This article was submitted by netizens.
Author: Jianghu person
Original title: A bug encountered when C#decompressing zip files at the end of 2022
Original link: jhrs.com/2022/46060.html
Recently, when checking an upload function, the client uploads a zip file. After going to the server, I use the C#code to decompress the zip file to decompress the uploaded file and verify whether it is a file type that is allowed to upload. I also need to verify that the file suffix is changed indiscriminately. I have to go through everything on the header of the file. As a result, there is a monster when decompressing the zip file.
C#Extract zip file
先说一下前文（或者上下文），在 IIS 上部署了一个文件服务站点，用于上传各类文件，流程上是先上传到站点根目录里面随机创建的一个临时目录（这里采用偷懒方案，直接使用 guid 作为目录名创建），先通过文件验证后再将其通过代码剪切或者复制到正式存档目录，C# 复制或者移动文件的代码可以参考江湖人士网的这篇文章。昨天快下班时发现上传 zip 文件时报错，在文件服务根站点创建了很多很多的 guid 开头的目录，我的妹呀，这下玩犊子了，事出反常必有妖啊，肯定代码出错了。
Bug decompression code
It's almost the end of 2022. After this bug occurred, I quickly set up a simulation environment to run around and found that the following original code did have problems. The original code is as follows:
/// <summary>
/// 解压文件
/// </summary>
/// <param name="saveDir">保存目录</param>
/// <param name="stream"></param>
public static void UnZipFiles(string saveDir, Stream stream)
{
using (ZipInputStream s = new ZipInputStream(stream))
{
ZipEntry theEntry;
while ((theEntry = s.GetNextEntry()) != null)
{
string directoryName = $"{saveDir}{Path.GetDirectoryName(theEntry.Name)}\\";
string fileName = Path.GetFileName(theEntry.Name);
Directory.CreateDirectory(directoryName);
using (FileStream streamWriter = File.Create(directoryName + fileName))
{
byte[] data = new byte[2048];
while (true)
{
int size = s.Read(data, 0, data.Length);
if (size > 0)
{
streamWriter.Write(data, 0, size);
}
else
{
break;
}
}
}
}
}
}
对了，这里需要说明一下，这是以前的老项目，因此压缩，解压使用了 ICSharpCode.SharpZipLib.Zip 这个组件。
When I opened the source code and took a look, I found the problem at a glance. The logic was not strict, and the decompression file was saved and the directory was directly spliced.
How to fix this bug?
知道了问题所在，修复自然简单，调用Path.Combine方法即可，解压时再判断一下是目录还是文件即可，最终修复后的代码如下：
/// <summary>
/// 解压文件
/// </summary>
/// <param name="saveDir">保存目录</param>
/// <param name="stream"></param>
public static void UnZipFiles(string saveDir, Stream stream)
{
using (ZipInputStream s = new ZipInputStream(stream))
{
ZipEntry theEntry;
string directoryName, file, fileName;
while ((theEntry = s.GetNextEntry()) != null)
{
directoryName = Path.Combine(saveDir, Path.GetDirectoryName(theEntry.Name));
fileName = Path.GetFileName(theEntry.Name);
Directory.CreateDirectory(directoryName);
file = Path.Combine(directoryName, fileName);
if (theEntry.IsFile)
{
using (FileStream streamWriter = File.Create(file))
{
byte[] data = new byte[2048];
while (true)
{
int size = s.Read(data, 0, data.Length);
if (size > 0)
{
streamWriter.Write(data, 0, size);
}
else
{
break;
}
}
}
}
}
}
}