BepInEx/BepInEx.Preloader/Entrypoint.cs

using System;
using System.IO;
using System.Linq;
using System.Reflection;
using BepInEx.Preloader.RuntimeFixes;
using HarmonyXInterop;

namespace BepInEx.Preloader
{
	internal static class PreloaderRunner
	{
		// This is a list of important assemblies in BepInEx core folder that should be force-loaded
		// Some games can ship these assemblies in Managed folder, in which case assembly resolving bypasses our LocalResolve
		// On the other hand, renaming these assemblies is not viable because 3rd party assemblies
		// that we don't build (e.g. MonoMod, Harmony, many plugins) depend on them
		// As such, we load them early so that the game uses our version instead
		// These assemblies should be known to be rarely edited and are known to be shipped as-is with Unity assets
		private static readonly string[] CriticalAssemblies =
		{
			"Mono.Cecil.dll",
			"Mono.Cecil.Mdb.dll",
			"Mono.Cecil.Pdb.dll",
			"Mono.Cecil.Rocks.dll",
		};

		private static void LoadCriticalAssemblies()
		{
			foreach (string criticalAssembly in CriticalAssemblies)
			{
				try
				{
					Assembly.LoadFile(Path.Combine(Paths.BepInExAssemblyDirectory, criticalAssembly));
				}
				catch (Exception)
				{
					// Suppress error for now
					// TODO: Should we crash here if load fails? Can't use logging at this point
				}
			}
		}

		public static void PreloaderPreMain()
		{
			PlatformUtils.SetPlatform();

			string bepinPath = Utility.ParentDirectory(Path.GetFullPath(EnvVars.DOORSTOP_INVOKE_DLL_PATH), 2);

			Paths.SetExecutablePath(EnvVars.DOORSTOP_PROCESS_PATH, bepinPath, EnvVars.DOORSTOP_MANAGED_FOLDER_DIR, EnvVars.DOORSTOP_DLL_SEARCH_DIRS);

			LoadCriticalAssemblies();
			AppDomain.CurrentDomain.AssemblyResolve += LocalResolve;
			// Remove temporary resolver early so it won't override local resolver
			AppDomain.CurrentDomain.AssemblyResolve -= Entrypoint.ResolveCurrentDirectory;
			PreloaderMain();
		}

		private static void PreloaderMain()
		{
			if (Preloader.ConfigApplyRuntimePatches.Value)
			{
				XTermFix.Apply();
				ConsoleSetOutFix.Apply();
			}

			Preloader.Run();
		}

		private static Assembly LocalResolve(object sender, ResolveEventArgs args)
		{
			if (!Utility.TryParseAssemblyName(args.Name, out var assemblyName))
				return null;

			// Use parse assembly name on managed side because native GetName() can fail on some locales
			// if the game path has "exotic" characters
			var validAssemblies = AppDomain.CurrentDomain
										 .GetAssemblies()
										 .Select(a => new { assembly = a, name = Utility.TryParseAssemblyName(a.FullName, out var name) ? name : null })
										 .Where(a => a.name != null && a.name.Name == assemblyName.Name)
										 .OrderByDescending(a => a.name.Version)
										 .ToList();

			// First try to match by version, then just pick the best match (generally highest)
			// This should mainly affect cases where the game itself loads some assembly (like Mono.Cecil) 
			var foundMatch = validAssemblies.FirstOrDefault(a => a.name.Version == assemblyName.Version) ?? validAssemblies.FirstOrDefault();
			var foundAssembly = foundMatch?.assembly;

			if (foundAssembly != null)
				return foundAssembly;
			
			if (Utility.TryResolveDllAssembly(assemblyName, Paths.BepInExAssemblyDirectory, out foundAssembly)
				|| Utility.TryResolveDllAssembly(assemblyName, Paths.PatcherPluginPath, out foundAssembly)
				|| Utility.TryResolveDllAssembly(assemblyName, Paths.PluginPath, out foundAssembly))
				return foundAssembly;

			return null;
		}
	}

	internal static class Entrypoint
	{
		private static string preloaderPath;

		/// <summary>
		///     The main entrypoint of BepInEx, called from Doorstop.
		/// </summary>
		public static void Main()
		{
			// We set it to the current directory first as a fallback, but try to use the same location as the .exe file.
			string silentExceptionLog = $"preloader_{DateTime.Now:yyyyMMdd_HHmmss_fff}.log";

			try
			{
				EnvVars.LoadVars();

				string gamePath = Path.GetDirectoryName(EnvVars.DOORSTOP_PROCESS_PATH) ?? ".";
				silentExceptionLog = Path.Combine(gamePath, silentExceptionLog);

				// Get the path of this DLL via Doorstop env var because Assembly.Location mangles non-ASCII characters on some versions of Mono for unknown reasons
				preloaderPath = Path.GetDirectoryName(Path.GetFullPath(EnvVars.DOORSTOP_INVOKE_DLL_PATH));

				AppDomain.CurrentDomain.AssemblyResolve += ResolveCurrentDirectory;

				// In some versions of Unity 4, Mono tries to resolve BepInEx.dll prematurely because of the call to Paths.SetExecutablePath
				// To prevent that, we have to use reflection and a separate startup class so that we can install required assembly resolvers before the main code
				typeof(Entrypoint).Assembly.GetType($"BepInEx.Preloader.{nameof(PreloaderRunner)}")
								  ?.GetMethod(nameof(PreloaderRunner.PreloaderPreMain))
								  ?.Invoke(null, null);
			}
			catch (Exception ex)
			{
				File.WriteAllText(silentExceptionLog, ex.ToString());
			}
			finally
			{
				AppDomain.CurrentDomain.AssemblyResolve -= ResolveCurrentDirectory;
			}
		}

		internal static Assembly ResolveCurrentDirectory(object sender, ResolveEventArgs args)
		{
			// Can't use Utils here because it's not yet resolved
			var name = new AssemblyName(args.Name);

			try
			{
				return Assembly.LoadFile(Path.Combine(preloaderPath, $"{name.Name}.dll"));
			}
			catch (Exception)
			{
				return null;
			}
		}

	}
}