mcs/class/referencesource/System.Web/Util/AppVerifier.cs

   1 namespace System.Web.Util {
   2     using System;
   3     using System.Collections.Generic;
   4     using System.Diagnostics;
   5     using System.Diagnostics.CodeAnalysis;
   6     using System.Globalization;
   7     using System.Linq;
   8     using System.Reflection;
   9     using System.Runtime.CompilerServices;
  10     using System.Runtime.InteropServices;
  11     using System.Security;
  12     using System.Security.Permissions;
  13     using System.Text;
  14     using System.Threading;
  15     using System.Web;
  16
  17     internal static class AppVerifier {
  18
  19         // It's possible that multiple error codes might get mapped to the same description string.
  20         // This can happen if there might be multiple ways for a single problem to manifest itself.
  21         private static readonly Dictionary<AppVerifierErrorCode, string> _errorStringMappings = new Dictionary<AppVerifierErrorCode, string>() {
  22             { AppVerifierErrorCode.HttpApplicationInstanceWasNull, SR.AppVerifier_Errors_HttpApplicationInstanceWasNull },
  23             { AppVerifierErrorCode.BeginHandlerDelegateWasNull, SR.AppVerifier_Errors_BeginHandlerDelegateWasNull },
  24             { AppVerifierErrorCode.AsyncCallbackInvokedMultipleTimes, SR.AppVerifier_Errors_AsyncCallbackInvokedMultipleTimes },
  25             { AppVerifierErrorCode.AsyncCallbackInvokedWithNullParameter, SR.AppVerifier_Errors_AsyncCallbackInvokedWithNullParameter },
  26             { AppVerifierErrorCode.AsyncCallbackGivenAsyncResultWhichWasNotCompleted, SR.AppVerifier_Errors_AsyncCallbackGivenAsyncResultWhichWasNotCompleted },
  27             { AppVerifierErrorCode.AsyncCallbackInvokedSynchronouslyButAsyncResultWasNotMarkedCompletedSynchronously, SR.AppVerifier_Errors_AsyncCallbackInvokedSynchronouslyButAsyncResultWasNotMarkedCompletedSynchronously },
  28             { AppVerifierErrorCode.AsyncCallbackInvokedAsynchronouslyButAsyncResultWasMarkedCompletedSynchronously, SR.AppVerifier_Errors_AsyncCallbackInvokedAsynchronouslyButAsyncResultWasMarkedCompletedSynchronously },
  29             { AppVerifierErrorCode.AsyncCallbackInvokedWithUnexpectedAsyncResultInstance, SR.AppVerifier_Errors_AsyncCallbackInvokedWithUnexpectedAsyncResultInstance },
  30             { AppVerifierErrorCode.AsyncCallbackInvokedAsynchronouslyThenBeginHandlerThrew, SR.AppVerifier_Errors_AsyncCallbackInvokedEvenThoughBeginHandlerThrew },
  31             { AppVerifierErrorCode.BeginHandlerThrewThenAsyncCallbackInvokedAsynchronously, SR.AppVerifier_Errors_AsyncCallbackInvokedEvenThoughBeginHandlerThrew },
  32             { AppVerifierErrorCode.AsyncCallbackInvokedSynchronouslyThenBeginHandlerThrew, SR.AppVerifier_Errors_AsyncCallbackInvokedEvenThoughBeginHandlerThrew },
  33             { AppVerifierErrorCode.AsyncCallbackInvokedWithUnexpectedAsyncResultAsyncState, SR.AppVerifier_Errors_AsyncCallbackInvokedWithUnexpectedAsyncResultAsyncState },
  34             { AppVerifierErrorCode.AsyncCallbackCalledAfterHttpApplicationReassigned, SR.AppVerifier_Errors_AsyncCallbackCalledAfterHttpApplicationReassigned },
  35             { AppVerifierErrorCode.BeginHandlerReturnedNull, SR.AppVerifier_Errors_BeginHandlerReturnedNull },
  36             { AppVerifierErrorCode.BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButWhichWasNotCompleted, SR.AppVerifier_Errors_BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButWhichWasNotCompleted },
  37             { AppVerifierErrorCode.BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButAsyncCallbackNeverCalled, SR.AppVerifier_Errors_BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButAsyncCallbackNeverCalled },
  38             { AppVerifierErrorCode.BeginHandlerReturnedUnexpectedAsyncResultInstance, SR.AppVerifier_Errors_AsyncCallbackInvokedWithUnexpectedAsyncResultInstance },
  39             { AppVerifierErrorCode.BeginHandlerReturnedUnexpectedAsyncResultAsyncState, SR.AppVerifier_Errors_BeginHandlerReturnedUnexpectedAsyncResultAsyncState },
  40             { AppVerifierErrorCode.SyncContextSendOrPostCalledAfterRequestCompleted, SR.AppVerifier_Errors_SyncContextSendOrPostCalledAfterRequestCompleted },
  41         };
  42
  43         // Provides an option for different wrappers to specify whether to collect the call stacks traces
  44         [FlagsAttribute]
  45         internal enum CallStackCollectionBitMasks : int {
  46             AllMask = -1,
  47
