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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~ 然因為種種原因..沒辦法用用純前端的框架(其實是學(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)來實現(xiàn)跨域訪問.

那么我們的JS運行在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

幸運的是ASP.NET Core 給我們提供了強大的中間件模式.

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現(xiàn)快速更換檢測前綴的規(guī)則.

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

實現(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 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 _logger;
        public ProxyMiddleware(               RequestDelegate next,               ILogger logger,               ProxyHttpClient proxyHttpClient)        {            _next = next;            _logger = logger;            _proxyHttpClient = proxyHttpClient;        }
        ///         /// 通過中間件,攔截訪問,檢測前綴,并轉(zhuǎn)發(fā)        /// 
        ///         ///         ///         public async Task Invoke(HttpContext context, IUrlRewriter urlRewriter)                {            var targetUri = await urlRewriter.RewriteUri(context);
            if (targetUri != null)            {                var requestMessage = GenerateProxifiedRequest(context, targetUri);                await SendAsync(context, requestMessage);
                return;            }
            await _next(context);        }
        private async Task SendAsync(HttpContext context, HttpRequestMessage requestMessage)        {       
            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()            .ConfigurePrimaryHttpMessageHandler(x => new HttpClientHandler()            {                AllowAutoRedirect = false,                MaxConnectionsPerServer = int.MaxValue,                UseCookies = false,            }); //注入我們定義的HttpClient services.AddSingleton(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項目,編寫接口如下:

        [HttpGet]        public ActionResultstring>> 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,而且這里我們只實現(xiàn)了Http的轉(zhuǎn)發(fā).ws的則沒有.

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

ASP.NET Core 奇技淫巧之接口代理轉(zhuǎn)發(fā)

一.創(chuàng)建檢測約定URL的接口與實現(xiàn)

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

三.創(chuàng)建代理轉(zhuǎn)發(fā)的中間件

四.注入和啟用我們的中間件和ProxyHttpClient

五.測試中間件效果