strata/lib/header/accept-encoding.js

A modular, streaming HTTP server

var util = require('util');
var Header = require('../header');
var Accept = require('./accept');

module.exports = AcceptEncoding;

/**
 * Represents an HTTP Accept-Encoding header according to the HTTP 1.1
 * specification, and provides several convenience methods for determining
 * acceptable content encodings.
 *
 * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
 */
function AcceptEncoding(value) {
  if (!(this instanceof AcceptEncoding)) {
    return new AcceptEncoding(value);
  }

  Header.call(this, 'Accept-Encoding', value);
}

util.inherits(AcceptEncoding, Header);

AcceptEncoding.prototype.qvalues = Accept.prototype.qvalues;
AcceptEncoding.prototype.values = Accept.prototype.values;
AcceptEncoding.prototype.accept = Accept.prototype.accept;

/**
 * Determines the quality factor (qvalue) of the given encoding.
 */
AcceptEncoding.prototype.qvalue = function (encoding) {
  var matches = this.matches(encoding);

  if (matches.length == 0) {
    return encoding == 'identity' ? 1 : 0;
  }

  var qvalues = this.qvalues();

  return Accept.normalizeQvalue(qvalues[matches[0]]);
};

/**
 * Returns an array of encodings from this header that match the given
 * encoding, ordered by precedence.
 */
AcceptEncoding.prototype.matches = function (encoding) {
  return this.values().filter(function (value) {
    return value == encoding || value == '*';
  }).sort(function (a, b) {
    // "*" gets least precedence, all others are equal.
    return a == '*' ? 1 : (b == '*' ? -1 : 0);
  });
};