C#限速下载网络文件

代码：

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using Common.Utils;
using Utils;

namespace 爬虫
{
    public partial class Form1 : Form
    {
        #region 变量
        /// <summary>
        /// 已完成字节数
        /// </summary>
        private long completedCount = ;
        /// <summary>
        /// 是否完成
        /// </summary>
        private bool isCompleted = true;
        /// <summary>
        /// 数据块队列
        /// </summary>
        private ConcurrentQueue<MemoryStream> msQueue = new ConcurrentQueue<MemoryStream>();
        /// <summary>
        /// 下载开始位置
        /// </summary>
        private long range = ;
        /// <summary>
        /// 文件大小
        /// </summary>
        private long total = ;
        /// <summary>
        /// 一段时间内的完成节点数，计算网速用
        /// </summary>
        private long unitCount = ;
        /// <summary>
        /// 上次计时时间，计算网速用
        /// </summary>
        private DateTime lastTime = DateTime.MinValue;
        /// <summary>
        /// 一段时间内的完成字节数，控制网速用
        /// </summary>
        private long unitCountForLimit = ;
        /// <summary>
        /// 上次计时时间，控制网速用
        /// </summary>
        private DateTime lastTimeForLimit = DateTime.MinValue;
        /// <summary>
        /// 下载文件sleep时间，控制速度用
        /// </summary>
        private int sleepTime = ;
        #endregion

        #region Form1
        public Form1()
        {
            InitializeComponent();
        }
        #endregion

        #region Form1_Load
        private void Form1_Load(object sender, EventArgs e)
        {
            lblMsg.Text = string.Empty;
            lblByteMsg.Text = string.Empty;
            lblSpeed.Text = string.Empty;
        }
        #endregion

        #region Form1_FormClosing
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {

        }
        #endregion

        #region btnDownload_Click 下载
        private void btnDownload_Click(object sender, EventArgs e)
        {
            isCompleted = false;
            btnDownload.Enabled = false;
            string url = txtUrl.Text.Trim();
            string filePath = CreateFilePath(url);

            #region 下载线程
            Thread thread = new Thread(new ThreadStart(() =>
            {
                int tryTimes = ;
                while (!HttpDownloadFile(url, filePath))
                {
                    Thread.Sleep();

                    tryTimes++;
                    LogUtil.Log("请求服务器失败，重新请求" + tryTimes.ToString() + "次");
                    this.Invoke(new InvokeDelegate(() =>
                    {
                        lblMsg.Text = "请求服务器失败，重新请求" + tryTimes.ToString() + "次";
                    }));
                    HttpDownloadFile(url, filePath);
                }
            }));
            thread.IsBackground = true;
            thread.Start();
            #endregion

            #region 保存文件线程
            thread = new Thread(new ThreadStart(() =>
            {
                while (!isCompleted)
                {
                    MemoryStream ms;
                    if (msQueue.TryDequeue(out ms))
                    {
                        using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Write))
                        {
                            fs.Seek(completedCount, SeekOrigin.Begin);
                            fs.Write(ms.ToArray(), , (int)ms.Length);
                            fs.Close();
                        }
                        completedCount += ms.Length;
                    }

                    if (total !=  && total == completedCount)
                    {
                        Thread.Sleep();
                        isCompleted = true;
                    }

                    Thread.Sleep();
                }
            }));
            thread.IsBackground = true;
            thread.Start();
            #endregion

            #region 计算网速/进度线程
            thread = new Thread(new ThreadStart(() =>
            {
                while (!isCompleted)
                {
                    Thread.Sleep();

                    if (lastTime != DateTime.MinValue)
                    {
                        double sec = DateTime.Now.Subtract(lastTime).TotalSeconds;
                        double speed = unitCount / sec / ;

                        try
                        {
                            #region 显示速度
                            if (speed < )
                            {
                                this.Invoke(new InvokeDelegate(() =>
                                {
                                    lblSpeed.Text = string.Format("{0}KB/S", speed.ToString("0.00"));
                                }));
                            }
                            else
                            {
                                this.Invoke(new InvokeDelegate(() =>
                                {
                                    lblSpeed.Text = string.Format("{0}MB/S", (speed / ).ToString("0.00"));
                                }));
                            }
                            #endregion

                            #region 显示进度
                            this.Invoke(new InvokeDelegate(() =>
                            {
                                string strTotal = (total /  / ).ToString("0.00") + "MB";
                                if (total <  * )
                                {
                                    strTotal = (total / ).ToString("0.00") + "KB";
                                }
                                string completed = (completedCount /  / ).ToString("0.00") + "MB";
                                if (completedCount <  * )
                                {
                                    completed = (completedCount / ).ToString("0.00") + "KB";
                                }
                                lblMsg.Text = string.Format("进度：{0}/{1}", completed, strTotal);
                                lblByteMsg.Text = string.Format("已下载：{0}\r\n总大小：{1}", completedCount, total);

