C#使用HttpClient对大文件进行断点上传和下载

　　string url = "http://file.cshelloworld.com/images/1771477326069108736.jpg";

　　long totalSize = 0;//文件总大小

　　long downLoadingSize = 0;//当前已经下载了多少

　　private void Button_Click(object sender, RoutedEventArgs e)

　　{

　　Task.Run(async () =>

　　{

　　//获取到文件总大小 通过head请求

　　using HttpClient client = new HttpClient();

　　HttpRequestMessage requestMessage = new HttpRequestMessage(HttpMethod.Head, url);

　　var response = await client.SendAsync(requestMessage);

　　totalSize = response.Content.Headers.ContentLength.Value;

　　using FileStream fileStream = new FileStream("d:a.jpj", FileMode.Create, FileAccess.Write, FileShare.Read);

　　//开始分片下载

　　while (downLoadingSize < totalSize)

　　{

　　//组装range 0,1000 1000,2000 0,9999

　　long start = downLoadingSize;

　　long end = start + 1000;

　　if (end > (totalSize - 1))

　　{

　　end = totalSize - 1;

　　}

　　client.DefaultRequestHeaders.Range = new System.Net.Http.Headers.RangeHeaderValue(start, end);

　　var res = await client.GetAsync(url);

　　byte[] bytes = await res.Content.ReadAsByteArrayAsync();

　　await fileStream.WriteAsync(bytes, 0, bytes.Length);

　　//更新UI的进度

　　downLoadingSize += bytes.Length;

　　int process = (int)((downLoadingSize / (decimal)totalSize) * 100);

　　this.Dispatcher.Invoke(() =>

　　{

　　cont.Text = process + "%";

　　this.processBar.Value = process;

　　});

　　}

　　fileStream.Close();

　　});

　　}