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C# 使用HTTP下载文件，支持续传
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内容图文
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
namespace Flames.Utils.Net
{
public class Http
{
/// <summary>
/// 下载进度
/// </summary>
public event Action<int> ShowDownloadPercent;
/// <summary>
/// 一次下载量
/// </summary>
private int ByteSize = 1000000;
/// <summary>
/// 下载中的后缀，下载完成去掉
/// </summary>
private const string Suffix = ".downloading";
/// <summary>
/// Http方式下载文件
/// </summary>
/// <param name="url">http地址</param>
/// <param name="localfile">本地文件</param>
/// <returns></returns>
public int DownloadFile(string url, string localfile)
{
int ret = 0;
string localfileReal = localfile;
string localfileWithSuffix = localfileReal + Suffix;
try
{
long startPosition = 0;
FileStream writeStream = null;
if (string.IsNullOrEmpty(url) || string.IsNullOrEmpty(localfileReal)) return 1;
if (File.Exists(localfileReal)) return 0;
//取得远程文件长度
long remoteFileLength = GetHttpLength(url);
if (remoteFileLength == 0) return 2;
//判断要下载的文件是否存在
if (File.Exists(localfileWithSuffix))
{
writeStream = File.OpenWrite(localfileWithSuffix);
startPosition = writeStream.Length;
if (startPosition > remoteFileLength)
{
writeStream.Close();
File.Delete(localfileWithSuffix);
writeStream = new FileStream(localfileWithSuffix, FileMode.Create);
}
else if (startPosition == remoteFileLength)
{
DownloadFileOk(localfileReal, localfileWithSuffix);
writeStream.Close();
return 0;
}
else
{
writeStream.Seek(startPosition, SeekOrigin.Begin);
}
}
else
{
writeStream = new FileStream(localfileWithSuffix, FileMode.Create);
}
HttpWebRequest req = null;
HttpWebResponse rsp = null;
try
{
req = (HttpWebRequest)HttpWebRequest.Create(url);
if (startPosition > 0) req.AddRange((int)startPosition);
rsp = (HttpWebResponse)req.GetResponse();
using (Stream readStream = rsp.GetResponseStream())
{
byte[] btArray = new byte[ByteSize];
long currPostion = startPosition;
int contentSize = 0;
while ((contentSize = readStream.Read(btArray, 0, btArray.Length)) > 0)
{
writeStream.Write(btArray, 0, contentSize);
currPostion += contentSize;
ShowDownloadPercent?.Invoke((int)(currPostion * 100 / remoteFileLength));
}
}
}
catch (Exception ex)
{
ret = 3;
}
finally
{
if (writeStream != null)
writeStream.Close();
if (rsp != null)
rsp.Close();
if (req != null)
req.Abort();
if (ret == 0)
DownloadFileOk(localfileReal, localfileWithSuffix);
}
}
catch (Exception ex)
{
//Log.Info("获取远程文件失败！exception：\n" + ex.ToString());
ret = 4;
}
return ret;
}
/// <summary>
/// 下载完成
/// </summary>
private void DownloadFileOk(string localfileReal, string localfileWithSuffix)
{
try
{
//去掉.downloading后缀
FileInfo fi = new FileInfo(localfileWithSuffix);
fi.MoveTo(localfileReal);
}
catch (Exception ex)
{
}
finally
{
//通知完成
if (ShowDownloadPercent != null)
ShowDownloadPercent(100);
}
}
// 从文件头得到远程文件的长度
private long GetHttpLength(string url)
{
long length = 0;
HttpWebRequest req = null;
HttpWebResponse rsp = null;
try
{
req = (HttpWebRequest)HttpWebRequest.Create(url);
rsp = (HttpWebResponse)req.GetResponse();
if (rsp.StatusCode == HttpStatusCode.OK)
length = rsp.ContentLength;
}
catch (Exception ex)
{
}
finally
{
if (rsp != null)
rsp.Close();
if (req != null)
req.Abort();
}
return length;
}
}
}
原文：https://www.cnblogs.com/flamegreat/p/14620733.html
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