bepin/BepInEx/Bootstrap/AssemblyPatcher.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using Harmony;
using Mono.Cecil;

namespace BepInEx.Bootstrap
{
    /// <summary>
    /// Delegate used in patching assemblies.
    /// </summary>
    /// <param name="assembly">The assembly that is being patched.</param>
    public delegate void AssemblyPatcherDelegate(ref AssemblyDefinition assembly);

    /// <summary>
    /// Worker class which is used for loading and patching entire folders of assemblies, or alternatively patching and loading assemblies one at a time.
    /// </summary>
    public static class AssemblyPatcher
    {
        /// <summary>
        /// Configuration value of whether assembly dumping is enabled or not.
        /// </summary>
        private static bool DumpingEnabled => Utility.SafeParseBool(Config.GetEntry("dump-assemblies", "false", "Preloader"));

        /// <summary>
        /// Patches and loads an entire directory of assemblies.
        /// </summary>
        /// <param name="directory">The directory to load assemblies from.</param>
        /// <param name="patcherMethodDictionary">The dictionary of patchers and their targeted assembly filenames which they are patching.</param>
        /// <param name="initializers">List of initializers to run before any patching starts</param>
        /// <param name="finalizers">List of finalizers to run before returning</param>
        public static void PatchAll(string directory, IDictionary<AssemblyPatcherDelegate, IEnumerable<string>> patcherMethodDictionary, IEnumerable<Action> initializers = null, IEnumerable<Action> finalizers = null)
        {
            //run all initializers
            if (initializers != null)
                foreach (Action init in initializers)
                    init.Invoke();

            //load all the requested assemblies
            Dictionary<string, AssemblyDefinition> assemblies = new Dictionary<string, AssemblyDefinition>();

            foreach (string assemblyPath in Directory.GetFiles(directory, "*.dll"))
            {
                var assembly = AssemblyDefinition.ReadAssembly(assemblyPath);

                //NOTE: this is special cased here because the dependency handling for System.dll is a bit wonky
                //System has an assembly reference to itself, and it also has a reference to Mono.Security causing a circular dependency
                //It's also generally dangerous to change system.dll since so many things rely on it, 
                // and it's already loaded into the appdomain since this loader references it, so we might as well skip it
                if (assembly.Name.Name == "System"
                    || assembly.Name.Name == "mscorlib") //mscorlib is already loaded into the appdomain so it can't be patched
                {
                    assembly.Dispose();
                    continue;
                }

                assemblies.Add(Path.GetFileName(assemblyPath), assembly);
                PatchedAssemblyResolver.AssemblyLocations.Add(assembly.FullName, Path.GetFullPath(assemblyPath));
            }

            HashSet<string> patchedAssemblies = new HashSet<string>();

            //call the patchers on the assemblies
            foreach (var patcherMethod in patcherMethodDictionary)
            {
                foreach (string assemblyFilename in patcherMethod.Value)
                {
                    if (assemblies.TryGetValue(assemblyFilename, out var assembly))
                    {
                        Patch(ref assembly, patcherMethod.Key);
                        assemblies[assemblyFilename] = assembly;
                        patchedAssemblies.Add(assemblyFilename);
                    }
                }
            }

            // Finally, load all assemblies into memory
            foreach (var kv in assemblies)
            {
                string filename = kv.Key;
                var assembly = kv.Value;

                if (DumpingEnabled && patchedAssemblies.Contains(filename))
                {
                    using (MemoryStream mem = new MemoryStream())
                    {
                        string dirPath = Path.Combine(Paths.PluginPath, "DumpedAssemblies");

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

                        assembly.Write(mem);
                        File.WriteAllBytes(Path.Combine(dirPath, filename), mem.ToArray());
                    }
                }

                Load(assembly);
                assembly.Dispose();
            }

            // Patch Assembly.Location and Assembly.CodeBase only if the assemblies were loaded from memory
            PatchedAssemblyResolver.ApplyPatch();

            //run all finalizers
            if (finalizers != null)
                foreach (Action finalizer in finalizers)
                    finalizer.Invoke();
        }

        /// <summary>
        /// Patches an individual assembly, without loading it.
        /// </summary>
        /// <param name="assembly">The assembly definition to apply the patch to.</param>
        /// <param name="patcherMethod">The patcher to use to patch the assembly definition.</param>
        public static void Patch(ref AssemblyDefinition assembly, AssemblyPatcherDelegate patcherMethod)
        {
            patcherMethod.Invoke(ref assembly);
        }

        /// <summary>
        /// Loads an individual assembly defintion into the CLR.
        /// </summary>
        /// <param name="assembly">The assembly to load.</param>
        public static void Load(AssemblyDefinition assembly)
        {
            using (MemoryStream assemblyStream = new MemoryStream())
            {
                assembly.Write(assemblyStream);
                Assembly.Load(assemblyStream.ToArray());
            }
        }
    }

    internal static class PatchedAssemblyResolver
    {
        public static Dictionary<string, string> AssemblyLocations { get; } = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase);

        public static void ApplyPatch()
        {
            HarmonyInstance.Create("com.bepis.bepinex.asmlocationfix").PatchAll(typeof(PatchedAssemblyResolver));
        }

        [HarmonyPatch(typeof(Assembly))]
        [HarmonyPatch(nameof(Assembly.Location), PropertyMethod.Getter)]
        [HarmonyPostfix]
        public static void GetLocation(ref string __result, Assembly __instance)
        {
            if (AssemblyLocations.TryGetValue(__instance.FullName, out string location))
                __result = location;
        }

        [HarmonyPatch(typeof(Assembly))]
        [HarmonyPatch(nameof(Assembly.CodeBase), PropertyMethod.Getter)]
        [HarmonyPostfix]
        public static void GetCodeBase(ref string __result, Assembly __instance)
        {
            if (AssemblyLocations.TryGetValue(__instance.FullName, out string location))
                __result = $"file://{location.Replace('\\', '/')}";
        }
    }
}