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HTML5 Web Workers-unleashed
Peter Lubbers from Kaazing gave a presentation on HTML5 features such as Web Workers, Geolocation, and WebSockets. He discussed how these new technologies allow for asynchronous background processing, location detection, and bi-directional real-time communications without polling. Browser support for HTML5 features was also reviewed.
HTML5 Web Workers-unleashed
- 1. Peter Lubbers Kaazing#dcodeHTML5WebSockets,WebWorkers,andGeolocationUnleashed!
- 2. About Peter LubbersDirectorof Documentation and Training, Kaazing (The HTML5 WebSocket Company)
- 3. Co-Founder San FranciscoHTML5 User Grouphttp://www.sfhtml5.org/
- 4. Co-author Pro HTML5Programming
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- 6. Twitter: @peterlubbersCopyright ©2010 - Kaazing Corporation. All rights reserved.
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- 11. Q&A And…the first ones to answer the quiz questions win a free book!Copyright © 2010 - Kaazing Corporation. All rights reserved.
- 12. AboutHTML5© 2009 –Kaazing Corporation
- 13. HTML5 Paves theCow PathsDegrade gracefully (Evolution not revolution)
- 14. Don't reinvent thewheel (or at least make a better one!)Copyright © 2010 - Kaazing Corporation. All rights reserved.
- 15. HTML5: Simple isBetterSimplify wherever possible
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- 17. Native browser abilityinstead of complex JavaScript code
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- 21. As they sayin Holland: “So simple, a child can do the laundry!”Copyright © 2010 - Kaazing Corporation. All rights reserved.
- 22. HTML5 : APlugin-Free ParadigmHTML5 provides native support for many features that were only possible with plugins or complex hacks
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- 24. May not beinstalled
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- 26. Are a separateattack vector
- 27. Are difficult tointegrate with the rest of an HTML document (plugin boundaries, clipping, and transparency issues)“Whenever a Mac crashes more often than not it’s because of Flash.”--Steve JobsCopyright © 2010 - Kaazing Corporation. All rights reserved.
- 29. Just Kidding!Copyright ©2010 - Kaazing Corporation. All rights reserved.
- 30. Is This HTML5?Manypieces of the HTML5 effort were originally part of the HTML5 specification
- 31. Moved to aseparate standards document to keep the specification focused
- 32. Industry still refersto the original set of features, including Web Sockets, as "HTML5“
- 33. See: http://www.whatwg.org/specs/web-apps/current-work/multipage/introduction.html#is-this-html5?Copyright ©2010 - Kaazing Corporation. All rights reserved.
- 34. HTML5 Web WorkersCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 35. HTML5 Web WorkersWithoutWeb Workers:
- 36. Long-running JavaScript taskscan block other JavaScript on the page
- 37. JavaScript can causesome browser UIs to hang
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- 39. Background processing capabilitiesto web applications can be added
- 40. Parallel operations canrun concurrentlyCopyright © 2010 - Kaazing Corporation. All rights reserved.
- 41. HTML5 Web WorkersWebWorkers are used for
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- 43. Background notification fromserver to a local database
- 44. Background price updatesfrom server
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- 46. Graceful degradation? Easy!Copyright© 2010, Kaazing Corporation,. All rights reserved.
- 47. DemoCopyright © 2010,Kaazing Corporation,. All rights reserved.
- 48. Using the WebWorkers APICopyright © 2010, Kaazing Corporation,. All rights reserved.
