Creating method dynamically, and executing it

Question

Background:

I want to define few static methods in C# , and generate IL code as byte array, from one of these methods, selected at runtime (on client), and send the byte array over network to another machine (server) where it should be executed after re-generating the IL code from the byte array.

My Attempt: (POC)

public static class Experiment
{
    public static int Multiply(int a, int b)
    {
        Console.WriteLine("Arguments ({0}, {1})", a, b);
        return a * b;
    }
}

And then I get the IL code of the method body, as:

BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
MethodInfo meth = typeof(Experiment).GetMethod("Multiply", flags);
byte[] il = meth.GetMethodBody().GetILAsByteArray();

So far I didn't create anything dynamically. But I've IL code as byte array, and I want to create an assembly, then a module in it, then a type, then a method - all dynamically. When creating the method body of the dynamically created method, I use the IL code which I got using reflection in the above code.

The code-generation code is as follows:

AppDomain domain = AppDomain.CurrentDomain;
AssemblyName aname = new AssemblyName("MyDLL");
AssemblyBuilder assemBuilder = domain.DefineDynamicAssembly(
                                               aname, 
                                               AssemblyBuilderAccess.Run);

ModuleBuilder modBuilder = assemBuilder.DefineDynamicModule("MainModule");

TypeBuilder tb = modBuilder.DefineType("MyType", 
                            TypeAttributes.Public | TypeAttributes.Class);

MethodBuilder mb = tb.DefineMethod("MyMethod", 
     MethodAttributes.Static | MethodAttributes.Public, 
     CallingConventions.Standard,
     typeof(int),                          // Return type
     new[] { typeof(int), typeof(int) });  // Parameter types

mb.DefineParameter(1, ParameterAttributes.None, "value1");  // Assign name 
mb.DefineParameter(2, ParameterAttributes.None, "value2");  // Assign name 

//using the IL code to generate the method body
mb.CreateMethodBody(il, il.Count()); 

Type realType = tb.CreateType();

var meth = realType.GetMethod("MyMethod");
try
{
    object result = meth.Invoke(null, new object[] { 10, 9878 });
    Console.WriteLine(result);  //should print 98780 (i.e 10 * 9878)
}
catch (Exception e)
{
    Console.WriteLine(e.ToString());
}

But instead of printing 98780 on the output window, it throws an exception saying,

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.TypeLoadException: Could not load type 'Invalid_Token.0x0100001E' from assembly 'MyDLL, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.
     at MyType.MyMethod(Int32 value1, Int32 value2) [...]

Please help me figuring out the cause of the error, and how to fix it.

Answer 1

Run ildasm.exe on an arbitrary assembly. Use View + Show token values and look at some disassembled code. You'll see that the IL contains references to other methods and variables through a number. The number is an index into the metadata tables for an assembly.

Perhaps you now see the problem, you cannot transplant a chunk of IL from one assembly to another unless that target assembly has the same metadata. Or unless you replace the metadata token values in the IL with values that match the metadata of the target assembly. This is wildly impractical of course, you essentially end up duplicating the assembly. Might as well make a copy of the assembly. Or for that matter, might as well use the existing IL in the original assembly.

You need to think this through a bit, it is pretty unclear what you actually try to accomplish. The System.CodeDom and Reflection.Emit namespaces are available to dynamically generate code.