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220 lines
6.4 KiB
220 lines
6.4 KiB
1 month ago
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'use strict';
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const Transform = require('stream').Transform;
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/**
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* Encodes a Buffer into a Quoted-Printable encoded string
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*
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* @param {Buffer} buffer Buffer to convert
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* @returns {String} Quoted-Printable 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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// usable characters that do not need encoding
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let ranges = [
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// https://tools.ietf.org/html/rfc2045#section-6.7
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[0x09], // <TAB>
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[0x0a], // <LF>
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[0x0d], // <CR>
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[0x20, 0x3c], // <SP>!"#$%&'()*+,-./0123456789:;
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[0x3e, 0x7e] // >?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}
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];
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let result = '';
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let ord;
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for (let i = 0, len = buffer.length; i < len; i++) {
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ord = buffer[i];
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// if the char is in allowed range, then keep as is, unless it is a WS in the end of a line
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if (checkRanges(ord, ranges) && !((ord === 0x20 || ord === 0x09) && (i === len - 1 || buffer[i + 1] === 0x0a || buffer[i + 1] === 0x0d))) {
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result += String.fromCharCode(ord);
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continue;
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}
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result += '=' + (ord < 0x10 ? '0' : '') + ord.toString(16).toUpperCase();
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}
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return result;
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}
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/**
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* Adds soft line breaks to a Quoted-Printable string
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*
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* @param {String} str Quoted-Printable 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 Quoted-Printable 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 pos = 0;
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let len = str.length;
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let match, code, line;
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let lineMargin = Math.floor(lineLength / 3);
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let result = '';
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// insert soft linebreaks where needed
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while (pos < len) {
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line = str.substr(pos, lineLength);
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if ((match = line.match(/\r\n/))) {
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line = line.substr(0, match.index + match[0].length);
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result += line;
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pos += line.length;
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continue;
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}
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if (line.substr(-1) === '\n') {
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// nothing to change here
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result += line;
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pos += line.length;
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continue;
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} else if ((match = line.substr(-lineMargin).match(/\n.*?$/))) {
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// truncate to nearest line break
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line = line.substr(0, line.length - (match[0].length - 1));
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result += line;
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pos += line.length;
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continue;
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} else if (line.length > lineLength - lineMargin && (match = line.substr(-lineMargin).match(/[ \t.,!?][^ \t.,!?]*$/))) {
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// truncate to nearest space
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line = line.substr(0, line.length - (match[0].length - 1));
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} else if (line.match(/[=][\da-f]{0,2}$/i)) {
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// push incomplete encoding sequences to the next line
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if ((match = line.match(/[=][\da-f]{0,1}$/i))) {
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line = line.substr(0, line.length - match[0].length);
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}
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// ensure that utf-8 sequences are not split
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while (line.length > 3 && line.length < len - pos && !line.match(/^(?:=[\da-f]{2}){1,4}$/i) && (match = line.match(/[=][\da-f]{2}$/gi))) {
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code = parseInt(match[0].substr(1, 2), 16);
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if (code < 128) {
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break;
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}
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line = line.substr(0, line.length - 3);
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if (code >= 0xc0) {
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break;
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}
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}
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}
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if (pos + line.length < len && line.substr(-1) !== '\n') {
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if (line.length === lineLength && line.match(/[=][\da-f]{2}$/i)) {
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line = line.substr(0, line.length - 3);
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} else if (line.length === lineLength) {
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line = line.substr(0, line.length - 1);
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}
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pos += line.length;
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line += '=\r\n';
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} else {
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pos += line.length;
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}
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result += line;
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}
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return result;
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}
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/**
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* Helper function to check if a number is inside provided ranges
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*
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* @param {Number} nr Number to check for
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* @param {Array} ranges An Array of allowed values
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* @returns {Boolean} True if the value was found inside allowed ranges, false otherwise
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*/
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function checkRanges(nr, ranges) {
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for (let i = ranges.length - 1; i >= 0; i--) {
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if (!ranges[i].length) {
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continue;
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}
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if (ranges[i].length === 1 && nr === ranges[i][0]) {
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return true;
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}
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if (ranges[i].length === 2 && nr >= ranges[i][0] && nr <= ranges[i][1]) {
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return true;
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}
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}
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return false;
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}
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/**
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* Creates a transform stream for encoding data to Quoted-Printable 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 length 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.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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let qp;
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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 done();
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}
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this.inputBytes += chunk.length;
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if (this.options.lineLength) {
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qp = this._curLine + encode(chunk);
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qp = wrap(qp, this.options.lineLength);
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qp = qp.replace(/(^|\n)([^\n]*)$/, (match, lineBreak, lastLine) => {
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this._curLine = lastLine;
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return lineBreak;
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});
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if (qp) {
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this.outputBytes += qp.length;
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this.push(qp);
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}
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} else {
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qp = encode(chunk);
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this.outputBytes += qp.length;
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this.push(qp, 'ascii');
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}
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done();
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}
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_flush(done) {
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if (this._curLine) {
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this.outputBytes += this._curLine.length;
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this.push(this._curLine, 'ascii');
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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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