- 49. HTML5 Web WorkersCannotaccess the web page’s window object (window.document)
- 50. No direct accessto the web page and the DOM API
- 51. Can use thefull JavaScript timing API, typically found on the global window
- 52. Although HTML5 WebWorkers cannot block the browser UI, they can still consume CPU cycles and make the system less responsiveCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 53. HTML5 Web WorkersAPICreate an HTML5 Web Worker object and pass in a JavaScript file to be executed
- 54. Use Cross DocumentMessaging API (PostMessage)
- 55. On the webpage:
- 56. Set up an(asynchronous) event listener to listen to incoming messages and errors from the worker
- 57. call postMessage topass data to a worker
- 58. On the webpage:
- 59. Set up an(asynchronous) event listener to listen to incoming messages and errors from the page
- 60. call postMessage topass data to the pageCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 61. JavaScript//Check if WebWorkers are supportedif (typeof(Worker) !== "undefined") { document.getElementById("support").innerHTML = “Your browser supports HTML5 Web Workers";}//Create a new worker//The URL for the JavaScript file can be a relative or //absolute URL with the same origin //(the same scheme, host, and port) as the main pageworker = new Worker("echoWorker.js");//to load additional JavaScriptimportScripts("helper.js, "anotherHelper.js");Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 62. JavaScript//Main Pageworker.postMessage("Here's amessage for you");//Add event listenerworker.addEventListener("message", messageHandler, true);//Process incoming messagesfunction messageHandler(e) { // process message from worker}//Handle errorsworker.addEventListener("error", errorHandler, true);//Stop workerworker.terminate();Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 63. JavaScript//Workerfunction messageHandler(e) { postMessage("worker says: " + e.data + " too");}addEventListener("message", messageHandler, true);//Using a Web Worker within a Web Worker var subWorker = new Worker("subWorker.js");Copyright © 2010, Kaazing Corporation,. All rights reserved.
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- 67. Opera 10.6+* Mayneed to be served up from a server (origin security)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 68. HTML5 GeolocationCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 69. Using GeolocationAllows usersto share their location for location-aware services
- 70. Show user's positionon map
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- 73. Alert users ofnearby points of interest
- 74. Social networkingCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 75. DemoCopyright © 2010,Kaazing Corporation,. All rights reserved.
- 76. Geolocation ArchitectureCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 77. Location DataLocation informationconsists of a pair of latitude and longitude coordinates and accuracy information
- 78. Latitude is thenumerical value indicating distance north or south of the equator
- 79. Longitude is thenumerical value indicating distance east or west of Greenwich, England
- 80. For Example, LakeTahoe:Latitude: 39.17222, Longitude: -120.13778Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 81. Location MetadataDepending onthe device, additional meta data can be provided:
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- 86. If this additionalmetadata is not available it will be returned as a null valueCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 87. Sources of LocationDataA device can use any of the following sources:
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- 91. Wi-Fi with MACaddresses from RFID, Wi-Fi, and Bluetooth
- 92. GSM or CDMAcell phone IDs
- 93. User definedCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 94. Location Source Pros& ConsCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 95. PrivacyHTML5 Geolocation specificationmandates that a mechanism is provided to protect the user's privacy
- 96. Location information shouldnot be made available unless the application’s users grant their express permission
- 97. Clear privacy practiceswith respect to collected location data are recommended (how long data is stored, how it is encrypted, how data is shared)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 98. Sharing a LocationCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 99. Location Sharing ExampleCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 100. Recommendations and RealityGeolocationprivacy study from UC Berkeley:http://bit.ly/aS9oqfCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 101. Using the GeolocationAPICopyright © 2010, Kaazing Corporation,. All rights reserved.
- 102. JavaScript//Checking for browsersupport:if(navigator.geolocation) { document.getElementById("support").innerHTML = "HTML5 Geolocation is supported."; } else { document.getElementById("support").innerHTML = "HTML5 Geolocation is not supported."; }Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 103. © 2009 –Kaazing CorporationQuiz Question: What are the names of the two main Geolocation API calls?
