推薦學(xué)習(xí)：Flurl使用Polly實(shí)現(xiàn)重試Policy！
?在使用Flurl作為HttpClient向Server請(qǐng)求時(shí)，由于網(wǎng)絡(luò)或者其它一些原因?qū)е抡?qǐng)求會(huì)有失敗的情況，比如
HttpStatusCode.NotFound、HttpStatusCode.ServiceUnavailable、HttpStatusCode.RequestTimeout等；網(wǎng)絡(luò)上有比較多的HttpClientFactory使用Polly來(lái)實(shí)現(xiàn)重試的內(nèi)容，奈何已經(jīng)習(xí)慣使用Flurl的人，要全部換回到IHttpClient的確有不方便的地方，因?yàn)楸疚氖褂肍lurl的Polly來(lái)實(shí)現(xiàn)重試機(jī)制做一個(gè)整理；
不使用Polly來(lái)測(cè)試
提供一個(gè)接口以便做請(qǐng)求測(cè)試
[Route("api/[controller]")]
[ApiController]
public class PollyController : ControllerBase
{
private readonly ILogger<PollyController> _logger;
public PollyController(ILogger<PollyController> logger)
{
_logger = logger;
}
// GET: api/<PollyController>
[HttpGet]
public IActionResult Get()
{
var random = new Random().Next(0, 8);
switch (random)
{
case 0:
_logger.LogInformation("About to serve a 404");
return StatusCode(StatusCodes.Status404NotFound);
case 1:
_logger.LogInformation("About to serve a 503");
return StatusCode(StatusCodes.Status503ServiceUnavailable);
case 2:
_logger.LogInformation("Sleeping for 10 seconds then serving a 504");
Thread.Sleep(10000);
_logger.LogInformation("About to serve a 504");
return StatusCode(StatusCodes.Status504GatewayTimeout);
default:
_logger.LogInformation("About to correctly serve a 200 response");
return Ok(new {time = DateTime.Now.ToLocalTime()});
}
}
}創(chuàng)建一個(gè)請(qǐng)求客戶端
public class HomeController : Controller
{
private readonly ILogger<HomeController> _logger;
public HomeController(ILogger<HomeController> logger)
{
_logger = logger;
}
public async Task<IActionResult> Index()
{
try
{
var time = await "http://127.0.0.1:5000/api/polly"
.GetJsonAsync();
_logger.LogInformation($"App: success - {time.time}");
return View(time.time);
}
catch (Exception e)
{
_logger.LogWarning($"App: failed - {e.Message}");
throw;
}
}
}嘗試請(qǐng)求，可以發(fā)現(xiàn)有很多請(qǐng)求失敗的地方，這個(gè)情況很不理想，服務(wù)器有較大的機(jī)率不能正常的響應(yīng)
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to serve a 404
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to correctly serve a 200 response
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to correctly serve a 200 response
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to correctly serve a 200 response
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to serve a 503
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to serve a 503
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to correctly serve a 200 response
info: SuppertRcsInterfaceTest.Controllers.PollyController[0]
About to serve a 404?
針對(duì)這個(gè)情況有沒(méi)有什么解決的辦法呢，答案是肯定的，粗暴的想法就是失敗了再重新做請(qǐng)求，直接在Flurl的返回結(jié)果中做這個(gè)邏輯處理會(huì)比較麻煩也不方便統(tǒng)一的管理，如此就找到了Polly
使用Polly來(lái)測(cè)試
首先安裝Polly,
Install-Package Polly下面先給出Polly的簡(jiǎn)單介紹后接著給出
Policy的代碼片段?
