具有取消支持 (CancellationTokenSource) 和进度报告的 PostSubmitter 的异步 CTP

Question

各位开发者！

我有一个使用 POST 或 GET 发布到网站并阅读响应的课程。现在都是异步的，不会导致 UI 挂起。

我现在需要升级它才能处理取消。使用的所有异步方法都不接受取消令牌。我需要了解原因以及我的选择是什么。如果可能的话，我应该在类中创建 CancellationTokenSource 对象还是从 UI 中对其进行参数化？

其次，我需要公开 PostData() 方法的进度。我该怎么做呢？

类：

using System;
using System.Collections.Specialized;
using System.IO;
using System.Net;
using System.Text;
using System.Threading.Tasks;
using System.Web;
using System.Windows.Forms;
using System.Collections.Generic;
using RESTClient.Core.UploadFile;
using System.Threading;

namespace RESTClient.Core {

    /// <summary>
    /// Submits post data to a url.
    /// </summary>
    public class PostSubmitter {

        #region Backing Store
        private string _URL = string.Empty;
        private NameValueCollection _PostValues = new NameValueCollection();
        private PostTypeEnum _PostType = PostTypeEnum.GET;
        #endregion

        #region Constructors
        /// <summary>
        /// Default constructor.
        /// </summary>
        public PostSubmitter() {

        }

        /// <summary>
        /// Constructor that accepts a url as a parameter
        /// </summary>
        /// <param name="url">The url where the post will be submitted to.</param>
        public PostSubmitter(string url)
            : this() {
            _URL = url;
        }

        /// <summary>
        /// Constructor allowing the setting of the url and items to post.
        /// </summary>
        /// <param name="url">the url for the post.</param>
        /// <param name="values">The values for the post.</param>
        public PostSubmitter(string url, NameValueCollection values)
            : this(url) {
            _PostValues = values;
        }
        #endregion

        #region Properties
        /// <summary>
        /// Gets or sets the url to submit the post to.
        /// </summary>
        public string Url {
            get {
                return _URL;
            }
            set {
                _URL = value;
            }
        }

        /// <summary>
        /// Gets or sets the name value collection of items to post.
        /// </summary>
        public NameValueCollection PostItems {
            get {
                return _PostValues;
            }
            set {
                _PostValues = value;
            }
        }

        /// <summary>
        /// Gets or sets the type of action to perform against the url.
        /// </summary>
        public PostTypeEnum Type {
            get {
                return _PostType;
            }
            set {
                _PostType = value;
            }
        }
        #endregion

        /// <summary>
        /// Posts the supplied data to specified url.
        /// </summary>
        /// <returns>a string containing the result of the post.</returns>
        public async Task<String> Post() {
            StringBuilder parameters = new StringBuilder();
            for (int i = 0; i < _PostValues.Count; i++) {
                EncodeAndAddItem(ref parameters, _PostValues.GetKey(i), _PostValues[i]);
            }
            string result = await PostData(_URL, parameters.ToString());
            return result;
        }

        /// <summary>
        /// Posts the supplied data to specified url.
        /// </summary>
        /// <param name="url">The url to post to.</param>
        /// <returns>a string containing the result of the post.</returns>
        public async Task<String> Post(string url) {
            _URL = url;
            return await this.Post();
        }

        /// <summary>
        /// Posts the supplied data to specified url.
        /// </summary>
        /// <param name="url">The url to post to.</param>
        /// <param name="values">The values to post.</param>
        /// <returns>a string containing the result of the post.</returns>
        public async Task<String> Post(string url, NameValueCollection values) {
            _PostValues = values;
            return await this.Post(url);
        }

        /// <summary>
        /// Posts data to a specified url. Note that this assumes that you have already url encoded the post data.
        /// </summary>
        /// <param name="postData">The data to post.</param>
        /// <param name="url">the url to post to.</param>
        /// <returns>Returns the result of the post.</returns>
        private async Task<String> PostData(string url, string postData) {
            HttpWebRequest request = null;

            if (_PostType == PostTypeEnum.POST) {
                Uri uri = new Uri(url);
                request = WebRequest.Create(uri) as HttpWebRequest;
                request.Method = "POST";
                request.ContentType = "application/x-www-form-urlencoded";
                request.ContentLength = postData.Length;

                using (Stream writeStream = await request.GetRequestStreamAsync()) {
                    UTF8Encoding encoding = new UTF8Encoding();
                    byte[] bytes = encoding.GetBytes(postData);
                    writeStream.Write(bytes, 0, bytes.Length);
                }
            }
            else {
                Uri uri = new Uri(url + "?" + postData);
                request = WebRequest.Create(uri) as HttpWebRequest;
                request.Method = "GET";
            }

            using (HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync()) {
                using (Stream responseStream = response.GetResponseStream()) {
                    using (StreamReader readStream = new StreamReader(responseStream, Encoding.UTF8)) {
                        return await readStream.ReadToEndAsync();
                    }
                }
            }
        }