  48             // used for a 3-parameter Begin* method [(T, AsyncCallback, object) -> IAsyncResult] wrapper
  49             BeginCallHandlerMask = 1,
  50             CallHandlerCallbackMask = 2,
  51
  52             // used for a BeginEventHandler method [(object, sender, EventArgs, object) -> IAsyncResult] wrapper
  53             BeginExecutionStepMask = 4,
  54             ExecutionStepCallbackMask = 8,
  55
  56             // when adding new bits above also update the following:
  57             AllHandlerMask = BeginCallHandlerMask | CallHandlerCallbackMask,
  58             AllStepMask = BeginExecutionStepMask | ExecutionStepCallbackMask,
  59
  60             AllBeginMask = BeginCallHandlerMask | BeginExecutionStepMask,
  61             AllCallbackMask = CallHandlerCallbackMask | ExecutionStepCallbackMask
  62         };
  63
  64         // The declarative order of these two fields is important; don't swap them!
  65         private static Action<AppVerifierException> DefaultAppVerifierBehavior = GetAppVerifierBehaviorFromRegistry();
  66         private static readonly bool IsAppVerifierEnabled = (DefaultAppVerifierBehavior != null);
  67         private static long AppVerifierErrorCodeCollectCallStackMask;
  68         private static long AppVerifierErrorCodeEnableAssertMask;
  69         private static CallStackCollectionBitMasks AppVerifierCollectCallStackMask;
  70
  71         private delegate void AssertDelegate(bool condition, AppVerifierErrorCode errorCode);
  72
  73         // Returns an AppVerifier handler (something that can record exceptions appropriately)
  74         // appropriate to what was set in the system registry. If the key we're looking for
  75         // doesn't exist or doesn't have a known value, we return 'null', signifying that
  76         // AppVerifier is disabled.
  77         private static Action<AppVerifierException> GetAppVerifierBehaviorFromRegistry() {
  78             // use 0 as the default value if the key doesn't exist or is of the wrong type
  79             int valueFromRegistry = (Misc.GetAspNetRegValue(subKey: null, valueName: "RuntimeVerificationBehavior", defaultValue: null) as int?) ?? 0;
  80
  81             // REG_QWORD used as a mask to disable individual asserts. No key means all asserts are enabled
  82             AppVerifierErrorCodeEnableAssertMask = (Misc.GetAspNetRegValue(subKey: null, valueName: "AppVerifierErrorCodeEnableAssertMask", defaultValue: (long)(-1)) as long?) ?? (long)(-1);
  83
  84             // REG_QWORD used as a mask to control call stack collection on individual asserts (useful if we event log only). No key means all asserts will collect stack traces
  85             AppVerifierErrorCodeCollectCallStackMask = (Misc.GetAspNetRegValue(subKey: null, valueName: "AppVerifierErrorCodeCollectCallstackMask", defaultValue: (long)(-1)) as long?) ?? (long)(-1);
  86
  87             // REG_DWORD mask to disable call stack collection on begin* / end* methods. No key means all call stacks are collected
  88             AppVerifierCollectCallStackMask = (CallStackCollectionBitMasks)((Misc.GetAspNetRegValue(subKey: null, valueName: "AppVerifierCollectCallStackMask", defaultValue: (int)(-1)) as int?) ?? (int)(-1));
  89
  90             switch (valueFromRegistry) {
  91                 case 1:
  92                     // Just write to the event log
  93                     return WriteToEventLog;
  94
  95                 case 2:
  96                     // Write to the event log and Debugger.Launch / Debugger.Break
  97                     return WriteToEventLogAndSoftBreak;
  98
  99                 case 3:
 100                     // Write to the event log and kernel32!DebugBreak
 101                     return WriteToEventLogAndHardBreak;
 102
 103                 default:
 104                     // not enabled
 105                     return null;
 106             }
 107         }
 108
 109         // Writes an exception to the Windows Event Log (Application section)
 110         private static void WriteToEventLog(AppVerifierException ex) {
 111             Misc.WriteUnhandledExceptionToEventLog(AppDomain.CurrentDomain, ex); // method won't throw
 112         }
 113
 114         [SecurityPermission(SecurityAction.Assert, UnmanagedCode = true)] // safe since AppVerifier can only be enabled via registry, which already requires admin privileges
 115         private static void WriteToEventLogAndSoftBreak(AppVerifierException ex) {
 116             // A "soft" break means that we prompt to launch a debugger, and if one is attached we'll signal it.
