185 lines
3.4 KiB
JavaScript
185 lines
3.4 KiB
JavaScript
/**
|
|
* 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 i = 0; i < params.length; i ++) {
|
|
var p = params[i].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;
|
|
}
|