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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