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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 = preferredMediaTypes; module.exports.preferredMediaTypes = preferredMediaTypes;
/** * Module variables. * @private */
var simpleMediaTypeRegExp = /^\s*([^\s\/;]+)\/([^;\s]+)\s*(?:;(.*))?$/;
/** * Parse the Accept header. * @private */
function parseAccept(accept) { var accepts = splitMediaTypes(accept);
for (var i = 0, j = 0; i < accepts.length; i++) { var mediaType = parseMediaType(accepts[i].trim(), i);
if (mediaType) { accepts[j++] = mediaType; } }
// trim accepts
accepts.length = j;
return accepts; }
/** * Parse a media type from the Accept header. * @private */
function parseMediaType(str, i) { var match = simpleMediaTypeRegExp.exec(str); if (!match) return null;
var params = Object.create(null); var q = 1; var subtype = match[2]; var type = match[1];
if (match[3]) { var kvps = splitParameters(match[3]).map(splitKeyValuePair);
for (var j = 0; j < kvps.length; j++) { var pair = kvps[j]; var key = pair[0].toLowerCase(); var val = pair[1];
// get the value, unwrapping quotes
var value = val && val[0] === '"' && val[val.length - 1] === '"' ? val.substr(1, val.length - 2) : val;
if (key === 'q') { q = parseFloat(value); break; }
// store parameter
params[key] = value; } }
return { type: type, subtype: subtype, params: params, q: q, i: i }; }
/** * Get the priority of a media type. * @private */
function getMediaTypePriority(type, accepted, index) { var priority = {o: -1, q: 0, s: 0};
for (var i = 0; i < accepted.length; i++) { var spec = specify(type, 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 media type. * @private */
function specify(type, spec, index) { var p = parseMediaType(type); var s = 0;
if (!p) { return null; }
if(spec.type.toLowerCase() == p.type.toLowerCase()) { s |= 4 } else if(spec.type != '*') { return null; }
if(spec.subtype.toLowerCase() == p.subtype.toLowerCase()) { s |= 2 } else if(spec.subtype != '*') { return null; }
var keys = Object.keys(spec.params); if (keys.length > 0) { if (keys.every(function (k) { return spec.params[k] == '*' || (spec.params[k] || '').toLowerCase() == (p.params[k] || '').toLowerCase(); })) { s |= 1 } else { return null } }
return { i: index, o: spec.i, q: spec.q, s: s, } }
/** * Get the preferred media types from an Accept header. * @public */
function preferredMediaTypes(accept, provided) { // RFC 2616 sec 14.2: no header = */*
var accepts = parseAccept(accept === undefined ? '*/*' : accept || '');
if (!provided) { // sorted list of all types
return accepts .filter(isQuality) .sort(compareSpecs) .map(getFullType); }
var priorities = provided.map(function getPriority(type, index) { return getMediaTypePriority(type, accepts, index); });
// sorted list of accepted types
return priorities.filter(isQuality).sort(compareSpecs).map(function getType(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 type string. * @private */
function getFullType(spec) { return spec.type + '/' + spec.subtype; }
/** * Check if a spec has any quality. * @private */
function isQuality(spec) { return spec.q > 0; }
/** * Count the number of quotes in a string. * @private */
function quoteCount(string) { var count = 0; var index = 0;
while ((index = string.indexOf('"', index)) !== -1) { count++; index++; }
return count; }
/** * Split a key value pair. * @private */
function splitKeyValuePair(str) { var index = str.indexOf('='); var key; var val;
if (index === -1) { key = str; } else { key = str.substr(0, index); val = str.substr(index + 1); }
return [key, val]; }
/** * Split an Accept header into media types. * @private */
function splitMediaTypes(accept) { var accepts = accept.split(',');
for (var i = 1, j = 0; i < accepts.length; i++) { if (quoteCount(accepts[j]) % 2 == 0) { accepts[++j] = accepts[i]; } else { accepts[j] += ',' + accepts[i]; } }
// trim accepts
accepts.length = j + 1;
return accepts; }
/** * Split a string of parameters. * @private */
function splitParameters(str) { var parameters = str.split(';');
for (var i = 1, j = 0; i < parameters.length; i++) { if (quoteCount(parameters[j]) % 2 == 0) { parameters[++j] = parameters[i]; } else { parameters[j] += ';' + parameters[i]; } }
// trim parameters
parameters.length = j + 1;
for (var i = 0; i < parameters.length; i++) { parameters[i] = parameters[i].trim(); }
return parameters; }
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