source: branches/WebApplication/MVC2/HLWebPluginHost/PluginLib/AssemblyResourceProvider.cs @ 4606

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Reflection;
using System.IO;
using System.Web.Hosting;
using System.Web.Caching;
using System.Collections;
using System.Diagnostics;

namespace HLWebPluginHost.PluginLib {

  /// <summary>
  /// The VirtualPathProvider class provides developers a way to intercept the calls MVC makes to 
  /// retrieve files from the filesystem and provide these files. In our case we look at the plugins 
  /// directory to find out if it provides the requested ressource. 
  /// In this case the data is pulled out of the plugin and returned if it was a file.
  /// In Fact this class provides parts of the routing and dispatching mechanism known from other mvc frameworks.
  /// </summary>
  public class AssemblyResourceProvider : System.Web.Hosting.VirtualPathProvider {

    /// <summary>
    /// FileExists() is called by the framework to check for the existence of a physical file. 
    /// We want to override the method so we can check for the “~/Plugins/” string in our path. 
    /// If we find it, then we use reflection to determine if we have an embedded view in the targeted assembly that matches the requested file name.  
    /// An example of a parameter that would be passed into this method would be “~/Plugins/FzySqrPlugin.dll/FzySqrPlugin.Views.HelloWorld.Index.aspx”.  
    /// Given this path for a view, this code would load the FzySqrPlugin.dll and look for a resource with named FzySqrPlugin.Views.HelloWorld.Index.aspx.
    /// If the”~/Plugins/” string is not found, then the super class’s FileExist() method is called and the normal behavior takes place.  
    /// </summary>
    /// <param name="virtualPath"></param>
    /// <returns></returns>
    public override bool FileExists(string virtualPath) {

      if (IsAppResourcePath(virtualPath)) {
        string path = VirtualPathUtility.ToAppRelative(virtualPath);
        string[] parts = path.Split('/');
        string assemblyName = parts[2];
        string resourceName = parts[3];

        assemblyName = Path.Combine(HttpRuntime.BinDirectory, assemblyName);
        byte[] assemblyBytes = File.ReadAllBytes(assemblyName);
        Assembly assembly = Assembly.Load(assemblyBytes);

        if (assembly != null) {
          string[] resourceList = assembly.GetManifestResourceNames();
          bool found = Array.Exists(resourceList, delegate(string r) { return r.Equals(resourceName); });

          return found;
        }
        return false;
      } else
        return base.FileExists(virtualPath);
    }

    /// <summary>
    /// If we have a plugin path, then return our custom AssemblyResourceVirtualFile type, 
    /// otherwise provide the standard behavior.
    /// </summary>
    /// <param name="virtualPath"></param>
    /// <returns></returns>
    public override VirtualFile GetFile(string virtualPath) {

      if (IsAppResourcePath(virtualPath)) {
        return new AssemblyResourceVirtualFile(virtualPath);
      } else {
        return base.GetFile(virtualPath);
      }
    }

    /// <summary>
    /// If we have a plugin path, return null (for now), otherwise invoke the super class’s method.
    /// </summary>
    /// <param name="virtualPath"></param>
    /// <param name="virtualPathDependencies"></param>
    /// <param name="utcStart"></param>
    /// <returns></returns>
    public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart) {

      if (IsAppResourcePath(virtualPath)) {
        return null;
      }
      return base.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
    }

    /// <summary>
    /// check a virtual path and decide whether the resource is provided by the plugin or the plugin host. 
    /// To do this, we use the convention that all paths destined for plugin modules will begin with “~/Plugins/”. 
    /// In other words, the path ~/Plugins/MyPlugin.dll/SomeResource.aspx indicates that the resource it represents 
    /// is not a physical file and needs to be loaded from the MyPlugin.dll.
    /// </summary>
    /// <param name="virtualPath"></param>
    /// <returns>True if a ressource at a given path is an app ressource</returns>
    private bool IsAppResourcePath(string virtualPath) {
      String checkPath = VirtualPathUtility.ToAppRelative(virtualPath);
      return checkPath.StartsWith("~/Plugins/", StringComparison.InvariantCultureIgnoreCase);
    }
  }
}