.NET Core HttpClientFactory+Consul實現服務發現

時間  2020-05-24
標籤 core httpclientfactory+consul httpclientfactory consul 實現 服務 發現 简体版
原文   原文鏈接

前言

　　上篇文章.NET Core HttpClient+Consul實現服務發現提到過，HttpClient存在套接字延遲釋放的問題，高併發狀況致使端口號被耗盡引發服務器拒絕服務的問題。好在微軟意識到了這個問題，從.NET Core 2.1版本開始推出了HttpClientFactory來彌補這個問題。關於更詳細的HttpClientFactory介紹能夠查看微軟官方文檔 https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-3.1#httpclient-and-lifetime-management 咱們瞭解到想把自定義的HttpMessageHandler注入到HttpClient內部，必需要經過構造函數。接下來咱們就慢慢發覺如何給HttpClientFactory使用咱們自定義的Handler。html

HttpClient的建立

　　相信你們都已經清楚使用HttpClientFactory從services.AddHttpClient()注入相關類開始，咱們就從這裏開始入手。先貼上源碼地址HttpClientFactoryServiceCollectionExtensions源碼而後咱們大概的看一下咱們關注的實現方法，大體以下，代碼有刪減git

/// <summary>
/// Adds the <see cref="IHttpClientFactory"/> and related services to the <see cref="IServiceCollection"/>.
/// </summary>
/// <param name="services">The <see cref="IServiceCollection"/>.</param>
/// <returns>The <see cref="IServiceCollection"/>.</returns>
public static IServiceCollection AddHttpClient(this IServiceCollection services)
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    .....

    //
    // Core abstractions
    //
    services.TryAddTransient<HttpMessageHandlerBuilder, DefaultHttpMessageHandlerBuilder>();
    services.TryAddSingleton<DefaultHttpClientFactory>();
    services.TryAddSingleton<IHttpClientFactory>(serviceProvider => serviceProvider.GetRequiredService<DefaultHttpClientFactory>());
    services.TryAddSingleton<IHttpMessageHandlerFactory>(serviceProvider => serviceProvider.GetRequiredService<DefaultHttpClientFactory>());

    .....

    return services;
}

經過源碼咱們能夠看到IHttpClientFactory的實現類注入實際上是DefaultHttpClientFactory，拿咱們繼續順着源碼繼續查找DefaultHttpClientFactory源碼地址找到了咱們熟悉的名字😄😄😄github

public HttpClient CreateClient(string name)
{
    if (name == null)
    {
        throw new ArgumentNullException(nameof(name));
    }
    var handler = CreateHandler(name);
    var client = new HttpClient(handler, disposeHandler: false);
    var options = _optionsMonitor.Get(name);
    for (var i = 0; i < options.HttpClientActions.Count; i++)
    {
        options.HttpClientActions[i](client);
    }
    return client;
}

在這裏咱們發現了CreateHandler方法由它建立了handler傳入了HttpClient，繼續向下看，發現這段代碼算法

public HttpMessageHandler CreateHandler(string name)
{
    if (name == null)
    {
        throw new ArgumentNullException(nameof(name));
    }
    var entry = _activeHandlers.GetOrAdd(name, _entryFactory).Value;
    StartHandlerEntryTimer(entry);
    return entry.Handler;
}

而後咱們_entryFactory這個委託，而後一直找啊找服務器

internal ActiveHandlerTrackingEntry CreateHandlerEntry(string name)
{
    .....
    try
    {
        var builder = services.GetRequiredService<HttpMessageHandlerBuilder>();
        builder.Name = name;
        Action<HttpMessageHandlerBuilder> configure = Configure;
        for (var i = _filters.Length - 1; i >= 0; i--)
        {
            configure = _filters[i].Configure(configure);
        }
        configure(builder);
        var handler = new LifetimeTrackingHttpMessageHandler(builder.Build());
        return new ActiveHandlerTrackingEntry(name, handler, scope, options.HandlerLifetime);

