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