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module.exports = preferredEncodings;
preferredEncodings.preferredEncodings = preferredEncodings;
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;
}
function parseEncoding(s, i) {
var match = s.match(/^\s*(\S+?)\s*(?:;(.*))?$/);
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
};
}
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;
}
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
}
};
function preferredEncodings(accept, provided) {
var accepts = parseAcceptEncoding(accept || '');
if (!provided) {
// sorted list of all encodings
return accepts.filter(isQuality).sort(compareSpecs).map(function getEncoding(spec) {
return spec.encoding;
});
}
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)];
});
}
function compareSpecs(a, b) {
return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
}
function isQuality(spec) {
return spec.q > 0;
}
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