 117             WriteToEventLog(ex);
 118             if (Debugger.Launch()) {
 119                 Debugger.Break();
 120             }
 121         }
 122
 123         [SecurityPermission(SecurityAction.Assert, UnmanagedCode = true)] // safe since AppVerifier can only be enabled via registry, which already requires admin privileges
 124         private static void WriteToEventLogAndHardBreak(AppVerifierException ex) {
 125             // A "hard" break means that we'll signal any attached debugger, and if none is attached
 126             // we'll just INT 3 and hope for the best. (This may cause a Watson dump depending on environment.)
 127             WriteToEventLog(ex);
 128             if (Debugger.IsAttached) {
 129                 Debugger.Break();
 130             }
 131             else {
 132                 NativeMethods.DebugBreak();
 133             }
 134         }
 135
 136         // Instruments a 3-parameter Begin* method [(T, AsyncCallback, object) -> IAsyncResult].
 137         // If AppVerifier is disabled, returns the original method unmodified.
 138         public static Func<T, AsyncCallback, object, IAsyncResult> WrapBeginMethod<T>(HttpApplication httpApplication, Func<T, AsyncCallback, object, IAsyncResult> originalDelegate) {
 139             if (!IsAppVerifierEnabled) {
 140                 return originalDelegate;
 141             }
 142
 143             return (arg, callback, state) => WrapBeginMethodImpl(
 144                 httpApplication: httpApplication,
 145                 beginMethod: (innerCallback, innerState) => originalDelegate(arg, innerCallback, innerState),
 146                 originalDelegate: originalDelegate,
 147                 errorHandler: HandleAppVerifierException,
 148                 callStackMask: CallStackCollectionBitMasks.AllHandlerMask)
 149                 (callback, state);
 150         }
 151
 152         // Instruments a BeginEventHandler method [(object, sender, EventArgs, object) -> IAsyncResult].
 153         // This pattern is commonly used, such as by IHttpModule, PageAsyncTask, and others.
 154         // If AppVerifier is disabled, returns the original method unmodified.
 155         public static BeginEventHandler WrapBeginMethod(HttpApplication httpApplication, BeginEventHandler originalDelegate) {
 156             if (!IsAppVerifierEnabled) {
 157                 return originalDelegate;
 158             }
 159
 160             return (sender, e, cb, extraData) => WrapBeginMethodImpl(
 161                 httpApplication: httpApplication,
 162                 beginMethod: (innerCallback, innerState) => originalDelegate(sender, e, innerCallback, innerState),
 163                 originalDelegate: originalDelegate,
 164                 errorHandler: HandleAppVerifierException,
 165                 callStackMask: CallStackCollectionBitMasks.AllStepMask)
 166                 (cb, extraData);
 167         }
 168
 169         /// <summary>
 170         /// Wraps the Begin* part of a Begin / End method pair to allow for signaling when assertions have been violated.
 171         /// The instrumentation can be a performance hit, so this method should not be called if AppVerifier is not enabled.
