Reading a custom attribute from an assembly without loading it for execution.

ManifestReader.cs

// 
//  Author: John Carruthers (johnc@frag-labs.com)
// 
//  Copyright (C) 2014 John Carruthers
// 
//  Permission is hereby granted, free of charge, to any person obtaining
//  a copy of this software and associated documentation files (the
//  "Software"), to deal in the Software without restriction, including
//  without limitation the rights to use, copy, modify, merge, publish,
//  distribute, sublicense, and/or sell copies of the Software, and to
//  permit persons to whom the Software is furnished to do so, subject to
//  the following conditions:
//   
//  The above copyright notice and this permission notice shall be
//  included in all copies or substantial portions of the Software.
//   
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
//  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
//  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
//  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
//  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
// 

using System;
using System.IO;
using System.Linq;
using AdjutantFramework.Plugins.Domains;
using IKVM.Reflection;
using Assembly = System.Reflection.Assembly;

namespace AdjutantFramework.Plugins.Assemblies
{
	/// <summary>
	/// Reads plugin manifests from assemblies without loading them.
	/// </summary>
	public class ManifestReader : DomainShareObject
	{
		public string AssemblyFileName { get; private set; }

		public ManifestReader(string assemblyFileName)
		{
			AssemblyFileName = assemblyFileName;
			if (assemblyFileName == null) throw new ArgumentNullException("assemblyFileName");
		}

		/// <summary>
		/// Reads the plugin manifest from the assembly.
		/// </summary>
		/// <returns></returns>
		public PluginManifestAttribute ReadManifestAttribute()
		{
			if (File.Exists(AssemblyFileName))
			{
				var universe = new Universe();
				universe.AssemblyResolve += (sender, args) =>
				{
					return null;
				};

				var mscorlib = universe.LoadFile(typeof(Assembly).Assembly.Location);
				//  todo: use the assembly resolver here instead of hard coded path.
				var apiAsm = universe.LoadFile(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Framework.dll"));
				var ikvmManifestType = apiAsm.GetType(typeof(PluginManifestAttribute).FullName);
				var ikvmAsm = universe.LoadFile(AssemblyFileName);
				var attrs = ikvmAsm.__GetCustomAttributes(ikvmManifestType, false).FirstOrDefault();

				if (attrs == null)
					return null;

				var pluginName = attrs.ConstructorArguments[0].Value as string;
				var pluginId = attrs.ConstructorArguments[1].Value as string;
				var pluginVersion = attrs.ConstructorArguments[2].Value as string;
				var author = attrs.ConstructorArguments[3].Value as string;
				var websiteUrl = attrs.ConstructorArguments[4].Value as string;
				var emailAddress = attrs.ConstructorArguments[5].Value as string;
				var copyright = attrs.ConstructorArguments[6].Value as string;

				universe.Dispose();

				return new PluginManifestAttribute(pluginName, pluginId, pluginVersion, author,
					websiteUrl, emailAddress, copyright);
			}

			return null;
		}
	}
}