apewer-dotnet/Apewer/Web/ApiProcessor.cs

using Apewer;
using Apewer.Models;
using Apewer.Network;
using Apewer.Source;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Net;
using System.Reflection;
using System.Text;

#if NETFX
using System.Web;
#endif

#if NETCORE
using Microsoft.AspNetCore.Http;
#endif

namespace Apewer.Web
{

    internal abstract class ApiProcessor
    {

        // 请求 Body 大于 100MB 时，不尝试解析 API。
        const long MaxRequestBody = 100L * 1024L * 1024L;

        #region fields & properties

        internal ApiInvoker Invoker = null;

        private DateTime Beginning = DateTime.Now;
        private DateTime Ending;

        private ApiRequest ApiRequest;
        private ApiResponse ApiResponse;

        public Dictionary<string, ApiApplication> Entries;

        public bool HaveContext { get; protected set; }

        // 抽象方法的返回值。
        private Uri Url;
        private HttpMethod Method;

        protected abstract object GetContext();

        protected abstract string GetClientIP();
        protected abstract HttpMethod GetMethod();
        protected abstract Uri GetURL();
        protected abstract Uri GetReferrer();
        protected abstract StringPairs GetHeaders();
        protected abstract StringPairs GetCookies();
        protected abstract long GetRequestLength();
        protected abstract byte[] ReadRequest();

        protected abstract void SetCacheControl(int seconds);
        protected abstract void SetContentType(string value);
        protected abstract void SetContentLength(long value);
        protected abstract void Redirect(string url);
        protected abstract string AddHeader(string name, string value);

        protected abstract void WriteResponse(byte[] bytes);
        protected abstract void WriteResponse(Stream stream);

        #endregion

        /// <summary>执行处理程序，返回错误信息。</summary>
        public string Run()
        {
            try
            {
                // 检查依赖的属性，若不通过，则无法执行。
                var preCheckError = PreCheck();
                if (!string.IsNullOrEmpty(preCheckError)) return preCheckError;

                // 准备变量。
                ApiRequest = GetRequest();
                ApiResponse = new ApiResponse();

                // 准备向 Controller 传递的属性。
                var an = ApiRequest.Application;
                var a = null as ApiApplication;
                var fn = ApiRequest.Function;
                var f = null as ApiFunction;
                var r = ApiRequest.Random;
                var t = ApiRequest.Ticket;

                // 调用。
                if (Entries.ContainsKey(an))
                {
                    a = Entries[an];
                    if (a.Functions.ContainsKey(fn))
                    {
                        f = a.Functions[fn];
                        Invoke(a, f, ApiRequest, ApiResponse);
                    }
                    else
                    {
                        Invoke(a, null, ApiRequest, ApiResponse);
                    }
                }
                else
                {
                    var @default = ApiOptions.Default;
                    if (@default != null)
                    {
                        Invoke(ApiInvoker.GetApplication(@default, false), null, ApiRequest, ApiResponse);
                    }
                    else
                    {
                        ApiResponse.Error("指定的 Application 无效。");
                        if (an.IsEmpty() && ApiOptions.AllowEnumerate) Enumerate(Entries);
                    }
                }

                // 记录结束时间。
                Ending = DateTime.Now;

                // 调整响应。
                ApiResponse.Beginning = Beginning;
                ApiResponse.Ending = Ending;
                ApiResponse.Application = an;
                ApiResponse.Function = fn;
                ApiResponse.Random = r;

                // 向客户端输出。
                return Output(ApiResponse);
            }
            catch (Exception ex)
            {
                Logger.Web.Exception(this, ex);
                return ex.Message;
            }
        }

        // 检查执行的前提条件。
        string PreCheck()
        {
            // Context
            if (!HaveContext) return "Context 无效。";

            // Entries
            if (Entries == null) return "Entries 无效。";

            // Method
            Method = GetMethod();
            if (Method == HttpMethod.NULL) return "Methods 无效。";

            // AccessControl
            // 在此之后可以输出
            if (ApiOptions.WithAccessControl)
            {
                AddHeader("Access-Control-Allow-Headers", "Content-Type");
                AddHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
                AddHeader("Access-Control-Allow-Origin", "*");

                var maxage = ApiOptions.AccessControlMaxAge;
                if (maxage > 0) AddHeader("Access-Control-Max-Age", maxage.ToString());
            }

