【源码解读】Vue与ASP.NET Core WebAPI的集成

目录

• 1.异步编程-ContinueWith
  • 1.1 ContinueWith
  • 1.2 内联中间件
• 2.启动进程-ProcessStartInfo
  • 2.1 确定vue开发服务器的端口
  • 2.2 执行npm命令
  • 2.3 读取并输出npm命令执行的日志
  • 2.4 读取输出流至开发服务器启动成功
  • 2.5 异步编程-TaskCompletionSource
  • 2.6 确保开发服务器访问正常
• 3.总结
  • 3.1 异步编程

在前面博文【Vue】Vue与ASP.NET Core WebAPI的集成中，介绍了集成原理：在中间件管道中注册SPA终端中间件，整个注册过程中，终端中间件会调用node，执行npm start命令启动vue开发服务器，向中间件管道添加路由匹配，即非api请求（请求静态文件,js css html）都代理转发至SPA开发服务器。

注册代码如下：

public void Configure(Microsoft.AspNetCore.Builder.IApplicationBuilder app, IWebHostEnvironment env)
{
    #region +Endpoints

    // Execute the matched endpoint.
	app.UseEndpoints(endpoints =>
                         {
                             endpoints.MapControllers();
                         });

    app.UseSpa(spa =>
               {
                   spa.Options.SourcePath = "ClientApp";

                   if (env.IsDevelopment())
                   {
                       //spa.UseReactDevelopmentServer(npmScript: "start");
                       spa.UseVueCliServer(npmScript: "start");
                       //spa.UseProxyToSpaDevelopmentServer("http://localhost:8080");
                   }
               });

    #endregion
}

可以看到先注册了能够匹配API请求的属性路由。

如果上面的属性路由无法匹配，请求就会在中间件管道中传递，至下一个中间件：SPA的终端中间件

以上便是集成原理。接下来我们对其中间件源码进行解读。整体还是有蛮多值得解读学习的知识点：

• 异步编程
• 内联中间件
• 启动进程
• 事件驱动

1.异步编程-ContinueWith

我们先忽略调用npm start命令执行等细节。映入我们眼帘的便是异步编程。众所周知，vue执行npm start(npm run dev)的一个比较花费时间的过程。要达成我们完美集成的目的：我们注册中间件，就需要等待vue前端开发服务器启动后，正常使用，接收代理请求至这个开发服务器。这个等待后一个操作完成后再做其他操作，这就是一个异步编程。

• 建立需要返回npm run dev结果的类：

class VueCliServerInfo
{
    public int Port { get; set; }
}

• 编写异步代码，启动前端开发服务器

private static async Task<VueCliServerInfo> StartVueCliServerAsync(
            string sourcePath, string npmScriptName, ILogger logger)
{
    //省略代码
}

1.1 ContinueWith

• 编写继续体

ContinueWith本身就会返回一个Task

var vueCliServerInfoTask = StartVueCliServerAsync(sourcePath, npmScriptName, logger);

//继续体
var targetUriTask = vueCliServerInfoTask.ContinueWith(
    task =>
    {
        return new UriBuilder("http", "localhost", task.Result.Port).Uri;
    });

1.2 内联中间件

• 继续使用这个继续体返回的task，并applicationBuilder.Use()配置一个内联中间件，即所有请求都代理至开发服务器

SpaProxyingExtensions.UseProxyToSpaDevelopmentServer(spaBuilder, () =>
            {
                var timeout = spaBuilder.Options.StartupTimeout;
                return targetUriTask.WithTimeout(timeout,
                    $"The Vue CLI process did not start listening for requests " +
                    $"within the timeout period of {timeout.Seconds} seconds. " +
                    $"Check the log output for error information.");
            });

public static void UseProxyToSpaDevelopmentServer(
    this ISpaBuilder spaBuilder,
    Func<Task<Uri>> baseUriTaskFactory)
{
    var applicationBuilder = spaBuilder.ApplicationBuilder;
    var applicationStoppingToken = GetStoppingToken(applicationBuilder);

