Understanding Request Handling Functions in .NET – Use(), Map(), and Run()

When building web applications in .NET, middleware plays a big role in handling incoming requests. In this blog post, we'll break down three important request-handling methods: Use(), Map(), and Run() – what they do, how they work, and when to use them.

What is Middleware?

Middleware in .NET is a piece of code that runs between the server receiving a request and the server sending a response. It can perform tasks like:

• Logging
• Authentication
• Exception handling
• Modifying requests/responses

Now let’s explore the three key methods used in setting up middleware: Use(), Map(), and Run().

Use() Method

The Use() method is used to add middleware components to the request pipeline. It can pass control to the next middleware using next().

Key Points:

• Can call the next middleware using next().
• Used for logging, authentication, exception handling, etc.
• If next() is not called, it short-circuits the pipeline.

Map() Method

The Map() method is used to create branches in the request pipeline. It runs specific middleware only if the request path matches a pattern.

Key Points:

• Routes requests to different branches.
• Used for API versioning, feature-based middleware, etc.
• Middleware inside Map() runs only if the path matches.

Run() Method

The Run() method is used to create terminal middleware — this means it handles the request and does not call any other middleware after it.

Key Points:

• Ends the middleware pipeline.
• Does not call the next middleware.
• Used for simple, final request handling.

Conclusion

By using Use(), Map(), and Run(), you can structure your request handling in .NET applications effectively:

• Use Use() to chain middleware.
• Use Map() to create route-specific middleware branches.
• Use Run() to finalize the request pipeline.