.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];
        }

    }