- 104. Types of PositionRequestsThere are two types of position requests:One-shot position request(getCurrentPosition)Repeated position updates(watchPosition)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 105. JavaScript//One shot requestvoidgetCurrentPosition( in PositionCallback successCallback, in optional PositionErrorCallback errorCallback, in optional PositionOptions options);//Access user’s positionnavigator.geolocation.getCurrentPosition( updateLocation, handleLocationError);Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 106. JavaScript//Update the UIfunctionupdateLocation(position) { var latitude = position.coords.latitude; var longitude = position.coords.longitude; var accuracy = position.coords.accuracy; document.getElementById("latitude").innerHTML = latitude; document.getElementById("longitude").innerHTML = longitude; document.getElementById(“accuracy”).innerHTML = “This location is accurate within “ + accuracy + “ meters.”}Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 107. Optional Request AttributesenableHighAccuracy—Requestthe HTML5 Geolocation service to use a higher accuracy-detection mode if available (only supports true or false)
- 108. Timeout—tells the browserthe maximum amount of time it is allowed to calculate the current location
- 109. maximumAge—indicates how olda location value can be before the browser must attempt to recalculate (default is zero, meaning that the browser must attempt to recalculate a value immediately.Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 110. Geolocation Error CodesUNKNOWN_ERROR(code 0)An error occurred that is not covered by the other error codes
- 111. PERMISSION_DENIED (code 1)The user chose not to let the browser have access to the location information
- 112. POSITION_UNAVAILABLE (code 2)Thetechnique used to determine the user’s location was attempted, but failed
- 113. TIMEOUT (code 3)Thetimeout value was exceededCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 114. JavaScript//Repeated position updatesvarwatchId =navigator.geolocation.watchPosition( updateLocation, handleLocationError);// do something with the location updates!// ... // Stop receiving location updatesnavigator.geolocation.clearWatch(watchId);Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 115. Example Geolocation AppwatchPosition()NewLocationHaversine formula,calculate distance between two longitude and latitude positions on a sphereCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 116. Google Map IntegrationCoordinatesare not easy to decipher, easier to see on a map
- 117. Google built supportfor HTML5 Geolocation into its user interface (Show My Location button) Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 118. JavaScript//Show coordinates ona Google Map// Create a Google Map//See Google API for more detailvar map = new google.maps.Map2(document.getElementById("map")); function updateLocation(position) { //pass the position to the Google Map and center it map.setCenter(new google.maps.LatLng( position.coords.latitude, position.coords.longitude, 13); // zoom level} navigator.geolocation.getCurrentPosition( updateLocation, handleLocationError);Copyright © 2010, Kaazing Corporation,. All rights reserved.
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- 122. Opera 10.6* Alsopossible through GearsCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 123. HTML5 WebSocketCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 124. Quiz Question: What do WebSockets and model trains have in common?Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 125. Using WebSocketToday’s Webapplications demand reliable, real-time communications with near-zero latency
- 126. Not just broadcast,but bi-directional communication
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- 131. Smart power gridCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 132. DemoCopyright © 2010,Kaazing Corporation,. All rights reserved.
- 133. About HTTPHTTP ishalf-duplex (traffic flows in only one direction at a time)
- 134. Header information issent with each HTTP request and response, which can be an unnecessary overheadCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 135. About Ajax andCometGreat toilet cleaners…
- 136. Ajax (Asynchronous JavaScriptand XML) is used to build highly interactive Web apps
- 137. Content can changewithout loading the entire page
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- 139. “Real-time” often achievedthrough polling and long-polling
- 140. Comet lack ofa standard implementation
- 141. Comet adds lotsof complexityCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 142. Comet Polling Underthe CoversCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 143. HTTP Request HeadersGET/PollingStock//PollingStock HTTP/1.1Host: localhost:8080User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8Accept-Language: en-usAccept-Encoding: gzip,deflateAccept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7Keep-Alive: 300Connection: keep-aliveReferer: http://localhost:8080/PollingStock/Cookie: showInheritedConstant=false; showInheritedProtectedConstant=false; showInheritedProperty=false; showInheritedProtectedProperty=false; showInheritedMethod=false; showInheritedProtectedMethod=false; showInheritedEvent=false; showInheritedStyle=false; showInheritedEffect=false;Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 144. HTTP Response HeadersHTTP/1.x200 OKX-Powered-By: Servlet/2.5Server: Sun Java System Application Server 9.1_02Content-Type: text/html;charset=UTF-8Content-Length: 321Date: Sat, 07 Nov 2009 00:32:46 GMTTotal (unnecessary) HTTP request and response header information overhead: 871 bytes (example)
- 145. Overhead can beas much as 2000 bytes
- 146. Does not scale!Copyright© 2010, Kaazing Corporation,. All rights reserved.
