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1/**2 * negotiator3 * Copyright(c) 2012 Isaac Z. Schlueter4 * Copyright(c) 2014 Federico Romero5 * Copyright(c) 2014-2015 Douglas Christopher Wilson6 * MIT Licensed7 */8 9'use strict';10 11/**12 * Module exports.13 * @public14 */15 16module.exports = preferredCharsets;17module.exports.preferredCharsets = preferredCharsets;18 19/**20 * Module variables.21 * @private22 */23 24var simpleCharsetRegExp = /^\s*([^\s;]+)\s*(?:;(.*))?$/;25 26/**27 * Parse the Accept-Charset header.28 * @private29 */30 31function parseAcceptCharset(accept) {32  var accepts = accept.split(',');33 34  for (var i = 0, j = 0; i < accepts.length; i++) {35    var charset = parseCharset(accepts[i].trim(), i);36 37    if (charset) {38      accepts[j++] = charset;39    }40  }41 42  // trim accepts43  accepts.length = j;44 45  return accepts;46}47 48/**49 * Parse a charset from the Accept-Charset header.50 * @private51 */52 53function parseCharset(str, i) {54  var match = simpleCharsetRegExp.exec(str);55  if (!match) return null;56 57  var charset = match[1];58  var q = 1;59  if (match[2]) {60    var params = match[2].split(';')61    for (var j = 0; j < params.length; j++) {62      var p = params[j].trim().split('=');63      if (p[0] === 'q') {64        q = parseFloat(p[1]);65        break;66      }67    }68  }69 70  return {71    charset: charset,72    q: q,73    i: i74  };75}76 77/**78 * Get the priority of a charset.79 * @private80 */81 82function getCharsetPriority(charset, accepted, index) {83  var priority = {o: -1, q: 0, s: 0};84 85  for (var i = 0; i < accepted.length; i++) {86    var spec = specify(charset, accepted[i], index);87 88    if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {89      priority = spec;90    }91  }92 93  return priority;94}95 96/**97 * Get the specificity of the charset.98 * @private99 */100 101function specify(charset, spec, index) {102  var s = 0;103  if(spec.charset.toLowerCase() === charset.toLowerCase()){104    s |= 1;105  } else if (spec.charset !== '*' ) {106    return null107  }108 109  return {110    i: index,111    o: spec.i,112    q: spec.q,113    s: s114  }115}116 117/**118 * Get the preferred charsets from an Accept-Charset header.119 * @public120 */121 122function preferredCharsets(accept, provided) {123  // RFC 2616 sec 14.2: no header = *124  var accepts = parseAcceptCharset(accept === undefined ? '*' : accept || '');125 126  if (!provided) {127    // sorted list of all charsets128    return accepts129      .filter(isQuality)130      .sort(compareSpecs)131      .map(getFullCharset);132  }133 134  var priorities = provided.map(function getPriority(type, index) {135    return getCharsetPriority(type, accepts, index);136  });137 138  // sorted list of accepted charsets139  return priorities.filter(isQuality).sort(compareSpecs).map(function getCharset(priority) {140    return provided[priorities.indexOf(priority)];141  });142}143 144/**145 * Compare two specs.146 * @private147 */148 149function compareSpecs(a, b) {150  return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;151}152 153/**154 * Get full charset string.155 * @private156 */157 158function getFullCharset(spec) {159  return spec.charset;160}161 162/**163 * Check if a spec has any quality.164 * @private165 */166 167function isQuality(spec) {168  return spec.q > 0;169}170