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Diffstat (limited to 'common/src/main/webapp/thirdparty/cometd/cometd/TimeSyncExtension.js')
| -rw-r--r-- | common/src/main/webapp/thirdparty/cometd/cometd/TimeSyncExtension.js | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/common/src/main/webapp/thirdparty/cometd/cometd/TimeSyncExtension.js b/common/src/main/webapp/thirdparty/cometd/cometd/TimeSyncExtension.js new file mode 100644 index 0000000..5063298 --- /dev/null +++ b/common/src/main/webapp/thirdparty/cometd/cometd/TimeSyncExtension.js @@ -0,0 +1,216 @@ +/* + * Copyright (c) 2010 the original author or authors. + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +(function() +{ + function bind(org_cometd) + { + /** + * With each handshake or connect, the extension sends timestamps within the + * ext field like: <code>{ext:{timesync:{tc:12345567890,l:23,o:4567},...},...}</code> + * where:<ul> + * <li>tc is the client timestamp in ms since 1970 of when the message was sent. + * <li>l is the network lag that the client has calculated. + * <li>o is the clock offset that the client has calculated. + * </ul> + * + * <p> + * A cometd server that supports timesync, can respond with an ext + * field like: <code>{ext:{timesync:{tc:12345567890,ts:1234567900,p:123,a:3},...},...}</code> + * where:<ul> + * <li>tc is the client timestamp of when the message was sent, + * <li>ts is the server timestamp of when the message was received + * <li>p is the poll duration in ms - ie the time the server took before sending the response. + * <li>a is the measured accuracy of the calculated offset and lag sent by the client + * </ul> + * + * <p> + * The relationship between tc, ts & l is given by <code>ts=tc+o+l</code> (the + * time the server received the messsage is the client time plus the offset plus the + * network lag). Thus the accuracy of the o and l settings can be determined with + * <code>a=(tc+o+l)-ts</code>. + * </p> + * <p> + * When the client has received the response, it can make a more accurate estimate + * of the lag as <code>l2=(now-tc-p)/2</code> (assuming symmetric lag). + * A new offset can then be calculated with the relationship on the client + * that <code>ts=tc+o2+l2</code>, thus <code>o2=ts-tc-l2</code>. + * </p> + * <p> + * Since the client also receives the a value calculated on the server, it + * should be possible to analyse this and compensate for some asymmetry + * in the lag. But the current client does not do this. + * </p> + * + * @param configuration + */ + return org_cometd.TimeSyncExtension = function(configuration) + { + var _cometd; + var _maxSamples = configuration && configuration.maxSamples || 10; + var _lags = []; + var _offsets = []; + var _lag = 0; + var _offset = 0; + + function _debug(text, args) + { + _cometd._debug(text, args); + } + + this.registered = function(name, cometd) + { + _cometd = cometd; + _debug('TimeSyncExtension: executing registration callback'); + }; + + this.unregistered = function() + { + _debug('TimeSyncExtension: executing unregistration callback'); + _cometd = null; + _lags = []; + _offsets = []; + }; + + this.incoming = function(message) + { + var channel = message.channel; + if (channel && channel.indexOf('/meta/') === 0) + { + if (message.ext && message.ext.timesync) + { + var timesync = message.ext.timesync; + _debug('TimeSyncExtension: server sent timesync', timesync); + + var now = new Date().getTime(); + var l2 = (now - timesync.tc - timesync.p) / 2; + var o2 = timesync.ts - timesync.tc - l2; + + _lags.push(l2); + _offsets.push(o2); + if (_offsets.length > _maxSamples) + { + _offsets.shift(); + _lags.shift(); + } + + var samples = _offsets.length; + var lagsSum = 0; + var offsetsSum = 0; + for (var i = 0; i < samples; ++i) + { + lagsSum += _lags[i]; + offsetsSum += _offsets[i]; + } + _lag = parseInt((lagsSum / samples).toFixed()); + _offset = parseInt((offsetsSum / samples).toFixed()); + _debug('TimeSyncExtension: network lag', _lag, 'ms, time offset with server', _offset, 'ms', _lag, _offset); + } + } + return message; + }; + + this.outgoing = function(message) + { + var channel = message.channel; + if (channel && channel.indexOf('/meta/') === 0) + { + if (!message.ext) + { + message.ext = {}; + } + message.ext.timesync = { + tc: new Date().getTime(), + l: _lag, + o: _offset + }; + _debug('TimeSyncExtension: client sending timesync', org_cometd.JSON.toJSON(message.ext.timesync)); + } + return message; + }; + + /** + * Get the estimated offset in ms from the clients clock to the + * servers clock. The server time is the client time plus the offset. + */ + this.getTimeOffset = function() + { + return _offset; + }; + + /** + * Get an array of multiple offset samples used to calculate + * the offset. + */ + this.getTimeOffsetSamples = function() + { + return _offsets; + }; + + /** + * Get the estimated network lag in ms from the client to the server. + */ + this.getNetworkLag = function() + { + return _lag; + }; + + /** + * Get the estimated server time in ms since the epoch. + */ + this.getServerTime = function() + { + return new Date().getTime() + _offset; + }; + + /** + * + * Get the estimated server time as a Date object + */ + this.getServerDate = function() + { + return new Date(this.getServerTime()); + }; + + /** + * Set a timeout to expire at given time on the server. + * @param callback The function to call when the timer expires + * @param atServerTimeOrDate a js Time or Date object representing the + * server time at which the timeout should expire + */ + this.setTimeout = function(callback, atServerTimeOrDate) + { + var ts = (atServerTimeOrDate instanceof Date) ? atServerTimeOrDate.getTime() : (0 + atServerTimeOrDate); + var tc = ts - _offset; + var interval = tc - new Date().getTime(); + if (interval <= 0) + { + interval = 1; + } + return org_cometd.Utils.setTimeout(_cometd, callback, interval); + }; + }; + } + + if (typeof define === 'function' && define.amd) + { + define(['org/cometd'], bind); + } + else + { + bind(org.cometd); + } +})(); |