How to: Compress and extract files

The System.IO.Compression namespace contains the following types for compressing and decompressing files and streams. You can also use these types to read and modify the contents of a compressed file:

The following examples show some of the functions you can perform when working with compressed files.

Example 1 - Create and extract a .zip file

The following example shows how to create and extract a compressed file that has a .zip file name extension by using the ZipFile class. It compresses the contents of a folder into a new .zip file and then extracts that content to a new folder. To use the ZipFile class, you must reference the System.IO.Compression.FileSystem assembly in your project.

using System;
using System.IO;
using System.IO.Compression;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            string startPath = @"c:\example\start";
            string zipPath = @"c:\example\result.zip";
            string extractPath = @"c:\example\extract";

            ZipFile.CreateFromDirectory(startPath, zipPath);

            ZipFile.ExtractToDirectory(zipPath, extractPath);
        }
    }
}
Imports System.IO
Imports System.IO.Compression

Module Module1

    Sub Main()
        Dim startPath As String = "c:\example\start"
        Dim zipPath As String = "c:\example\result.zip"
        Dim extractPath As String = "c:\example\extract"

        ZipFile.CreateFromDirectory(startPath, zipPath)

        ZipFile.ExtractToDirectory(zipPath, extractPath)
    End Sub

End Module

Example 2 - Extract specific file extensions

The next example shows how to iterate through the contents of an existing .zip file and extract files that have a .txt extension. It uses the ZipArchive class to access an existing .zip file, and the ZipArchiveEntry class to inspect the individual entries in the compressed file. It uses an extension method (ExtractToFile) for the ZipArchiveEntry object. The extension method is available in the System.IO.Compression.ZipFileExtensions class. To use the ZipFileExtensions class, you must reference the System.IO.Compression.FileSystem assembly in your project.

Important

When unzipping files, you must look for malicious file paths which can escape out of the directory where you want to unzip into. This is known as a path traversal attack.

The following example demonstrates how to check for malicious file paths and provides a safe way to unzip:

using System;
using System.IO;
using System.IO.Compression;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string zipPath = @"c:\example\start.zip";

            Console.WriteLine("Provide path where to extract the zip file:");
            string extractPath = Console.ReadLine();
            
            // Normalizes the path.
            extractPath = Path.GetFullPath(extractPath);

            // Ensures that the last character on the extraction path
            // is the directory separator char. 
            // Without this, a malicious zip file could try to traverse outside of the expected
            // extraction path.
            if (!extractPath.EndsWith(Path.DirectorySeparatorChar))
                extractPath += Path.DirectorySeparatorChar;

            using (ZipArchive archive = ZipFile.OpenRead(zipPath))
            {
                foreach (ZipArchiveEntry entry in archive.Entries)
                {
                    if (entry.FullName.EndsWith(".txt", StringComparison.OrdinalIgnoreCase))
                    {
                        // Gets the full path to ensure that relative segments are removed.
                        string destinationPath = Path.GetFullPath(Path.Combine(extractPath, entry.FullName));
 
                        // Ordinal match is safest, case-sensitive volumes can be mounted within volumes that
                        // are case-insensitive.
                        if (destinationPath.StartsWith(extractPath, StringComparison.Ordinal))
                            entry.ExtractToFile(destinationPath);                        
                    }
                }
            }
        }
    }
}
Imports System.IO
Imports System.IO.Compression

Module Module1

    Sub Main()
        Dim zipPath As String = "c:\example\start.zip"

        Console.WriteLine("Provide path where to extract the zip file:")
        Dim extractPath As String = Console.ReadLine()

        ' Normalizes the path.
        extractPath = Path.GetFullPath(extractPath)

        ' Ensures that the last character on the extraction path
        ' is the directory separator char. 
        ' Without this, a malicious zip file could try to traverse outside of the expected
        ' extraction path.
        If Not extractPath.EndsWith(Path.DirectorySeparatorChar) Then
            extractPath += Path.DirectorySeparatorChar
        End If

        Using archive As ZipArchive = ZipFile.OpenRead(zipPath)
            For Each entry As ZipArchiveEntry In archive.Entries
                If entry.FullName.EndsWith(".txt", StringComparison.OrdinalIgnoreCase) Then

                    ' Gets the full path to ensure that relative segments are removed.
                    Dim destinationPath As String = Path.GetFullPath(Path.Combine(extractPath, entry.FullName))
                    
                    ' Ordinal match is safest, case-sensitive volumes can be mounted within volumes that
                    ' are case-insensitive.
                    If destinationPath.StartsWith(extractPath, StringComparison.Ordinal) Then 
                        entry.ExtractToFile(destinationPath)
                    End If

                End If
            Next
        End Using
    End Sub

End Module

Example 3 - Add a new file to an existing .zip file

The following example uses the ZipArchive class to access an existing .zip file, and adds a new file to the compressed file. The new file gets compressed when you add it to the existing .zip file.

using System;
using System.IO;
using System.IO.Compression;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            using (FileStream zipToOpen = new FileStream(@"c:\users\exampleuser\release.zip", FileMode.Open))
            {
                using (ZipArchive archive = new ZipArchive(zipToOpen, ZipArchiveMode.Update))
                {
                    ZipArchiveEntry readmeEntry = archive.CreateEntry("Readme.txt");
                    using (StreamWriter writer = new StreamWriter(readmeEntry.Open()))
                    {
                            writer.WriteLine("Information about this package.");
                            writer.WriteLine("========================");
                    }
                }
            }
        }
    }
}
Imports System.IO
Imports System.IO.Compression

