Differences between HttpClient and HttpClientFactory

1. HttpClient

What is HttpClient?

• HttpClient is a class provided by .NET (in the System.Net.Http namespace) used to send HTTP requests and receive HTTP responses from a resource identified by a URI.
• It is designed to be reusable for multiple requests.

Problems with Direct Usage

• Socket Exhaustion: If you instantiate HttpClient in a using block or create a new instance for every request, it can lead to socket exhaustion. This is because each instance opens a new socket, and sockets are not immediately released after disposal.
• DNS Issues: If you reuse a single static HttpClient instance for a long time, DNS changes (e.g., server IP changes) are not picked up, as the underlying connection may persist.
• Thread Safety: HttpClient is thread-safe and intended to be reused, but managing its lifecycle manually can be error-prone.

2. HttpClientFactory

What is HttpClientFactory?

• HttpClientFactory is a feature introduced in .NET Core 2.1 (in the Microsoft.Extensions.Http namespace) to address the issues with HttpClient lifecycle management.
• It provides a central place to configure and create HttpClient instances.

How It Works

• It manages the underlying HttpMessageHandler lifetimes, preventing socket exhaustion.
• It allows for named and typed clients, making it easier to configure different clients for different purposes.
• It integrates with dependency injection (DI), making it easy to inject HttpClient into your services.

4. Best Practices

• Do not instantiate HttpClient per request. Use a single instance or use HttpClientFactory.
• Prefer HttpClientFactory for modern .NET applications, as it solves most lifecycle and configuration issues.
• Use named or typed clients if you need different configurations for different endpoints.

6. When to Use What?

• Use HttpClientFactory in all new .NET Core and .NET 5+ applications.
• Direct HttpClient usage is only recommended for legacy applications or very simple scenarios where you can guarantee proper lifecycle management.