- 147. HTTP Header TrafficAnalysisExample network throughput for HTTP request and response headers associated with polling
- 148. Use case A:1,000 clients polling every second:
- 149. Network throughput is(871 x 1,000) = 871,000 bytes = 6,968,000 bits per second (~6.6 Mbps)
- 150. Use case B:10,000 clients polling every second:
- 151. Network throughput is(871 x 10,000) = 8,710,000 bytes = 69,680,000 bits per second (~66 Mbps)
- 152. Use case C:100,000 clients polling every second:
- 153. Network throughput is(871 x 100,000) = 87,100,000 bytes = 696,800,000 bits per second (~665 Mbps)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 154. Comet: Headache 2.0UseComet to spellCOMplExiTy…Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 155. HTML5 WebSocketW3C APIand IETF Protocol
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- 157. Enables web pagesto communicate with a remote host
- 158. Traverses firewalls, proxies,and routers seamlessly
- 159. Leverages Cross-Origin ResourceSharing (CORS)
- 160. Share port withexisting HTTP content
- 161. Dramatic overhead reductionCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 162. HTML5 WebSocket SchemesWebSocketws://www.websocket.org/textWebSocketSecurewss://www.websocket.org/encrypted-textCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 163. WebSocket ArchitectureCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 164. HTML5 WebSocketConnection establishedby upgrading from the HTTP protocol to the WebSocket protocol using the same TCP connection
- 165. Once upgraded, WebSocketdata frames can be sent back and forth between the client and the server in full-duplex modeCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 166. HTML5 WebSocket HandshakeClientGET/text HTTP/1.1Upgrade: WebSocketConnection: UpgradeHost: www.example.comOrigin: http://example.comWebSocket-Protocol: sample…\r\nServerHTTP/1.1 101 WebSocket Protocol HandshakeUpgrade: WebSocketConnection: UpgradeWebSocket-Origin: http://example.comWebSocket-Location: ws://example.com/demoWebSocket-Protocol: sample…\r\nCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 167. HTML5 WebSocket FramesFramescan be sent full-duplex, in either direction at any the same time
- 168. Each frame ofdata:
- 169. Starts with a0x00 byte
- 170. Ends with a0xFF byte
- 171. Contains UTF-8 datain between
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- 173. \x00Hello, WebSocket\0xffCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 174. Dramatic Reduction inNetwork TrafficWith WebSocket, each frame has only 2 bytes of packaging (a 500:1 or even 1000:1 reduction)
- 175. No latency involvedin establishing new TCP connections for each HTTP message
- 176. Dramatic reduction inunnecessary network traffic and latency
- 177. Remember the PollingHTTP header traffic? 665 Mbps network throughput for just headersCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 178. WebSocket Framing AnalysisExamplenetwork throughput overhead associated with WebSocket framing
- 179. Use case A:1,000 clients receive 1 message per second: Network throughput is (2 x 1,000) = 2,000 bytes = 16,000 bits per second (~0.015 Mbps)
- 180. Use case B:10,000 clients receive 1 message per second: Network throughput is (2 x 10,000) = 20,000 bytes = 160,000 bits per second (~0.153 Mbps)
- 181. Use case C:100,000 clients receive 1 message per second: Network throughput is (2 x 100,000) = 200,000 bytes = 1,600,000 bits per second (~1.526 Mbps)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 182. Polling vs. WebSocketCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 183. Latency ReductionCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 184. Overheard… “Reducing kilobytes of data to 2 bytes…and reducing latency from 150ms to 50ms is far more than marginal. In fact, these two factors alone are enough to make WebSocket seriously interesting to Google.”—Ian Hickson (Google, HTML5 spec lead)Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 185. Using the WebSocketAPICopyright © 2010, Kaazing Corporation,. All rights reserved.
- 186. JavaScript//Checking for browsersupportif (window.WebSocket) { document.getElementById("support").innerHTML = "HTML5 WebSocket is supported"; } else { document.getElementById("support").innerHTML = "HTML5 WebSocket is not supported"; }Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 187. JavaScript//Create new WebSocketvarmySocket = new WebSocket(“ws://www.websocket.org”);// Associate listenersmySocket.onopen = function(evt) { alert(“Connection open…”);};mySocket.onmessage = function(evt) { alert(“Received message: “ + evt.data);};mySocket.onclose = function(evt) { alert(“Connection closed…”);};Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 188. JavaScript// Sending datamySocket.send(“HTML5WebSocket Rocks!”);//Close WebSocketmySocket.close();Copyright © 2010, Kaazing Corporation,. All rights reserved.
- 189. Extending WebSocketOnce youhave WebSocket, you can communicate with WebSocket Servers and back-end servers and directly with message brokers
- 190. You can extendclient-server protocols to the web:
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- 195. Browser becomes afirst-class network communication citizenCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 196. Quake II Gamehttp://code.google.com/p/quake2-gwt-portCopyright© 2010, Kaazing Corporation,. All rights reserved.
- 197. WebSocket Server SupportKaazingWebSocket Gateway
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- 203. And moreCopyright ©2010, Kaazing Corporation,. All rights reserved.
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- 206. Firefox 4 (Beta)*Emulation available through Kaazing WebSocket GatewayCopyright © 2010, Kaazing Corporation,. All rights reserved.