Module Module1

    Sub Main()
        Using zipToOpen As FileStream = New FileStream("c:\users\exampleuser\release.zip", FileMode.Open)
            Using archive As ZipArchive = New ZipArchive(zipToOpen, ZipArchiveMode.Update)
                Dim readmeEntry As ZipArchiveEntry = archive.CreateEntry("Readme.txt")
                Using writer As StreamWriter = New StreamWriter(readmeEntry.Open())
                    writer.WriteLine("Information about this package.")
                    writer.WriteLine("========================")
                End Using
            End Using
        End Using
    End Sub

End Module

Example 4 - Compress and decompress a directory of .gz files

You can also use the GZipStream and DeflateStream classes to compress and decompress data. They use the same compression algorithm. Compressed GZipStream objects that are written to a file that has an extension of .gz can be decompressed by using many common tools in addition to the methods provided by GZipStream. The following example shows how to compress and decompress a directory of files by using the GZipStream class:

using System;
using System.IO;
using System.IO.Compression;

namespace zip
{
    public class Program
    {
        private static string directoryPath = @"c:\temp";
        public static void Main()
        {
            DirectoryInfo directorySelected = new DirectoryInfo(directoryPath);
            Compress(directorySelected);

            foreach (FileInfo fileToDecompress in directorySelected.GetFiles("*.gz"))
            {
                Decompress(fileToDecompress);
            }
        }

        public static void Compress(DirectoryInfo directorySelected)
        {
            foreach (FileInfo fileToCompress in directorySelected.GetFiles())
            {
                using (FileStream originalFileStream = fileToCompress.OpenRead())
                {
                    if ((File.GetAttributes(fileToCompress.FullName) & 
                       FileAttributes.Hidden) != FileAttributes.Hidden & fileToCompress.Extension != ".gz")
                    {
                        using (FileStream compressedFileStream = File.Create(fileToCompress.FullName + ".gz"))
                        {
                            using (GZipStream compressionStream = new GZipStream(compressedFileStream, 
                               CompressionMode.Compress))
                            {
                                originalFileStream.CopyTo(compressionStream);

                            }
                        }
                        FileInfo info = new FileInfo(directoryPath + "\\" + fileToCompress.Name + ".gz");
                        Console.WriteLine("Compressed {0} from {1} to {2} bytes.",
                        fileToCompress.Name, fileToCompress.Length.ToString(), info.Length.ToString());
                    }

                }
            }
        }

        public static void Decompress(FileInfo fileToDecompress)
        {
            using (FileStream originalFileStream = fileToDecompress.OpenRead())
            {
                string currentFileName = fileToDecompress.FullName;
                string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);

                using (FileStream decompressedFileStream = File.Create(newFileName))
                {
                    using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
                    {
                        decompressionStream.CopyTo(decompressedFileStream);
                        Console.WriteLine("Decompressed: {0}", fileToDecompress.Name);
                    }
                }
            }
        }
    }
}
Imports System.IO
Imports System.IO.Compression
Module Module1

    Private directoryPath As String = "c:\temp"
    Public Sub Main()
        Dim directorySelected As New DirectoryInfo(directoryPath)
        Compress(directorySelected)

        For Each fileToDecompress As FileInfo In directorySelected.GetFiles("*.gz")
            Decompress(fileToDecompress)
        Next
    End Sub

    Public Sub Compress(directorySelected As DirectoryInfo)
        For Each fileToCompress As FileInfo In directorySelected.GetFiles()
            Using originalFileStream As FileStream = fileToCompress.OpenRead()
                If (File.GetAttributes(fileToCompress.FullName) And FileAttributes.Hidden) <> FileAttributes.Hidden And fileToCompress.Extension <> ".gz" Then
                    Using compressedFileStream As FileStream = File.Create(fileToCompress.FullName & ".gz")
                        Using compressionStream As New GZipStream(compressedFileStream, CompressionMode.Compress)

                            originalFileStream.CopyTo(compressionStream)
                        End Using
                    End Using
                    Dim info As New FileInfo(directoryPath & "\" & fileToCompress.Name & ".gz")
                    Console.WriteLine("Compressed {0} from {1} to {2} bytes.", fileToCompress.Name,
                                      fileToCompress.Length.ToString(), info.Length.ToString())

                End If
            End Using
        Next
    End Sub


    Private Sub Decompress(ByVal fileToDecompress As FileInfo)
        Using originalFileStream As FileStream = fileToDecompress.OpenRead()
            Dim currentFileName As String = fileToDecompress.FullName
            Dim newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length)

            Using decompressedFileStream As FileStream = File.Create(newFileName)
                Using decompressionStream As GZipStream = New GZipStream(originalFileStream, CompressionMode.Decompress)
                    decompressionStream.CopyTo(decompressedFileStream)
                    Console.WriteLine("Decompressed: {0}", fileToDecompress.Name)
                End Using
            End Using
        End Using
    End Sub
End Module

See also

ZipArchive
ZipFile
ZipArchiveEntry
DeflateStream
GZipStream
File and Stream I/O