permessage-deflate/lib/server_session.js

Per-message DEFLATE compression extension for WebSocket connections

'use strict';

var util    = require('util'),
    common  = require('./common'),
    Session = require('./session');

var ServerSession = function(options, params) {
  Session.call(this, options);
  this._params = params;
};
util.inherits(ServerSession, Session);

ServerSession.validParams = function(params) {
  if (!common.validParams(params)) return false;

  if (params.hasOwnProperty('client_max_window_bits')) {
    if ([true].concat(common.VALID_WINDOW_BITS).indexOf(params.client_max_window_bits) < 0)
      return false;
  }
  return true;
};

ServerSession.prototype.generateResponse = function() {
  var response = {};

  // https://tools.ietf.org/html/rfc7692#section-7.1.1.1

  this._ownContextTakeover = !this._acceptNoContextTakeover &&
                             !this._params.server_no_context_takeover;

  if (!this._ownContextTakeover) response.server_no_context_takeover = true;

  // https://tools.ietf.org/html/rfc7692#section-7.1.1.2

  this._peerContextTakeover = !this._requestNoContextTakeover &&
                              !this._params.client_no_context_takeover;

  if (!this._peerContextTakeover) response.client_no_context_takeover = true;

  // https://tools.ietf.org/html/rfc7692#section-7.1.2.1

  this._ownWindowBits = Math.min(this._acceptMaxWindowBits || common.MAX_WINDOW_BITS,
                                 this._params.server_max_window_bits || common.MAX_WINDOW_BITS);

  // In violation of the spec, Firefox closes the connection if it does not
  // send server_max_window_bits but the server includes this in its response
  if (this._ownWindowBits < common.MAX_WINDOW_BITS && this._params.server_max_window_bits)
    response.server_max_window_bits = this._ownWindowBits;

  // https://tools.ietf.org/html/rfc7692#section-7.1.2.2

  var clientMax = this._params.client_max_window_bits, requestMax;
  if (clientMax) {
    if (clientMax === true) clientMax = common.MAX_WINDOW_BITS;
    this._peerWindowBits = Math.min(this._requestMaxWindowBits || common.MAX_WINDOW_BITS, clientMax);
  } else {
    this._peerWindowBits = common.MAX_WINDOW_BITS;
  }

  if (this._peerWindowBits < common.MAX_WINDOW_BITS)
    response.client_max_window_bits = this._peerWindowBits;

  return response;
};

module.exports = ServerSession;