    //省略部分代码
    
    // Proxy all requests to the SPA development server
    applicationBuilder.Use(async (context, next) =>
                           {
                               var didProxyRequest =
                                   await SpaProxy.PerformProxyRequest(
                                   context, neverTimeOutHttpClient, baseUriTaskFactory(), applicationStoppingToken,
                                   proxy404s: true);
                           });
}

• 所有的后续请求，都会类似nginx一样的操作：

public static async Task<bool> PerformProxyRequest(
    HttpContext context,
    HttpClient httpClient,
    Task<Uri> baseUriTask,
    CancellationToken applicationStoppingToken,
    bool proxy404s)
{
    //省略部分代码...
    
    //获取task的结果，即开发服务器uri
    var baseUri = await baseUriTask;
    
    //把请求代理至开发服务器
    //接收开发服务器的响应 给到 context，由asp.net core响应
}

2.启动进程-ProcessStartInfo

接下来进入StartVueCliServerAsync的内部，执行node进程，执行npm start命令。

2.1 确定vue开发服务器的端口

确定一个随机的、可用的开发服务器端口，代码如下：

internal static class TcpPortFinder
{
    public static int FindAvailablePort()
    {
        var listener = new TcpListener(IPAddress.Loopback, 0);
        listener.Start();
        try
        {
            return ((IPEndPoint)listener.LocalEndpoint).Port;
        }
        finally
        {
            listener.Stop();
        }
    }
}

2.2 执行npm命令

确定好可用的端口，根据前端项目目录spa.Options.SourcePath = "ClientApp";

private static async Task<VueCliServerInfo> StartVueCliServerAsync(
    string sourcePath, string npmScriptName, ILogger logger)
{
    var portNumber = TcpPortFinder.FindAvailablePort();
    logger.LogInformation($"Starting Vue/dev-server on port {portNumber}...");
    
    //执行命令
    var npmScriptRunner = new NpmScriptRunner(
        //sourcePath, npmScriptName, $"--port {portNumber}");
        sourcePath, npmScriptName, $"{portNumber}");
}

NpmScriptRunner内部便在开始调用node执行cmd命令:

internal class NpmScriptRunner
{
    public EventedStreamReader StdOut { get; }
    public EventedStreamReader StdErr { get; }
    public NpmScriptRunner(string workingDirectory, string scriptName, string arguments)
    {
        var npmExe = "npm";
        var completeArguments = $"run {scriptName} {arguments ?? string.Empty}";
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            npmExe = "cmd";
            completeArguments = $"/c npm {completeArguments}";
        }

        var processStartInfo = new ProcessStartInfo(npmExe)
        {
            Arguments = completeArguments,
            UseShellExecute = false,
            RedirectStandardInput = true,
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            WorkingDirectory = workingDirectory
        };

        var process = LaunchNodeProcess(processStartInfo);
        
        //读取文本输出流
        StdOut = new EventedStreamReader(process.StandardOutput);
        
        //读取错误输出流
        StdErr = new EventedStreamReader(process.StandardError);
    }
}

private static Process LaunchNodeProcess(ProcessStartInfo startInfo)
{
    try
    {
        var process = Process.Start(startInfo);
        process.EnableRaisingEvents = true;
        return process;
    }
    catch (Exception ex)
    {
        var message = $"Failed to start 'npm'. To resolve this:.

"
            + "[1] Ensure that 'npm' is installed and can be found in one of the PATH directories.
"
            + $"    Current PATH enviroment variable is: { Environment.GetEnvironmentVariable("PATH") }
"
            + "    Make sure the executable is in one of those directories, or update your PATH.

