.Net Core 3.0后台使用httpclient请求网络网页和图片_使用Core3.0做一个简单的代理服务器

public class domainmappingmiddleware : basemiddleware
    {
        public configsetting configsetting { get; set; }

        public ilogger<domainmappingmiddleware> logger { get; set; }

        public httpclient httpclient = null;

        private static object _obj = new object();
        public domainmappingmiddleware(requestdelegate next, iconfiguration configuration, imemorycache memorycache, configsetting configsetting, ilogger<domainmappingmiddleware> logger, ihttpclientfactory clientfactory) : base(next, configuration, memorycache)
        {
            this.configsetting = configsetting;
            this.logger = logger;
            this.httpclient = clientfactory.createclient("domainserviceclient");
        }


        public async task invoke(httpcontext httpcontext)
        {
            string requesturl = null;
            string requesthost = null;

            string dateflag = datetime.now.tostring("yyyy-mm-dd hh:mm:ss:fff");

            requesturl = httpcontext.request.getdisplayurl();

            bool isexistdomain = false;
            bool islocalwebsite = this.configsetting.getvalue("islocaldomainservice") == "true";

            if (httpcontext.request.query.containskey("returnurl"))
            {
                requesturl = httpcontext.request.query["returnurl"].tostring();
                requesturl = httputility.urldecode(requesturl);
                islocalwebsite = false;
            }

            match match = regex.match(requesturl, this.configsetting.getvalue("domainhostregex"));
            if (match.success)
            {
                isexistdomain = true;
                requesthost = match.value;
            }

#if debug
            requesturl = "http://139.199.128.86:444/?returnurl=https%3a%2f%2f3w.huanqiu.com%2fa%2fc36dc8%2f9cakrnknonm";
#endif

            if (isexistdomain)
            {
                this.logger.loginformation($"{dateflag}_记录请求地址：{requesturl},是否存在当前域：{isexistdomain},是否是本地环境：{islocalwebsite}");

                bool isfile = false;

                //1-设置响应的内容类型
                mediatypeheadervalue mediatype = null;

                if (requesturl.contains(".js"))
                {
                    mediatype = new mediatypeheadervalue("application/x-javascript");
                    //mediatype.encoding = system.text.encoding.utf8;
                }
                else if (requesturl.contains(".css"))
                {
                    mediatype = new mediatypeheadervalue("text/css");
                    //mediatype.encoding = system.text.encoding.utf8;
                }
                else if (requesturl.contains(".png"))
                {
                    mediatype = new mediatypeheadervalue("image/png");
                    isfile = true;
                }
                else if (requesturl.contains(".jpg"))
                {
                    mediatype = new mediatypeheadervalue("image/jpeg");
                    isfile = true;
                }
                else if (requesturl.contains(".ico"))
                {
                    mediatype = new mediatypeheadervalue("image/x-icon");
                    isfile = true;
                }
                else if (requesturl.contains(".gif"))
                {
                    mediatype = new mediatypeheadervalue("image/gif");
                    isfile = true;
                }
                else if (requesturl.contains("/api/") && !requesturl.contains("/views"))
                {
                    mediatype = new mediatypeheadervalue("application/json");
                }
                else
                {
                    mediatype = new mediatypeheadervalue("text/html");
                    mediatype.encoding = system.text.encoding.utf8;
                }

                //2-获取响应结果

                if (islocalwebsite)
                {
                    //本地服务器将请求转发到远程服务器
                    requesturl = this.configsetting.getvalue("mydomainagenthost") + "?returnurl=" + httputility.urlencode(requesturl);
                }

                if (isfile == false)
                {
                    string result = await this.httpclient.myget(requesturl);

                    if (httpcontext.response.hasstarted == false)
                    {
                        this.logger.loginformation($"{dateflag}_请求结束_{requesturl}_长度{result.length}");

                        //请求结果展示在客户端，需要重新请求本地服务器，因此需要将https转为http
                        result = result.replace("https://", "http://");
                        //替换"/a.ico" 为："http://www.baidu.com/a.ico"
                        result = regex.replace(result, "\"\\/(?=[a-za-z0-9]+)", $"\"{requesthost}/");
                        //替换"//www.baidu.com/a.ico" 为："http://www.baidu.com/a.ico"
                        result = regex.replace(result, "\"\\/\\/(?=[a-za-z0-9]+)", "\"http://");

                        //必须有请求结果才能给内容类型赋值；如果请求过程出了异常再赋值，会报错：the response headers cannot be modified because the response has already started.
                        httpcontext.response.contenttype = mediatype.tostring();

                        await httpcontext.response.writeasync(result ?? "");
                    }
                    else
                    {
                        this.logger.loginformation($"{dateflag}_请求结束_{requesturl}_图片字节流长度{result.length}_response已启动");
                    }
                }
                else
                {
                    byte[] result = await this.httpclient.mygetfile(requesturl);

                    if (httpcontext.response.hasstarted == false)
                    {
                        this.logger.loginformation($"{dateflag}_请求结束_{requesturl}_图片字节流长度{result.length}");

                        httpcontext.response.contenttype = mediatype.tostring();
                        await httpcontext.response.body.writeasync(result, 0, result.length);
                    }
                    else
                    {
                        this.logger.loginformation($"{dateflag}_请求结束_{requesturl}_图片字节流长度{result.length}_response已启动");
                    }
                }
            }
        }
    }

/// <summary>
    /// 中间件基类
    /// </summary>
    public abstract class basemiddleware
    {
        /// <summary>
        /// 等同于asp.net里面的webcache(httpruntime.cache)
        /// </summary>
        protected imemorycache memorycache { get; set; }

        /// <summary>
        /// 获取配置文件里面的配置内容
        /// </summary>
        protected iconfiguration configuration { get; set; }

        public basemiddleware(requestdelegate next, params object[] @params)
        {
            foreach (var item in @params)
            {
                if (item is imemorycache)
                {
                    this.memorycache = (imemorycache)item;
                }
                else if (item is iconfiguration)
                {
                    this.configuration = (iconfiguration)item;
                }
            }
        }

    }

public static class httpclientsingleston
    {
        public async static task<string> myget(this httpclient httpclient, string url)
        {
            string result = null;

            using (httprequestmessage request = new httprequestmessage(httpmethod.get, url))
            {
                using (var response = await httpclient.sendasync(request))
                {
                    if (response.issuccessstatuscode)
                    {
                        using (stream stream = await response.content.readasstreamasync())
                        {
                            using (streamreader streamreader = new streamreader(stream, encoding.utf8))
                            {
                                result = await streamreader.readtoendasync();
                            }
                        }

                    }
                }
            }
            return result ?? "";
        }

        public async static task<byte[]> mygetfile(this httpclient httpclient, string url)
        {
            byte[] result = null;
            using (httprequestmessage request = new httprequestmessage(httpmethod.get, url))
            {
                using (var response = await httpclient.sendasync(request))
                {
                    if (response.issuccessstatuscode)
                    {
                        result = await response.content.readasbytearrayasync();
                    }
                }
            }
            return result ?? new byte[0];
        }

    }