/**
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* negotiator
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* Copyright(c) 2012 Isaac Z. Schlueter
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* Copyright(c) 2014 Federico Romero
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* Copyright(c) 2014-2015 Douglas Christopher Wilson
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* MIT Licensed
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*/
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'use strict';
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/**
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* Module exports.
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* @public
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*/
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module.exports = preferredEncodings;
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module.exports.preferredEncodings = preferredEncodings;
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/**
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* Module variables.
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* @private
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*/
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var simpleEncodingRegExp = /^\s*([^\s;]+)\s*(?:;(.*))?$/;
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/**
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* Parse the Accept-Encoding header.
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* @private
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*/
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function parseAcceptEncoding(accept) {
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var accepts = accept.split(',');
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var hasIdentity = false;
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var minQuality = 1;
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for (var i = 0, j = 0; i < accepts.length; i++) {
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var encoding = parseEncoding(accepts[i].trim(), i);
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if (encoding) {
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accepts[j++] = encoding;
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hasIdentity = hasIdentity || specify('identity', encoding);
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minQuality = Math.min(minQuality, encoding.q || 1);
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}
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}
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if (!hasIdentity) {
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/*
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* If identity doesn't explicitly appear in the accept-encoding header,
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* it's added to the list of acceptable encoding with the lowest q
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*/
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accepts[j++] = {
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encoding: 'identity',
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q: minQuality,
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i: i
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};
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}
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// trim accepts
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accepts.length = j;
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return accepts;
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}
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/**
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* Parse an encoding from the Accept-Encoding header.
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* @private
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*/
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function parseEncoding(str, i) {
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var match = simpleEncodingRegExp.exec(str);
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if (!match) return null;
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var encoding = match[1];
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var q = 1;
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if (match[2]) {
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var params = match[2].split(';');
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for (var j = 0; j < params.length; j++) {
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var p = params[j].trim().split('=');
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if (p[0] === 'q') {
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q = parseFloat(p[1]);
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break;
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}
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}
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}
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return {
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encoding: encoding,
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q: q,
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i: i
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};
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}
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/**
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* Get the priority of an encoding.
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* @private
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*/
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function getEncodingPriority(encoding, accepted, index) {
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var priority = {o: -1, q: 0, s: 0};
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for (var i = 0; i < accepted.length; i++) {
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var spec = specify(encoding, accepted[i], index);
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if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {
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priority = spec;
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}
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}
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return priority;
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}
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/**
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* Get the specificity of the encoding.
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* @private
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*/
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function specify(encoding, spec, index) {
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var s = 0;
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if(spec.encoding.toLowerCase() === encoding.toLowerCase()){
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s |= 1;
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} else if (spec.encoding !== '*' ) {
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return null
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}
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return {
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i: index,
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o: spec.i,
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q: spec.q,
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s: s
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}
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};
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/**
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* Get the preferred encodings from an Accept-Encoding header.
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* @public
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*/
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function preferredEncodings(accept, provided) {
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var accepts = parseAcceptEncoding(accept || '');
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if (!provided) {
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// sorted list of all encodings
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return accepts
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.filter(isQuality)
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.sort(compareSpecs)
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.map(getFullEncoding);
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}
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var priorities = provided.map(function getPriority(type, index) {
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return getEncodingPriority(type, accepts, index);
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});
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// sorted list of accepted encodings
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return priorities.filter(isQuality).sort(compareSpecs).map(function getEncoding(priority) {
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return provided[priorities.indexOf(priority)];
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});
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}
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/**
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* Compare two specs.
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* @private
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*/
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function compareSpecs(a, b) {
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return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
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}
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/**
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* Get full encoding string.
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* @private
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*/
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function getFullEncoding(spec) {
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return spec.encoding;
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}
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/**
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* Check if a spec has any quality.
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* @private
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*/
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function isQuality(spec) {
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return spec.q > 0;
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}
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