Program.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Security.Principal;

namespace TerrariaPatcher
{
    internal class Program
    {
        static readonly string TmpDir = "apitmp";
#if CLIENT
        static readonly string AssemblyName = "Terraria";
#elif SERVER
        static readonly string AssemblyName = "TerrariaServer";
#else
#error Invalid Defines
#endif

        private static void Main(string[] args)
        {
            try
            {
                if (Environment.OSVersion.Version.Major >= 6 && !IsAdministrator())
                {
                    Console.WriteLine("TerrariaPatcher requires admin privileges.");

                    var selfProc = new Process();
                    selfProc.StartInfo.FileName = Assembly.GetExecutingAssembly().Location;
                    selfProc.StartInfo.Verb = "runas";
                    selfProc.Start();
                    return;
                }

                if (!File.Exists(AssemblyName + ".exe"))
                {
                    Output(AssemblyName + ".exe not found");
                    Console.ReadLine();
                    return;
                }

                string md5;
                using (var fs = new FileStream(AssemblyName + ".exe", FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    md5 = MD5(fs);
                }

                string apitmp = Path.Combine(Environment.CurrentDirectory, "apitmp");

                Output("Downloading Patches Information");
                var patches = DownloadPatches();

                if (!patches.Contains(md5))
                {
                    Output(AssemblyName + " hash not found ({0})", md5);
                    Console.ReadLine();
                    return;
                }

                if (!Directory.Exists(TmpDir))
                    Directory.CreateDirectory(TmpDir);

                Output("Downloading Diff");
                string patch = DownloadPatch(md5);
                File.WriteAllText(Path.Combine(TmpDir, AssemblyName + ".diff"), patch);

                Output("Extracting Resources");
                File.WriteAllBytes(Path.Combine(TmpDir, "ildasm.exe"), Properties.Resources.ildasm);
                File.WriteAllBytes(Path.Combine(TmpDir, "IlDasmrc.dll"), Properties.Resources.IlDasmrc);
                File.WriteAllBytes(Path.Combine(TmpDir, "patch.exe"), Properties.Resources.patch);

                Output("Running IlDasm");
                var proc = new Process();
                proc.StartInfo.FileName = "apitmp/ildasm.exe";
                proc.StartInfo.Arguments = AssemblyName + ".exe /output:" + Path.Combine(TmpDir, AssemblyName + ".il");
                proc.StartInfo.UseShellExecute = false;
                proc.StartInfo.RedirectStandardOutput = true;
                proc.StartInfo.RedirectStandardError = true;
                proc.Start();
                proc.WaitForExit();
                Log(proc.StandardOutput.ReadToEnd());
                Log(proc.StandardError.ReadToEnd());

                Output("Running Patch");
                proc = new Process();
                proc.StartInfo.FileName = "apitmp/patch.exe";
                proc.StartInfo.Arguments = "-u -o New" + AssemblyName + ".il -i " + AssemblyName + ".diff";
                proc.StartInfo.WorkingDirectory = apitmp;
                proc.StartInfo.UseShellExecute = false;
                proc.StartInfo.RedirectStandardOutput = true;
                proc.StartInfo.RedirectStandardError = true;
                proc.Start();
                proc.WaitForExit();
                Log(proc.StandardOutput.ReadToEnd());
                Log(proc.StandardError.ReadToEnd());

                if (File.Exists(Path.Combine(apitmp, "New" + AssemblyName + ".il.rej")))
                    Log("\n\n[[{0}]]\n\n", File.ReadAllText(Path.Combine(apitmp, "New" + AssemblyName + ".il.rej")));

                Output("Running Ilasm");
                proc = new Process();
                proc.StartInfo.FileName = Path.Combine(RuntimeEnvironment.GetRuntimeDirectory(), "ilasm.exe");
                proc.StartInfo.Arguments = "New" + AssemblyName + ".il /quiet /output=" + AssemblyName + ".exe /res=" + AssemblyName + ".res";
                proc.StartInfo.WorkingDirectory = apitmp;
                proc.StartInfo.UseShellExecute = false;
                proc.StartInfo.RedirectStandardOutput = true;
                proc.StartInfo.RedirectStandardError = true;
                proc.Start();
                proc.WaitForExit();
                Log(proc.StandardOutput.ReadToEnd());
                Log(proc.StandardError.ReadToEnd());

                Output("Finishing");
                if (File.Exists(Path.Combine(TmpDir, AssemblyName+".exe")))
                {
                    File.Copy(Path.Combine(TmpDir, AssemblyName + ".exe"), AssemblyName + "API.exe", true);
                    Output("Success");
                }
                else
                {
                    Output("Failed");
                }
            }
            catch (Exception ex)
            {
                Log(ex.ToString());
                Output("Exception: " + ex);
            }
            finally
            {
                if (Directory.Exists(TmpDir))
                    Directory.Delete(TmpDir, true);
            }

            Console.ReadLine();
        }

        public static bool IsAdministrator()
        {
            var identity = WindowsIdentity.GetCurrent();
            var principal = new WindowsPrincipal(identity);
            return principal.IsInRole(WindowsBuiltInRole.Administrator);
        }

        private static void Output(string str)
        {
            if (str.Length < 1)
                return;
            Console.WriteLine(str);
            Log(str);
        }

        private static void Output(string str, params object[] objs)
        {
            Output(string.Format(str, objs));
        }

        private static void Log(string str)
        {
            if (str.Length < 1)
                return;
            File.AppendAllText("patchlog.txt", str + "\n");
        }

        private static void Log(string str, params object[] objs)
        {
            Log(string.Format(str, objs));
        }

        private static List<string> DownloadPatches()
        {
            var ret = new List<string>();

            string patches = new WebClient().DownloadString("http://dl.dropbox.com/u/29760911/" + AssemblyName + "Api/patches.txt");
            var ps = patches.Split('\n', '\r');
            foreach (var p in ps)
            {
                var kv = p.Split('|');
                if (kv.Length != 2)
                    continue;

                ret.Add(kv[1]);
            }
            return ret;
        }

        private static string DownloadPatch(string md5)
        {
            return new WebClient().DownloadString("http://dl.dropbox.com/u/29760911/" + AssemblyName + "Api/" + AssemblyName + "_" + md5 + ".diff");
        }

        private static string MD5(Stream stream)
        {
            using (var sha = MD5CryptoServiceProvider.Create())
            {
                var bytes = sha.ComputeHash(stream);
                return bytes.Aggregate("", (s, b) => s + b.ToString("X2"));
            }
        }
    }
}