        .....
    }
    catch
    {
        .....
    }
}

發現了HttpMessageHandlerBuilder的身影，由它構建了HttpMessageHandler，咦！好像在哪見過，恍然大悟原來是在AddHttpClient擴展方法裏併發

services.TryAddTransient<HttpMessageHandlerBuilder, DefaultHttpMessageHandlerBuilder>();

而後找到了DefaultHttpMessageHandlerBuilder在這裏我看到了熟悉的身影
找到這裏心裏一陣澎湃，也就是說只要把我實現的HttpClientHandler替換掉默認的就行了，但是感受無地方下手啊。這時忽然想到DefaultHttpMessageHandlerBuilder這類是註冊進來的，那我本身實現一個ConsulHttpMessageHandlerBuilder替換掉默認註冊的DefaultHttpMessageHandlerBuilder就能夠了，說時遲那時快。動手寫了一個以下實現負載均衡

自定義HttpMessageHandlerBuilder

public class ConsulHttpMessageHandlerBuilder: HttpMessageHandlerBuilder
{
    public ConsulHttpMessageHandlerBuilder(ConsulDiscoveryHttpClientHandler consulDiscoveryHttpClientHandler)
    {
        PrimaryHandler = consulDiscoveryHttpClientHandler;
    }
    private string _name;
    public override IList<DelegatingHandler> AdditionalHandlers => new List<DelegatingHandler>();
    public override string Name {
        get => _name;
        set
        {
            if (value == null)
            {
                throw new ArgumentNullException(nameof(value));
            }
            _name = value;
        }
    }
    public override HttpMessageHandler PrimaryHandler { get; set; }
    public override HttpMessageHandler Build()
    {
        if (PrimaryHandler == null)
        {
            throw new InvalidOperationException(nameof(PrimaryHandler));
        }
        return CreateHandlerPipeline(PrimaryHandler, AdditionalHandlers);
    }
}

相對於原來的代碼其實就變更了一點，就是用本身的ConsulDiscoveryHttpClientHandler替換了默認的HttpClientHandler，具體ConsulDiscoveryHttpClientHandler的實現能夠參考上篇文章的實現。而後在註冊的地方，替換掉默認的DefaultHttpMessageHandlerBuilder。框架

public void ConfigureServices(IServiceCollection services)
{
      services.AddHttpClient();
      services.AddTransient<ConsulDiscoveryHttpClientHandler>();
      services.Replace(new ServiceDescriptor(typeof(HttpMessageHandlerBuilder),typeof(ConsulHttpMessageHandlerBuilder),ServiceLifetime.Transient));
}

試了下，沒毛病，心中暗喜了幾秒。可是冷靜下來想想，感受不是很合理還要本身寫Builder替換默認的方式。不符合開放封閉原則,對原有代碼自己的入侵比較大，彷佛不是很合理。要不就說，學習必定要仔細，特別是剛開始的時候，能少踩好多坑。在微軟的幫助文檔裏已經提到了能經過IHttpClientBuilder的擴展方法能夠用自定義的實現替換掉默認的PrimaryHandler實例，大體修改註冊的地方以下。async

public void ConfigureServices(IServiceCollection services)
{
      services.AddTransient<ConsulDiscoveryHttpClientHandler>();
      services.AddHttpClient().ConfigurePrimaryHttpMessageHandler<ConsulDiscoveryHttpClientHandler>();;
}

HttpClientBuilderExtensions擴展類實現

接下來咱們來看看ConfigurePrimaryHttpMessageHandler這個擴展方法到底作了什麼，該方法來自HttpClientBuilderExtensions擴展類具體實現以下ide

public static IHttpClientBuilder ConfigurePrimaryHttpMessageHandler<THandler>(this IHttpClientBuilder builder)
            where THandler : HttpMessageHandler
{
    if (builder == null)
    {
        throw new ArgumentNullException(nameof(builder));
    }
    builder.Services.Configure<HttpClientFactoryOptions>(builder.Name, options =>
    {
        options.HttpMessageHandlerBuilderActions.Add(b => b.PrimaryHandler = b.Services.GetRequiredService<THandler>());
    });
    return builder;
}