Polly的七種策略：重試、斷路、超時(shí)、隔離、回退和緩存策略，本文使用到了重試、超時(shí)策略
重試（Retry）：出現(xiàn)故障自動(dòng)重試，這個(gè)是常見的場(chǎng)景
斷路（Circuit-breaker）：當(dāng)系統(tǒng)遇到嚴(yán)重的問(wèn)題時(shí)，快速回饋失敗比讓用戶/調(diào)用者等待要好，限制系統(tǒng)出錯(cuò)的消耗，有助于系統(tǒng)恢復(fù)，比如，當(dāng)我們?nèi)フ{(diào)用一個(gè)第三方的API，有很長(zhǎng)一段時(shí)間API都沒(méi)有響應(yīng)，可能對(duì)方服務(wù)器癱瘓了，如果我們的系統(tǒng)還不停地重試，不僅會(huì)加重系統(tǒng)的負(fù)擔(dān)，還有可能導(dǎo)致系統(tǒng)其它任務(wù)受影響，因此，當(dāng)系統(tǒng)出錯(cuò)的次數(shù)超過(guò)了指定的閾值，就得中斷當(dāng)前線程，等待一段時(shí)間后再繼續(xù)；比如:
Policy.Handle<SomeException>().CircuitBreaker(2, TimeSpan.FromMinutes(1));表示當(dāng)系統(tǒng)出現(xiàn)兩次某個(gè)異常時(shí)就停下來(lái)，等待1分鐘后再繼續(xù)，還可以在斷路時(shí)定義中斷的回調(diào)和重啟的回調(diào)。超時(shí)（Timeout）：當(dāng)系統(tǒng)超過(guò)一定時(shí)間的等待，就可以判斷不可能會(huì)有成功的結(jié)果；比如平時(shí)一個(gè)網(wǎng)絡(luò)請(qǐng)求瞬間就完成了，如果有一次網(wǎng)絡(luò)請(qǐng)求超過(guò)了30秒還沒(méi)有完成，我們就可以判定不可能會(huì)返回成功的結(jié)果了，因此，我們需要設(shè)置系統(tǒng)的超時(shí)時(shí)間，避免系統(tǒng)長(zhǎng)時(shí)間無(wú)謂的等待；比如：
Policy.Timeout(30, (context, span, task) => {// do something});表示設(shè)置了超時(shí)時(shí)間不能超過(guò)30秒，否則就認(rèn)為是錯(cuò)誤的結(jié)果，并執(zhí)行回調(diào)。隔離（Bulkhead Isolation）：當(dāng)系統(tǒng)的一處出現(xiàn)故障時(shí)，可能觸發(fā)多個(gè)失敗的調(diào)用，對(duì)資源有較大的消耗，下游系統(tǒng)出現(xiàn)故障可能導(dǎo)致上游的故障的調(diào)用，甚至可能蔓延到導(dǎo)致系統(tǒng)崩潰，所以要將可控的操作限制在一個(gè)固定大小的資源池中，以隔離有潛在可能相互影響的操作；比如：
Policy.Bulkhead(12, context => {// do something});表示最多允許12個(gè)線程并發(fā)執(zhí)行，如果執(zhí)行被拒絕，則執(zhí)行回調(diào)。回退（Fallback）：有些錯(cuò)誤無(wú)法避免，就要有備用的方案，當(dāng)無(wú)法避免的錯(cuò)誤發(fā)生時(shí)，我們要有一個(gè)合理的返回來(lái)代替失敗；比如：
Policy.Handle<Whatever>().Fallback<UserAvatar>(() => UserAvatar.GetRandomAvatar());表示當(dāng)用戶沒(méi)有上傳頭像時(shí)，我們就給他一個(gè)默認(rèn)頭像。緩存（Cache）：一般我們會(huì)把頻繁使用且不會(huì)怎么變化的資源緩存起來(lái)，以提高系統(tǒng)的響應(yīng)速度，如果不對(duì)緩存資源的調(diào)用進(jìn)行封裝，那么我們調(diào)用的時(shí)候就要先判斷緩存中有沒(méi)有這個(gè)資源，有的話就從緩存返回，否則就從資源存儲(chǔ)的地方獲取后緩存起來(lái)再返回，而且有時(shí)還要考慮緩存過(guò)期和如何更新緩存的問(wèn)題；Polly提供了緩存策略的支持，使得問(wèn)題變得簡(jiǎn)單。
策略包（Policy Wrap）：一種操作會(huì)有多種不同的故障，而不同的故障處理需要不同的策略，這些不同的策略必須包在一起，作為一個(gè)策略包，才能應(yīng)用在同一種操作上，這就是Polly的彈性特性，即各種不同的策略能夠靈活地組合起來(lái)
更多...
