HttpClient One-Pager

March 15, 2023

one-pagers aspnetcore csharp

• Introduction
• HttpClient
• HttpResponseMessage
• HttpRequestException
• HttpProxy
• IHttpClientFactory
• HttpClient lifetime Management
• SocketsHttpHandler
• Use named clients in singleton service.
• Message Handler DI Scope
• Guidelines for using HttpClient
• Rate limit an Http handler
• Http/3 support

Introduction

• The HttpClient class sends http requests and receives http responses from a Uri.

• An HttpClient object instance is a collection of settings that is applied to all requests.

• Each object instance uses its own connection pool, which isolates its requests from the others.

HttpClient

• Create an HttpClient with a base address

• The HttpContent type is used to represent an Http body and content headers. Use the HttpContent class to specify the body of the request. It also represents the response body accessible on the HttpResponseMessage.Content property. See HttpContent

• Send an HttpGet with a string response

• Send an HttpGet with a strongly-typed response

• Send an HttpPost request with a json body formatted as a string

• Send an HttpPost request with a strongly typed object as Json

• Send an HttpPut request with a json body formatted as a string

• Send an HttpPut request with a strongly typed object as Json

• Send an HttpPatch request with a json body formatted as a string

• Send an HttpDelete request with a json body formatted as a string

• The Http Head request returns only the headers associated with a resource. A response to the Head request does not return a body. Http Head

• The Http Options request is used to identify which Http methods a server or endpoint supports. Http Options

HttpResponseMessage

• The HttpResponseMessage type contains the HttpResponse.

• Handling an Http Response

• You can access the response body using the Content property. Handling valid Http Content responses

HttpRequestException

• HttpRequestException is thrown when an HttpRequest fails. Handling an HttpRequestException

HttpProxy

• A proxy can be configured in 2 ways.

  • A default is specified on the HttpClient.DefaultProxy property.

  • Or you can specify the HttpClientHandler.Proxy property.

• The HttpClient.DefaultProxy is a static property that determines the default proxy that all HttpClient instances use. See Global default proxy

• See Proxy per client

IHttpClientFactory

• IHttpClientFactory serves as an abstraction that can create HttpClient instances with custom configurations.

• If your app uses cookies then it is better to avoid IHttpClientFactory.

• Use IHttpClientFactory for short-lived clients. Use PooledConnectionLifetime for long-lived clients.

• See IHttpClientFactory

• To regiser IHttpClientFactory, call AddHttpClient. See Basic Usage

• Use named clients, if your app needs to connect to multiple services. See Named Clients

• Typed clients are the same as named clients but without the use of strings. Probably better to use this. See Typed Clients

• Get, post, put method calls are no different from HttpClient. See Get, Post, Put

HttpClient lifetime Management

• IHttpClientFactory creates a new instance of HttpClient for every call to CreateClient.

• One HttpClientHandler is created per client name.

• The factory manages the lifetimes of the HttpClientHandler instances.

• To reduce resource consumption, IHttpClientFactory caches HttpClientHandler instances.

• An HttpClientHandler instance may be reused from the cache if its lifetime has not expired.

• Caching of handlers is desirable as each handler manages its own underlying connection pool.

• Creating more handlers may lead to socket exhaustion and connection delays.

• Some handlers may also keep the connection open indefinitely, which can prevent the handler reacting to DNS changes.

• The default handler lifetime is two minutes.

• You can change the lifetime value. see HttpClient Lifetime Management.

SocketsHttpHandler

• The SocketsHttpHandler implementation of HttpMessageHandler allows PooledConnectionLifetime to be configured.

• This setting is used to ensure that the handler reacts to DNS changes, so using SocketsHttpHandler is an alternative to using IHttpClientFactory.

• IHttpClientFactory and SocketsHttpHandler can be used together. See the details

Use named clients in singleton service.

• With named clients, IHttpClientFactory is injected into services, a new HttpClient is created everytime CreateClient is called.

• Typed clients are transient objects usually injected into services. Typed clients are supposed to be short-lived. Singleton services are supposed to be long-lived. See the problem there.

• For more information

Message Handler DI Scope

• IHttpClientFactory creates a seperate DI scope per each HttpMessageHandler instance.

• They are separate from application DI scope like aspnetcore request scope or user-created manual DI scope.

• HttpMessageHandler scopes can outlive application scopes.

• Do not cache scope related information inside HttpMessageHandler instances.

• Generally avoid such code gymnastics. Use this section more like an fyi.

• For more information

Guidelines for using HttpClient

• If a DNS entry changes regularly, the client wont respect those updates. Limit the lifetime of the connection by setting the PooledConnectionLifetime property, so that DNS lookup is repeated when the connection is replaced. For more information

• To avoid port exhaustion problems, reusing HttpClient instance for as many Http requests as possible is recommended. Recommended usage

Rate limit an Http handler

• To use rate limiting in .Net, add a reference to System.Threading.RateLimiting nuget package.

• Here is a sample implementation

• There is now a rate limiting middleware option. In case there is a rate limiting requirment for your application, click here for a sample implementation of how to set it up.

Http/3 support

• In case, you really want to use Http/3. I would not recommend using it at this point of time.

• If you are curious