When using services.AddHttpClient, where is the HttpClient created?

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06-10-2024

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Understanding HttpClient Creation with services.AddHttpClient

In ASP.NET Core, when you use services.AddHttpClient in your ConfigureServices method, you're essentially registering an HttpClient factory into the dependency injection container. This means the actual HttpClient instance isn't created immediately, but rather when you request it from the container.

Let's break this down with an example:

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpClient("MyApi", client =>
    {
        client.BaseAddress = new Uri("https://api.example.com");
    });

    // ... other service registrations
}

Here, we register an HttpClient named "MyApi" with a base address for our API. But where is the HttpClient actually created?

The Answer:

The HttpClient is created when you first inject it into a service or controller. This happens lazily, meaning the creation only occurs when it's needed, which is when a request is made to your API.

How it Works:

1. Registration: When you call services.AddHttpClient, you register a factory that creates HttpClient instances. This factory is responsible for configuring the HttpClient with the provided options, like the base address.
2. Injection: When a service or controller requests an HttpClient with the registered name ("MyApi" in our example), the dependency injection container uses the factory to create a new instance of the HttpClient.
3. Usage: This newly created HttpClient is then used to make requests to the API.

Benefits of this approach:

• Lazy Creation: This ensures that resources are only allocated when needed, minimizing overhead and improving application performance.
• Scope and Isolation: Each service or controller gets its own HttpClient instance, providing proper isolation and preventing potential conflicts.
• Configuration: The factory allows you to easily customize the HttpClient with options like base address, headers, timeouts, and more.

Important Considerations:

• Disposal: HttpClient is a disposable resource. Remember to properly dispose of it after use to avoid resource leaks. While the framework helps with managing the lifetime of the HttpClient within the scope of a request, it's best practice to follow the IDisposable pattern for clean resource management.
• Naming: Using descriptive names for your registered HttpClient instances helps maintain clarity and simplifies their usage in your code.
• Shared Configuration: If you have multiple services or controllers that need the same configuration for their HttpClient, consider using a custom factory to share the configuration logic and reduce code duplication.

By understanding the process of HttpClient creation with services.AddHttpClient, you can leverage the benefits of dependency injection and manage your network resources effectively in your ASP.NET Core application.

References:

• Microsoft Docs: HttpClientFactory
• GitHub: HttpClientFactory