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//------------------------------------------------------------
// 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);
}
}
}
}
}
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