 172         /// </summary>
 173         /// <param name="httpApplication">The HttpApplication instance for this request, used to get HttpContext and related items.</param>
 174         /// <param name="beginMethod">The Begin* part of a Begin / End method pair, likely wrapped in a lambda so only the AsyncCallback and object parameters are exposed.</param>
 175         /// <param name="originalDelegate">The original user-provided delegate, e.g. the thing that 'beginMethod' wraps. Provided so that we can show correct methods when asserting.</param>
 176         /// <param name="errorHandler">The listener that can handle verification failures.</param>
 177         /// <returns>The instrumented Begin* method.</returns>
 178         internal static Func<AsyncCallback, object, IAsyncResult> WrapBeginMethodImpl(HttpApplication httpApplication, Func<AsyncCallback, object, IAsyncResult> beginMethod, Delegate originalDelegate, Action<AppVerifierException> errorHandler, CallStackCollectionBitMasks callStackMask) {
 179             return (callback, state) => {
 180                 // basic diagnostic info goes at the top since it's used during generation of the error message
 181                 AsyncCallbackInvocationHelper asyncCallbackInvocationHelper = new AsyncCallbackInvocationHelper();
 182                 CallStackCollectionBitMasks myBeginMask = callStackMask & CallStackCollectionBitMasks.AllBeginMask;
 183                 bool captureBeginStack = (myBeginMask & (CallStackCollectionBitMasks)AppVerifierCollectCallStackMask) == myBeginMask;
 184
 185                 InvocationInfo beginHandlerInvocationInfo = InvocationInfo.Capture(captureBeginStack);
 186                 Uri requestUrl = null;
 187                 RequestNotification? currentNotification = null;
 188                 bool isPostNotification = false;
 189                 Type httpHandlerType = null;
 190
 191                 // need to collect all this up-front since it might go away during the async operation
 192                 if (httpApplication != null) {
 193                     HttpContext context = httpApplication.Context;
 194                     if (context != null) {
 195                         if (!context.HideRequestResponse && context.Request != null) {
 196                             requestUrl = context.Request.Unvalidated.Url;
 197                         }
 198
 199                         if (context.NotificationContext != null) {
 200                             currentNotification = context.NotificationContext.CurrentNotification;
 201                             isPostNotification = context.NotificationContext.IsPostNotification;
 202                         }
 203
 204                         if (context.Handler != null) {
 205                             httpHandlerType = context.Handler.GetType();
 206                         }
 207                     }
 208                 }
 209
 210                 // If the condition passed to this method evaluates to false, we will raise an error to whoever is listening.
 211                 AssertDelegate assert = (condition, errorCode) => {
 212                     long mask = 1L<<(int)errorCode;
 213                     // assert only if it was not masked out by a bit set
 214                     bool enableAssert = (AppVerifierErrorCodeEnableAssertMask & mask) == mask;
 215
 216                     if (!condition && enableAssert) {
 217                         // capture the stack only if it was not masked out by a bit set
 218                         bool captureStack = (AppVerifierErrorCodeCollectCallStackMask & mask) == mask;
 219
 220                         InvocationInfo assertInvocationInfo = InvocationInfo.Capture(captureStack);
 221
 222                         // header
 223                         StringBuilder errorString = new StringBuilder();
 224                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_Title));
 225                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_Subtitle));
 226                         errorString.AppendLine();
 227
 228                         // basic info (about the assert)
 229                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_URL, requestUrl));
 230                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_ErrorCode, (int)errorCode));
 231                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_Description, GetLocalizedDescriptionStringForError(errorCode)));
 232                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_ThreadInfo, assertInvocationInfo.ThreadId, assertInvocationInfo.Timestamp.ToLocalTime()));
 233                         errorString.AppendLine(assertInvocationInfo.StackTrace.ToString());
 234
 235                         // Begin* method info
 236                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BeginMethodInfo_EntryMethod, PrettyPrintDelegate(originalDelegate)));
 237                         if (currentNotification != null) {
 238                             errorString.AppendLine(FormatErrorString(SR.AppVerifier_BeginMethodInfo_RequestNotification_Integrated, currentNotification, isPostNotification));
 239                         }
 240                         else {
 241                             errorString.AppendLine(FormatErrorString(SR.AppVerifier_BeginMethodInfo_RequestNotification_NotIntegrated));
 242                         }
 243                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BeginMethodInfo_CurrentHandler, httpHandlerType));
 244                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_BeginMethodInfo_ThreadInfo, beginHandlerInvocationInfo.ThreadId, beginHandlerInvocationInfo.Timestamp.ToLocalTime()));
 245                         errorString.AppendLine(beginHandlerInvocationInfo.StackTrace.ToString());
 246
 247                         // AsyncCallback info
 248                         int totalAsyncInvocationCount;
