Comet (programming) Comet is a web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it.[1][2] Comet is an umbrella term, encompassing multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as JavaScript, rather than on non-default plugins. The Comet approach differs from the original model of the web, in which a browser requests a complete web page at a time.[3] The use of Comet techniques in web development predates the use of the word Comet as a neologism for the collective techniques. The ability to embed Java applets into browsers (starting with Netscape 2.0 in March 1996[10]) made real-time communications possible, using a raw TCP socket[11] to communicate between the browser and the server. Even if not yet known by that name, the very first Comet implementations date back to 2000,[18] with the Pushlets, Lightstreamer, and KnowNow projects.
The WebSocket API Abstract This specification defines an API that enables Web pages to use the WebSocket protocol (defined by the IETF) for two-way communication with a remote host. Status of This document This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the most recently formally published revision of this technical report can be found in the W3C technical reports index at If you wish to make comments regarding this document, you can enter feedback using this form: You can also e-mail feedback to public-webapps@w3.org (subscribe, archives), or whatwg@whatwg.org (subscribe, archives). Implementors should be aware that this specification is not stable. The latest stable version of the editor's draft of this specification is always available on the W3C CVS server and in the WHATWG Subversion repository. E-mail notifications of changes Table of Contents 1 Introduction WebIDL
How to write a Long Polling Event Push Server with node.js – go-left Software Quick jumps: The API – Installing node – The Skeleton – POSTing Events – GETting Events – Pausing and Resuming Requests – Final Disclaimer For one of my JavaScript projects I’ve needed a push technology to push server events to my web clients. After looking at several options I’ve decided to write a long polling server with node.js. I am going to explain step by step how I’ve done that. Feedback is welcome. The sample code is available on gist.github git clone The long polling server performs only the task of pushing server events to the client. To make the server more useful we assume that a user can connect simultaneously with multiple browsers and an event pushed for that user is pushed to all browsers the user is currently using (one producer, many consumers). We further want the client/server communication to be robust therefore we don’t know anything about the state of the client and leave it up to the client to request the events it wants to see.
How HTML5 Web Sockets Interact With Proxy Servers With the recent explosion of WebSocket server implementations, a lot of questions have come up about how HTML5 Web Sockets deal with proxy servers, firewalls, and load-balancing routers. Will proxy servers automatically kill WebSocket connections? Do HTML5 Web Sockets handle firewalls and proxy server issues better than Comet? Are Web Sockets the silver bullet in seamless proxy server traversal? About HTML5 Web Sockets and Proxy Servers Let's start with some basic concepts: what exactly are HTML5 Web Sockets and proxy servers? HTML5 Web Sockets The HTML5 Web Sockets specification defines the Web Sockets API that enables web pages to use the Web Socket protocol for full-duplex communication with a remote host. To use HTML5 Web Sockets to connect from a Web client to a remote end-point, you create a new WebSocket instance and provide it with the URL that represents the end-point to which you want to connect. Proxy Servers HTML5 Web Sockets and Proxy Servers The WebSocket Upgrade Let's recap.
WebSockets is cool, but what can you do today? | Clay Lenhart’s Blog WebSockets is a new feature that appears to be a great way to send messages from the server to the browser, however today there isn’t much support, both in browsers and on the server in IIS and ASP.Net. Today you can use a Comet technique (in particular, Ajax with long polling ) which is available in all browsers. Using this concept, the browser makes a standard AJAX call to the server that waits until it receives a message. Asynchronous Pages and Asynchronous Controller allow you to have long running HTTP requests without using precious ASP.Net threads. On the server, there are two resource limits to consider with IIS and ASP.Net: HTTP request limits — in IIS7 the default limit is 5000 ASP.Net thread limits — in IIS7 the default limit is 12 x number of CPUs For a typical ASP.Net application (and ASP.Net MVC application), an HTTP request always uses an ASP.Net thread. Take for example an email web application that has jQuery code to check for new mail. $( function () { checkEmail(); } else {
HTML5 Web Sockets: A Quantum Leap in Scalability for the Web Lately there has been a lot of buzz around HTML5 Web Sockets, which defines a full-duplex communication channel that operates through a single socket over the Web. HTML5 Web Sockets is not just another incremental enhancement to conventional HTTP communications; it represents a colossal advance, especially for real-time, event-driven web applications. HTML5 Web Sockets provides such a dramatic improvement from the old, convoluted "hacks" that are used to simulate a full-duplex connection in a browser that it prompted Google's Ian Hickson - the HTML5 specification lead - to say: " 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 Web Sockets seriously interesting to Google." Let's look at how HTML5 Web Sockets can offer such an incredibly dramatic reduction of unnecessary network traffic and latency by comparing it to conventional solutions. HTML5 Web Sockets to the Rescue!
Stream Updates with Server-Sent Events Introduction I wouldn't be surprised if you've stumbled on this article wondering, "What the heck are Server-Sent Events (SSEs)?" Many people have never heard of them, and rightfully so. Over the years, the specification has seen significant changes, and the API has taken somewhat of a backseat to newer, sexier communication protocols such as the WebSocket API. Polling is a traditional technique used by the vast majority of AJAX applications. Long polling (Hanging GET / COMET) is a slight variation on polling. Server-Sent Events on the other hand, have been designed from the ground up to be efficient. The main difference between Server-Sent Events and long-polling is that SSEs are handled directly by the browser and the user simply has to listen for messages. Server-Sent Events vs. Why would you choose Server-Sent Events over WebSockets? SSEs are sent over traditional HTTP. JavaScript API To subscribe to an event stream, create an EventSource object and pass it the URL of your stream: <!
Real-Time Web Test - Does your browser supports WebSockets? WebSocket WebSocket is a protocol providing full-duplex communications channels over a single TCP connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011, and the WebSocket API in Web IDL is being standardized by the W3C. Technical overview[edit] Browser implementation[edit] WebSocket protocol handshake[edit] To establish a WebSocket connection, the client sends a WebSocket handshake request, for which the server returns a WebSocket handshake response, as shown in the following example:[9]:section 1.2 Client request: GET /chat HTTP/1.1 Host: server.example.com Upgrade: websocket Connection: Upgrade Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw== Sec-WebSocket-Protocol: chat, superchat Sec-WebSocket-Version: 13 Origin: Server response: HTTP/1.1 101 Switching Protocols Upgrade: websocket Connection: Upgrade Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk= Sec-WebSocket-Protocol: chat Note that each line ends with an EOL (end of line) sequence, \r\n.