Understanding IIS Handlers – Microsoft Community Hub

• What is an IIS Handler?
• Where are handlers kicked out in the IIS pipeline?
• There is a handler type
• What custom handlers can I create?
• How does this feature intercept traffic and modify incoming and outgoing requests?
• Advantages and Uses
• Best Practices
• conclusion

Internet Information Services (IIS) handlers are components of the IIS Web server that handle specific types of requests. They are an essential part of the request processing pipeline and determine how requests for specific resources (such as .html, .aspx, or .jpg files) are handled by the server.

A handler can be thought of as an intermediary that translates a request into a task that the server can execute, allowing for a more structured and efficient processing system.

Handlers are called during the “Execute Request Handler” phase of the IIS request processing pipeline. This phase occurs after the request has been authenticated, authorized, and filtered by all applicable modules. When a request reaches this phase, the IIS pipeline looks for an appropriate handler based on the request type and any configured paths or mappings.

IIS has several built-in handlers, which are categorized into three types:

1. Static file handler

These handlers are responsible for serving static files such as HTML, CSS, JavaScript, and images.

2. Script Handler

Script handlers handle dynamic content. Examples include ASP.NET handlers for .aspx files and PHP handlers for .php files.

3. Custom handler

These are custom handlers that you can create to handle custom scenarios or specific types of requests that are not covered by the default handlers.

Custom handlers can be developed to meet specific requirements that the default handlers fall short of. For example, a custom handler could be written as follows:

• Handles unique file types.
• Performs special logging or request processing.
• Interacts with third-party APIs before providing a response.
• Implement security features such as custom authentication or request validation.

Creating a custom handler typically involves implementing the `IHttpHandler` interface in .NET, which allows you to define the logic for processing requests. In upcoming blogs, we will discuss how to create a custom handler and call various functions.

Handlers can intercept traffic by attaching to the request pipeline at a specific stage. They can also inspect, modify, or abort requests based on custom logic. Here’s how it generally works:

1. Incoming requests

For incoming requests, the handler can:

• Read the request headers and body.
• Modify request parameters or headers before passing to the next step.
• Route requests to different resources based on user-defined rules.

  

2. Outgoing response

For outgoing responses, the processor can:

• Modify the response header or status code.
• Transforms the response body, such as applying compression or encryption.
• Log response details for analysis and debugging.

Using IIS handlers has several advantages:

• Flexibility: Handlers provide a flexible way to handle different types of requests and responses.
• Performance: Handlers can improve performance by interacting directly with the request pipeline, reducing the overhead of additional processing.
• Custom: Custom handlers allow developers to tailor request processing to their specific application needs, facilitating unique functionality. In upcoming blogs, we will look at how to create custom handlers in ASP.NET and ASP.NET Core, and how to intercept incoming and outgoing traffic to modify values.

Place of use

IIS handlers are particularly useful in the following scenarios:

• You need to handle custom file types or protocols.
• Specialized request handling such as logging or monitoring is required.
• You need to implement custom security measures.
• Legacy systems need to integrate with modern web applications.

To get the most out of IIS handlers, consider the following best practices:

• Keep it simple: Make sure the logic within your handlers is as simple and efficient as possible to minimize performance overhead.
• Security: Always validate and sanitize input in your custom handlers to avoid security vulnerabilities.
• Modular design: Design your handlers to be modular and reusable across different applications and projects.
• Logging: Implement comprehensive logging to track the performance and behavior of your handlers, helping with troubleshooting and optimization.
• Testing: Thoroughly test your custom handlers in a variety of scenarios to ensure they handle all exceptions and do not cause unexpected behavior.

IIS handlers are a powerful tool in the web server arsenal, providing flexibility in handling a wide range of request types and scenarios. Whether you are handling static files, dynamic content, or custom processing requirements, understanding and effectively utilizing handlers can greatly improve the performance and functionality of your web applications.

By following best practices and leveraging the unique benefits of handlers, you can ensure a robust and efficient request processing pipeline for your application.