ASP.NET Core by Ken

HTTP Client Handling in ASP.NET Core

ASP.NET Core provides robust support for making outbound HTTP requests using HttpClient, often via the IHttpClientFactory. This section covers advanced features for managing these requests, including the use of DelegatingHandler for building custom request/response pipelines. These handlers enable cross-cutting concerns like logging, authentication, and retries in a modular and testable way.

This section includes:

  • Introduction to DelegatingHandler
  • Creating and registering custom handlers
  • Chaining multiple handlers
  • Practical use cases
  • Differences between DelegatingHandler and middleware
  • Testing strategies for handlers
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IHttpClientFactory
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DelegatingHandler is a powerful mechanism in ASP.NET that enables developers to intercept and manipulate HTTP requests and responses. Functioning similarly to middleware, it allows for the implementation of cross-cutting concerns such as logging, authentication, and error handling in a modular and reusable manner.

Key Features:

  • Middleware-like Behavior: Processes HTTP requests and responses in a pipeline fashion.
  • Cross-Cutting Concerns: Ideal for tasks like logging, authentication, and error handling.
  • Reusability: Handlers can be reused across different HttpClient instances.
  • Testability: Facilitates unit testing by isolating concerns

 

Common Use Cases for DelegatingHandler

DelegatingHandler is versatile and can be employed for various purposes:

  • Authentication: Attach tokens or API keys to outgoing requests.
  • Logging: Log request and response details for monitoring and debugging.
  • Error Handling: Implement retry policies or handle specific HTTP status codes.
  • Caching: Cache responses to reduce redundant network calls.
  • Header Manipulation: Add or modify headers in requests or responses.

 

DelegatingHandler vs. Middleware

While both DelegatingHandler and middleware can process HTTP requests and responses, they serve different purposes:

  • Middleware: Operates on incoming HTTP requests to the server.
  • DelegatingHandler: Operates on outgoing HTTP requests from HttpClient.

Use middleware for server-side concerns and DelegatingHandler for client-side HTTP request processing.

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