 249                         InvocationInfo firstAsyncInvocation = asyncCallbackInvocationHelper.GetFirstInvocationInfo(out totalAsyncInvocationCount);
 250                         errorString.AppendLine(FormatErrorString(SR.AppVerifier_AsyncCallbackInfo_InvocationCount, totalAsyncInvocationCount));
 251                         if (firstAsyncInvocation != null) {
 252                             errorString.AppendLine(FormatErrorString(SR.AppVerifier_AsyncCallbackInfo_FirstInvocation_ThreadInfo, firstAsyncInvocation.ThreadId, firstAsyncInvocation.Timestamp.ToLocalTime()));
 253                             errorString.AppendLine(firstAsyncInvocation.StackTrace.ToString());
 254                         }
 255
 256                         AppVerifierException ex = new AppVerifierException(errorCode, errorString.ToString());
 257                         errorHandler(ex);
 258                         throw ex;
 259                     }
 260                 };
 261
 262                 assert(httpApplication != null, AppVerifierErrorCode.HttpApplicationInstanceWasNull);
 263                 assert(originalDelegate != null, AppVerifierErrorCode.BeginHandlerDelegateWasNull);
 264
 265                 object lockObj = new object(); // used to synchronize access to certain locals which can be touched by multiple threads
 266                 IAsyncResult asyncResultReturnedByBeginHandler = null;
 267                 IAsyncResult asyncResultPassedToCallback = null;
 268                 object beginHandlerReturnValueHolder = null; // used to hold the IAsyncResult returned by or Exception thrown by BeginHandler; see comments on Holder<T> for more info
 269                 Thread threadWhichCalledBeginHandler = Thread.CurrentThread; // used to determine whether the callback was invoked synchronously
 270                 bool callbackRanToCompletion = false; // don't need to lock when touching this local since it's only read in the synchronous case
 271
 272                 HttpContext assignedContextUponCallingBeginHandler = httpApplication.Context; // used to determine whether the underlying request disappeared
 273
 274                 try {
 275                     asyncResultReturnedByBeginHandler = beginMethod(
 276                        asyncResult => {
 277                            try {
 278                                CallStackCollectionBitMasks myCallbackMask = callStackMask & CallStackCollectionBitMasks.AllCallbackMask;
 279                                bool captureEndCallStack = (myCallbackMask & AppVerifierCollectCallStackMask ) == myCallbackMask;
 280                                // The callback must never be called more than once.
 281                                int newAsyncCallbackInvocationCount = asyncCallbackInvocationHelper.RecordInvocation(captureEndCallStack);
 282                                assert(newAsyncCallbackInvocationCount == 1, AppVerifierErrorCode.AsyncCallbackInvokedMultipleTimes);
 283
 284                                // The 'asyncResult' parameter must never be null.
 285                                assert(asyncResult != null, AppVerifierErrorCode.AsyncCallbackInvokedWithNullParameter);
 286
 287                                object tempBeginHandlerReturnValueHolder;
 288                                Thread tempThreadWhichCalledBeginHandler;
 289                                lock (lockObj) {
 290                                    asyncResultPassedToCallback = asyncResult;
 291                                    tempBeginHandlerReturnValueHolder = beginHandlerReturnValueHolder;
 292                                    tempThreadWhichCalledBeginHandler = threadWhichCalledBeginHandler;
 293                                }
 294
 295                                // At this point, 'IsCompleted = true' is mandatory.
 296                                assert(asyncResult.IsCompleted, AppVerifierErrorCode.AsyncCallbackGivenAsyncResultWhichWasNotCompleted);
 297
 298                                if (tempBeginHandlerReturnValueHolder == null) {
 299                                    // BeginHandler hasn't yet returned, so this call may be synchronous or asynchronous.
 300                                    // We can tell by comparing the current thread with the thread which called BeginHandler.
 301                                    // From a correctness perspective, it is valid to invoke the AsyncCallback delegate either
 302                                    // synchronously or asynchronously. From [....]: if 'CompletedSynchronously = true', then
 303                                    // AsyncCallback invocation can happen either on the same thread or on a different thread,
 304                                    // just as long as BeginHandler hasn't yet returned (which in true in this case).
 305                                    if (!asyncResult.CompletedSynchronously) {
 306                                        // If 'CompletedSynchronously = false', we must be on a different thread than the BeginHandler invocation.
 307                                        assert(tempThreadWhichCalledBeginHandler != Thread.CurrentThread, AppVerifierErrorCode.AsyncCallbackInvokedSynchronouslyButAsyncResultWasNotMarkedCompletedSynchronously);
 308                                    }
 309                                }
 310                                else {
 311                                    // BeginHandler already returned, so this invocation is definitely asynchronous.
 312
 313                                    Holder<IAsyncResult> asyncResultHolder = tempBeginHandlerReturnValueHolder as Holder<IAsyncResult>;
 314                                    if (asyncResultHolder != null) {
 315                                        // We need to verify that the IAsyncResult we're given is the same that was returned by BeginHandler
 316                                        // and that the IAsyncResult is marked 'CompletedSynchronously = false'.