- 207. Q&ACopyright © 2010,Kaazing Corporation,. All rights reserved.
- 208.
- 209. WebSocket protocol specification:http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol
- 210. Web Workers specification:http://dev.w3.org/html5/workers/
- 211. Geolocation specification:http://dev.w3.org/geo/api/spec-source.htmlCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 212. Thanks!@peterlubbersE-mail: peter.lubbers@kaazing.comCopyright ©2010, Kaazing Corporation,. All rights reserved.
- 213. Copyright © 2010Kaazing Corporation, All rights reserved.Course materials, including labs and other handouts are property of Kaazing Corporation. Except when expressly permitted by Kaazing Corporation, you may not copy, reproduce, publish, or display any part of this training material, in any form, or by any means.Copyright © 2010, Kaazing Corporation,. All rights reserved.
Editor's Notes
- #13 Google Chrome – every tab is its own program (not one tab within a program). So if one tab goes down, the whole app doesn't crash.
- #16 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
- #26 The following steps are shown in the diagram: A user navigates to a location-aware application in the browser.The application web page loads and requests coordinates from the browser by making a Geolocation function call. The browser intercepts this and requests user permission. Let's assume that the permission is granted.The browser retrieves coordinate information from the device it is running on. For example, the IP address, Wi-Fi, or GPS coordinates. This is an internal function of the browser.The browser sends these coordinates to a trusted external location service, which returns a detailed location that can now be sent back to the host of the HTML5 Geolocation application.
- #39 The successCallback function parameter tells the browser which function you want called when the location data is made available. This is important because operations such as fetching location data may take a long time to complete. No user wants the browser to be locked up while the location is retrieved, and no developer wants his program to pause indefinitely—especially because fetching the location data will often be waiting on a user to grant permission. The successCallback is where you will receive the actual location information and act on it.However, as in most programming scenarios, it is good to plan for failure cases. It is quite possible that the request for location information may not complete for reasons beyond your control, and for those cases you will want to provide an errorCallback function that can present the user with an explanation, or perhaps make an attempt to try again. While optional, it is recommended that you provide one.Finally, an options object can be provided to the HTML5 Geolocation service to fine-tune the way it gathers data. This is an optional parameter that we will examine later.
- #41 The timeout value deals with the duration needed to calculate the location value, while maximumAge refers to the frequency of the location calculation. If any single calculation takes longer than the timeout value, an error is triggered. However, if the browser does not have an up-to-date location value that is younger than maximumAge, it must refetch another value. Special values apply here: setting the maximumAge to “0” requires the value to always be re-fetched, while setting it to Infinity means it should never be refetched.
- #44 This sample works by using the watchPosition() capability we discussed in the last section. Every time a new position is sent to us, we will compare it to the last known position and calculate the distance traveled. This is accomplished using a well-known calculation known as the Haversine formula, which allows us to calculate distance between two longitude and latitude positions on a sphere.
- #57 High-message volume, small message size scenario where long-polling is potentially worse than polling.
- #59 WebSocket is text-only
- #63 HTTP used for handshake onlyOperates over a single socketTraverses firewalls and routers seamlesslyAllows authorized cross-site communicationCookie-based authenticationExisting HTTP load balancersNavigates proxies using HTTP CONNECT, same technique as https, but without the encryption
- #64 Text type requires high-order bit setBinary type requires high-order bit _not_ setThere is no defined maximum size. However, the protocol allows either side (browser or server) to terminate the connection if it cannot receive a large frame. So far, the definition of too large is left up to the implementation.If the user agent is faced with content that is too large to behandled appropriately, then it must fail the Web Socket connection.There is probably a practical maximum, but we have not discovered it as far as I know.You can't have four gigabytes of data in JavaScript, so the practical max is <4GB for the JavaScript implementation.
- #69 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
- #70 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
- #74 Text type requires high-order bit setBinary type requires high-order bit _not_ setThere is no defined maximum size. However, the protocol allows either side (browser or server) to terminate the connection if it cannot receive a large frame. So far, the definition of too large is left up to the implementation.If the user agent is faced with content that is too large to behandled appropriately, then it must fail the Web Socket connection.There is probably a practical maximum, but we have not discovered it as far as I know.You can't have four gigabytes of data in JavaScript, so the practical max is <4GB for the JavaScript implementation.