            // URL
            Url = GetURL();
            var lowerPath = TextUtility.ToLower(Url.AbsolutePath);

            // favicon.ico
            if (!ApiOptions.AllowFavIcon)
            {
                if (lowerPath.StartsWith("/favicon.ico"))
                {
                    SetCacheControl(0);
                    Output(null as byte[]);
                    return "已取消对 favicon.ico 的请求。";
                }
            }

            // robots.txt
            if (!ApiOptions.AllowRobots)
            {
                if (lowerPath.StartsWith("/robots.txt"))
                {
                    const string text = "User-agent: *\nDisallow: / \n";
                    SetCacheControl(0);
                    Output(text);
                    return "已取消对 robots.txt 的请求。";
                }
            }

            return null;
        }

        void Enumerate(Dictionary<string, ApiApplication> applications)
        {
            var count = 0;
            var list = Json.NewArray();
            if (applications != null)
            {
                foreach (var i in applications)
                {
                    if (!i.Value.Visible) continue;
                    var item = Json.NewObject();
                    item["name"] = i.Value.Name;
                    item["caption"] = i.Value.Caption;
                    if (ApiOptions.WithModuleName) item["module"] = i.Value.Module;
                    if (ApiOptions.WithTypeName) item["type"] = i.Value.Type.FullName;
                    list.AddItem(item);
                    count = count + 1;
                }
            }
            ApiResponse.Data.Reset(Json.NewObject());
            ApiResponse.Data.SetProperty("count", count);
            ApiResponse.Data.SetProperty("list", list);
        }

        void Enumerate(Dictionary<string, ApiFunction> functions)
        {
            var count = 0;
            var list = Json.NewArray();
            if (functions != null)
            {
                foreach (var i in functions)
                {
                    if (!i.Value.Visible) continue;
                    var item = Json.NewObject();
                    item["name"] = i.Value.Name;
                    item["caption"] = i.Value.Caption;
                    item["description"] = i.Value.Description;
                    list.AddItem(item);
                    count = count + 1;
                }
            }
            ApiResponse.Data.Reset(Json.NewObject());
            ApiResponse.Data.SetProperty("count", count);
            ApiResponse.Data.SetProperty("list", list);
        }

        internal static ApiController CreateController(Type type)
        {
            try
            {
                return (ApiController)Activator.CreateInstance(type);
            }
            catch { }
            return null;
        }

        void Invoke(ApiApplication application, ApiFunction function, ApiRequest request, ApiResponse response)
        {
            if (request == null || response == null) return;

            // 创建控制器实例。
            if (application == null)
            {
                response.Error("指定的 Application 无效，无法创建实例。");
                return;
            }
            var controller = CreateController(application.Type);
            if (controller == null)
            {
                response.Error("创建控制器实例失败。");
                return;
            }

            controller.Application = application;
            controller.Function = function;
            controller.Request = request;
            controller.Response = response;
            Invoke(controller);
        }

        void Invoke(ApiController controller)
        {
            if (controller == null) return;
            var application = controller.Application;
            var function = controller.Function;
            var request = controller.Request;
            var response = controller.Response;
            if (application == null) return;
            if (request == null || response == null) return;

            // 调用功能。
            try
            {
                if (controller.AfterInitialized != null) controller.AfterInitialized.Invoke();

                // 控制器要求单独处理，此时框架不再处理 Function。
                var allowFunction = controller.AllowFunction;
                if (application.Independent) allowFunction = false;

                // 由框架调用 Function。
                if (allowFunction)
                {
                    if (function == null)
                    {
                        var @default = controller.DefaultFunction;
                        if (@default != null)
                        {
                            @default.Invoke();
                        }
                        else
                        {
                            controller.Response.Error("指定的 Function 无效。");
                            if (ApiOptions.AllowEnumerate) Enumerate(application.Functions);
                        }
                    }
                    else
                    {
                        var result = function.Method.Invoke(controller, null);
                        if (response.Status.IsBlank()) response.Status = "ok";
                        if (function.Returnable && result != null)
                        {
                            if (result is string)
                            {
                                var error = (string)result;
                                if (!string.IsNullOrEmpty(error)) response.Error(error);
                            }
                        }
                    }
                }
            }
            catch (Exception exception)
            {
                response.Error(exception.InnerException);
            }