而後經過DefaultHttpClientFactory類的CreateHandlerEntry方法裏能夠看到HttpClientFactoryOptions類的HttpMessageHandlerBuilderActions調用的的地方其實傳入的就死當前註冊到HttpMessageHandlerBuilder的DefaultHttpMessageHandlerBuilder，大體調用代碼以下

internal ActiveHandlerTrackingEntry CreateHandlerEntry(string name)
{
    .....
    try
    {
        var builder = services.GetRequiredService<HttpMessageHandlerBuilder>();
        builder.Name = name;
        Action<HttpMessageHandlerBuilder> configure = Configure;
        for (var i = _filters.Length - 1; i >= 0; i--)
        {
            configure = _filters[i].Configure(configure);
        }
        configure(builder);
        var handler = new LifetimeTrackingHttpMessageHandler(builder.Build());
        return new ActiveHandlerTrackingEntry(name, handler, scope, options.HandlerLifetime);

        void Configure(HttpMessageHandlerBuilder b)
        {
            for (var i = 0; i < options.HttpMessageHandlerBuilderActions.Count; i++)
            {
                options.HttpMessageHandlerBuilderActions[i](b);
            }
        }
    }
    catch
    {
        .....
    }
}

回頭來看HttpClientBuilderExtensions擴展類還有一個ConfigureHttpMessageHandlerBuilder擴展方法

public static IHttpClientBuilder AddHttpMessageHandler<THandler>(this IHttpClientBuilder builder)
            where THandler : DelegatingHandler
{
    if (builder == null)
    {
        throw new ArgumentNullException(nameof(builder));
    }
    builder.Services.Configure<HttpClientFactoryOptions>(builder.Name, options =>
    {
        options.HttpMessageHandlerBuilderActions.Add(b => b.AdditionalHandlers.Add(b.Services.GetRequiredService<THandler>()));
    });
    return builder;
}

這個是對DefaultHttpMessageHandlerBuilder附加的Handler作添加操做，那麼PrimaryHandler和AdditionalHandlers之間到底有什麼關係呢？咱們回過頭來看一下DefaultHttpMessageHandlerBuilder類相關方法的具體實現，大體代碼以下

public override HttpMessageHandler Build()
{
    if (PrimaryHandler == null)
    {
        var message = Resources.FormatHttpMessageHandlerBuilder_PrimaryHandlerIsNull(nameof(PrimaryHandler));
        throw new InvalidOperationException(message);
    }    
    return CreateHandlerPipeline(PrimaryHandler, AdditionalHandlers);
}

protected internal static HttpMessageHandler CreateHandlerPipeline(HttpMessageHandler primaryHandler, IEnumerable<DelegatingHandler> additionalHandlers)
{
    if (primaryHandler == null)
    {
        throw new ArgumentNullException(nameof(primaryHandler));
    }
    if (additionalHandlers == null)
    {
        throw new ArgumentNullException(nameof(additionalHandlers));
    }

    var additionalHandlersList = additionalHandlers as IReadOnlyList<DelegatingHandler> ?? additionalHandlers.ToArray();
    var next = primaryHandler;
    for (var i = additionalHandlersList.Count - 1; i >= 0; i--)
    {
        var handler = additionalHandlersList[i];
        if (handler == null)
        {
            var message = Resources.FormatHttpMessageHandlerBuilder_AdditionalHandlerIsNull(nameof(additionalHandlers));
            throw new InvalidOperationException(message);
        }
        if (handler.InnerHandler != null)
        {
            var message = Resources.FormatHttpMessageHandlerBuilder_AdditionHandlerIsInvalid(
                nameof(DelegatingHandler.InnerHandler),
                nameof(DelegatingHandler),
                nameof(HttpMessageHandlerBuilder),
                Environment.NewLine,
                handler);
            throw new InvalidOperationException(message);
        }
        handler.InnerHandler = next;
        next = handler;
    }
    return next;
}

