How do I ZIP a file in C#, using no 3rd-party APIs?

How can I programatically (C#) ZIP a file (in Windows) without using any third party libraries?

If using the 4.5+ Framework, there is now the ZipArchive and ZipFile classes.

using (ZipArchive zip = ZipFile.Open("test.zip", ZipArchiveMode.Create))
{
    zip.CreateEntryFromFile(@"c:\something.txt", "data/path/something.txt");
}

You need to add references to:

• System.IO.Compression
• System.IO.Compression.FileSystem

For .NET Core targeting net46, you need to add dependencies for

• System.IO.Compression
• System.IO.Compression.ZipFile

Example project.json:

"dependencies": {
  "System.IO.Compression": "4.1.0",
  "System.IO.Compression.ZipFile": "4.0.1"
},

"frameworks": {
  "net46": {}
}

For .NET Core 2.0, just adding a simple using statement is all that is needed:

• using System.IO.Compression;

Are you using .NET 3.5? You could use the ZipPackage class and related classes. Its more than just zipping up a file list because it wants a MIME type for each file you add. It might do what you want.

I'm currently using these classes for a similar problem to archive several related files into a single file for download. We use a file extension to associate the download file with our desktop app. One small problem we ran into was that its not possible to just use a third-party tool like 7-zip to create the zip files because the client side code can't open it -- ZipPackage adds a hidden file describing the content type of each component file and cannot open a zip file if that content type file is missing.

Add these 4 functions to your project:

        public const long BUFFER_SIZE = 4096;
    public static void AddFileToZip(string zipFilename, string fileToAdd)
    {
        using (Package zip = global::System.IO.Packaging.Package.Open(zipFilename, FileMode.OpenOrCreate))
        {
            string destFilename = ".\\" + Path.GetFileName(fileToAdd);
            Uri uri = PackUriHelper.CreatePartUri(new Uri(destFilename, UriKind.Relative));
            if (zip.PartExists(uri))
            {
                zip.DeletePart(uri);
            }
            PackagePart part = zip.CreatePart(uri, "", CompressionOption.Normal);
            using (FileStream fileStream = new FileStream(fileToAdd, FileMode.Open, FileAccess.Read))
            {
                using (Stream dest = part.GetStream())
                {
                    CopyStream(fileStream, dest);
                }
            }
        }
    }
    public static void CopyStream(global::System.IO.FileStream inputStream, global::System.IO.Stream outputStream)
    {
        long bufferSize = inputStream.Length < BUFFER_SIZE ? inputStream.Length : BUFFER_SIZE;
        byte[] buffer = new byte[bufferSize];
        int bytesRead = 0;
        long bytesWritten = 0;
        while ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) != 0)
        {
            outputStream.Write(buffer, 0, bytesRead);
            bytesWritten += bytesRead;
        }
    }
    public static void RemoveFileFromZip(string zipFilename, string fileToRemove)
    {
        using (Package zip = global::System.IO.Packaging.Package.Open(zipFilename, FileMode.OpenOrCreate))
        {
            string destFilename = ".\\" + fileToRemove;
            Uri uri = PackUriHelper.CreatePartUri(new Uri(destFilename, UriKind.Relative));
            if (zip.PartExists(uri))
            {
                zip.DeletePart(uri);
            }
        }
    }
    public static void Remove_Content_Types_FromZip(string zipFileName)
    {
        string contents;
        using (ZipFile zipFile = new ZipFile(File.Open(zipFileName, FileMode.Open)))
        {
            /*
            ZipEntry startPartEntry = zipFile.GetEntry("[Content_Types].xml");
            using (StreamReader reader = new StreamReader(zipFile.GetInputStream(startPartEntry)))
            {
                contents = reader.ReadToEnd();
            }
            XElement contentTypes = XElement.Parse(contents);
            XNamespace xs = contentTypes.GetDefaultNamespace();
            XElement newDefExt = new XElement(xs + "Default", new XAttribute("Extension", "sab"), new XAttribute("ContentType", @"application/binary; modeler=Acis; version=18.0.2application/binary; modeler=Acis; version=18.0.2"));
            contentTypes.Add(newDefExt);
            contentTypes.Save("[Content_Types].xml");
            zipFile.BeginUpdate();
            zipFile.Add("[Content_Types].xml");
            zipFile.CommitUpdate();
            File.Delete("[Content_Types].xml");
            */
            zipFile.BeginUpdate();
            try
            {
                zipFile.Delete("[Content_Types].xml");
                zipFile.CommitUpdate();
            }
            catch{}
        }
    }

And use them like this:

foreach (string f in UnitZipList)
{
    AddFileToZip(zipFile, f);
    System.IO.File.Delete(f);
}
Remove_Content_Types_FromZip(zipFile);

There is now an officially documented section in the dotnet docs on how to compress and decompress without third-party libraries. It includes full code samples too!

https://docs.microsoft.com/en-us/dotnet/standard/io/how-to-compress-and-extract-files

Looks like Windows might just let you do this...

Unfortunately I don't think you're going to get around starting a separate process unless you go to a third party component.