使用的Mvc，直接返回byte格式的数据，文本及图片都可以直接返回。注释已经很清楚了，代码如下：

public class HomeController : Controller
{
    /// <summary>
    /// 本地请求中转
    /// </summary>
    /// <returns></returns>
    public byte[] Index()
    {
            //跨域访问
        HttpContext.Response.AppendHeader("Access-Control-Allow-Origin", "*");
        
        var respone = HttpContext.Response;
        var request = HttpContext.Request;
        
        //初始化 本应用程序 Url
        string FromUrl = request.Url.ToString();
        
        //获取实际请求目标的HOST
        //string ToHost = "192.168.20.1:8080";
        if (string.IsNullOrWhiteSpace(Request["host"]))
        {
            return System.Text.Encoding.Default.GetBytes("");
        }
        //获取实际请求目标的地址+参数
        if (string.IsNullOrWhiteSpace(Request["query"]))
        {
            return System.Text.Encoding.Default.GetBytes("");
        }
        string ToHost = Request["host"].ToString();
        string query = Request["query"].ToString();
        //请求的地址
        string ToUrl = string.Format("http://{0}/{1}", ToHost, query);
        //创建 Http 请求 用于将 替换后 请求报文 发往 目标 Url
        System.Net.HttpWebRequest hRequest = System.Net.HttpWebRequest.CreateHttp(ToUrl);
        //设置请求头
        foreach (var key in request.Headers.AllKeys)
        {
            try
            {
                hRequest.Headers.Add(key, request.Headers[key]);
            }
            catch (Exception)
            {
                continue;
            }
        }
        #region 设置特殊请求头
        if (!string.IsNullOrEmpty(request.Headers["Accept"]))
        {
            hRequest.Accept = request.Headers["Accept"];
        }
        if (!string.IsNullOrEmpty(request.Headers["Connection"]))
        {
            string connection = request.Headers["Connection"];
            hRequest.KeepAlive =
                string.Compare(connection, "keep-alive", StringComparison.CurrentCultureIgnoreCase) == 0;
        }
        if (!string.IsNullOrEmpty(request.Headers["Content-Type"]))
        {
            hRequest.ContentType = request.Headers["Content-Type"];
        }
        if (!string.IsNullOrEmpty(request.Headers["Expect"]))
        {
            hRequest.Expect = request.Headers["Expect"];
        }
        if (!string.IsNullOrEmpty(request.Headers["Date"]))
        {
            hRequest.Date = Convert.ToDateTime(request.Headers["Date"]);
        }
        if (!string.IsNullOrEmpty(request.Headers["Host"]))
        {
            hRequest.Host = ToHost;
        }
        if (!string.IsNullOrEmpty(request.Headers["If-Modified-Since"]))
        {
            hRequest.IfModifiedSince = Convert.ToDateTime(request.Headers["If-Modified-Since"]);
        }
        if (!string.IsNullOrEmpty(request.Headers["Referer"]))
        {
            hRequest.Referer = request.Headers["Referer"].ToString();
        }
        if (!string.IsNullOrEmpty(request.Headers["User-Agent"]))
        {
            hRequest.UserAgent = request.Headers["User-Agent"];
        }
        if (!string.IsNullOrEmpty(request.Headers["Content-Length"]))
        {
            hRequest.ContentLength = Convert.ToInt32(request.Headers["Content-Length"]);
        }
        #endregion
        //判断是否是Get请求,如果不是Get就写入请求报文体
        if (String.Compare(request.HttpMethod, "get", StringComparison.CurrentCultureIgnoreCase) != 0)
        {
            //设置请求体
            hRequest.Method = "POST";
            var hStream = hRequest.GetRequestStream();
            byte[] hbuffer = new byte[1024 * 2];
            int hLength = 0;
            do
            {
                hLength = Request.InputStream.Read(hbuffer, 0, hbuffer.Length);
                hStream.Write(hbuffer, 0, hLength);
            } while (hLength > 0);
        }
        //获取响应报文
        System.Net.WebResponse hRespone = null;
        try
        {
            hRespone = hRequest.GetResponse();
        }
        catch (Exception exp)
        {
            respone.Write(exp.Message);
            respone.End();
        }
        //设置响应头
        //this.SetResponeHead(hRespone, respone);
        foreach (var key in respone.Headers.AllKeys)
        {
            try
            {
                hRespone.Headers.Add(key, respone.Headers[key]);
            }
            catch (Exception)
            {
                continue;
            }
        }
        //#region 设置特殊响应头
        if (!string.IsNullOrEmpty(hRespone.Headers["Content-Type"]))
        {
            respone.ContentType = hRespone.Headers["Content-Type"];
        }
        if (!string.IsNullOrEmpty(hRespone.Headers["Host"]))
        {
            respone.AddHeader("Host", FromUrl);
        }
        if (!string.IsNullOrEmpty(hRespone.Headers["Referer"]))
        {
            respone.AddHeader("Referer", hRespone.Headers["Referer"]);
        }
        //#endregion
        //写入响应内容
        //this.SetResponeBody(hRespone, respone);
        var nStream = hRespone.GetResponseStream();
        byte[] buffer = new byte[1024 * 2];
        int rLength = 0;
        do
        {
            rLength = nStream.Read(buffer, 0, buffer.Length);
            respone.OutputStream.Write(buffer, 0, rLength);
        } while (rLength > 0);
        respone.End();
        return buffer;
    }
}