Introduction

In the ever-evolving landscape of web development, managing and optimizing the flow of incoming and outgoing traffic is crucial. Internet Information Services (IIS) provides a robust platform for web applications, and one of its powerful features is the ability to use handlers.

Custom handlers allow developers to create tailored solutions that enhance the functionality and performance of their applications. In this blog, we will explore what handlers are in IIS, how to create custom handlers in an ASP.NET framework application, and the advantages of using them.

Read more about this on my previous blog :
IIS Handlers

If you want to do the same using modules, you can read more on below :
Remove unwanted HTTP headers using IIS Modules

What are Handlers in IIS

Handlers in IIS are components responsible for processing requests made to the server. When a client sends a request, IIS determines the appropriate handler to process that request based on its type. Handlers work at a lower level than modules, directly interacting with the HTTP request and response. They can control the entire request pipeline, making them essential for tasks that require specific handling of HTTP requests, such as file downloads, dynamic content generation, and custom authentication mechanisms.

How to Create Custom Handler in ASP.NET Framework Application

Creating a custom handler in an ASP.NET framework application involves several steps:

I am making use of .NET framework version 4.8.1 for creating this class library on Visual studio 2022

Step 1: Create a new Visual Studio Project

Open Visual Studio and create a new Class Library project.

Name it appropriately, e.g., ” MyCustomHandler “.

Step 2: Implement the IHttpHandler Interface

To create a custom handler, you need to implement the `IHttpHandler` interface, which requires defining two methods: `ProcessRequest` and `IsReusable`.

namespace RemoveHeadersUsingHandlers
{
// You may need to install the Microsoft.AspNetCore.Http.Abstractions package into your project
public class RemoveHeadersMiddleware
{
private readonly RequestDelegate _next;

public RemoveHeadersMiddleware(RequestDelegate next)
{
_next = next;
}

public async Task InvokeAsync(HttpContext context)
{
context.Response.OnStarting(() =>
{
// List of headers to remove
var headersToRemove = new[] { “X-AspNetMvc-Version”, “Server”, “Content-Type” };
foreach (var header in headersToRemove)
{
context.Response.Headers.Remove(header);
}
context.Response.Headers.Add(“X-Frame-Options”,”SAMEORIGIN”);
context.Response.Headers.Add(“X-Powered-By”, “123.123.123.123”);
context.Response.Headers.Add(“X-Content-Type”, “nosniff”);
return Task.CompletedTask;
});
// Call the next delegate/middleware in the pipeline
await _next(context);
}
}

// Extension method used to add the middleware to the HTTP request pipeline.
public static class RemoveHeadersMiddlewareExtensions
{
public static IApplicationBuilder UseRemoveHeadersMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<RemoveHeadersMiddleware>();
}
}

Step 3A: Register the Handler in Web.config

After creating the handler class, you need to register it in the `Web.config` file of your application.

<handlers>
<add name=” MyCustomHandler ” path=”C:inetpubURLRewritebinCustomHandler.dll” verb=”*” type=” MyCustomHandler. MyCustomHandler, MyCustomHandler “/>
</handlers>

Step 3B: Register the Handler Via IIS UI

After creating the handler class, you can place the ‘DLL’ in the bin folder of your application.
Then go to the ‘Handler Mapping’

and click on ‘Add Managed Handler’

Enter the details of the handler

This is how you can add the Custom handler to your application hosted on IIS

Step 3: Access the Custom Handler

Once registered, you can access your custom handler through the specified path. In this example, navigating to `[URL]` will trigger the custom handler and return the response defined in the `ProcessRequest` method, from your custom handler class library.

How Does Custom Handler Modify Incoming and Outgoing Traffic

Custom handlers have the ability to inspect, modify, or replace the incoming and outgoing HTTP traffic. This capability is particularly useful for implementing custom logic that cannot be achieved with standard handlers. For instance, you might use a custom handler to:

Filter and validate incoming requests before they reach the application.
Modify request headers or body content to meet specific requirements.
Generate dynamic responses based on request parameters.
Log detailed information about the request and response for auditing purposes.
Implement custom caching mechanisms to optimize performance.

By leveraging custom handlers, developers can create highly specialized solutions that enhance the security, performance, and functionality of their web applications.

How are Custom Handlers Traced in FREB Logs

Failed Request Event Buffering (FREB) logs in IIS provide detailed information about the request processing pipeline, including the execution of custom handlers. To trace custom handlers in FREB logs, follow these steps:

Enable FREB Logging: In IIS Manager, select your site, and navigate to “Failed Request Tracing Rules.” Enable FREB and configure the rules to capture relevant information.
Configure Trace Rules: Specify the conditions that should trigger tracing, such as status codes, time taken, or specific request URLs.
Analyze FREB Logs: After enabling FREB, you can analyze the logs generated for each request. The logs provide detailed insights into each stage of the request processing pipeline, including the execution of custom handlers. Look for entries related to your custom handler’s path and examine the events recorded during its execution.

FREB logs offer a powerful tool for debugging and optimizing custom handlers, as they provide granular visibility into the request processing flow and help identify performance bottlenecks or errors.

When and Why to Use Custom Handlers

Custom handlers are best suited for scenarios where you need fine-grained control over the request and response process. Consider using custom handlers in the following situations:

Custom Authentication and Authorization: Implement custom authentication mechanisms that go beyond the capabilities of standard handlers.
Dynamic Content Generation: Generate content on the fly based on request parameters, user roles, or other dynamic factors.
Request Filtering and Validation: Filter and validate incoming requests to ensure they meet specific criteria before processing.
Custom Logging: Log detailed information about requests and responses for auditing, monitoring, or debugging purposes.
Performance Optimization: Implement custom caching, compression, or other performance-enhancing techniques.

By using custom handlers, developers can create tailored solutions that address specific business needs and improve the overall functionality and performance of their web applications.

Advantages of Using Custom Handlers

Custom handlers offer several advantages that make them a valuable tool in a developer’s toolkit:

Flexibility: Custom handlers provide the flexibility to implement unique request processing logic that cannot be achieved with standard handlers.
Performance: By optimizing request and response processing, custom handlers can significantly improve the performance of web applications.
Security: Implementing custom authentication and authorization mechanisms enhances the security of web applications.
Extensibility: Custom handlers can be easily extended and adapted to meet changing business requirements.
Debugging and Logging: Custom handlers offer detailed logging capabilities, aiding in debugging and performance monitoring.

These advantages make custom handlers an essential tool for developers looking to create sophisticated and high-performing web applications.

Conclusion

The ability to create custom handlers in IIS and ASP.NET framework applications offers developers unparalleled control over the request and response lifecycle. By implementing custom handlers, you can address specific business requirements, optimize performance, and enhance the security of your web applications. Whether you need to filter requests, generate dynamic content, or implement custom authentication, custom handlers provide the flexibility and power to achieve your goals.

As you explore the potential of custom handlers, remember to leverage tools like FREB logs to trace and optimize their performance, ensuring your applications run smoothly and efficiently.

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