HttpClient 从不在 IIS 上发送请求

Question

我有一个奇怪的问题，并尝试了各种方法来解决这个问题。

我的 Web API 项目中有一个反向代理委托处理程序，该处理程序用于拦截对内部资源、文件等的请求，从我们的外部站点到我们 DMZ 内的内部站点...

using System;
using System.Configuration;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Formatting;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;

namespace Resources.API
{
    public class ProxyHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var routes = new[]{
                "/api/videos",
                "/api/documents"
            };

            // check whether we need to proxy this request
            var passThrough = !routes.Any(route => request.RequestUri.LocalPath.StartsWith(route));
            if (passThrough)
                return await base.SendAsync(request, cancellationToken);

            // got a hit forward the request to the proxy Web API
            return await ForwardRequest(request, cancellationToken);
        }

        private static async Task<HttpResponseMessage> ForwardRequest(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            //Clone the request and forward to the internal proxy site
            var proxyUrl = ConfigurationManager.AppSettings["ProxyUrl"];
            var baseUri = new UriBuilder(proxyUrl);

            //clone the requestUri and point it at the proxy site
            var forwardedUri = new UriBuilder(request.RequestUri)
            {
                Scheme = baseUri.Scheme,
                Host = baseUri.Host,
                Port = baseUri.Port
            };

            var forwardRequest = new HttpRequestMessage(request.Method, forwardedUri.Uri);

            if (request.Method == HttpMethod.Post || request.Method == HttpMethod.Put)
            {
                var stream = new MemoryStream();
                await request.Content.CopyToAsync(stream);
                stream.Seek(0, SeekOrigin.Begin);
                forwardRequest.Content = new StreamContent(stream);

                //copy the content headers
                foreach (var header in request.Content.Headers)
                {
                    forwardRequest.Content.Headers.TryAddWithoutValidation(header.Key, header.Value);
                }
            };

            forwardRequest.Version = request.Version;

            foreach (var prop in request.Properties)
            {
                forwardRequest.Properties.Add(prop);
            }

            foreach (var header in request.Headers)
            {
                forwardRequest.Headers.TryAddWithoutValidation(header.Key, header.Value);
            }

            var client = new HttpClient(new HttpClientHandler(), disposeHandler: false);
            var task = await Task.Factory
               .StartNew(async () => await client.SendAsync(forwardRequest, HttpCompletionOption.ResponseHeadersRead,
                   cancellationToken),
                   CancellationToken.None,
                   TaskCreationOptions.LongRunning,
                   TaskScheduler.Default);
            try
            {
                task.Wait(cancellationToken);
            }
            catch (Exception e)
            {
                return new HttpResponseMessage(HttpStatusCode.InternalServerError)
                {
                    Content =
                        new ObjectContent<HttpError>(new HttpError(e, includeErrorDetail: true),
                            new JsonMediaTypeFormatter())
                };
            }

            return task.Result;
        }
    }
}

编辑：还尝试等待并返回任务...

            try
            {
                return await task;
            }

这适用于 IIS Express 8.0，但不适用于 Windows 7 Professional（我的开发机器）上的 IIS 7.5 或 Windows Server 2012 上的 IIS 8.0。

创建的 HttpClient 从未真正通过网络发送请求（由 Fiddler 检查）并最终超时并抛出带有子 TaskCanceledException 的 AggregateException。

在task.Wait 上设置断点，我注意到，由于某种原因，断点被命中 10 次，而不是在通过 IIS Express 运行时被命中一次。

我已经尝试了各种方法来尝试使其正常工作，包括大量搜索 Google 和 SO，但似乎没有任何工作。

有人知道为什么会这样吗？或者可以解释我做错了什么？

Answer 1

想通了。必须更改请求上的 Host 标头才能正确发送。它本质上忽略了 RequestUri 并使用 Host 标头来决定实际发送请求的位置。

forwardRequest.Headers.Host = forwardRequest.RequestUri.Host;

现在就像一个魅力，IIS 现在将适当地发送请求。仍然让我想知道为什么 IIS Express 似乎不需要更改 Host 标头！

完整的代码...添加了 X-Forwarded-For 和 X-Forwarded-Host 以及更好的衡量标准。

using System;
using System.Configuration;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Formatting;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Web;
using System.Web.Http;

namespace Resources.API
{
    public class ProxyHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var routes = new[]{
                "/api/videos",
                "/api/documents"
            };

            // check whether we need to proxy this request
            var passThrough = !routes.Any(route => request.RequestUri.LocalPath.StartsWith(route));
            if (passThrough)
                return await base.SendAsync(request, cancellationToken);

            // got a hit forward the request to the proxy Web API
            //return GetResponseFromProxy(request);

            //Nicer method using HttpClient - but it doesn't work on IIS!
            return await ForwardRequest(request, cancellationToken);
        }

        private static async Task<HttpResponseMessage> ForwardRequest(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            //Clone the request and forward to the internal proxy site
            var proxyUrl = ConfigurationManager.AppSettings["ProxyUrl"];
            var baseUri = new UriBuilder(proxyUrl);

            //clone the requestUri and point it at the proxy site
            var forwardedUri = new UriBuilder(request.RequestUri)
            {
                Scheme = baseUri.Scheme,
                Host = baseUri.Host,
                Port = baseUri.Port
            };

            var forwardRequest = new HttpRequestMessage(request.Method, forwardedUri.Uri);

            if (request.Method == HttpMethod.Post || request.Method == HttpMethod.Put)
            {
                var stream = new MemoryStream();
                await request.Content.CopyToAsync(stream);
                stream.Seek(0, SeekOrigin.Begin);
                forwardRequest.Content = new StreamContent(stream);

                //copy the content headers
                foreach (var header in request.Content.Headers)
                {
                    forwardRequest.Content.Headers.TryAddWithoutValidation(header.Key, header.Value);
                }
            };

            forwardRequest.Version = request.Version;

            foreach (var prop in request.Properties)
            {
                forwardRequest.Properties.Add(prop);
            }

            foreach (var header in request.Headers)
            {
                forwardRequest.Headers.TryAddWithoutValidation(header.Key, header.Value);
            }

            // Don't forget to change the Host header to refer to the proxy
            forwardRequest.Headers.Host = forwardRequest.RequestUri.Host;

            //Add the relevant X-Forwarded headers
            var xForwardedHost = request.Headers.Host;
            forwardRequest.Headers.Add("X-Forwarded-Host", xForwardedHost);

            var xForwardedFor = HttpContext.Current.Request.UserHostAddress;
            forwardRequest.Headers.Add("X-Forwarded-For", xForwardedFor);

            var client = new HttpClient(new HttpClientHandler(), disposeHandler: false);

            try
            {
                return await client.SendAsync(forwardRequest, HttpCompletionOption.ResponseHeadersRead,
                    cancellationToken);
            }
            catch (Exception e)
            {
                return new HttpResponseMessage(HttpStatusCode.InternalServerError)
                {
                    Content =
                        new ObjectContent<HttpError>(new HttpError(e, includeErrorDetail: true),
                            new JsonMediaTypeFormatter())
                };
            }
        }
    }
}