16 .net core http请求

偏执的太偏执、 2023-03-02 10:59 6阅读 0赞

可以注册 IHttpClientFactory 并将其用于配置和创建应用中的 HttpClient 实例

## 系统必备 ##

面向.NET Framework 的项目要求安装 Microsoft.Extensions.Http NuGet 包。  
面向 .NET Core 且引用 Microsoft.AspNetCore.App 元包的项目已经包括 Microsoft.Extensions.Http 包。

## 基本用法 ##

注册服务

services.AddHttpClient();

依赖注入

public class BasicUsageModel : PageModel { 
        private readonly IHttpClientFactory _clientFactory;
    
    	public IEnumerable<GitHubBranch> Branches {  get; private set; }
    	
    	public bool GetBranchesError {  get; private set; }
    	
    	    // 注入 IHttpClientFactory
    	    public BasicUsageModel (IHttpClientFactory clientFactory) { 
    	        _clientFactory = clientFactory;
    	}
    
        public async Task OnGet () { 
            var request = new HttpRequestMessage (HttpMethod.Get, "https://api.github.com/repos/aspnet/docs/branches");
            request.Headers.Add ("Accept", "application/vnd.github.v3+json");
            request.Headers.Add ("User-Agent", "HttpClientFactory-Sample");
    
            // 生成 Http 客户端
            var client = _clientFactory.CreateClient ();
            // 发送请求
            var response = await client.SendAsync (request);
    
            if (response.IsSuccessStatusCode) { 
                Branches = await response.Content.ReadAsAsync<IEnumerable<GitHubBranch>> ();
            } else { 
                GetBranchesError = true;
                Branches = Array.Empty<GitHubBranch> ();
            }
        }
    }

## 命名客户端 ##

services.AddHttpClient ("github",
        c => { 
            c.BaseAddress = new Uri ("https://api.github.com/");
            c.DefaultRequestHeaders.Add ("Accept", "application/vnd.github.v3+json");
            // Github API versioning 
            c.DefaultRequestHeaders.Add ("User-Agent", "HttpClientFactory-Sample");
            // Github requires a user-agent 
        }
    );
    
    // 创建命名客户端
    var client = _clientFactory.CreateClient("github");

## 出站请求中间件 ##

要创建处理程序，请定义一个派生自 DelegatingHandler 的类。 重写 SendAsync 方法，在将请求传递至管道中的下一个处理程序之前执行代码

public class ValidateHeaderHandler : DelegatingHandler { 
        protected override async Task<HttpResponseMessage> SendAsync (HttpRequestMessage request,
            CancellationToken cancellationToken) { 
            if (!request.Headers.Contains ("X-API-KEY")) { 
                return new HttpResponseMessage (HttpStatusCode.BadRequest) { 
                    Content = new StringContent ("You must supply an API key header called X-API-KEY")
                };
            }
    
            return await base.SendAsync (request, cancellationToken);
        }
    }

services.AddTransient<ValidateHeaderHandler> ();
    
    services.AddHttpClient ("externalservice", c => { 
            c.BaseAddress = new Uri ("https://localhost:5000/"); // assume this is an "external" service which requires an API KEY
        })
        .AddHttpMessageHandler<ValidateHeaderHandler> ();