Extract a 7z file in C#

Call Archive.Extract with the .7z file and a target folder. The program below lists and extracts the 7-Zip source code, a real 7z archive you can download to try it.

dotnet new console -o Extract7z && cd Extract7z
dotnet add package RecursiveAI.OneArchive --version 1.0.0
curl -LO https://github.com/ip7z/7zip/releases/download/24.09/7z2409-src.7z

Put this in Program.cs and run dotnet run:

using RecursiveAI.OneArchive;
 
// List what is inside.
using (var archive = Archive.Open("7z2409-src.7z"))
{
    var files = archive.Entries.Where(e => e.Kind == ArchiveEntryKind.File).ToList();
    Console.WriteLine($"{files.Count} files, {files.Sum(e => e.Size):N0} bytes");
    foreach (var e in files.Take(5))
        Console.WriteLine($"  {e.Size,9:N0}  {e.Name}");
}
 
// Extract everything into a folder.
Archive.Extract("7z2409-src.7z", "7zip-src");
int count = Directory.GetFiles("7zip-src", "*", SearchOption.AllDirectories).Length;
Console.WriteLine($"extracted {count} files to 7zip-src/");

1290 files, 9,933,274 bytes
      1,466  Asm/arm/7zCrcOpt.asm
      3,146  Asm/arm64/7zAsm.S
     37,757  Asm/arm64/LzmaDecOpt.S
      5,785  Asm/x86/7zAsm.asm
      6,711  Asm/x86/7zCrcOpt.asm
extracted 1290 files to 7zip-src/

Archive.Open recognizes the format from the bytes, not the file name, so the same code extracts zip, tar, tar.gz, tar.xz, cpio, ar, ISO and cab files. Extraction is safe by default: nothing is written outside the target folder, and limits on size, compression ratio and entry count are on (Extract untrusted archives safely).

A password-protected 7z

For a 7z encrypted with AES-256, pass the password when you open it:

using RecursiveAI.OneArchive;
 
using var archive = Archive.Open("secret.7z",
    new ArchiveOpenOptions { Password = "correct horse" });
archive.Extract("secret");

A missing or wrong password throws ArchivePasswordException, whose Problem says Required or Incorrect.

Limits

• No BCJ2 filter. 7-Zip applies BCJ2 to executables at its higher settings, and such archives (7-Zip’s own 7z2409-extra.7z is one) throw ArchiveUnsupportedException: “the coder with method ID 0x303011B (BCJ2) is not supported”. LZMA, LZMA2, PPMd, bzip2, Deflate and the BCJ, ARM and other single-stream filters are read.
• RAR is read-only and partial. RAR 5 archives can be listed, but only entries stored without compression can be extracted.
• Random access into a solid 7z is slow. Solid archives compress files together, so reading one entry with OpenEntry decodes the entries before it in its block; Extract, which reads in order, doesn’t pay that.
• .NET 10. The packages target net10.0.

To make an archive, see Create a zip file. Every format and option is in Archives and safety.