How does an HttpModule differ from an HttpHandler?
An HTTP module and an HTTP handler are both components in ASP.NET that participate in the request processing pipeline but serve different purposes and have different points of interaction.
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Purpose:
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HTTP Module: An HTTP module is designed to extend or modify the behavior of the ASP.NET application by intercepting and processing requests and responses at various stages of the pipeline. It allows you to add custom logic or functionality to the request/response processing without modifying individual pages or handlers.
- HTTP Handler: An HTTP handler is responsible for processing specific types of requests and generating corresponding responses. It handles the actual processing of the request and response generation.
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Execution:
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HTTP Module: An HTTP module is executed at various stages of the request processing pipeline. It subscribes to events in the pipeline and performs custom logic before, during, or after specific events occur. An HTTP module participates in the entire lifetime of a request and can interact with multiple requests in a single instance.
- HTTP Handler: An HTTP handler is invoked to handle a specific request that matches its configured URL pattern or file extension. The handler is instantiated and its ProcessRequest method is called to process the request and generate the response. An HTTP handler is specific to an individual request and typically does not persist beyond that request.
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Interaction:
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HTTP Module: An HTTP module can intercept and modify the request or response at various stages of the pipeline. It can modify headers, perform custom authentication/authorization, manipulate URL rewriting, handle caching, or add additional processing logic. It operates on the entire request and response and can modify them as needed.
- HTTP Handler: An HTTP handler is responsible for generating the response for a specific request. It can read request data, generate dynamic content, write to the response stream, set response headers, and handle redirects. The handler focuses on the processing and generation of the response for a specific request.
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Reusability:
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HTTP Module: HTTP modules are designed to be reusable components that can be registered and used across multiple applications or within the same application to provide consistent functionality. They can be added or removed as needed.
- HTTP Handler: HTTP handlers are specific to handling certain types of requests. While you can reuse a handler within the same application, they are typically designed for specific functionalities or file types.
In summary, an HTTP module allows you to modify the behavior of the request/response processing pipeline and perform custom processing at various stages, while an HTTP handler is responsible for processing specific types of requests and generating responses. Modules provide more extensive and reusable customization options, while handlers focus on handling specific requests and generating responses.