Get the kind of assembly using System.Reflection.Metadata

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Threading.Tasks;

using System.Reflection;
using System.Reflection.Emit;
using System.Reflection.Metadata;
using System.Reflection.PortableExecutable;

namespace SoCSharp
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                foreach (PEFileKinds kind in Enum.GetValues(typeof(PEFileKinds)))
                {
                    var program = new Program(kind);
                    program.WriteWithSREmit();
                    program.ReadWithSRMetadata();

                    Console.WriteLine();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex);
            }
        }

        private readonly PEFileKinds peFileKind;
        private readonly string filename, extension, filenameAndExtension;

        private Program(PEFileKinds kind)
        {
            switch (kind)
            {
                case PEFileKinds.Dll:
                    filename = "Library";
                    extension = ".dll";
                    break;
                case PEFileKinds.ConsoleApplication:
                    filename = "ConsoleApp";
                    extension = ".exe";
                    break;
                case PEFileKinds.WindowApplication:
                    filename = "WindowsApp";
                    extension = ".exe";
                    break;
                default:
                    throw new NotImplementedException();
            }

            peFileKind = kind;
            filenameAndExtension = filename + extension;
        }

        private void WriteWithSREmit()
        {
            Console.WriteLine($"Writing {filenameAndExtension} with System.Reflection.Emit");
            Console.WriteLine($"  Kind: {peFileKind}");

            var asmName = new AssemblyName(filename);
            var asm = AssemblyBuilder.DefineDynamicAssembly(asmName, AssemblyBuilderAccess.Save);
            var mod = asm.DefineDynamicModule(filenameAndExtension);

            var type = mod.DefineType("MyType", TypeAttributes.Public);

            var method = type.DefineMethod("EntryPoint", MethodAttributes.Public | MethodAttributes.Static);
            var methodIL = method.GetILGenerator();
            methodIL.Emit(OpCodes.Ret);

            type.CreateType();
            asm.SetEntryPoint(method, peFileKind);
            
            asm.Save(filenameAndExtension, PortableExecutableKinds.ILOnly, ImageFileMachine.I386);
        }
        
        private void ReadWithSRMetadata()
        {
            using (var stream = File.OpenRead(filenameAndExtension))
            {
                using (var peFile = new PEReader(stream))
                {
                    var headers = peFile.PEHeaders;
                    Console.WriteLine($"Reading {filenameAndExtension} with System.Reflection.Metadata");
                    Console.WriteLine($"  IsDll: {headers.IsDll}");
                    Console.WriteLine($"  IsExe: {headers.IsExe}");
                    Console.WriteLine($"  IsConsoleApplication: {headers.IsConsoleApplication}");

                    PEFileKinds reverseEngineeredKind;

                    // NOTE: the header values cause IsConsoleApplication to return
                    //       true for DLLs, so we need to check IsDll first
                    if (headers.IsDll)
                    {
                        reverseEngineeredKind = PEFileKinds.Dll;
                    }
                    else if (headers.IsConsoleApplication)
                    {
                        reverseEngineeredKind = PEFileKinds.ConsoleApplication;
                    }
                    else
                    {
                        reverseEngineeredKind = PEFileKinds.WindowApplication;
                    }
                    Console.WriteLine($"  Reverse-engineered kind: {reverseEngineeredKind}");
                }
            }
        }
    }
}