How would you implement a custom HttpHandler in ASP.NET?

To implement a custom HTTP handler in ASP.NET, you would typically follow these steps:

1. Create a class that implements the 'IHttpHandler' interface. This interface defines the methods and properties required for processing requests. The key method to implement is 'ProcessRequest(HttpContext context)', which handles the request and generates the appropriate response.

   
   
   public class CustomHandler : IHttpHandler
   {
       public bool IsReusable => true;
   
       public void ProcessRequest(HttpContext context)
       {
           // Custom request processing logic
           // Generate response, manipulate headers, etc.
       }
   }
   
   

2. Within the 'ProcessRequest' method, write the custom logic to handle the specific type of request. You can access the request and response information through the HttpContext object passed as a parameter. Perform any necessary processing, such as generating content, manipulating headers, or handling specific request parameters.
3. Optionally, you can implement the 'IsReusable' property to indicate whether the handler instance can be reused for multiple requests. If your handler is stateless and thread-safe, you can set this property to 'true' to enable reuse, improving performance.
4. Register the custom HTTP handler in the web.config file or programmatically. The registration process associates the handler with specific URLs or file extensions so that it gets invoked for matching requests.
   • Register in web.config: Add the following configuration within the '<system.web>' section:

     
     
     <system.web>
       <httpHandlers>
         <add verb="*" path="customhandler.ashx" type="Namespace.CustomHandler, AssemblyName" />
       </httpHandlers>
     </system.web>
     
     

     In this example, the handler is registered for requests to "customhandler.ashx". Adjust the verb, path, and type attributes as per your requirements.
   • Register programmatically: In the 'Application_Start' event in 'Global.asax'or a custom initialization module, use the 'Routes' or 'Handlers' collection to add the custom handler.

     
     
         void Application_Start(object sender, EventArgs e)
         {
             // Register the custom handler programmatically
             RouteTable.Routes.Add(new Route("customhandler.ashx", new CustomHandler()));
         }
     

     In this example, the custom handler is registered using the 'RouteTable.Routes.Add' method.
5. Build and deploy your application to make the custom HTTP handler available for processing requests.

With these steps, you have implemented a custom HTTP handler in ASP.NET. The handler will be invoked when a matching request is received, and you can define the specific logic to handle the request and generate the response within the 'ProcessRequest' method.