            // 释放控制器。
            RuntimeUtility.Dispose(controller);
        }

        void Output(string text, string type = "text/plain; charset=utf-8")
        {
            var bytes = TextUtility.ToBinary(text);
            Output(bytes, type);
        }

        void Output(byte[] bytes, string type = "application/octet-stream")
        {
            var length = bytes == null ? 0 : bytes.LongLength;
            SetContentType(type);
            SetContentLength(length);
            if (bytes != null && bytes.LongLength > 0L)
            {
                WriteResponse(bytes);
            }
        }

        void Output(Stream stream, string type = "application/octet-stream")
        {
            SetContentType(type);
            if (stream != null)
            {
                var length = stream.Length - stream.Position;
                SetContentLength(length);
                if (length > 0 && stream.CanRead) WriteResponse(stream);
                RuntimeUtility.Dispose(stream);
            }
        }

        // 输出 ApiResponse，返回错误信息。
        string Output(ApiResponse apiResponse)
        {
            // Ticket。
            if (ApiRequest.Method == HttpMethod.GET)
            {
                if (apiResponse.Ticket != null && !apiResponse.Cookies.HasKey("ticket", true))
                {
                    apiResponse.Cookies.Add("ticket", apiResponse.Ticket);
                }
            }

            // 设置自定义头。
            AddHeaders(apiResponse.Headers);
            var setCookies = SetCookies(apiResponse.Cookies);
            if (setCookies.NotEmpty())
            {
                apiResponse.Error("系统错误。");
                apiResponse.Data.Reset(Json.NewObject());
                apiResponse.Data["cookies"] = setCookies;
            }

            //
            if (apiResponse.Type == ApiFormat.Redirect)
            {
                SetCacheControl(0);
                Redirect(apiResponse.RedirectUrl);
                return null;
            }

            // 
            if (apiResponse.Type == ApiFormat.Json)
            {
                SetCacheControl(apiResponse.Expires);
                Output(ExportJson(apiResponse));
                return null;
            }

            // 
            if (apiResponse.Type == ApiFormat.Text)
            {
                SetCacheControl(apiResponse.Expires);
                Output(apiResponse.TextString, apiResponse.TextType);
                return null;
            }

            //
            if (apiResponse.Type == ApiFormat.Binary)
            {
                var type = apiResponse.BinaryType ?? "application/octet-stream";
                if (apiResponse.BinaryBytes != null)
                {
                    SetCacheControl(apiResponse.Expires);
                    Output(apiResponse.BinaryBytes, type);
                }
                else if (apiResponse.BinaryStream != null)
                {
                    SetCacheControl(apiResponse.Expires);
                    Output(apiResponse.BinaryStream, type);
                }
                return null;
            }

            //
            if (apiResponse.Type == ApiFormat.File)
            {
                if (apiResponse.FileStream != null)
                {
                    SetCacheControl(apiResponse.Expires);
                    AddHeader("Content-Disposition", $"attachment; filename={TextUtility.EncodeUrl(apiResponse.FileName)}");
                    Output(apiResponse.FileStream, apiResponse.FileType ?? "application/octet-stream");
                }
                return null;
            }

            // Context.Response.Flush();
            // Context.Response.End();

            return null;
        }

        void AddHeaders(StringPairs headers)
        {
            foreach (var header in headers) AddHeader(header.Key, header.Value);
        }

        string SetCookies(IEnumerable<KeyValuePair<string, string>> cookies)
        {
            if (cookies == null) return null;

            var ps = new List<string>();
            foreach (var kvp in cookies)
            {
                var k = kvp.Key ?? "";
                var v = kvp.Value ?? "";
                if (k.IsEmpty()) continue;
                ps.Add(TextUtility.Merge(k, "=", v));
            }

            if (ps.Count < 1) return null;

            var value = TextUtility.Join("; ", ps);
            return AddHeader("Set-Cookie", value);
        }

        // 从 Context 获取 ApiRequest 模型。
        ApiRequest GetRequest()
        {
            // 检查 URL 的 Path。
            // if (string.IsNullOrEmpty(request.Path)) return null;

            // 创建数据对象。
            var apiRequest = new ApiRequest();

            // Http Method。
            apiRequest.Method = Method;

            // 基本信息。
            apiRequest.Headers = GetHeaders();
            apiRequest.IP = GetClientIP();
            apiRequest.Url = Url;
            apiRequest.Referrer = GetReferrer();
            apiRequest.Parameters = WebUtility.ParseParameters(Url.Query);

