WebSockets enables the real-time web where the information is available to the user the moment it is published. WebSockets are standard based, Interoperable across browsers and very simple to use. We got the WebSockets support everywhere it is available on browsers, windows run time, WCF, ASP, IIS etc. This post gives you the basic idea about WebSockets and the technicalities behind this concept.

There is a deep desire for speed to get the information as quickly as possible.

Typical examples where user wants to see the information in real time

- Stock Market data
- Live Scores
- Airline Location
- Twitter Search Results
- Interactive games

The Problem

HTTP is a state less protocol where server can communicate with client only once per request received. Real time web needs asynchronous communication with client.



In the above example when you are 7 letters of text and sending to the server , it actually sending the 4kb of data to the server. We can do better and it clearly tells us the HTTP is not adequate for the real-time web.

Solution

WebSocket – is an enabler of the real-time web. Sockets are full-duplex bi-directional protocol. These Sockets are not directly available to the developers. So we need richness of Sockets and reach of Web. All together called WebSockets.

WebSockets Characteristics

- Full duplex bidirectional communication
- Supports unsecure(TCP) and secure(HTTPS) channels
- It can traverse proxies and firewalls
- It keeps the connection alive



Step1: You start the communication with HTTP and tells the server you want to do the communication using sockets.

Step2: The server checks and accepts the request then it starts the socket communication. At this stage both of them drop-down to start communication using sockets.

How the protocol operates?

The request from client looks like as below



It basically saying it supports websocket communication. The security key in the header is to both side to understand the sockets.

The Response from the server looks like below



WebSocket API it is defined in W3C Primary methods and events are as below



You have the call-back method if connection is opened or if you connection is closed or message is received.

The request URI in this communication looks as below



notice it has a special scheme name WS , ws indicates to the browser this is not something that not goes through the wire and says it is web sockets request is coming on and you need to do the HTTP hand shake down before actual communication start. ws never goes on the wire, it is HTTP that goes on the wire.

Creating a WebSocket is simple



Sending a Text message using this socket



Capturing the server response in onmessage event as below



WebSockets is an emerging standard which enables secure, real-time , bi-directional communication across the web. Microsoft supporting this in IE10, Windows 8 Apps, IIS, ASP.NET and WCF.

This post discuss about using WebSockets in ASP.NET 4.5. You can read this post to get an understanding about WebSockets. This post shows piece of code which uses WebSockets in ASP.NET 4.5 and the code is related to simple chat application.

The HTML of Web Form chat application looks as below



It contains a text box where you can type your text message and button where it sends a message to the server. You can notice there is <ul> element which shows the list of other messages which are arriving from the server.

Instantiate a W3C WebSocket JavaScript object and pointed to url to establish a connection to WebSockets Server.



The url starts with ws which runs on HTTP and pointing to .ashx handler which runs on ASP.NET server.

The Chat Handler code looks as below, The handler code checks whether sender is looking for WebSockets connection.





AcceptWebSocketRequest is a new method on Context object in ASP.NET 4.5.

ChatHandler is a wrapper API which implements lower level of WebSockets Handler.

The ChatHandler code looks as below



Override the OnOpen method in ChatHandler Class as below



We are modifying the OnOpen method code by adding the set WebSockets collection variable which contains the set of connection objects.





chatapp exposes a method BroadCast which accepts string or binary payload and send the message to all the objects in the collection. The payload in this piece of code is a JSON object.



Now To handle the messages that coming from the server, we are adding below piece of code in JavaScript by implementing a handler for OnMessage.

<image>

In above code we are actually parsing the JSON object that coming from server using JSON.parse method.

To send a message from client to server you can use the below code



Once this message comes to the server, you can check the type of message and can write the code as below



There is a OnClose method which you can override to close your WebSockets connection. For example when user closes the browser this method will fire and closes the connection.



When you run the application then output is as below

This post discuss about using WebSockets in ASP.NET 4.5. You can read this post to get an understanding about WebSockets. This post shows piece of code which uses WebSockets in ASP.NET 4.5 and the code is related to simple chat application.

The HTML of Web Form chat application looks as below



It contains a text box where you can type your text message and button where it sends a message to the server. You can notice there is <ul> element which shows the list of other messages which are arriving from the server.

Instantiate a W3C WebSocket JavaScript object and pointed to url to establish a connection to WebSockets Server.



The url starts with ws which runs on HTTP and pointing to .ashx handler which runs on ASP.NET server.

The Chat Handler code looks as below, The handler code checks whether sender is looking for WebSockets connection.





AcceptWebSocketRequest is a new method on Context object in ASP.NET 4.5.

ChatHandler is a wrapper API which implements lower level of WebSockets Handler.

The ChatHandler code looks as below



Override the OnOpen method in ChatHandler Class as below



We are modifying the OnOpen method code by adding the set WebSockets collection variable which contains the set of connection objects.





chatapp exposes a method BroadCast which accepts string or binary payload and send the message to all the objects in the collection. The payload in this piece of code is a JSON object.



Now To handle the messages that coming from the server, we are adding below piece of code in JavaScript by implementing a handler for OnMessage.

