Creating a ZIP Archive in Memory Using System.IO.C

Question

I'm trying to create a ZIP archive with a simple demo text file using a MemoryStream as follows:

using (var memoryStream = new MemoryStream())
using (var archive = new ZipArchive(memoryStream , ZipArchiveMode.Create))
{
    var demoFile = archive.CreateEntry("foo.txt");

    using (var entryStream = demoFile.Open())
    using (var streamWriter = new StreamWriter(entryStream))
    {
        streamWriter.Write("Bar!");
    }

    using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
    {
        stream.CopyTo(fileStream);
    }
}

If I run this code, the archive file itself is created but foo.txt isn't.

However, if I replace the MemoryStream directly with the file stream, the archive is created correctly:

using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
using (var archive = new ZipArchive(fileStream, FileMode.Create))
{
    // ...
}

Is it possible to use a MemoryStream to create the ZIP archive without the FileStream?

Answer 1

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

namespace ConsoleApplication
{
    class Program`enter code here`
    {
        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("========================");
                    }
                }
            }
        }
    }
}

Answer 2

You need to finish writing the memory stream then read the buffer back.

        using (var memoryStream = new MemoryStream())
        {
            using (var archive = new ZipArchive(memoryStream, ZipArchiveMode.Create))
            {
                var demoFile = archive.CreateEntry("foo.txt");

                using (var entryStream = demoFile.Open())
                using (var streamWriter = new StreamWriter(entryStream))
                {
                    streamWriter.Write("Bar!");
                }
            }

            using (var fileStream = new FileStream(@"C:\Temp\test.zip", FileMode.Create))
            {
                var bytes = memoryStream.GetBuffer();
                fileStream.Write(bytes,0,bytes.Length );
            }
        }