/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Extensions.Loading
* File: AssemblyLoader.cs
*
* AssemblyLoader.cs is part of VNLib.Plugins.Extensions.Loading which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Extensions.Loading is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Plugins.Extensions.Loading is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.IO;
using System.Linq;
using System.Threading;
using System.Reflection;
using System.Runtime.Loader;
using System.Runtime.InteropServices;
using VNLib.Utils.IO;
using VNLib.Utils.Resources;
namespace VNLib.Plugins.Extensions.Loading
{
///
///
/// Represents a disposable assembly loader wrapper for
/// exporting a signle type from a loaded assembly
///
///
/// If the loaded type implements the
/// dispose method is called when the loader is disposed
///
///
/// The exported type to manage
public sealed class AssemblyLoader : OpenResourceHandle
{
private readonly CancellationTokenRegistration _reg;
private readonly Lazy _instance;
private readonly AssemblyLoadContext _loadContext;
private readonly AssemblyDependencyResolver _resolver;
private readonly string _assemblyPath;
///
/// The instance of the loaded type
///
public override T Resource => _instance.Value;
private AssemblyLoader(string assemblyPath, AssemblyLoadContext parentContext, CancellationToken unloadToken)
{
_loadContext = parentContext;
_resolver = new(assemblyPath);
_assemblyPath = assemblyPath;
//Add resolver for context
parentContext.Resolving += OnDependencyResolving;
parentContext.ResolvingUnmanagedDll += OnNativeLibraryResolving;
//Init lazy loader
_instance = new(LoadAndGetExportedType, LazyThreadSafetyMode.PublicationOnly);
//Register dispose
_reg = unloadToken.Register(Dispose);
}
/*
* Resolves a native libary isolated to the requested assembly, which
* should be isolated to this assembly or one of its dependencies.
*/
private IntPtr OnNativeLibraryResolving(Assembly assembly, string libname)
{
//Resolve the desired asm dependency for the current context
string? requestedDll = _resolver.ResolveUnmanagedDllToPath(libname);
//if the dep is resolved, seach in the assembly directory for the manageed dll only
return requestedDll == null ? IntPtr.Zero : NativeLibrary.Load(requestedDll, assembly, DllImportSearchPath.AssemblyDirectory);
}
private Assembly? OnDependencyResolving(AssemblyLoadContext context, AssemblyName asmName)
{
//Resolve the desired asm dependency for the current context
string? desiredAsm = _resolver.ResolveAssemblyToPath(asmName);
//If the asm exists in the dir, load it
return desiredAsm == null ? null : _loadContext.LoadFromAssemblyPath(desiredAsm);
}
///
/// Loads the default assembly and gets the expected export type,
/// creates a new instance, and calls its parameterless constructor
///
/// The desired type instance
///
private T LoadAndGetExportedType()
{
//Load the assembly into the parent context
Assembly asm = _loadContext.LoadFromAssemblyPath(_assemblyPath);
Type resourceType = typeof(T);
//See if the type is exported
Type exp = (from type in asm.GetExportedTypes()
where resourceType.IsAssignableFrom(type)
select type)
.FirstOrDefault()
?? throw new EntryPointNotFoundException($"Imported assembly does not export desired type {resourceType.FullName}");
//Create instance
return (T)Activator.CreateInstance(exp)!;
}
///
/// Creates a method delegate for the given method name from
/// the instance wrapped by the current loader
///
///
/// The name of the method to recover
/// The delegate method wrapper if found, null otherwise
///
///
public TDelegate? TryGetMethod(string methodName) where TDelegate : Delegate
{
//get the type info of the actual resource
return Resource!.GetType()
.GetMethod(methodName, BindingFlags.Public | BindingFlags.Instance)
?.CreateDelegate(Resource);
}
///
protected override void Free()
{
//Remove resolving event handlers
_loadContext.Resolving -= OnDependencyResolving;
_loadContext.ResolvingUnmanagedDll -= OnNativeLibraryResolving;
//If the instance is disposable, call its dispose method on unload
if (_instance.IsValueCreated && _instance.Value is IDisposable)
{
(_instance.Value as IDisposable)?.Dispose();
}
_reg.Dispose();
}
///
/// Creates a new loader for the desired assembly. The assembly and its dependencies
/// will be loaded into the parent context, meaning all loaded types belong to the
/// current which belongs the current plugin instance.
///
/// The name of the assmbly within the current plugin directory
/// The plugin unload token
///
internal static AssemblyLoader Load(string assemblyName, CancellationToken unloadToken)
{
//Make sure the file exists
if (!FileOperations.FileExists(assemblyName))
{
throw new FileNotFoundException($"The desired assembly {assemblyName} could not be found at the file path");
}
/*
* Dynamic assemblies are loaded directly to the exe assembly context.
* This should always be the plugin isolated context.
*/
Assembly executingAsm = Assembly.GetExecutingAssembly();
AssemblyLoadContext currentCtx = AssemblyLoadContext.GetLoadContext(executingAsm) ?? throw new InvalidOperationException("Could not get default assembly load context");
return new(assemblyName, currentCtx, unloadToken);
}
}
}