XamlHttpHandlerFactory.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / cdf / src / NetFx40 / System.Xaml.Hosting / System / Xaml / Hosting / XamlHttpHandlerFactory.cs / 1305376 / XamlHttpHandlerFactory.cs
                        

                        
                            //------------------------------------------------------------ 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------

namespace System.Xaml.Hosting 
{
    using System; 
    using System.Web; 
    using System.Web.Hosting;
    using System.Web.Compilation; 
    using System.CodeDom.Compiler;
    using System.Collections.Generic;
    using System.IO;
    using System.Diagnostics.CodeAnalysis; 
    using System.Reflection;
    using System.Xaml.Hosting.Configuration; 
    using System.Configuration; 
    using System.Diagnostics;
    using System.Threading; 
    using System.Net;
    using System.Runtime;
    using System.Security;
    using System.Collections; 

    [SuppressMessage(FxCop.Category.Performance, FxCop.Rule.AvoidUninstantiatedInternalClasses, 
        Justification = "This is instantiated by AspNet.")] 
    sealed class XamlHttpHandlerFactory : IHttpHandlerFactory
    { 
        public IHttpHandler GetHandler(HttpContext context, string requestType,
            string url, string pathTranslated)
        {
            //Get the "cache pointer" for the virtual path - if does not exist, create a cache pointer 
            //This should happen under global lock
            PathInfo pathInfo = PathCache.EnsurePathInfo(context.Request.AppRelativeCurrentExecutionFilePath); 
            return pathInfo.GetHandler(context, requestType, url, pathTranslated); 
        }
 
        public void ReleaseHandler(IHttpHandler httphandler)
        {
            //Check whether the handler was created by an internal factory
            if (httphandler is HandlerWrapper) 
            {
                ((HandlerWrapper)(httphandler)).ReleaseWrappedHandler(); 
            } 
        }
 
        static object CreateInstance(Type type)
        {
            //The handler/factory should have an empty constructor but need not be public
            return Activator.CreateInstance(type, 
                BindingFlags.CreateInstance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance,
                null, null, null); 
        } 

        static class PathCache 
        {
            [Fx.Tag.Cache(
                typeof(PathInfo),
                Fx.Tag.CacheAttrition.None, 
                Scope = "instance of declaring class",
                SizeLimit = "unbounded", 
                Timeout = "infinite" 
                )]
            static Hashtable pathCache = new Hashtable(StringComparer.OrdinalIgnoreCase); 
            static object writeLock = new object();

            public static PathInfo EnsurePathInfo(string path)
            { 
                PathInfo pathInfo = (PathInfo)pathCache[path];
                if (pathInfo != null) 
                { 
                    return pathInfo;
                } 

                lock (writeLock)
                {
                    pathInfo = (PathInfo)pathCache[path]; 
                    if (pathInfo != null)
                    { 
                        return pathInfo; 
                    }
 
                    if (HostingEnvironment.VirtualPathProvider.FileExists(path))
                    {
                        pathInfo = new PathInfo();
                        pathCache.Add(path, pathInfo); 
                        return pathInfo;
                    } 
                    else 
                    {
                        throw FxTrace.Exception.AsError(new HttpException((int)HttpStatusCode.NotFound, SR.ResourceNotFound)); 
                    }
                }
            }
        } 

        class HandlerWrapper : IHttpHandler 
        { 
            IHttpHandlerFactory factory;
 
            IHttpHandler httpHandler;

            private HandlerWrapper(IHttpHandler httpHandler, IHttpHandlerFactory factory)
            { 
                this.httpHandler = httpHandler;
                this.factory = factory; 
            } 

            public bool IsReusable 
            {
                get { return httpHandler.IsReusable; }
            }
 
            public static IHttpHandler Create(
                IHttpHandler httpHandler, IHttpHandlerFactory factory) 
            { 
                if (httpHandler is IHttpAsyncHandler)
                { 
                    return new AsyncHandlerWrapper((IHttpAsyncHandler)httpHandler, factory);
                }
                else
                { 
                    return new HandlerWrapper(httpHandler, factory);
                } 
            } 

            public void ProcessRequest(HttpContext context) 
            {
                httpHandler.ProcessRequest(context);
            }
 
            public void ReleaseWrappedHandler()
            { 
                this.factory.ReleaseHandler(httpHandler); 
            }
 
            class AsyncHandlerWrapper : HandlerWrapper, IHttpAsyncHandler
            {
                //Storing a local copy to avoid unnecessary typecasts during begin/end
                IHttpAsyncHandler httpAsyncHandler; 

                public AsyncHandlerWrapper(IHttpAsyncHandler httpAsyncHandler, IHttpHandlerFactory factory) 
                    : base(httpAsyncHandler, factory) 
                {
                    this.httpAsyncHandler = httpAsyncHandler; 
                }

                public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
                { 
                    return this.httpAsyncHandler.BeginProcessRequest(context, cb, extraData);
                } 
 
                public void EndProcessRequest(IAsyncResult result)
                { 
                    this.httpAsyncHandler.EndProcessRequest(result);
                }
            }
        } 

        class PathInfo 
        { 
            object cachedResult;
            Type hostedXamlType; 
            object writeLock;

            public PathInfo()
            { 
                this.writeLock = new object();
            } 
 