 317                                        assert(asyncResult == asyncResultHolder.Value, AppVerifierErrorCode.AsyncCallbackInvokedWithUnexpectedAsyncResultInstance);
 318                                        assert(!asyncResult.CompletedSynchronously, AppVerifierErrorCode.AsyncCallbackInvokedAsynchronouslyButAsyncResultWasMarkedCompletedSynchronously);
 319                                    }
 320                                    else {
 321                                        // If we reached this point, BeginHandler threw an exception.
 322                                        // The AsyncCallback should never be invoked if BeginHandler has already failed.
 323                                        assert(false, AppVerifierErrorCode.BeginHandlerThrewThenAsyncCallbackInvokedAsynchronously);
 324                                    }
 325                                }
 326
 327                                // AsyncState must match the 'state' parameter passed to BeginHandler
 328                                assert(asyncResult.AsyncState == state, AppVerifierErrorCode.AsyncCallbackInvokedWithUnexpectedAsyncResultAsyncState);
 329
 330                                // Make sure the underlying HttpApplication is still assigned to the captured HttpContext instance.
 331                                // If not, this AsyncCallback invocation could end up completing *some other request's* operation,
 332                                // resulting in data corruption.
 333                                assert(assignedContextUponCallingBeginHandler == httpApplication.Context, AppVerifierErrorCode.AsyncCallbackCalledAfterHttpApplicationReassigned);
 334                            }
 335                            catch (AppVerifierException) {
 336                                // We want to ---- any exceptions thrown by our verification logic, as the failure
 337                                // has already been recorded by the appropriate listener. Just go straight to
 338                                // invoking the callback.
 339                            }
 340
 341                            // all checks complete - delegate control to the actual callback
 342                            if (callback != null) {
 343                                callback(asyncResult);
 344                            }
 345                            callbackRanToCompletion = true;
 346                        },
 347                        state);
 348
 349                     // The return value must never be null.
 350                     assert(asyncResultReturnedByBeginHandler != null, AppVerifierErrorCode.BeginHandlerReturnedNull);
 351
 352                     lock (lockObj) {
 353                         beginHandlerReturnValueHolder = new Holder<IAsyncResult>(asyncResultReturnedByBeginHandler);
 354                     }
 355
 356                     if (asyncResultReturnedByBeginHandler.CompletedSynchronously) {
 357                         // If 'CompletedSynchronously = true', the IAsyncResult must be marked 'IsCompleted = true'
 358                         // and the AsyncCallback must have been invoked synchronously (checked in the AsyncCallback verification logic).
 359                         assert(asyncResultReturnedByBeginHandler.IsCompleted, AppVerifierErrorCode.BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButWhichWasNotCompleted);
 360                         assert(asyncCallbackInvocationHelper.TotalInvocations != 0, AppVerifierErrorCode.BeginHandlerReturnedAsyncResultMarkedCompletedSynchronouslyButAsyncCallbackNeverCalled);
 361                     }
 362
 363                     IAsyncResult tempAsyncResultPassedToCallback;
 364                     lock (lockObj) {
 365                         tempAsyncResultPassedToCallback = asyncResultPassedToCallback;
 366                     }
 367
 368                     // The AsyncCallback may have been invoked (either synchronously or asynchronously). If it has been
 369                     // invoked, we need to verify that it was given the same IAsyncResult returned by BeginHandler.
 370                     // If the AsyncCallback hasn't yet been called, we skip this check, as the AsyncCallback verification
 371                     // logic will eventually perform the check at the appropriate time.
 372                     if (tempAsyncResultPassedToCallback != null) {
 373                         assert(tempAsyncResultPassedToCallback == asyncResultReturnedByBeginHandler, AppVerifierErrorCode.BeginHandlerReturnedUnexpectedAsyncResultInstance);
 374                     }
 375
 376                     // AsyncState must match the 'state' parameter passed to BeginHandler
 377                     assert(asyncResultReturnedByBeginHandler.AsyncState == state, AppVerifierErrorCode.BeginHandlerReturnedUnexpectedAsyncResultAsyncState);
 378
 379                     // all checks complete
 380                     return asyncResultReturnedByBeginHandler;
 381                 }
 382                 catch (AppVerifierException) {
 383                     // We want to ---- any exceptions thrown by our verification logic, as the failure
 384                     // has already been recorded by the appropriate listener. Just return the original
 385                     // IAsyncResult so that the application continues to run.