        /// <summary>
        /// Encodes an item and ads it to the string.
        /// </summary>
        /// <param name="baseRequest">The previously encoded data.</param>
        /// <param name="dataItem">The data to encode.</param>
        /// <returns>A string containing the old data and the previously encoded data.</returns>
        private void EncodeAndAddItem(ref StringBuilder baseRequest, string key, string dataItem) {
            if (baseRequest == null) {
                baseRequest = new StringBuilder();
            }
            if (baseRequest.Length != 0) {
                baseRequest.Append("&");
            }
            baseRequest.Append(key);
            baseRequest.Append("=");
            baseRequest.Append(HttpUtility.UrlEncode(dataItem));
        }

        public async void HttpUploadFile(string url, string file, string paramName, string contentType, NameValueCollection nvc) {
            //log.Debug(string.Format("Uploading {0} to {1}", file, url));
            string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
            byte[] boundarybytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

            HttpWebRequest wr = WebRequest.Create(url) as HttpWebRequest;
            wr.ContentType = "multipart/form-data; boundary=" + boundary;
            wr.Method = "POST";
            wr.KeepAlive = true;
            wr.Credentials = CredentialCache.DefaultCredentials;

            Stream rs = await wr.GetRequestStreamAsync();

            string formdataTemplate = "Content-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}";
            foreach (string key in nvc.Keys) {
                await rs.WriteAsync(boundarybytes, 0, boundarybytes.Length);
                string formitem = string.Format(formdataTemplate, key, nvc[key]);
                byte[] formitembytes = Encoding.UTF8.GetBytes(formitem);
                await rs.WriteAsync(formitembytes, 0, formitembytes.Length);
            }
            await rs.WriteAsync(boundarybytes, 0, boundarybytes.Length);

            string headerTemplate = "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: {2}\r\n\r\n";
            string header = string.Format(headerTemplate, paramName, file, contentType);
            byte[] headerbytes = Encoding.UTF8.GetBytes(header);
            rs.WriteAsync(headerbytes, 0, headerbytes.Length);

            FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Read);
            byte[] buffer = new byte[4096];
            int bytesRead = 0;
            while ((bytesRead = await fileStream.ReadAsync(buffer, 0, buffer.Length)) != 0) {
                await rs.WriteAsync(buffer, 0, bytesRead);
            }
            fileStream.Close();

            byte[] trailer = Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
            await rs.WriteAsync(trailer, 0, trailer.Length);
            rs.Close();

            WebResponse wresp = null;
            try {
                wresp = await wr.GetResponseAsync();
                Stream stream2 = wresp.GetResponseStream();
                StreamReader reader2 = new StreamReader(stream2);
                //log.Debug(string.Format("File uploaded, server response is: {0}", reader2.ReadToEnd()));
            }
            catch (Exception ex) {
                //log.Error("Error uploading file", ex);
                if (wresp != null) {
                    wresp.Close();
                    wresp = null;
                }
            }
            finally {
                wr = null;
            }

            /**
            NameValueCollection nvc = new NameValueCollection();
            nvc.Add("id", "TTR");
            nvc.Add("btn-submit-photo", "Upload");
            HttpUploadFile("http://your.server.com/upload",          @"C:\test\test.jpg", "file", "image/jpeg", nvc);        
            **/
        }

        public async Task<String> ExecutePostRequest(Uri url, Dictionary<string, string> postData, FileInfo fileToUpload, string fileMimeType, string fileFormKey) {
            HttpWebRequest request = WebRequest.Create(url.AbsoluteUri) as HttpWebRequest;
            request.Method = "POST";
            request.KeepAlive = true;

            String boundary = Utility.CreateFormDataBoundary();
            request.ContentType = "multipart/form-data; boundary=" + boundary;

            Stream requestStream = await request.GetRequestStreamAsync();
            postData.WriteMultipartFormData(requestStream, boundary);

            if (fileToUpload != null) {
                //TODO: Need async here...
                fileToUpload.WriteMultipartFormData(requestStream, boundary, fileMimeType, fileFormKey);
            }

            byte[] endBytes = Encoding.UTF8.GetBytes("--" + boundary + "--");

            await requestStream.WriteAsync(endBytes, 0, endBytes.Length);
            requestStream.Close();

            using (WebResponse response = await request.GetResponseAsync()) {
                using (StreamReader reader = new StreamReader(response.GetResponseStream())) {
                    return await reader.ReadToEndAsync();
                }
            }
        }

    }

}

注意：最后有3个方法用于文件上传。我仍然需要弄清楚，在此之前，我需要了解取消和进度报告。

相关问题Async CTP for a PostSubmitter

任何帮助将不胜感激。

Answer 1

您可以通过采用 IProgress 和 CancellationToken 参数来支持进度和取消。

对于取消，请定期检查是否已通过调用 CancellationToken.ThrowIfCancellationRequested 请求取消。有关详细信息，请参阅 MSDN 上的取消。

为了进步，你需要首先决定什么样的“进步”才有意义。例如，如果“进度”只是传输的字节数，则可以使用 IProgress。确定进度类型后，请调用 IProgress.Report 报告进度。对于 IProgress 有两件事需要注意：

1. IProgress 参数可能为 null。
2. IProgress.Report 异步运行。这意味着您必须： A) 在 IProgress 中使用 T 的值类型； B) 对传递给 IProgress.Report 的每个 T 对象执行深度复制；或 C) 每次调用 IProgress.Report 时创建一个新的 T 对象。