1/** 2 * negotiator 3 * Copyright(c) 2012 Isaac Z. Schlueter 4 * Copyright(c) 2014 Federico Romero 5 * Copyright(c) 2014-2015 Douglas Christopher Wilson 6 * MIT Licensed 7 */ 8 9'use strict'; 10 11/** 12 * Module exports. 13 * @public 14 */ 15 16module.exports = preferredEncodings; 17module.exports.preferredEncodings = preferredEncodings; 18 19/** 20 * Module variables. 21 * @private 22 */ 23 24var simpleEncodingRegExp = /^\s*([^\s;]+)\s*(?:;(.*))?$/; 25 26/** 27 * Parse the Accept-Encoding header. 28 * @private 29 */ 30 31function parseAcceptEncoding(accept) { 32 var accepts = accept.split(','); 33 var hasIdentity = false; 34 var minQuality = 1; 35 36 for (var i = 0, j = 0; i < accepts.length; i++) { 37 var encoding = parseEncoding(accepts[i].trim(), i); 38 39 if (encoding) { 40 accepts[j++] = encoding; 41 hasIdentity = hasIdentity || specify('identity', encoding); 42 minQuality = Math.min(minQuality, encoding.q || 1); 43 } 44 } 45 46 if (!hasIdentity) { 47 /* 48 * If identity doesn't explicitly appear in the accept-encoding header, 49 * it's added to the list of acceptable encoding with the lowest q 50 */ 51 accepts[j++] = { 52 encoding: 'identity', 53 q: minQuality, 54 i: i 55 }; 56 } 57 58 // trim accepts 59 accepts.length = j; 60 61 return accepts; 62} 63 64/** 65 * Parse an encoding from the Accept-Encoding header. 66 * @private 67 */ 68 69function parseEncoding(str, i) { 70 var match = simpleEncodingRegExp.exec(str); 71 if (!match) return null; 72 73 var encoding = match[1]; 74 var q = 1; 75 if (match[2]) { 76 var params = match[2].split(';'); 77 for (var j = 0; j < params.length; j++) { 78 var p = params[j].trim().split('='); 79 if (p[0] === 'q') { 80 q = parseFloat(p[1]); 81 break; 82 } 83 } 84 } 85 86 return { 87 encoding: encoding, 88 q: q, 89 i: i 90 }; 91} 92 93/** 94 * Get the priority of an encoding. 95 * @private 96 */ 97 98function getEncodingPriority(encoding, accepted, index) { 99 var priority = {o: -1, q: 0, s: 0}; 100 101 for (var i = 0; i < accepted.length; i++) { 102 var spec = specify(encoding, accepted[i], index); 103 104 if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) { 105 priority = spec; 106 } 107 } 108 109 return priority; 110} 111 112/** 113 * Get the specificity of the encoding. 114 * @private 115 */ 116 117function specify(encoding, spec, index) { 118 var s = 0; 119 if(spec.encoding.toLowerCase() === encoding.toLowerCase()){ 120 s |= 1; 121 } else if (spec.encoding !== '*' ) { 122 return null 123 } 124 125 return { 126 i: index, 127 o: spec.i, 128 q: spec.q, 129 s: s 130 } 131}; 132 133/** 134 * Get the preferred encodings from an Accept-Encoding header. 135 * @public 136 */ 137 138function preferredEncodings(accept, provided) { 139 var accepts = parseAcceptEncoding(accept || ''); 140 141 if (!provided) { 142 // sorted list of all encodings 143 return accepts 144 .filter(isQuality) 145 .sort(compareSpecs) 146 .map(getFullEncoding); 147 } 148 149 var priorities = provided.map(function getPriority(type, index) { 150 return getEncodingPriority(type, accepts, index); 151 }); 152 153 // sorted list of accepted encodings 154 return priorities.filter(isQuality).sort(compareSpecs).map(function getEncoding(priority) { 155 return provided[priorities.indexOf(priority)]; 156 }); 157} 158 159/** 160 * Compare two specs. 161 * @private 162 */ 163 164function compareSpecs(a, b) { 165 return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0; 166} 167 168/** 169 * Get full encoding string. 170 * @private 171 */ 172 173function getFullEncoding(spec) { 174 return spec.encoding; 175} 176 177/** 178 * Check if a spec has any quality. 179 * @private 180 */ 181 182function isQuality(spec) { 183 return spec.q > 0; 184} 185