Notification in the browser - what is it?

Many Internet users ask the question: "Notification in the browser - what is this?" It displays a specific style of Internet surfing, where a request for a transaction is initiated from the central server. This contrasts with the reverse direction of the data, where the request for information transfer is initiated by the recipient or the client.

Notification services are often based on information preferences expressed in advance. This is called the publication subscription model. The client "writes out" to itself various information "channels" provided by the server. Whenever new content is available on one of these channels, the server sends this information to it. Notification in the browser sometimes emulates with the polling technique, especially in conditions where a real request is not possible - for example, on sites with a serious security policy that require the refusal of incoming HTTP / S requests.

Operating principle

Synchronous conferencing and instant messaging are typical examples of how notification looks. What is it and how does it work? Chat messages and sometimes files are ejected to the user as soon as they are received, using the messaging service. Both decentralized LVS peer-to-peer connections and centralized programs (such as IRC or XMPP) allow you to "push" files. This means that it is the sender that initiates the data transfer, not the receiver.

E-mail can also work with notifications - the SMTP protocol is, in its essence, a "push". However, the last "step" from the mail server on the computer usually makes such a load protocol as POP3 or IMAP. The IMAP protocol includes an IDLE command that allows the server to notify the client of new messages. The original BlackBerry was the first popular device where the notification in the browser worked actively. What is it in these gadgets - can be seen in the work of e-mail (with wireless communication).

What was earlier?

Another example is the PointCast network, which was known in the 1990s. It provided news and data on the stock market. Both Netscape and Microsoft's applications integrated it into their software in each version of their browsers, but it was never popular, and later it completely disappeared. Browsers subsequently replaced this functionality in the 2000s with the RSS-based subscriptions system, where there is a better notification in the browser. What is subscription data? Every reader of blogs knows.

Other uses of notification with support for web applications include informing about market data (stock quotes), online chat rooms and messaging systems (WebChat), auctions, online betting and games, sports betting, monitoring consoles and the like.

Notification in the browser - what is today?

Notification with IEFT is a simple protocol that uses HTTP / 2 to deliver instant notification (about incoming calls and messages). The protocol combines all real-time events in one session, which provides more efficient use of network and radio resources. A single service unites all events, distributing them for applications as they arrive. This requires only one session, which allows you to avoid unnecessary time and traffic.

Notification in the browser - what is this from a technical point of view?

HTTP-notification (also known as streaming HTTP) is a mechanism for sending data from a web server to a browser. It can be achieved through any of several mechanisms. Typically, the web server does not terminate the connection after the notification has been sent to the client. The web server leaves the connection open, and in the event of a new event (for example, changing the data sent in the message), this will be displayed instantly. Otherwise, the event will have to be queued until the next client request is received.

Most web servers offer this function using CGI (for example, unformatted script headers on Apache). The basic mechanism of this approach is the block coding of the transmission. A classic example is the notification in the browser in "Classmates". What is it on this site? First of all, this is information about incoming messages and the likes of "Like."

Alternative mechanisms

Another mechanism is associated with a special type of MIME, which is called a multicomponent substitution. For the first time, it was introduced in 1995 by Netscape, when browsers "on the fly" changed the document whenever a new version came on the server. It is still supported in Firefox, Opera, Safari and today, but it is not available in Internet Explorer. This mechanism can be applied to HTML documents, as well as for streaming images in webcam applications.

WHATWG Web Applications 1.0 includes a mechanism that guides the changed content to the client. It has been known since September 1, 2006, when Opera introduced this new experimental system called Server-SentEvents in the Web browser. Currently, it is standardized as part of HTML5. In this method, the server uses a persistent HTTP connection, resulting in a constant "open" response (i.e., the server never stops responding) effectively "cheating" the browser. Thus, the application always remains in the download mode, after the page has already opened in full. The server then periodically sends JavaScript snippets to update the page content, thereby providing the ability to notify. Using this technique, the client does not need Java applets or other plug-ins to keep an open connection to the server - the client automatically receives notification of new events coming from the server. One serious drawback of this method, however, is the lack of server control over the browser's running time. Updating the page is always necessary if there is a timeout on the open page.

Data storage

The technique of memorizing in itself is not a true notification. It only allows to emulate the notification mechanism in conditions when it is not possible. For example, on sites with a demanding security policy that require the refusal of incoming HTTP / S requests. It is impossible to notify in the browser (what it is and how it works - it is indicated above). In this case, the client requests information exactly as in a normal request, but because of the waiting, the server can not immediately respond. If the server does not have any new information for the client, when the request is received - instead of sending an empty response, the request remains open while waiting for new information. After such data appears, it immediately sends an HTTP / S response to the client, having completed the open connection.

After receiving the response, the client often immediately issues a request to another server. Thus, the normal response delay time (the time between when the information becomes available, and the next client request) associated with the receipt of requests is eliminated.

XML Socket

Notification in the browser, working with this method, is used by CBOX and other applications for chat. It uses XML Socket objects in one-pixel AdobeFlash files. Under JavaScript control, the client establishes a TCP connection to unicast nodes on the server. The request remains unread, instead, the node immediately sends the client a unique identifier. Then an HTTP request is made to the web server, which contains the received identifier. A web application can then issue messages addressed to the client to the local relay server interface that passes them through Flash. The advantage of this approach is that it uses the natural asymmetry of read-write.

This is typical for many web applications, including chats, and as a result, it provides high efficiency. Since it does not accept data for outgoing sockets, the server does not need to request outgoing TCP connections, and this makes it possible to establish tens of thousands of simultaneous connections. This is how the notification in the browser on "Odnoklassniki" occurs in some services of the site.

Available notification services

This function is available on many services that support the above connections. As it was already established, notification in the browser is the ability to receive instant messages and notifications without reloading the page. Services where this service is available include:

• Apple Notification Service.
• Google Cloud Messaging.
• "Classmates."
• Facebook.
• Xtremepush.
• Amazon SNS.