VssHttpMessageHandler 和 HttpMessageHandler 池化

Question

我目前正在使用用于 C# 的 Azure Devops 客户端库。 由于许多原因（例如避免端口耗尽或可测试性），我想使用 dotnetcore 提供的 IHttpMessageHandlerFactory 来为我的 VssConnection 提供处理程序。 目前，我使用这个：

var vssHttpMessageHandler = new VssHttpMessageHandler(new VssBasicCredential(string.Empty, options.Pat), VssClientHttpRequestSettings.Default.Clone(), _httpMessageHandlerFactory.CreateHandler(HttpClientName));

但是，这并不总是有效，因为当处理程序被重用时，会引发异常：

System.InvalidOperationException 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw 处理： 在 System.Net.Http.SocketsHttpHandler.CheckDisposedOrStarted（System.Net.Http，版本=4.2.2.0，文化=中性，PublicKeyToken=b03f5f7f11d50a3a） 在 Microsoft.VisualStudio.Services.Common.VssHttpMessageHandler.ApplySettings（Microsoft.VisualStudio.Services.Common，版本=16.0.0.0，Culture=neutral，PublicKeyToken=b03f5f7f11d50a3a）

事实上，在构造VssHttpMessageHandler时，新的设置被应用到了HttpMessageHandler，然而，这个不支持在它开始使用后被修改（它的所有属性在设置时调用CheckDisposedOrStarted）。

我可以做些什么来实现我想做的事情？

编辑：这是我的代码的复制品

var azureDevopsUri = "https://dev.azure.com/mycollection";
var pat = "mypathere";

var services = new ServiceCollection();
services.AddHttpClient();
services.AddTransient(s =>
{
    var handlerFactory = s.GetRequiredService<IHttpMessageHandlerFactory>();    
    var vssHandler = new VssHttpMessageHandler(
        new VssBasicCredential(string.Empty, pat),
        VssClientHttpRequestSettings.Default.Clone(),
        handlerFactory.CreateHandler());
    return new VssConnection(
                        new Uri(azureDevopsUri),
                        vssHandler,
                        new DelegatingHandler[] { });
});

var provider = services.BuildServiceProvider();

using(var scope = provider.CreateScope())
{
    var connection = scope.ServiceProvider.GetRequiredService<VssConnection>();
    var client = await connection.GetClientAsync<ProjectCollectionHttpClient>();
    await client.GetProjectCollections();
}

using (var scope = provider.CreateScope())
{
    var connection = scope.ServiceProvider.GetRequiredService<VssConnection>(); // <-- Exception thrown here
    var client = await connection.GetClientAsync<ProjectCollectionHttpClient>();
    await client.GetProjectCollections();
}

如您所见，当我将 VssConnection 配置为不作为单例时（这是我发现现在正在工作的解决方法），第二次创建实例时，我将异常抛出为用于池的 IHttpMessageHandlerFactory可能已经被使用了。

异常详情：

This instance has already started one or more requests. Properties can only be modified before sending the first request. 
   at System.Net.Http.SocketsHttpHandler.CheckDisposedOrStarted()
   at System.Net.Http.HttpClientHandler.set_AllowAutoRedirect(Boolean value)
   at Microsoft.VisualStudio.Services.Common.VssHttpMessageHandler.ApplySettings(HttpMessageHandler handler, ICredentials defaultCredentials, VssHttpRequestSettings settings)
   at UserQuery.<>c__DisplayClass4_0.<Main>b__0(IServiceProvider s), line 9
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitDisposeCache(ServiceCallSite transientCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at UserQuery.Main(), line 31 

Answer 1

我使用VssHttpMessageHandler 进行了测试，但无法重现此问题。

我想分享 C# 示例：

 var azureDevopsUri = "https://dev.azure.com/org";
            var pat = "PAT";

            var services = new ServiceCollection();
            services.AddHttpClient();
            services.AddTransient(s =>
            {
                var handlerFactory = s.GetRequiredService<IHttpMessageHandlerFactory>();
                var vssHandler = new VssHttpMessageHandler(
                    new VssBasicCredential(string.Empty, pat),
                    VssClientHttpRequestSettings.Default.Clone());
                return new VssConnection(
                                    new Uri(azureDevopsUri),
                                    vssHandler,
                                    new DelegatingHandler[] { });
            });

            var provider = services.BuildServiceProvider();

            using (var scope = provider.CreateScope())
            {
                var connection = scope.ServiceProvider.GetRequiredService<VssConnection>();
                var client = await connection.GetClientAsync<ProjectCollectionHttpClient>();
                await client.GetProjectCollections();
            }

            using (var scope = provider.CreateScope())
            {
                var connection = scope.ServiceProvider.GetRequiredService<VssConnection>(); // <-- Exception thrown here
                var client = await connection.GetClientAsync<ProjectCollectionHttpClient>();
                await client.GetProjectCollections();
            }

注意：包：Microsoft.TeamFoundationServer.Client:16.143.2.

在包中，VssHttpMessageHandler 定义：

public VssHttpMessageHandler(VssCredentials credentials, VssHttpRequestSettings settings, HttpMessageHandler innerHandler);