 386                     return asyncResultReturnedByBeginHandler;
 387                 }
 388                 catch (Exception ex) {
 389                     if (asyncResultReturnedByBeginHandler == null) {
 390                         // If we reached this point, an exception was thrown by BeginHandler, so we need to
 391                         // record it and rethrow it.
 392
 393                         IAsyncResult tempAsyncResultPassedToCallback;
 394                         lock (lockObj) {
 395                             beginHandlerReturnValueHolder = new Holder<Exception>(ex);
 396                             tempAsyncResultPassedToCallback = asyncResultPassedToCallback;
 397                         }
 398
 399                         try {
 400                             // The AsyncCallback should only be invoked if BeginHandler ran to completion.
 401                             if (tempAsyncResultPassedToCallback != null) {
 402
 403                                 // If AsyncCallback was invoked asynchronously, then by definition it was
 404                                 // scheduled prematurely since BeginHandler hadn't yet run to completion
 405                                 // (since whatever additional work it did after invoking the callback failed).
 406                                 // Therefore it is always wrong for BeginHandler to both throw and
 407                                 // asynchronously invoke AsyncCallback.
 408                                 assert(tempAsyncResultPassedToCallback.CompletedSynchronously, AppVerifierErrorCode.AsyncCallbackInvokedAsynchronouslyThenBeginHandlerThrew);
 409
 410                                 // If AsyncCallback was invoked synchronously, then it must have been invoked
 411                                 // before BeginHandler surfaced the exception (since otherwise BeginHandler
 412                                 // wouldn't have reached the line of code that invoked AsyncCallback). But
 413                                 // AsyncCallback itself could have thrown, bubbling the exception up through
 414                                 // BeginHandler and back to us. If AsyncCallback ran to completion, then this
 415                                 // means BeginHandler did extra work (which failed) after invoking AsyncCallback,
 416                                 // so BeginHandler by definition hadn't yet run to completion.
 417                                 assert(!callbackRanToCompletion, AppVerifierErrorCode.AsyncCallbackInvokedSynchronouslyThenBeginHandlerThrew);
 418                             }
 419                         }
 420                         catch (AppVerifierException) {
 421                             // We want to ---- any exceptions thrown by our verification logic, as the failure
 422                             // has already been recorded by the appropriate listener. Propagate the original
 423                             // exception upward.
 424                         }
 425
 426                         throw;
 427                     }
 428                     else {
 429                         // We want to ---- any exceptions thrown by our verification logic, as the failure
 430                         // has already been recorded by the appropriate listener. Just return the original
 431                         // IAsyncResult so that the application continues to run.
 432                         return asyncResultReturnedByBeginHandler;
 433                     }
 434                 }
 435                 finally {
 436                     // Since our local variables are GC-rooted in an anonymous object, we should
 437                     // clear references to objects we no longer need so that the GC can reclaim
 438                     // them if appropriate.
 439                     lock (lockObj) {
 440                         threadWhichCalledBeginHandler = null;
 441                     }
 442                 }
 443             };
 444         }
 445
 446         // Gets a delegate that checks for application code trying to call into the SyncContext after
 447         // the request is already completed. The Action returned by this method could be null.
 448         public static Action GetSyncContextCheckDelegate(ISyncContext syncContext) {
 449             if (!IsAppVerifierEnabled) {
 450                 return null;
 451             }
 452
 453             return GetSyncContextCheckDelegateImpl(syncContext, HandleAppVerifierException);
 454         }
 455
 456         /// <summary>
 457         /// Returns an Action that determines whether SynchronizationContext.Send or Post was called after the underlying request finished.
 458         /// The instrumentation can be a performance hit, so this method should not be called if AppVerifier is not enabled.
 459         /// </summary>
 460         /// <param name="syncContext">The ISyncContext (HttpApplication, WebSocketPipeline, etc.) on which to perform the check.</param>
 461         /// <param name="errorHandler">The listener that can handle verification failures.</param>
 462         /// <returns>A callback which performs the verification.</returns>
 463         internal static Action GetSyncContextCheckDelegateImpl(ISyncContext syncContext, Action<AppVerifierException> errorHandler) {
 464             Uri requestUrl = null;
 465             object originalThreadContextId = null;
 466
 467             // collect all of the diagnostic information upfront
 468             HttpContext originalHttpContext = (syncContext != null) ? syncContext.HttpContext : null;
 469             if (originalHttpContext != null) {
 470                 if (!originalHttpContext.HideRequestResponse && originalHttpContext.Request != null) {
 471                     requestUrl = originalHttpContext.Request.Unvalidated.Url;
 472                 }
 473
 474                 // This will be used as a surrogate for the captured HttpContext so that we don't
 475                 // have a long-lived reference to a heavy object graph. See comments on ThreadContextId
 476                 // for more info.
