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mediaType.js
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mediaType.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 = 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;
}