            // Headers。
            apiRequest.UserAgent = WebUtility.GetUserAgent(apiRequest.Headers);
            apiRequest.Cookies = GetCookies();

            // 匹配 API。
            var application = null as string;
            var function = null as string;
            var random = null as string;
            var ticket = null as string;
            var session = null as string;
            var page = null as string;

            // 解析 POST 请求。
            if (apiRequest.Method == Apewer.Network.HttpMethod.POST)
            {
                var post = null as byte[];
                var length = GetRequestLength();
                if (length < 0 || (length > 0 && length <= MaxRequestBody))
                {
                    post = ReadRequest();
                }

                // 解析 POST。
                if (post != null && post.Length > 1L)
                {
                    // 检查 JSON 的格式，第一位必须是“{”或“[”。
                    if (post[0] == 123 || post[0] == 91)
                    {
                        var text = TextUtility.FromBinary(post);
                        var json = Json.Parse(text);
                        if (json != null && json.IsObject)
                        {
                            application = json["application"];
                            function = json["function"];
                            random = json["random"];
                            ticket = json["ticket"];
                            session = json["session"];
                            page = json["page"];

                            var data = json.GetProperty("data");
                            apiRequest.PostData = post;
                            apiRequest.PostText = text;
                            apiRequest.PostJson = json;
                            apiRequest.Data = data ?? Json.NewObject();
                        }
                    }
                }
            }

            // 解析 URL 参数。
            // URL 参数的优先级应高于 URL 路径，以避免反向代理产生的路径问题。
            if (string.IsNullOrEmpty(application)) application = WebUtility.GetParameter(apiRequest.Parameters, "application");
            if (string.IsNullOrEmpty(function)) function = WebUtility.GetParameter(apiRequest.Parameters, "function");
            if (string.IsNullOrEmpty(random)) random = WebUtility.GetParameter(apiRequest.Parameters, "random");
            if (string.IsNullOrEmpty(ticket)) ticket = WebUtility.GetParameter(apiRequest.Parameters, "ticket");
            if (string.IsNullOrEmpty(session)) session = WebUtility.GetParameter(apiRequest.Parameters, "session");
            if (string.IsNullOrEmpty(page)) page = WebUtility.GetParameter(apiRequest.Parameters, "page");

            // 从 Cookie 中获取 Ticket。
            if (string.IsNullOrEmpty(ticket)) ticket = apiRequest.Cookies.GetValue("ticket");

            // 最后检查 URL 路径。
            var paths = (apiRequest.Url.AbsolutePath ?? "").Split('/');
            if (string.IsNullOrEmpty(application) && paths.Length >= 2) application = TextUtility.DecodeUrl(paths[1]);
            if (string.IsNullOrEmpty(function) && paths.Length >= 3) function = TextUtility.DecodeUrl(paths[2]);

            // 修正内容。
            application = application.SafeLower().SafeTrim();
            function = function.SafeLower().SafeTrim();
            random = random.SafeLower().SafeTrim();
            ticket = ticket.SafeLower().SafeTrim();
            session = session.SafeLower().SafeTrim();
            page = page.SafeTrim();

            // 设置请求：回传。
            apiRequest.Application = application;
            apiRequest.Function = function;
            apiRequest.Random = random;

            // 设置请求：不回传。
            apiRequest.Ticket = ticket;
            apiRequest.Session = session;
            apiRequest.Page = page;

            // 返回结果。
            return apiRequest;
        }

        private static string ExportJson(ApiResponse response)
        {
            if (response == null) return "{}";

            var json = Json.NewObject();

            // 执行时间。
            if (ApiOptions.WithClock)
            {
                json.SetProperty("clock", response.Ending.ToLucid());
            }

            // 持续时间。
            if (ApiOptions.WithDuration)
            {
                var seconds = Math.Floor((response.Ending - response.Beginning).TotalMilliseconds) / 1000D;
                json.SetProperty("duration", seconds);
            }

            // 随机值。
            if (response.Random.NotEmpty()) json.SetProperty("random", response.Random);

            // 调用。
            if (ApiOptions.WithTarget)
            {
                json.SetProperty("application", response.Application);
                json.SetProperty("function", response.Function);
            }

            // 状态。
            json.SetProperty("status", (TextUtility.IsBlank(response.Status) ? TextUtility.EmptyString : response.Status.ToLower()));
            json.SetProperty("message", response.Message);

