How Can I Successfully Embed and Use an Unmanaged DLL within a Managed C# DLL?

Embedding Unmanaged DLLs into Managed C# DLLs

Embedding unmanaged DLLs within managed DLLs is a useful technique to consolidate and protect dependencies. However, it can be challenging to achieve.

Issue:

When attempting to embed an unmanaged DLL into a managed DLL using DllImport, you encounter an access denied error.

Explanation:

To embed an unmanaged DLL as a resource, you need to take additional steps beyond simply adding it as an embedded resource in the project.

Solution:

To successfully embed and use an unmanaged DLL in a managed DLL:

1. Extract and Load the Embedded DLL:

   • Extract the unmanaged DLL from the embedded resource stream to a temporary directory.
   • Explicitly load the extracted DLL using LoadLibrary before using DllImport.

2. Use a Unique Temporary Directory:

   • Create a unique temporary directory for each version of your assembly to avoid version conflicts.

3. Handle File Copying Exceptions:

   • Handle exceptions when attempting to copy the embedded DLL to the temporary directory. You may be able to ignore the exception if the file already exists in the directory.

Example Code:

The following code snippet demonstrates the embedding process:

// Get a unique temporary directory for this assembly version
string dirName = Path.Combine(Path.GetTempPath(), "MyAssembly." +
  Assembly.GetExecutingAssembly().GetName().Version.ToString());
if (!Directory.Exists(dirName))
  Directory.CreateDirectory(dirName);
string dllPath = Path.Combine(dirName, "MyAssembly.Unmanaged.dll");

// Extract the embedded DLL to the temporary location
using (Stream stm = Assembly.GetExecutingAssembly().GetManifestResourceStream(
  "MyAssembly.Properties.MyAssembly.Unmanaged.dll"))
{
  using (Stream outFile = File.Create(dllPath))
  {
    CopyBytes(stm, outFile);
  }
}

// Load the extracted DLL explicitly
IntPtr h = LoadLibrary(dllPath);
Debug.Assert(h != IntPtr.Zero, "Unable to load library " + dllPath);

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