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ASP.NET Core 奇技淫巧之接口代理轉(zhuǎn)發(fā)的實(shí)現(xiàn)

 更新時間：2020年08月13日 14:35:16   作者：GuZhenYin  
這篇文章主要介紹了ASP.NET Core 奇技淫巧之接口代理轉(zhuǎn)發(fā)的實(shí)現(xiàn)，文中通過示例代碼介紹的非常詳細(xì)，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

前言

先講講本文的開發(fā)背景吧..

在如今前后端分離的大背景下,咱的客戶又有要求啦~

要前后端分離~ 然因?yàn)榉N種原因..沒辦法用用純前端的框架(其實(shí)是學(xué)習(xí)成本高,又沒錢請前端開發(fā)人員)...

所以最終決定了一種方案..

那就是采用MVC(只處理前端視圖層,單純是為了托管在.net core上)+Webapi的方式來實(shí)現(xiàn)前后端分離(講真,很奇葩)..

那么問題就隨之而來了.

現(xiàn)在主流的前端框架都是托管在nodejs上,是通過axios來訪問后端API,可以通過配置axios的代理配置(proxyTable)來實(shí)現(xiàn)跨域訪問.

那么我們的JS運(yùn)行在MVC上,托管在.net core上..那咋辦呢?..沒有現(xiàn)成的轉(zhuǎn)發(fā)輪子..我們只有自己造了..

所以這就是本篇的背景 - -.~

正文

幸運(yùn)的是ASP.NET Core 給我們提供了強(qiáng)大的中間件模式.

我們完全可以通過定義一個轉(zhuǎn)發(fā)中間件的形式來實(shí)現(xiàn)代理接口轉(zhuǎn)發(fā),流程如圖:

廢話不多說,我們來創(chuàng)建我們的中間件:

一.創(chuàng)建檢測約定URL的接口與實(shí)現(xiàn)

首先定義一個接口IUrlRewriter 用來檢測我們的URL是否有對應(yīng)前綴,如果有,則產(chǎn)生新的URL地址:

這里我們定義接口是為了方便以后更好的更換注入類來實(shí)現(xiàn)快速更換檢測前綴的規(guī)則.

public interface IUrlRewriter
{
    Task<Uri> RewriteUri(HttpContext context);
}

實(shí)現(xiàn)這個接口,如下(解釋都在注釋里了):

public class PrefixRewriter : IUrlRewriter
  {
    private readonly PathString _prefix; //前綴值
    private readonly string _newHost; //轉(zhuǎn)發(fā)的地址

    public PrefixRewriter(PathString prefix, string newHost)
    {
      _prefix = prefix;
      _newHost = newHost;
    }

    public Task<Uri> RewriteUri(HttpContext context)
    {
      if (context.Request.Path.StartsWithSegments(_prefix))//判斷訪問是否含有前綴
      {
        var newUri = context.Request.Path.Value.Remove(0, _prefix.Value.Length) + context.Request.QueryString;
        var targetUri = new Uri(_newHost + newUri);
        return Task.FromResult(targetUri);
      }

      return Task.FromResult((Uri)null);
    }
  }

二.創(chuàng)建代理轉(zhuǎn)發(fā)需要的ProxyHttpClient

創(chuàng)建獨(dú)立的ProxyHttpClient,主要是為了區(qū)分代理轉(zhuǎn)發(fā)的httpClient,方便后期添加日志或做別的處理.代碼如下:

public class ProxyHttpClient
  {
    public HttpClient Client { get; private set; }

    public ProxyHttpClient(HttpClient httpClient)
    {
      Client = httpClient;
    }
  }

三.創(chuàng)建代理轉(zhuǎn)發(fā)的中間件

代碼如下,中間件嘛,主要就是Invoke方法了,說明可以看注釋.

public class ProxyMiddleware
  {
    // private ProxyHttpClient _proxyHttpClient;
    private const string CDN_HEADER_NAME = "Cache-Control";
    private static readonly string[] NotForwardedHttpHeaders = new[] { "Connection", "Host" };
    private readonly RequestDelegate _next;
    private readonly ILogger<ProxyMiddleware> _logger;

    public ProxyMiddleware(
        RequestDelegate next,
        ILogger<ProxyMiddleware> logger
        
        )
    {
      _next = next;
      _logger = logger;
      //_proxyHttpClient = proxyHttpClient;
    }

