Tutorial 2: Instruction and Method Manipulation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace Tutorial2Code
{
    class Program
    {
        static void Main(string[] args)
        {
            // Loads the assembly from the start arguments
            AssemblyDefinition asm = AssemblyDefinition.ReadAssembly(args[0]);

            // Iterates through the assembly's modules, aspects of the program
            foreach (ModuleDefinition mod in asm.Modules)
            {
                // Iterates through the classes of the assembly
                foreach (TypeDefinition td in mod.Types)
                {
                    // Writes the types name,
                    DoType(td);
                }
            }
            asm.Write(@"C:\Tut\out.exe");
            Console.ReadLine();
        }
        static void DoType(TypeDefinition td)
        {
            foreach (TypeDefinition ntd in td.NestedTypes)
            {
                // Repeat if the class has nested classes.
                DoType(ntd);
            }
            foreach (MethodDefinition md in td.Methods)
            {
                // First check if it an important method, like a constructor or runtime special name which will crash our app if renamed
                if (!md.IsRuntimeSpecialName && !md.IsRuntime)
                {
                    // Create a random name from a random number
                    md.Name = new Random().Next(5, 50000).ToString();

                    // Very Important, Make sure the method has a body!
                    if (md.HasBody)
                    {
                        // Iterate through the methods instructions
                        for (int i = 0; i < md.Body.Instructions.Count; i++)
                        {
                            // Make it easier to call the instruction by creating an instance of it
                            Instruction inst = md.Body.Instructions[i];

                            // Lets see what the instruction is about?
                            Log(inst.ToString());

                            // If the opcode is ldstr, load string to stack
                            if (inst.OpCode == OpCodes.Ldstr)
                            {
                                // Change the value of the string to something funny!
                                inst.Operand = "Hello World";
                            }
                        }
                    }
                }
            }
        }
        static void Log(string text)
        {
            Console.WriteLine(text);
        }
    }
}