Can you give an example of how you would implement a custom HttpModule in ASP.NET?

Here's an example of how you can implement a custom HTTP module in ASP.NET:

1. Create a class that implements the 'IHttpModule' interface. This interface requires the implementation of the 'Init' and Dispose methods.

   
   
   public class CustomModule : IHttpModule
   {
       public void Init(HttpApplication context)
       {
           // Subscribe to the desired event handlers
           context.BeginRequest += OnBeginRequest;
           context.EndRequest += OnEndRequest;
       }
   
       public void Dispose()
       {
           // Cleanup resources, if needed
       }
   
       private void OnBeginRequest(object sender, EventArgs e)
       {
           // Custom logic at the beginning of request processing
           HttpContext context = ((HttpApplication)sender).Context;
   
           // Access and modify request details
           HttpRequest request = context.Request;
           HttpResponse response = context.Response;
   
           // Log the incoming request
           string requestUrl = request.Url.ToString();
           string clientIpAddress = request.UserHostAddress;
           string timestamp = DateTime.Now.ToString();
   
           string logMessage = $"[{timestamp}] Request from IP {clientIpAddress}: {requestUrl}";
   
           // Replace Console.WriteLine with your logging implementation
           Console.WriteLine(logMessage);
       }
   
       private void OnEndRequest(object sender, EventArgs e)
       {
           // Custom logic at the end of request processing
           HttpContext context = ((HttpApplication)sender).Context;
   
           // Access and modify response details
           HttpResponse response = context.Response;
   
           // Add a custom header to the response
           response.Headers.Add("X-Custom-Header", "Hello from CustomModule!");
       }
   }
   
   

2. In the 'Init' method of your custom module, subscribe to the desired event handlers. In this example, we subscribe to the 'BeginRequest' and 'EndRequest' events.
3. In the event handlers ('OnBeginRequest' and 'OnEndRequest' in the example above), you can access and modify the request and response objects to perform custom processing. Here, we log the incoming request in the 'OnBeginRequest' handler and add a custom header to the response in the 'OnEndRequest' handler.
4. Register the custom HTTP module in the web.config file:

   
   
       <system.webServer>
           <modules>
               <add name="CustomModule" type="Namespace.CustomModule" />
           </modules>
       </system.webServer>
   
   

   Replace "Namespace.CustomModule" with the actual namespace and class name of your custom module.

By implementing the 'IHttpModule' interface and subscribing to the appropriate event handlers, you can customize the behavior of the ASP.NET application at various stages of the request processing pipeline. In this example, the custom module logs the incoming request and adds a custom header to the response, but you can modify it to suit your specific requirements.