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kestrel Server的源码分析

NeilHu 人气:0

今天这一篇博客讲的是.net core 自带的kestrel server,当你开发微服务k8s部署在linux环境下,一般默认开启这个高性能服务,如果大家之前看过我的owin katana的博客,会发现.net core 的好多实现在之前.net standard 的版本已经实现过了,当时开发的asp.net 程序与IIS紧紧耦合在一起,后来的微软团队意识到这个问题并尝试将asp.net 解耦server,制定了owin标准并启动了一个开源项目katana,这个项目的结果并没有带动社区效应,但是此时微软已经制订了.net core的开发,并在katana文档暗示了.net vnext 版本,这个就是。net core 与owin katana 的故事。强烈建议大家有时间看看owin katana,里面有一些 dependency inject, hash map, raw http 协议等等实现。非常收益。说到这些我们开始步入正题吧。原代码在github上的asp.net core 源码。

 

 上图大致地描述了一个asp.net core 的请求过程,但是我们会发现appication 依赖了server,所以我们需要一个Host 的去解耦server 和aplication 的实现,只要server符合host标准可以任意更换,解耦之后的代码与下图所示。

 

 

 所以我们的代码都是创建一个web host然后使用usekestrel,如下所示。

            var host = new WebHostBuilder()
                .UseKestrel(options =>
                {
                    options.Listen(IPAddress.Loopback, 5001);
                })
                .UseStartup<Startup>();

 首先我们知道一个server 实现需要网络编程,所以我们需要socket库来快速编程,它已经帮你实现了tcp与udp协议,不需要自己重复的造轮子。首先我们需要看UseKestrel的方法做了什么。

 1    public static IWebHostBuilder UseKestrel(this IWebHostBuilder hostBuilder)
 2         {
 3             return hostBuilder.ConfigureServices(services =>
 4             {
 5                 // Don't override an already-configured transport
 6                 services.TryAddSingleton<IConnectionListenerFactory, SocketTransportFactory>();
 7 
 8                 services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
 9                 services.AddSingleton<IServer, KestrelServer>();
10             });
11         }

依赖注入注册了三个对象,一个连接池,一个配置类还有一个是server,会和web host注册了IServer 的实现类,然后我们继续看一下,当你调用run的时候会将控制权从web host 转移给server,如下代码第18行所示。

 1   public virtual async Task StartAsync(CancellationToken cancellationToken = default)
 2         {
 3             HostingEventSource.Log.HostStart(); 6 
 7             var application = BuildApplication();
 8 
12             // Fire IHostedService.Start
13             await _hostedServiceExecutor.StartAsync(cancellationToken).ConfigureAwait(false);//启动后台服务
14 
15             var diagnosticSource = _applicationServices.GetRequiredService<DiagnosticListener>();
16             var httpContextFactory = _applicationServices.GetRequiredService<IHttpContextFactory>();
17             var hostingApp = new HostingApplication(application, _logger, diagnosticSource, httpContextFactory);
18             await Server.StartAsync(hostingApp, cancellationToken).ConfigureAwait(false);//socket 启动
19             _startedServer = true;
20 
21             // Fire IApplicationLifetime.Started
22             _applicationLifetime?.NotifyStarted();
23 
24 
25             _logger.Started();
26 
27             // Log the fact that we did load hosting startup assemblies.
28             if (_logger.IsEnabled(LogLevel.Debug))
29             {
30                 foreach (var assembly in _options.GetFinalHostingStartupAssemblies())
31                 {
32                     _logger.LogDebug("Loaded hosting startup assembly {assemblyName}", assembly);
33                 }
34             }
35 
36             if (_hostingStartupErrors != null)
37             {
38                 foreach (var exception in _hostingStartupErrors.InnerExceptions)
39                 {
40                     _logger.HostingStartupAssemblyError(exception);
41                 }
42             }
43         }

 

当我们转进到StartAsync方法时会看到如下代码

 1       public async Task StartAsync<TContext>(IHttpApplication<TContext> application, CancellationToken cancellationToken)
 2         {
 3             try
 4             {
19                // ServiceContext.Heartbeat?.Start();//一个是连接池一个是日期时间
20 
21                 async Task OnBind(ListenOptions options)
22                 {
23                     // Add the HTTP middleware as the terminal connection middleware
24                     options.UseHttpServer(ServiceContext, application, options.Protocols);//注册中间件
25 
26                     var connectionDelegate = options.Build();
27 
28                     // Add the connection limit middleware
29                     if (Options.Limits.MaxConcurrentConnections.HasValue)
30                     {
31                         connectionDelegate = new ConnectionLimitMiddleware(connectionDelegate, Options.Limits.MaxConcurrentConnections.Value, Trace).OnConnectionAsync;
32                     }
33 
34                     var connectionDispatcher = new ConnectionDispatcher(ServiceContext, connectionDelegate);
35                     var transport = await _transportFactory.BindAsync(options.EndPoint).ConfigureAwait(false);
36 
37                     // Update the endpoint
38                     options.EndPoint = transport.EndPoint;
39                     var acceptLoopTask = connectionDispatcher.StartAcceptingConnections(transport);
40 
41                     _transports.Add((transport, acceptLoopTask));
42                 }
43 
44                 await AddressBinder.BindAsync(_serverAddresses, Options, Trace, OnBind).ConfigureAwait(false);
45             }
46             catch (Exception ex)
47             {51             }
52         }