            [Fx.Tag.Throws(typeof(ConfigurationErrorsException), "Invalid Configuration.")]
            public IHttpHandler GetHandler(HttpContext context, string requestType, 
                string url, string pathTranslated)
            {
                if (this.cachedResult == null)
                { 
                    //Cache won't be available if it is invoked first time
                    //Use a local "lock" specifically for this url 
                    lock (this.writeLock) 
                    {
                        if (this.cachedResult == null) 
                        {
                            return GetHandlerFirstTime(context, requestType, url, pathTranslated);
                        }
                    } 
                }
 
                return GetHandlerSubSequent(context, requestType, url, pathTranslated); 
            }
 
            [Fx.Tag.SecurityNote(Critical = "Uses SecurityCritical method UnsafeImpersonate to establish the impersonation context",
                Safe = "Does not leak anything, does not let caller influence impersonation.")]
            // Why this triple try blocks instead of using "using" statement:
            // 1. "using" will do the impersonation prior to entering the try, 
            //    which leaves an opertunity to Thread.Abort this thread and get it to exit the method still impersonated.
            // 2. put the assignment of unsafeImpersonate in a finally block 
            //    in order to prevent Threat.Abort after impersonation but before the assignment. 
            // 3. the finally of a "using" doesn't run until exception filters higher up the stack have executed.
            //    they will do so in the impersonated context if an exception is thrown inside the try. 
            // In sumary, this should prevent the thread from existing this method well still impersonated.
            Type GetCompiledCustomString(string normalizedVirtualPath)
            {
                try 
                {
                    IDisposable unsafeImpersonate = null; 
                    try 
                    {
                        try 
                        {
                        }
                        finally
                        { 
                            unsafeImpersonate = HostingEnvironmentWrapper.UnsafeImpersonate();
                        } 
                        return BuildManager.GetCompiledType(normalizedVirtualPath); 
                    }
                    finally 
                    {
                        if (null != unsafeImpersonate)
                        {
                            unsafeImpersonate.Dispose(); 
                        }
                    } 
                } 
                catch
                { 
                    throw;
                }
            }
 

            //This function is invoked the first time a request is made to XAMLx file 
            //It caches url as key and one of the 
            //following 4 as value -> "Handler/Factory/HandlerCLRType/Exception"
            IHttpHandler GetHandlerFirstTime(HttpContext context, string requestType, 
                string url, string pathTranslated)
            {
                Type httpHandlerType;
                ConfigurationErrorsException configException; 

                //GetCompiledType is costly - invoke it just once. 
                //This null check is required for "error after GetCompiledType on first attempt" cases only 
                if (this.hostedXamlType == null)
                { 
                    this.hostedXamlType = GetCompiledCustomString(context.Request.AppRelativeCurrentExecutionFilePath);
                }

                if (XamlHostingConfiguration.TryGetHttpHandlerType(url, this.hostedXamlType, out httpHandlerType)) 
                {
                    if (TD.HttpHandlerPickedForUrlIsEnabled()) 
                    { 
                        TD.HttpHandlerPickedForUrl(url, hostedXamlType.FullName, httpHandlerType.FullName);
                    } 
                    if (typeof(IHttpHandler).IsAssignableFrom(httpHandlerType))
                    {
                        IHttpHandler handler = (IHttpHandler)CreateInstance(httpHandlerType);
                        if (handler.IsReusable) 
                        {
                            this.cachedResult = handler; 
                        } 
                        else
                        { 
                            this.cachedResult = httpHandlerType;
                        }
                        return handler;
                    } 
                    else if (typeof(IHttpHandlerFactory).IsAssignableFrom(httpHandlerType))
                    { 
                        IHttpHandlerFactory factory = (IHttpHandlerFactory)CreateInstance(httpHandlerType); 
                        this.cachedResult = factory;
                        IHttpHandler handler = factory.GetHandler(context, requestType, url, pathTranslated); 
                        return HandlerWrapper.Create(handler, factory);
                    }
                    else
                    { 
                        configException =
                            new ConfigurationErrorsException(SR.NotHttpHandlerType(url, this.hostedXamlType, httpHandlerType.FullName)); 
                        this.cachedResult = configException; 
                        throw FxTrace.Exception.AsError(configException);
                    } 
                }
                configException =
                    new ConfigurationErrorsException(SR.HttpHandlerForXamlTypeNotFound(url, this.hostedXamlType, XamlHostingConfiguration.XamlHostingSection));
                this.cachedResult = configException; 
                throw FxTrace.Exception.AsError(configException);
            } 
 
            //This function retrievs the cached object and uses it to get handler or exception
            IHttpHandler GetHandlerSubSequent(HttpContext context, string requestType, 
                string url, string pathTranslated)
            {
                if (this.cachedResult is IHttpHandler)
                { 
                    return ((IHttpHandler)this.cachedResult);
                } 
                else if (this.cachedResult is IHttpHandlerFactory) 
                {
                    IHttpHandlerFactory factory = ((IHttpHandlerFactory)this.cachedResult); 
                    IHttpHandler handler = factory.GetHandler(context, requestType, url, pathTranslated);
                    return HandlerWrapper.Create(handler, factory);
                }
                else if (this.cachedResult is Type) 
                {
                    return (IHttpHandler)CreateInstance((Type)this.cachedResult); 
                } 
                else
                { 
                    throw FxTrace.Exception.AsError((ConfigurationErrorsException)this.cachedResult);
                }
            }
 
        }
    } 
} 


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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