim();
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}
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/**
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* Creates a transform stream for encoding data to base64 encoding
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*
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* @constructor
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* @param {Object} options Stream options
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* @param {Number} [options.lineLength=76] Maximum lenght for lines, set to false to disable wrapping
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*/
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class Encoder extends Transform {
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constructor(options) {
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super();
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// init Transform
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this.options = options || {};
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if (this.options.lineLength !== false) {
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this.options.lineLength = this.options.lineLength || 76;
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}
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this._curLine = '';
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this._remainingBytes = false;
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this.inputBytes = 0;
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this.outputBytes = 0;
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}
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_transform(chunk, encoding, done) {
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if (encoding !== 'buffer') {
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chunk = Buffer.from(chunk, encoding);
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}
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if (!chunk || !chunk.length) {
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return setImmediate(done);
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}
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this.inputBytes += chunk.length;
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if (this._remainingBytes && this._remainingBytes.length) {
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chunk = Buffer.concat([this._remainingBytes, chunk], this._remainingBytes.length + chunk.length);
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this._remainingBytes = false;
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}
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if (chunk.length % 3) {
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this._remainingBytes = chunk.slice(chunk.length - (chunk.length % 3));
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chunk = chunk.slice(0, chunk.length - (chunk.length % 3));
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} else {
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this._remainingBytes = false;
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}
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let b64 = this._curLine + encode(chunk);
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if (this.options.lineLength) {
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b64 = wrap(b64, this.options.lineLength);
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// remove last line as it is still most probably incomplete
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let lastLF = b64.lastIndexOf('\n');
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if (lastLF < 0) {
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this._curLine = b64;
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b64 = '';
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} else if (lastLF === b64.length - 1) {
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this._curLine = '';
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} else {
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this._curLine = b64.substr(lastLF + 1);
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b64 = b64.substr(0, lastLF + 1);
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}
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}
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if (b64) {
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this.outputBytes += b64.length;
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this.push(Buffer.from(b64, 'ascii'));
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}
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setImmediate(done);
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}
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_flush(done) {
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if (this._remainingBytes && this._remainingBytes.length) {
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this._curLine += encode(this._remainingBytes);
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}
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if (this._curLine) {
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this._curLine = wrap(this._curLine, this.options.lineLength);
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this.outputBytes += this._curLine.length;
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this.push(this._curLine, 'ascii');
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this._curLine = '';
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}
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done();
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}
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}
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// expose to the world
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module.exports = {
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encode,
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wrap,
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Encoder
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};
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