經過這段代碼能夠看出原來是用PrimaryHandler和AdditionalHandlers集合構建了一個Handler執行管道，PrimaryHandler做爲管道的最後執行點，附加管道按照代碼注入的順序執行。看到這裏相信你基本上對HttpClientFactory大體的工做方式就有必定的認知。其實從編碼的角度上來說，除非有特殊要求，不然咱們不會替換掉PrimaryHandler，只須要將咱們的Handler添加到AdditionalHandlers集合便可。

最終實現方式

經過上面的分析咱們基本上能夠動手實現一個最合理的實現方式了

public void ConfigureServices(IServiceCollection services)
{
    //consul地址
    services.AddConsul("http://localhost:8500/");
    //HttpPClient查找名稱(建議使用服務註冊名稱)
    services.AddHttpClient("PersonService", c =>
    {
        //服務註冊的名稱(建議和HttpPClient查找名稱一致)
        c.BaseAddress = new Uri("http://PersonService/");
    }).AddHttpMessageHandler<ConsulDiscoveryDelegatingHandler>();
}

AddConsul擴展方法

public static IServiceCollection AddConsul(this IServiceCollection services, string consulAddress)
{
    services.AddTransient(provider => {
        return new ConsulClient(x =>
        {
            // consul 服務地址
            x.Address = new Uri(consulAddress);
        });
    });
    //註冊自定義的DelegatingHandler
    services.AddTransient<ConsulDiscoveryDelegatingHandler>();
    return services;
}

自定義的ConsulDiscoveryDelegatingHandler

public class ConsulDiscoveryDelegatingHandler : DelegatingHandler
{
     private readonly ConsulClient _consulClient;
     private readonly ILogger<ConsulDiscoveryDelegatingHandler> _logger;
     public ConsulDiscoveryDelegatingHandler(ConsulClient consulClient, 
           ILogger<ConsulDiscoveryDelegatingHandler> logger)
     {
        _consulClient = consulClient; 
        _logger = logger;
     }
            
     protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
     {
          var current = request.RequestUri;
          try
          {              
              //調用的服務地址裏的域名(主機名)傳入發現的服務名稱便可
              request.RequestUri = new Uri($"{current.Scheme}://{LookupService(current.Host)}/{current.PathAndQuery}");
              return await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
          }
          catch (Exception e)
          {
              _logger?.LogDebug(e, "Exception during SendAsync()");
              throw;
          }
          finally
          {
              request.RequestUri = current;
          }
      }

      private string LookupService(string serviceName)
      {
          var services = _consulClient.Catalog.Service(serviceName).Result.Response;
          if (services != null && services.Any())
          {
                //模擬負載均衡算法(隨機獲取一個地址)
                int index = r.Next(services.Count());
                var service = services.ElementAt(index);
                return $"{service.ServiceAddress}:{service.ServicePort}");
           }
           return null;
      }
}

編寫PersonTestController測試代碼

public class PersonTestController : Controller
{
    private readonly IHttpClientFactory _clientFactory;
    public PersonTestController(IHttpClientFactory clientFactory)
    {
        _clientFactory = clientFactory;
    }

    public async Task<ActionResult<string>> GetPersonInfo(int personId)
    {
        var client = _clientFactory.CreateClient("PersonService");
        var response = await client.GetAsync($"/Person/Get/{personId}");
        var result = await response.Content.ReadAsStringAsync();
        return result;
    }
}

總結

經過這兩篇文章，主要講解了HttpClientFactory和HttpClient結合Consul完成服務發現，我的更推薦在後續的開發和實踐中採用HttpClientFactory的方式。本文可能重在講思路，具體的實現方式可能不夠精細 。其中還涉及到了部分框架源碼，不熟悉源碼的話可能某些地方不是很好理解，再加上本人文筆不足，若是帶來閱讀不便敬請諒解。主要仍是想把本身的理解和思路轉達給你們，望批評指導，以便後期改正。

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