using System;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Flurl.Http.Configuration;
using Microsoft.Extensions.Logging;
using Polly;
using Polly.Retry;
using Polly.Timeout;
using Polly.Wrap;
namespace WithPollyClient.Services
{
public class Policies
{
private readonly ILogger<Policies> _logger;
public Policies(ILogger<Policies> logger)
{
_logger = logger;
}
private AsyncTimeoutPolicy<HttpResponseMessage> TimeoutPolicy
{
get
{
return Policy.TimeoutAsync<HttpResponseMessage>(3, (context, span, task) =>
{
_logger.LogInformation($"Policy: Timeout delegate fired after {span.Seconds} seconds");
return Task.CompletedTask;
});
}
}
private AsyncRetryPolicy<HttpResponseMessage> RetryPolicy
{
get
{
HttpStatusCode[] retryStatus =
{
HttpStatusCode.NotFound,
HttpStatusCode.ServiceUnavailable,
HttpStatusCode.RequestTimeout
};
return Policy
.HandleResult<HttpResponseMessage>(r => retryStatus.Contains(r.StatusCode))
.Or<TimeoutRejectedException>()
.WaitAndRetryAsync(new[]
{
// 表示重試3次，第一次1秒后重試，第二次2秒后重試，第三次4秒后重試
TimeSpan.FromSeconds(1),
TimeSpan.FromSeconds(2),
TimeSpan.FromSeconds(4)
}, (result, span, count, context) =>
{
_logger.LogInformation($"Policy: Retry delegate fired, attempt {count}");
});
}
}
public AsyncPolicyWrap<HttpResponseMessage> PolicyStrategy =>
Policy.WrapAsync(RetryPolicy, TimeoutPolicy);
}
public class PolicyHandler : DelegatingHandler
{
private readonly Policies _policies;
public PolicyHandler(Policies policies)
{
_policies = policies;
}
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
return _policies.PolicyStrategy.ExecuteAsync(ct => base.SendAsync(request, ct), cancellationToken);
}
}
public class PollyHttpClientFactory : DefaultHttpClientFactory
{
private readonly Policies _policies;
public PollyHttpClientFactory(Policies policies)
{
_policies = policies;
}
public override HttpMessageHandler CreateMessageHandler()
{
return new PolicyHandler(_policies)
{
InnerHandler = base.CreateMessageHandler()
};
}
}
}接下來(lái)在
Starup中對(duì)Flurl進(jìn)行配置public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
services.AddSingleton<Policies>();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
var policies = app.ApplicationServices.GetService<Policies>();
FlurlHttp.Configure(setting =>
setting.HttpClientFactory = new PollyHttpClientFactory(policies));
......再次嘗試請(qǐng)求，可以看到結(jié)果非常之理想
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 1
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:14
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 1
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:17
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:22
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:23
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 1
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:25
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:31
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 1
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:34
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:39
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 1
WithPollyClient.Services.Policies: Information: Policy: Timeout delegate fired after 3 seconds
WithPollyClient.Services.Policies: Information: Policy: Retry delegate fired, attempt 2
WithPollyClient.Controllers.HomeController: Information: App: success - 2021/3/14 16:50:46
富客戶端中使用的情況
?有時(shí)候呢，例如在
WPF或者是其它的富客戶端上面也會(huì)經(jīng)常使用到Flurl的情況，如下
var time = await Policy
.Handle<FlurlHttpException>()
.OrResult<IFlurlResponse>(r => !r.ResponseMessage.IsSuccessStatusCode)
.WaitAndRetryAsync(new[]
{
TimeSpan.FromSeconds(1),
TimeSpan.FromSeconds(2),
TimeSpan.FromSeconds(4)
}, (result, span, count, context) =>
{
_logger.LogInformation(count.ToString());
})
.ExecuteAsync(() => "http://127.0.0.1:5000/api/polly".WithTimeout(3).GetAsync())
.ReceiveJson();
_logger.LogInformation($"App: success - {time.time}");
return View(time.time);
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