How to Resolve ILMerge Issues with Web Resources in ASP.NET

When working with an ASP.NET application, developers often face the challenge of merging multiple DLLs into a single executable file for easier deployment and version management. While the tool ILMerge is fantastic for this task, it can bring about unexpected issues with web resources.

In this blog post, we will explore the problem of 404 errors that occur with ClientScript.RegisterClientScriptResource after merging DLLs using ILMerge, and provide a step-by-step solution to rectify this issue.

Understanding the Problem

When you merge your DLLs using ILMerge, you might experience 404 errors when trying to access JavaScript resources that were working perfectly before the merge. This problem arises because the assembly attributes for web resources from different DLLs might not be properly retained in the merged assembly.

Example Scenario

Take for example a control defined as follows:

namespace Company.WebControls
{
  public class ControlA : CompositeControl, INamingContainer
  {
    protected override void OnPreRender(EventArgs e)
    {
        base.OnPreRender(e);
        this.Page.ClientScript.RegisterClientScriptResource(typeof(ControlA), "Company.WebControls.ControlA.js");                
    }      
  }
}

Here, ControlA.js is an embedded resource. In the AssemblyInfo.cs, it’s marked as:

[assembly: System.Web.UI.WebResource("Company.WebControls.ControlA.js", "application/x-javascript")]

After merging all required DLLs into CompanyA.dll, you find that accessing ControlA.js results in a 404 error.

The Solution

The key to resolving this issue lies in properly handling the assembly attributes during the merging process. Here’s how to do it:

Step 1: Create a Dummy Project

1. Set up a dummy project that references all the DLLs that contain web resources.
2. Include all web resources from the original projects into the AssemblyInfo.cs of this dummy project.

Step 2: Adjust Your AssemblyInfo.cs

Make sure your AssemblyInfo.cs in the dummy project looks something like this:

[assembly: System.Web.UI.WebResource("Company.WebControls.ControlA.js", "application/x-javascript")]
// Include additional resources as necessary from other projects

Step 3: Use ILMerge Command Correctly

Update your ILMerge command line as follows:

"C:\Program Files\Microsoft\ILMerge\ILMerge.exe" /keyfile:../../Company.snk /wildcards:True /out:Company.dll Company.Merge.dll Company.*.dll

This command should now merge the DLLs while ensuring the necessary web resource attributes are included.

Step 4: Testing the Merge

After executing the merge command with the updated structure, deploy your application and ensure that the JavaScript resources are accessible without any 404 errors. Test your web controls extensively to verify everything is functioning correctly.

Conclusion

Merging DLLs with ILMerge can simplify deployment but may introduce challenges with web resources in ASP.NET applications. By creating a dummy project to consolidate web resource attributes, you can ensure that your embedded JavaScript files are correctly loaded after the merge.

Implementing this solution will help ensure a seamless integration of your merged assemblies while maintaining access to crucial client-side resources.

If you encounter persistent issues, consider reviewing the documentation for ILMerge or seeking support from the community for more complex scenarios.

With this knowledge in hand, you can effectively navigate the tricky waters of DLL merging in ASP.NET, ensuring your applications perform as intended without frustration.