How to decompress a Fody.Costura packed assembly

Question

A friend of mine gave me the challenge to decompress an assembly that was packed with Fody.Costura. The assembly has a dll dependency that was embedded as a resource. I tried to extract this .zip resource with dotPeek and decompress it with this code here

public static void Decompress(string path)
{
    using (var stream = File.OpenRead(path))
    using (var compressStream = new DeflateStream(stream, CompressionMode.Decompress))
    {
        compressStream.Seek(0, SeekOrigin.Begin);
        var fs = File.Create(path + ".decompressed");
        compressStream.CopyTo(fs);
        fs.Close();
    }
}

This works when it comes to extracting the .zip but the result is quite unuseful

Is there a suitable solution to decompress this packed dll?

The .text file might contain the code but it is not readable, it's a binary file — Christian Klemm, May 15 '17 at 14:30
Did you expect to find source code in there? After unzipping, you'd still need to decompile the code. — C.Evenhuis, May 15 '17 at 14:33
I didn't expected to find source code in there. My question aims at the process of decompiling the code itself. — Christian Klemm, May 15 '17 at 14:33
Have you tried manually unzipping it using your favorite unzip tool? — C.Evenhuis, May 15 '17 at 14:40
"Didn't works" - error message? password required? malformed output? 7-Zip crashed? We can't see what you're seeing :) — C.Evenhuis, May 15 '17 at 14:43
At this question they have the extraction bit working: http://stackoverflow.com/questions/39368405/mef-get-assembly-from-embedded-dll — C.Evenhuis, May 15 '17 at 14:47
Your code is fine. The assembly should have a name and end with `.dll` instead of `.dll.zip.decompressed`. I'm not sure what you're expecting. — Cameron MacFarland, May 15 '17 at 17:39
@CameronMacFarland wow, you're right! I expected that the reference is a zip that has to be unpacked. — Christian Klemm, May 15 '17 at 17:41
Well you'd be partly right. I needed to called the compressed resource something, so I used `zip` but it's not actually a zip, and I never expected people to want to extract the resources themselves. — Cameron MacFarland, May 15 '17 at 17:51
Ahh I see, you're one of the devs of Costura. Well sometimes you have no other option (somebody passing you the binary of an unknown assembly that was packed with Costura and you shall have a look over it). — Christian Klemm, May 15 '17 at 17:54

score 2 · Answer 1 · answered Oct 03 '19 at 16:38

2

To decompress those resources there is this project to.

answered Oct 03 '19 at 16:38

Fábio Augusto Pandolfo

105
6

score 2 · Answer 2 · answered Jan 03 '20 at 17:05

This is my simple C# Console App code (Framework 4), which I`m using simply by "drag and drop" (Costura Compressed) files over compiled (ConsoleApp1) executable.

using System;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Text.RegularExpressions;

namespace ConsoleApp1
{
  class Program
  {
    static void CopyTo(Stream source, Stream destination) {
      int count;
      var array = new byte[81920];
      while ((count = source.Read(array, 0, array.Length)) != 0) {
        destination.Write(array, 0, count);
      }
    }

    static Stream LoadStream(string fullname) {
      FileStream stream = default(FileStream);
      if (fullname.EndsWith(".zip")) {
        using (stream = new FileStream(fullname, FileMode.Open)) {
          using (var compressStream = new DeflateStream(stream, CompressionMode.Decompress)) {
            var memStream = new MemoryStream();
            CopyTo(compressStream, memStream);
            memStream.Position = 0;
            return memStream;
          }
        }
      }
      return stream;
    }

    static void Main(string[] args) {
      Stream stream; Stream file;
      string RefilePath = @"^.+[^\\]+\\"; string fullname; string newFile;
      for (int i = 0; i < args.Count(); i++) {
        fullname = args[i];
        newFile = Regex.Replace(fullname, "\\.zip$", string.Empty);
        Console.Write("{0} -> {1}\r\n",
          Regex.Replace(fullname, RefilePath, string.Empty),
          Regex.Replace(newFile, RefilePath, string.Empty));
        try
        {
          stream = LoadStream(fullname);
          using (file = File.Create(newFile)) {
            CopyTo(stream, file);
          }
        }
        catch (Exception ex) {
          Console.Write("{0}", ex.ToString());
        }
      }
    }
  }
}

Based On Cameron MacFarland Answer

score 1 · Accepted Answer · answered May 15 '17 at 18:01

The code that Costura uses to decompress those resources is here.

https://github.com/Fody/Costura/blob/master/src/Costura.Template/Common.cs

static void CopyTo(Stream source, Stream destination)
{
    var array = new byte[81920];
    int count;
    while ((count = source.Read(array, 0, array.Length)) != 0)
    {
        destination.Write(array, 0, count);
    }
}

static Stream LoadStream(string fullname)
{
    var executingAssembly = Assembly.GetExecutingAssembly();

    if (fullname.EndsWith(".zip"))
    {
        using (var stream = executingAssembly.GetManifestResourceStream(fullname))
        using (var compressStream = new DeflateStream(stream, CompressionMode.Decompress))
        {
            var memStream = new MemoryStream();
            CopyTo(compressStream, memStream);
            memStream.Position = 0;
            return memStream;
        }
    }

    return executingAssembly.GetManifestResourceStream(fullname);
}

Just a small question regarding the source: why a own CopyTo method? Has this a specific manner or is this code from times before it was implemented into the standard libraries? — Christian Klemm, May 15 '17 at 18:17
Costura supports .net 2, which yes doesn't have a native CopyTo method. — Cameron MacFarland, May 15 '17 at 18:22
To be clear, this code is copied into the assembly being modified, so it's .net 2 compatible. — Cameron MacFarland, May 15 '17 at 18:22

How to decompress a Fody.Costura packed assembly

3 Answers3