AddressBinder就是server绑定的ip地址,这个可以在StartUp方法或者环境变量里面配置,里面传了一个回调方法OnBind, 在第24行的UseHttpServer会注册server 内部的中间件去处理这个请求,在第35行socet会绑定地址,用tcp协议,默认使用512个最大pending队列,在接受socket会有多处异步编程和开启线程,建议大家在调试的时候可以修改代码用尽可能少的线程来进行调试。accept 的代码如下图所示

 1      private void StartAcceptingConnectionsCore(IConnectionListener listener)
 2         {
 3             // REVIEW: Multiple accept loops in parallel?
 4             _ = AcceptConnectionsAsync();
 5 
 6             async Task AcceptConnectionsAsync()
 7             {
 8                 try
 9                 {
10                     while (true)
11                     {
12                         var connection = await listener.AcceptAsync();
13 19 
20                         // Add the connection to the connection manager before we queue it for execution
21                         var id = Interlocked.Increment(ref _lastConnectionId);
22                         var kestrelConnection = new KestrelConnection(id, _serviceContext, _connectionDelegate, connection, Log);
23 
24                         _serviceContext.ConnectionManager.AddConnection(id, kestrelConnection);27 
28                         ThreadPool.UnsafeQueueUserWorkItem(kestrelConnection, preferLocal: false);
29                        }
30                 }
31                 catch (Exception ex)
32                 {
33                     // REVIEW: If the accept loop ends should this trigger a server shutdown? It will manifest as a hang
34                     Log.LogCritical(0, ex, "The connection listener failed to accept any new connections.");
35                 }
36                 finally
37                 {
38                     _acceptLoopTcs.TrySetResult(null);
39                 }
40             }
41         }

 

接收到accept socket的时候,会创建一个kestrelconnection 对象,这个对象实现线程方法,然后它会重新去等待一个请求的到来,而用户代码的执行则交给线程池执行。在第14行就是之前kerstrel server 内部的中间件build生成的方法,他的主要功能就是解析socket的携带http信息。

 1     internal async Task ExecuteAsync()
 2         {
 3             var connectionContext = TransportConnection;
 4 
 5             try
 6             {
10                 using (BeginConnectionScope(connectionContext))
11                 {
12                     try
13                     {
14                         await _connectionDelegate(connectionContext);
15                     }
16                     catch (Exception ex)
17                     {
18                         Logger.LogError(0, ex, "Unhandled exception while processing {ConnectionId}.", connectionContext.ConnectionId);
19                     }
20                 }
21             }
22             finally
23             {
34                 _serviceContext.ConnectionManager.RemoveConnection(_id);
35             }
36         }

 

由于http协议版本的不一致导致解析方式的不同,如果有兴趣的小伙伴可以具体查看这一块的逻辑。

 1                 switch (SelectProtocol())
 2                 {
 3                     case HttpProtocols.Http1:
 4                         // _http1Connection must be initialized before adding the connection to the connection manager
 5                         requestProcessor = _http1Connection = new Http1Connection<TContext>(_context);
 6                         _protocolSelectionState = ProtocolSelectionState.Selected;
 7                         break;
 8                     case HttpProtocols.Http2:
 9                         // _http2Connection must be initialized before yielding control to the transport thread,
10                         // to prevent a race condition where _http2Connection.Abort() is called just as
11                         // _http2Connection is about to be initialized.
12                         requestProcessor = new Http2Connection(_context);
13                         _protocolSelectionState = ProtocolSelectionState.Selected;
14                         break;
15                     case HttpProtocols.None:
16                         // An error was already logged in SelectProtocol(), but we should close the connection.
17                         break;
18                     default:
19                         // SelectProtocol() only returns Http1, Http2 or None.
20                         throw new NotSupportedException($"{nameof(SelectProtocol)} returned something other than Http1, Http2 or None.");
21                 }

 

然后server解析完请求之后所做的重要的一步就是创建httpContext,然后server在第40行将控制权转给web host,web host 会自动调用application code 也就是用户代码。

 

  1      private async Task ProcessRequests<TContext>(IHttpApplication<TContext> application)
  2         {
  3             while (_keepAlive)
  4             {
 33                 var context = application.CreateContext(this);
 34 
 35                 try
 36                 {
 37                     KestrelEventSource.Log.RequestStart(this);
 38 
 39                     // Run the application code for this request
 40                     await application.ProcessRequestAsync(context);
 41  55                 }
 56                 catch (BadHttpRequestException ex)
 57                 {
 58                     // Capture BadHttpRequestException for further processing
 59                     // This has to be caught here so StatusCode is set properly before disposing the HttpContext
 60                     // (DisposeContext logs StatusCode).
 61                     SetBadRequestState(ex);
 62                     ReportApplicationError(ex);
 63                 }
 64                 catch (Exception ex)
 65                 {
 66                     ReportApplicationError(ex);
 67                 }
 68 
 69                 KestrelEventSource.Log.RequestStop(this);129             }
130         }

到这里server 的工作大部分都结束了,在之前的描述中我们看到web host 怎么将控制权给到server 的, server 创建好httpContext规则后又是如何将控制权给到web host , web host 又如何去调用application code的, web host 实际上build 的时候将用户的中间件定义为链表结构暴露一个入口供web host调用,其他的有时间我会再写博客描述这一块。谢谢大家今天的阅读了。欢迎大家能够留言一起讨论。最后谢谢大家的阅读,如果有任何不懂的地方可以私信我。

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