HttpClientFactory

HttpClientFactory is a factory for HttpClient instances in the .NET platform that centralizes the creation and lifetime management of HttpClient and HttpMessageHandler objects. It was designed to address common issues with manual HttpClient usage, such as socket exhaustion from improper disposal and stale DNS resolution due to long-lived underlying handlers. By pooling handlers and coordinating lifetimes, the factory enables the use of long-lived HttpClient instances without resource leaks and with up-to-date DNS information.

In ASP.NET Core and other .NET applications, HttpClientFactory is provided through the dependency injection system (Microsoft.Extensions.Http). Developers configure it with services.AddHttpClient, and can create named clients or typed clients. Named clients are registered with an identifier and optional configuration, for example AddHttpClient("GitHub", c => c.BaseAddress = new Uri("https://api.github.com/")). Typed clients register a class that receives HttpClient in its constructor (services.AddHttpClient<MyService>()). The factory also supports configuring a pipeline of DelegatingHandler instances, enabling cross-cutting concerns such as authentication, logging, and resilience policies.

Benefits of using HttpClientFactory include centralized and reusable configuration, improved resource efficiency through handler pooling, and easier application-wide concerns like authentication and logging. It also simplifies resilience strategies by allowing policies to be composed with HttpClient instances. Potential considerations include ensuring appropriate client configuration in tests, understanding that the factory manages lifetimes rather than requiring outright long-lived HttpClient usage, and avoiding misconfigurations that could lead to unintended request defaults. Overall, it provides a robust, scalable approach to HttpClient usage in modern .NET applications.