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; }