codekingpro/portable-devtools

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 = {encoding: encoding, 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    encoding: encoding,
127    i: index,
128    o: spec.i,
129    q: spec.q,
130    s: s
131  }
132};
133
134/**
135 * Get the preferred encodings from an Accept-Encoding header.
136 * @public
137 */
138
139function preferredEncodings(accept, provided, preferred) {
140  var accepts = parseAcceptEncoding(accept || '');
141
142  var comparator = preferred ? function comparator (a, b) {
143    if (a.q !== b.q) {
144      return b.q - a.q // higher quality first
145    }
146
147    var aPreferred = preferred.indexOf(a.encoding)
148    var bPreferred = preferred.indexOf(b.encoding)
149
150    if (aPreferred === -1 && bPreferred === -1) {
151      // consider the original specifity/order
152      return (b.s - a.s) || (a.o - b.o) || (a.i - b.i)
153    }
154
155    if (aPreferred !== -1 && bPreferred !== -1) {
156      return aPreferred - bPreferred // consider the preferred order
157    }
158
159    return aPreferred === -1 ? 1 : -1 // preferred first
160  } : compareSpecs;
161
162  if (!provided) {
163    // sorted list of all encodings
164    return accepts
165      .filter(isQuality)
166      .sort(comparator)
167      .map(getFullEncoding);
168  }
169
170  var priorities = provided.map(function getPriority(type, index) {
171    return getEncodingPriority(type, accepts, index);
172  });
173
174  // sorted list of accepted encodings
175  return priorities.filter(isQuality).sort(comparator).map(function getEncoding(priority) {
176    return provided[priorities.indexOf(priority)];
177  });
178}
179
180/**
181 * Compare two specs.
182 * @private
183 */
184
185function compareSpecs(a, b) {
186  return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i);
187}
188
189/**
190 * Get full encoding string.
191 * @private
192 */
193
194function getFullEncoding(spec) {
195  return spec.encoding;
196}
197
198/**
199 * Check if a spec has any quality.
200 * @private
201 */
202
203function isQuality(spec) {
204  return spec.q > 0;
205}
206