            // Ticket。
            if (response.Ticket != null) json.SetProperty("ticket", response.Ticket);

            // 异常。
            if (ApiOptions.AllowException && response.Exception != null)
            {
                try
                {
                    var exMessage = null as string;
                    var exStackTrace = null as string;
                    var exSource = null as string;
                    var exHelpLink = null as string;

                    exMessage = response.Exception.Message;
                    exStackTrace = response.Exception.StackTrace;
                    exSource = response.Exception.Source;
                    exHelpLink = response.Exception.HelpLink;

                    // Exception 对象的主要属性。
                    var exJson = Json.NewObject();
                    exJson.SetProperty("type", response.Exception.GetType().FullName);
                    exJson.SetProperty("message", exMessage);
                    exJson.SetProperty("stack", Json.Parse((exStackTrace ?? "").Replace("\r", "").Split('\n'), false));
                    exJson.SetProperty("source", exSource);
                    exJson.SetProperty("helplink", exHelpLink);

                    // WebException 附加数据。
                    var webex = response.Exception as System.Net.WebException;
                    if (webex != null) exJson.SetProperty("data", Json.Parse(webex.Data));

                    json.SetProperty("exception", exJson);
                }
                catch (Exception ex)
                {
                    var exJson = Json.NewObject();
                    exJson.SetProperty("message", TextUtility.Merge("设置 Exception 时再次发生异常：", ex.Message));
                    json.SetProperty("exception", exJson);
                }
            }

            // 用户数据。
            json.SetProperty("data", response.Data);

            var indented = ApiOptions.JsonIndent || response.Indented;
            var text = json.ToString(indented);
            return text;
        }

    }

    internal sealed class ApiProcessorListener : ApiProcessor
    {

        private HttpListenerContext Context;
        private HttpListenerRequest Request;
        private HttpListenerResponse Response;

        /// <exception cref="ArgumentNullException"></exception>
        public ApiProcessorListener(HttpListenerContext context)
        {
            if (context == null) throw new ArgumentNullException(nameof(context));
            Context = context;
            Request = context.Request;
            Response = context.Response;
            HaveContext = true;
        }

        protected override object GetContext() => Context;

        protected override string GetClientIP() => WebUtility.GetClientIP(Request);
        protected override HttpMethod GetMethod() => WebUtility.GetMethod(Request);
        protected override Uri GetURL() => WebUtility.GetUrl(Request);
        protected override Uri GetReferrer() => Request.UrlReferrer;
        protected override StringPairs GetHeaders() => WebUtility.GetHeaders(Request);
        protected override StringPairs GetCookies() => WebUtility.GetCookies(Request);
        protected override long GetRequestLength() => Request.ContentLength64;
        protected override byte[] ReadRequest() => BinaryUtility.Read(Request.InputStream);

        protected override void SetCacheControl(int seconds) => WebUtility.SetCacheControl(Response, seconds);
        protected override void SetContentType(string value) => Response.ContentType = value ?? "";
        protected override void SetContentLength(long value) => AddHeader("Content-Length", value.ToString());
        protected override void Redirect(string url) => WebUtility.Redirect(Response, url);
        protected override string AddHeader(string name, string value) => WebUtility.AddHeader(Response, name, value);
        protected override void WriteResponse(byte[] bytes) => BinaryUtility.Write(Response.OutputStream, bytes);
        protected override void WriteResponse(Stream stream) => BinaryUtility.Read(stream, Response.OutputStream);

    }

#if NETFX

    internal sealed class ApiProcessorIIS : ApiProcessor
    {

        private System.Web.HttpContext Context;
        private System.Web.HttpRequest Request;
        private System.Web.HttpResponse Response;

        /// <exception cref="ArgumentNullException"></exception>
        public ApiProcessorIIS(HttpContext context)
        {
            if (context == null) context = HttpContext.Current;
            if (context == null) throw new ArgumentNullException(nameof(context));
            Context = context;
            Request = context.Request;
            Response = context.Response;
            HaveContext = true;
        }

        protected override object GetContext() => Context;

        protected override string GetClientIP() => WebUtility.GetClientIP(Request);
        protected override HttpMethod GetMethod() => WebUtility.GetMethod(Request);
        protected override Uri GetURL() => WebUtility.GetUrl(Request);
        protected override Uri GetReferrer() => Request.UrlReferrer;
        protected override StringPairs GetHeaders() => WebUtility.GetHeaders(Request);
        protected override StringPairs GetCookies() => WebUtility.GetCookies(Request);
        protected override long GetRequestLength() => Request.ContentLength;
        protected override byte[] ReadRequest() => BinaryUtility.Read(Request.InputStream);

