How to check if an assembly has changed

Question

is it possible to tell if an assembly has changed?

I have a standard project that generates an assembly called MyAssembly.dll.

In a separate project i read the assembly and generate a hash.

When i generate a hash for the assembly it is different each time i recompile. I have set the assembly version to be static, are there any other attributes that i need to change?

class Program
{
    static void Main(string[] args)
    {
        var array = File.ReadAllBytes(@"MyAssembly.dll");
        SHA256Managed algo = new SHA256Managed();
        var hash = algo.ComputeHash(array);

        Console.WriteLine(Convert.ToBase64String(hash));
    }
}

Thanks

Rohan

Answer 1

You are probably going to need to use the version number attribute. A hash will not work because any time you recompile an assembly, it's going to be different -- even if the code didn't change at all. The reason is that every time you compile, the compiler embeds a guid into the assembly, and it puts the same guid into the corresponding .pdb file. The guid will change every time the assembly is compiled.

This is how the debugger matches an assembly to the correct version of its .pdb file (it's also why you have to always save the .pdb's on anything you release, and you cannot rely upon being able to generate a pdb to match an existing assembly)

Answer 2

Every assembly has a ModuleVersionId GUID that works like a hash. If you change a single character, module id changes, but if you revert it you get the old id back. It's useful for comparing two versions of an assembly.

var assembly = Assembly.GetEntryAssembly();
var hashId = assembly.ManifestModule.ModuleVersionId;
Console.WriteLine(hashId);

40744db8-a8fe-4591-9b2c-d9e3e04a2f0a

https://docs.microsoft.com/en-us/dotnet/api/system.reflection.module.moduleversionid?view=net-5.0