"
            + "[2] See the InnerException for further details of the cause.";
        throw new InvalidOperationException(message, ex);
    }
}

internal class EventedStreamReader
{
    public delegate void OnReceivedChunkHandler(ArraySegment<char> chunk);
    public delegate void OnReceivedLineHandler(string line);
    public delegate void OnStreamClosedHandler();

    public event OnReceivedChunkHandler OnReceivedChunk;
    public event OnReceivedLineHandler OnReceivedLine;
    public event OnStreamClosedHandler OnStreamClosed;

    private readonly StreamReader _streamReader;
    private readonly StringBuilder _linesBuffer;

    //构造函数中启动线程读流
    public EventedStreamReader(StreamReader streamReader)
    {
        _streamReader = streamReader ?? throw new ArgumentNullException(nameof(streamReader));
        _linesBuffer = new StringBuilder();
        Task.Factory.StartNew(Run);
    }
    private async Task Run()
    {
        var buf = new char[8 * 1024];
        while (true)
        {
            var chunkLength = await _streamReader.ReadAsync(buf, 0, buf.Length);
            if (chunkLength == 0)
            {
                //触发事件的方法
                OnClosed();
                break;
            }
            //触发事件的方法
            OnChunk(new ArraySegment<char>(buf, 0, chunkLength));
            var lineBreakPos = Array.IndexOf(buf, '
', 0, chunkLength);
            if (lineBreakPos < 0)
            {
                _linesBuffer.Append(buf, 0, chunkLength);
            }
            else
            {
                _linesBuffer.Append(buf, 0, lineBreakPos + 1);
                
                //触发事件的方法
                OnCompleteLine(_linesBuffer.ToString());
                _linesBuffer.Clear();
                _linesBuffer.Append(buf, lineBreakPos + 1, chunkLength - (lineBreakPos + 1));
            }
        }
    }
    private void OnChunk(ArraySegment<char> chunk)
    {
        var dlg = OnReceivedChunk;
        dlg?.Invoke(chunk);
    }

    private void OnCompleteLine(string line)
    {
        var dlg = OnReceivedLine;
        dlg?.Invoke(line);
    }

    private void OnClosed()
    {
        var dlg = OnStreamClosed;
        dlg?.Invoke();
    }
}

2.3 读取并输出npm命令执行的日志

npmScriptRunner.AttachToLogger(logger);

注册OnReceivedLine与OnReceivedChunk事件，由读文本流和错误流触发：

internal class EventedStreamReader
{
    public void AttachToLogger(ILogger logger)
    {
        StdOut.OnReceivedLine += line =>
        {
            if (!string.IsNullOrWhiteSpace(line))
            {
                logger.LogInformation(StripAnsiColors(line));
            }
        };

        StdErr.OnReceivedLine += line =>
        {
            if (!string.IsNullOrWhiteSpace(line))
            {
                logger.LogError(StripAnsiColors(line));
            }
        };

        StdErr.OnReceivedChunk += chunk =>
        {
            var containsNewline = Array.IndexOf(
                chunk.Array, '
', chunk.Offset, chunk.Count) >= 0;
            if (!containsNewline)
            {
                Console.Write(chunk.Array, chunk.Offset, chunk.Count);
            }
        };
    }
}

2.4 读取输出流至开发服务器启动成功

正常情况下，Vue开发服务器启动成功后，如下图：

所以代码中只需要读取输入流中的http://localhost:port，这里使用了正则匹配：

Match openBrowserLine; 
openBrowserLine = await npmScriptRunner.StdOut.WaitForMatch(
    new Regex("- Local:   (http:\S+/)", RegexOptions.None, RegexMatchTimeout));

2.5 异步编程-TaskCompletionSource

TaskCompletionSource也是一种创建Task的方式。这里的异步方法WaitForMatch便使用了TaskCompletionSource，会持续读取流，每一行文本输出流，进行正则匹配:

• 匹配成功便调用SetResult()给Task完成信号
• 匹配失败便调用SetException()给Task异常信号

internal class EventedStreamReader
{
    public Task<Match> WaitForMatch(Regex regex)
    {
        var tcs = new TaskCompletionSource<Match>();
        var completionLock = new object();