                                if (completedCount == total)
                                {
                                    MessageBox.Show("完成");
                                }
                            }));
                            #endregion
                        }
                        catch { }

                        lastTime = DateTime.Now;
                        unitCount = ;
                    }
                }
            }));
            thread.IsBackground = true;
            thread.Start();
            #endregion

            #region 限制网速线程
            thread = new Thread(new ThreadStart(() =>
            {
                while (!isCompleted)
                {
                    Thread.Sleep();

                    if (lastTimeForLimit != DateTime.MinValue)
                    {
                        double sec = DateTime.Now.Subtract(lastTimeForLimit).TotalSeconds;
                        double speed = unitCountForLimit / sec / ;

                        try
                        {
                            #region 限速/解除限速
                            double limitSpeed = ;
                            if (double.TryParse(txtSpeed.Text.Trim(), out limitSpeed))
                            {
                                if (speed > limitSpeed && sleepTime < )
                                {
                                    sleepTime += ;
                                }
                                if (speed < limitSpeed -  && sleepTime >= )
                                {
                                    sleepTime -= ;
                                }
                            }
                            else
                            {
                                this.Invoke(new InvokeDelegate(() =>
                                {
                                    txtSpeed.Text = "";
                                }));
                            }
                            #endregion
                        }
                        catch { }

                        lastTimeForLimit = DateTime.Now;
                        unitCountForLimit = ;
                    }
                }
            }));
            thread.IsBackground = true;
            thread.Start();
            #endregion

        }
        #endregion

        #region HttpDownloadFile 下载文件
        /// <summary>
        /// Http下载文件
        /// </summary>
        public bool HttpDownloadFile(string url, string filePath)
        {
            try
            {
                if (!File.Exists(filePath))
                {
                    using (FileStream fs = new FileStream(filePath, FileMode.Create))
                    {
                        fs.Close();
                    }
                }
                else
                {
                    FileInfo fileInfo = new FileInfo(filePath);
                    range = fileInfo.Length;
                }

                // 设置参数
                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
                request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)";
                request.Proxy = null;
                //发送请求并获取相应回应数据
                HttpWebResponse response = request.GetResponse() as HttpWebResponse;
                if (response.ContentLength == range)
                {
                    this.Invoke(new InvokeDelegate(() =>
                    {
                        lblMsg.Text = "文件已下载";
                    }));
                    return true;
                }

                // 设置参数
                request = WebRequest.Create(url) as HttpWebRequest;
                request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)";
                request.Proxy = null;
                request.AddRange(range);
                //发送请求并获取相应回应数据
                response = request.GetResponse() as HttpWebResponse;
                //直到request.GetResponse()程序才开始向目标网页发送Post请求
                Stream responseStream = response.GetResponseStream();

                total = range + response.ContentLength;
                completedCount = range;

                MemoryStream ms = new MemoryStream();
                byte[] bArr = new byte[];
                lastTime = DateTime.Now;
                lastTimeForLimit = DateTime.Now;
                int size = responseStream.Read(bArr, , (int)bArr.Length);
                unitCount += size;
                unitCountForLimit += size;
                ms.Write(bArr, , size);
                while (!isCompleted)
                {
                    size = responseStream.Read(bArr, , (int)bArr.Length);
                    unitCount += size;
                    unitCountForLimit += size;
                    ms.Write(bArr, , size);
                    if (ms.Length > )
                    {
                        msQueue.Enqueue(ms);
                        ms = new MemoryStream();
                    }
                    if (completedCount + ms.Length == total)
                    {
                        msQueue.Enqueue(ms);
                        ms = new MemoryStream();
                    }

                    Thread.Sleep(sleepTime);
                }
                responseStream.Close();
                return true;
            }
            catch (Exception ex)
            {
                LogUtil.LogError(ex.Message + "\r\n" + ex.StackTrace);
                return false;
            }
        }
        #endregion

        #region 根据URL生成文件保存路径
        private string CreateFilePath(string url)
        {
            string path = Application.StartupPath + "\\download";
            if (!Directory.Exists(path))
            {
                Directory.CreateDirectory(path);
            }

            string fileName = Path.GetFileName(url);
            if (fileName.IndexOf("?") > )
            {
                return path + "\\" + fileName.Substring(, fileName.IndexOf("?"));
            }
            else
            {
                return path + "\\" + fileName;
            }
        }
        #endregion

    } //end Form1类
}

测试截图：