        protected override void SetCacheControl(int seconds) => WebUtility.SetCacheControl(Response, seconds);
        protected override void SetContentType(string value) => Response.ContentType = value ?? "";
        protected override void SetContentLength(long value) => AddHeader("Content-Length", value.ToString());
        protected override void Redirect(string url) => WebUtility.Redirect(Response, url);
        protected override string AddHeader(string name, string value) => WebUtility.AddHeader(Response, name, value);

        protected override void WriteResponse(byte[] bytes)
        {
            BinaryUtility.Write(Context.Response.OutputStream, bytes);
        }

        protected override void WriteResponse(Stream stream)
        {
            BinaryUtility.Read(stream, Context.Response.OutputStream);
        }

    }

#endif

#if NETCORE

    internal sealed class ApiProcessorCore : ApiProcessor
    {

        private bool AllowSynchronousIO = true;

        private Microsoft.AspNetCore.Http.HttpContext Context;
        private Microsoft.AspNetCore.Http.HttpRequest Request;
        private Microsoft.AspNetCore.Http.HttpResponse Response;

        /// <exception cref="ArgumentNullException"></exception>
        public ApiProcessorCore(HttpContext context)
        {
            if (context == null) throw new ArgumentNullException(nameof(context));
            Context = context;
            Request = context.Request;
            Response = context.Response;
            HaveContext = true;
        }

        protected override object GetContext() => Context;

        protected override string GetClientIP() => WebUtility.GetClientIP(Request);
        protected override HttpMethod GetMethod() => WebUtility.GetMethod(Request);
        protected override Uri GetURL() => WebUtility.GetUrl(Request);
        protected override Uri GetReferrer() => null;
        protected override StringPairs GetHeaders() => WebUtility.GetHeaders(Request);
        protected override StringPairs GetCookies() => WebUtility.GetCookies(Request);
        protected override long GetRequestLength() => Request.ContentLength ?? -1;
        protected override byte[] ReadRequest() => BinaryUtility.Read(Request.Body);

        protected override void SetCacheControl(int seconds) => WebUtility.SetCacheControl(Response, seconds);
        protected override void SetContentType(string value) => Response.ContentType = value ?? "";
        protected override void SetContentLength(long value) => AddHeader("Content-Length", value.ToString());
        protected override void Redirect(string url) => WebUtility.Redirect(Response, url);
        protected override string AddHeader(string name, string value) => WebUtility.AddHeader(Response, name, value);

        protected override void WriteResponse(byte[] bytes)
        {
            var body = Context.Response.Body;

            // sync
            BinaryUtility.Write(body, bytes);

            // async
            // body.BeginWrite(bytes, 0, bytes.Length, (ar) => body.EndWrite(ar), null);
        }

        protected override void WriteResponse(Stream stream)
        {
            var body = Context.Response.Body;

            // sync
            BinaryUtility.Read(stream, body);

            // async
        }

        private static void ReadAsync(Stream source, Stream destination, Func<long, bool> progress = null, int buffer = 4096, Action after = null)
        {
            if (source == null || !source.CanRead || destination == null || !destination.CanWrite)
            {
                after?.Invoke();
                return;
            }

            ReadAsync(source, destination, progress, buffer, after, 0L);
        }

        private static void ReadAsync(Stream source, Stream destination, Func<long, bool> progress, int buffer, Action after, long total)
        {
            // 缓冲区。
            var limit = buffer < 1 ? 1 : buffer;
            var temp = new byte[limit];

            // 读取一次。
            try
            {
                source.BeginRead(temp, 0, limit, (ar1) =>
                {
                    var count = source.EndRead(ar1);
                    if (count > 0)
                    {
                        destination.BeginWrite(temp, 0, count, (ar2) =>
                        {
                            destination.EndWrite(ar2);
                            total += count;
                            if (progress != null)
                            {
                                var @continue = progress.Invoke(total);
                                if (!@continue)
                                {
                                    after?.Invoke();
                                    return;
                                }
                            }
                            ReadAsync(source, destination, progress, buffer, after, total);
                        }, null);
                    }
                    else after?.Invoke();
                }, null);
            }
            catch { }
        }

    }

#endif

}