    /// <summary>
    /// 通過中間件,攔截訪問,檢測前綴,并轉(zhuǎn)發(fā)
    /// </summary>
    /// <param name="context"></param>
    /// <param name="urlRewriter"></param>
    /// <returns></returns>
    public async Task Invoke(HttpContext context, IUrlRewriter urlRewriter, ProxyHttpClient proxyHttpClient)
    {
      var targetUri = await urlRewriter.RewriteUri(context);

      if (targetUri != null)
      {
        var requestMessage = GenerateProxifiedRequest(context, targetUri);
        await SendAsync(context, requestMessage, proxyHttpClient);

        return;
      }

      await _next(context);
    }

    private async Task SendAsync(HttpContext context, HttpRequestMessage requestMessage, ProxyHttpClient proxyHttpClient)
    {
    

      using (var responseMessage = await proxyHttpClient.Client.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead, context.RequestAborted))
      {
        context.Response.StatusCode = (int)responseMessage.StatusCode;

        foreach (var header in responseMessage.Headers)
        {
          context.Response.Headers[header.Key] = header.Value.ToArray();
        }

        foreach (var header in responseMessage.Content.Headers)
        {
          context.Response.Headers[header.Key] = header.Value.ToArray();
        }

        context.Response.Headers.Remove("transfer-encoding");

        if (!context.Response.Headers.ContainsKey(CDN_HEADER_NAME))
        {
          context.Response.Headers.Add(CDN_HEADER_NAME, "no-cache, no-store");
        }

        await responseMessage.Content.CopyToAsync(context.Response.Body);
      }
    }

    private static HttpRequestMessage GenerateProxifiedRequest(HttpContext context, Uri targetUri)
    {
      var requestMessage = new HttpRequestMessage();
      CopyRequestContentAndHeaders(context, requestMessage);
      requestMessage.RequestUri = targetUri;
      requestMessage.Headers.Host = targetUri.Host;
      requestMessage.Method = GetMethod(context.Request.Method);
      return requestMessage;
    }

    private static void CopyRequestContentAndHeaders(HttpContext context, HttpRequestMessage requestMessage)
    {
      var requestMethod = context.Request.Method;
      if (!HttpMethods.IsGet(requestMethod) &&
        !HttpMethods.IsHead(requestMethod) &&
        !HttpMethods.IsDelete(requestMethod) &&
        !HttpMethods.IsTrace(requestMethod))
      {
        var streamContent = new StreamContent(context.Request.Body);
        requestMessage.Content = streamContent;
      }

      foreach (var header in context.Request.Headers)
      {
        if (!NotForwardedHttpHeaders.Contains(header.Key))
        {
          if (header.Key != "User-Agent")
          {
            if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray()) && requestMessage.Content != null)
            {
              requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray());
            }
          }
          else
          {
            string userAgent = header.Value.Count > 0 ? (header.Value[0] + " " + context.TraceIdentifier) : string.Empty;

            if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, userAgent) && requestMessage.Content != null)
            {
              requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, userAgent);
            }
          }

        }
      }
    }

    private static HttpMethod GetMethod(string method)
    {
      if (HttpMethods.IsDelete(method)) return HttpMethod.Delete;
      if (HttpMethods.IsGet(method)) return HttpMethod.Get;
      if (HttpMethods.IsHead(method)) return HttpMethod.Head;
      if (HttpMethods.IsOptions(method)) return HttpMethod.Options;
      if (HttpMethods.IsPost(method)) return HttpMethod.Post;
      if (HttpMethods.IsPut(method)) return HttpMethod.Put;
      if (HttpMethods.IsTrace(method)) return HttpMethod.Trace;
      return new HttpMethod(method);
    }

四.注入和啟用我們的中間件和ProxyHttpClient

我們在Startup的ConfigureServices中添加如下代碼,注入我們的HttpClient與IUrlRewriter,如下:

services.AddHttpClient<ProxyHttpClient>()
      .ConfigurePrimaryHttpMessageHandler(x => new HttpClientHandler()
      {
        AllowAutoRedirect = false,
        MaxConnectionsPerServer = int.MaxValue,
        UseCookies = false,
      }); //注入我們定義的HttpClient
 services.AddSingleton<IUrlRewriter>(new PrefixRewriter("/webapp", "http://localhost:63445"));//這里填寫前綴與需要轉(zhuǎn)發(fā)的地址

然后在Startup的Configure中,啟動我們的中間件,如下:

app.UseMiddleware<ProxyMiddleware>();

五.測試中間件效果

我們編寫前端代碼如下:

created: function () {
        this.mockTableData1();
        axios.get("/webapp/api/values/get", "123").then(res => { alert(res.data[0]) });
        axios.post("/webapp/api/values/post",{value: 'david'}).then(res => { alert(res.data.message) });

      }

在另外的WebApi項(xiàng)目,編寫接口如下:

[HttpGet]
    public ActionResult<IEnumerable<string>> Get()
    {
      return new string[] { "value1", accstring.ToString() };
    }

    [HttpPost]
    public AjaxResult Post(dynamic value)
    {
      string aaa = JsonConvert.SerializeObject(value);
      return Success("OK");
    }

效果如下,可以看到我們的視圖正確的獲取到了返回值:

寫在最后

這里我們通過中間件的形式實(shí)現(xiàn)了接口的代理轉(zhuǎn)發(fā),在具體的使用過程中肯定還會有一些小問題,而且這里我們只實(shí)現(xiàn)了Http的轉(zhuǎn)發(fā).ws的則沒有.

如果要使用的話,其實(shí)國外有一個開源的項(xiàng)目:https://github.com/ProxyKit, 已經(jīng)有900多個star了.應(yīng)該還不錯.

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