<image>

In above code we are actually parsing the JSON object that coming from server using JSON.parse method.

To send a message from client to server you can use the below code



Once this message comes to the server, you can check the type of message and can write the code as below



There is a OnClose method which you can override to close your WebSockets connection. For example when user closes the browser this method will fire and closes the connection.



When you run the application then output is as below

WebSockets are required to develop the rich and real time web applications. WebSockets can securely enable the real-time web. Before explaining the need of WebSockets we see what current Web is and it’s limitations.

What is Current Web?



We have rich web applications in current web which does the bi-directional communication. HTTP is a request-reply protocol and it is hard to PUSH on top of this protocol. Current programming model use different techniques to get connect with server, one of them is Periodic Polling.



example: Browser uses XmlHttpRequest to periodically query the server.



In Long Polling Server holds the HTTP request until there is a data to return. Client Sends the data as soon as previous request completes.

The limitations with current programming model

- Periodic polling technique uses high-latency.
- Long polling programming model is unintuitive.

Many scale out and Bandwidth issues with current programming model and limited cross domain support too.

What All WebSockets about is?

WebSockets is a new interoperable technology still undergoing standardization.

- It is full duplex bidirectional socket.
- You can program against using a browser and JavaScript API.
- WebSockets runs over SSL
- Designed for high performance – it is a light weight messaging protocol, it requires low bandwidth and latency.
- Important thing is it is designed to broad reach.
- WebSockets also has the built-in capability to make cross-domain calls.

What Applications can get benefit from WebSockets?

It supports

- Rich web applications
- Real-time applications and services(stock tickers and monitoring systems)
- Beyond browser – Windows 8 and mobile
- Online games

WebSockets are in

- Windows 8
- Internet Explorer 10
- .NET 4.5

How it works?

The secret source for WebSockets protocol is HTTP handshake which enables the socket connection. When a client sends an HTTP request to WebSockets server, it contains the some information in header which tells the server to establish connection over WebSockets. If Server is happy to accepts the request and it then sends the HTTP response back to client and switches the protocol and starts the communication.

Once the handshake is complete client and server communicates over WebSockets using HTTP connection. The Message communication is in either binary or UTF8 format.

The next version of Microsoft’s ASP.Net framework is currently in Beta and there are some pretty cool changes to how Request Validation works in version 4.5. Up until now, there were two ways to enable or disable request validation:

1. Globally – This controls request validation for the entire application.
2. Per Page – This controls request validation on a per-page basis.

In 4.5, the idea is to allow disabling request validation at the field level. This is a huge improvement, because it allows request validation to be enabled on a much larger scale and only be disabled for specific functionality. The first step in taking advantage of this is to make sure that the request validation mode is set to 4.5 in the web.config (shown below).

<system.web>
  <compilation debug="true" targetFramework="4.5" />
  <httpRuntime requestValidationMode="4.5" targetFramework="4.5"
               encoderType="System.Web.Security.AntiXss.AntiXssEncoder,
               System.Web, Version=4.0.0.0, Culture=neutral,
               PublicKeyToken=b03f5f7f11d50a3a" />

Now that the application is set up for the new validation mode, we can start taking advantage of this.

There are two ways to disable request validation on a specific control, a textbox for example. The first way, and probably the easiest, is to set the validation request mode to “disabled” in the html markup. The code below shows how this would look.

<asp:TextBox ID="txtASPNet" ValidateRequestMode="Disabled" runat="server" />

The second way is to set the validation request mode programmatically. This must be done in one of the earlier events for it to be effective. During my testing, it worked in the Page_Init event, but not in the Page_Load event. The code below shows how to do this in the Page_Init event.

protected void Page_Init(object sender, EventArgs e)
{
    txtASPNet.ValidateRequestMode = System.Web.UI.ValidateRequestMode.Disabled;
}

Web controls are not the only way to have such granular control over retrieving data without having it run the request validation. A new collection that was added to the request object is called “Unvalidated”. This collection allows accessing specific parameters, form variables for example, without checking the value against request validation. This is possible because Request validation has been modified to run when a variable is used, not when the request is made. It is important to note that web controls are always used, because the framework populates the controls automatically. Lets take a look at accessing an html input field without triggering request validation.

protected void cmdTest_Click(object sender, EventArgs e)
{
    // Access directly from the Unvalidated collection.
    Response.Write(Request.Unvalidated["txtHtml"].ToString());

    // Specify which Unvalidated collection to access.
    Response.Write(Request.Unvalidated.Form["txtHtml"].ToString());
}

As you can see, there are two ways to access the Unvalidated collections. You can pass the index to the collection directly, or specify exactly which collection you want to retrieve this data from. In this case, it was the forms collection.

Through my testing, I have not yet been able to access Unvalidated.Querystring values because the URL gets run against Request Validation so an exception is thrown before I get a chance to access the unvalidated version. I have not tried the other collections yet.

It is important to remember that manual validation should be performed in addition to using Request Validation. This is especially true for the unvalidated fields, but should also be practiced for fields that are validated. Request Validation is a very limited input validation and does not perform enough validation to be appropriate on its own.

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