        OnReceivedLineHandler onReceivedLineHandler = null;
        OnStreamClosedHandler onStreamClosedHandler = null;

        //C#7.0 本地函数
        void ResolveIfStillPending(Action applyResolution)
        {
            lock (completionLock)
            {
                if (!tcs.Task.IsCompleted) 
                {
                    OnReceivedLine -= onReceivedLineHandler;
                    OnStreamClosed -= onStreamClosedHandler;
                    applyResolution();
                }
            }
        }

        onReceivedLineHandler = line =>
        {
            var match = regex.Match(line);
            
            //匹配成功
            if (match.Success)
            {
                ResolveIfStillPending(() => tcs.SetResult(match));
            }
        };

        onStreamClosedHandler = () =>
        {
            //一直到文本流结束
            ResolveIfStillPending(() => tcs.SetException(new EndOfStreamException()));
        };

        OnReceivedLine += onReceivedLineHandler;
        OnStreamClosed += onStreamClosedHandler;

        return tcs.Task;
    }
}

2.6 确保开发服务器访问正常

并从正则匹配结果获取uri，即使在Vue CLI提示正在监听请求之后，如果过快地发出请求，在很短的一段时间内它也会给出错误(可能就是代码层级才会出现)。所以还得继续添加异步方法WaitForVueCliServerToAcceptRequests()确保开发服务器的的确确准备好了。

private static async Task<VueCliServerInfo> StartVueCliServerAsync(
    string sourcePath, string npmScriptName, ILogger logger)
{
    var portNumber = TcpPortFinder.FindAvailablePort();
    logger.LogInformation($"Starting Vue/dev-server on port {portNumber}...");

    //执行命令
    var npmScriptRunner = new NpmScriptRunner(
        //sourcePath, npmScriptName, $"--port {portNumber}");
        sourcePath, npmScriptName, $"{portNumber}");

    npmScriptRunner.AttachToLogger(logger);

    Match openBrowserLine;

    //省略部分代码

    openBrowserLine = await npmScriptRunner.StdOut.WaitForMatch(
        new Regex("- Local:   (http:\S+/)", RegexOptions.None, RegexMatchTimeout));

    var uri = new Uri(openBrowserLine.Groups[1].Value);
    var serverInfo = new VueCliServerInfo { Port = uri.Port };

    await WaitForVueCliServerToAcceptRequests(uri);
    return serverInfo;
} 

private static async Task WaitForVueCliServerToAcceptRequests(Uri cliServerUri)
{
    var timeoutMilliseconds = 1000;
    using (var client = new HttpClient())
    {
        while (true)
        {
            try
            {
                await client.SendAsync(
                    new HttpRequestMessage(HttpMethod.Head, cliServerUri),
                    new CancellationTokenSource(timeoutMilliseconds).Token);
                return;
            }
            catch (Exception)
            {
                //它创建Task，但并不占用线程
                await Task.Delay(500);
                if (timeoutMilliseconds < 10000)
                {
                    timeoutMilliseconds += 3000;
                }
            }
        }
    }
}

Task.Delay()的魔力：创建Task，但并不占用线程，相当于异步版本的Thread.Sleep，且可以在后面编写继续体:ContinueWith

3.总结

3.1 异步编程

• 通过ContinueWiht继续体返回Task的特性创建Task，并在后续配置内联中间件时使用这个Task

app.Use(async (context, next)=>{
    
});

使ASP.NET Core的启动与中间件注册顺滑。

• 通过TaskCompletionSource可以在稍后开始和结束的任意操作中创建Task,这个Task，可以手动指示操作何时结束（SetResult），何时发生故障（SetException），这两种状态都意味着Task完成tcs.Task.IsCompleted，对经常需要等IO-Bound类工作比较理想。

---

作者：Garfield

同步更新至个人博客:http://www.randyfield.cn/

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