 477                 originalThreadContextId = originalHttpContext.ThreadContextId;
 478                 originalHttpContext = null;
 479             }
 480
 481             // If the condition passed to this method evaluates to false, we will raise an error to whoever is listening.
 482             AssertDelegate assert = (condition, errorCode) => {
 483                 long mask = 1L << (int)errorCode;
 484                 // assert only if it was not masked out by a bit set
 485                 bool enableAssert = (AppVerifierErrorCodeEnableAssertMask & mask) == mask;
 486
 487                 if (!condition && enableAssert) {
 488                     // capture the stack only if it was not masked out by a bit set
 489                     bool captureStack = (AppVerifierErrorCodeCollectCallStackMask & mask) == mask;
 490                     InvocationInfo assertInvocationInfo = InvocationInfo.Capture(captureStack);
 491
 492                     // header
 493                     StringBuilder errorString = new StringBuilder();
 494                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_Title));
 495                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_Subtitle));
 496                     errorString.AppendLine();
 497
 498                     // basic info (about the assert)
 499                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_URL, requestUrl));
 500                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_ErrorCode, (int)errorCode));
 501                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_Description, GetLocalizedDescriptionStringForError(errorCode)));
 502                     errorString.AppendLine(FormatErrorString(SR.AppVerifier_BasicInfo_ThreadInfo, assertInvocationInfo.ThreadId, assertInvocationInfo.Timestamp.ToLocalTime()));
 503                     errorString.AppendLine(assertInvocationInfo.StackTrace.ToString());
 504
 505                     AppVerifierException ex = new AppVerifierException(errorCode, errorString.ToString());
 506                     errorHandler(ex);
 507                     throw ex;
 508                 }
 509             };
 510
 511             return () => {
 512                 try {
 513                     // Make sure that the ISyncContext is still associated with the same HttpContext that
 514                     // we captured earlier.
 515                     HttpContext currentHttpContext = (syncContext != null) ? syncContext.HttpContext : null;
 516                     object currentThreadContextId = (currentHttpContext != null) ? currentHttpContext.ThreadContextId : null;
 517                     assert(currentThreadContextId != null && ReferenceEquals(originalThreadContextId, currentThreadContextId), AppVerifierErrorCode.SyncContextSendOrPostCalledAfterRequestCompleted);
 518                 }
 519                 catch (AppVerifierException) {
 520                     // We want to ---- any exceptions thrown by our verification logic, as the failure
 521                     // has already been recorded by the appropriate listener. Propagate the original
 522                     // exception upward.
 523                 }
 524             };
 525         }
 526
 527         // This is the default implementation of an AppVerifierException handler;
 528         // it just delegates to the configured behavior.
 529         [SuppressMessage("Microsoft.Reliability", "CA2004:RemoveCallsToGCKeepAlive", Justification = "Want to keep these locals on the stack to assist with debugging.")]
 530         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]
 531         private static void HandleAppVerifierException(AppVerifierException ex) {
 532             // This method is specifically written to maximize the chance of
 533             // useful information being on the stack as a local, where it's more
 534             // easily observed by the debugger.
 535
 536             AppVerifierErrorCode errorCode = ex.ErrorCode;
 537             string fullMessage = ex.Message;
 538
 539             DefaultAppVerifierBehavior(ex);
 540
 541             GC.KeepAlive(errorCode);
 542             GC.KeepAlive(fullMessage);
 543             GC.KeepAlive(ex);
 544         }
 545
 546         internal static string PrettyPrintDelegate(Delegate del) {
 547             return PrettyPrintMemberInfo((del != null) ? del.Method : null);
 548         }
 549
 550         // prints "TResult MethodName(TArg1, TArg2, ...) [Module.dll!Namespace.TypeName]"
 551         internal static string PrettyPrintMemberInfo(MethodInfo method) {
 552             if (method == null) {
 553                 return null;
 554             }
 555
 556             string retVal = method.ToString();
 557
 558             Type type = method.ReflectedType;
 559             if (type != null) {
 560                 retVal = retVal + " [";
 561                 if (type.Module != null) {
 562                     retVal += type.Module.Name + "!";
 563                 }
 564
 565                 retVal += type.FullName + "]";
 566             }
 567
 568             return retVal;
 569         }
 570
 571         internal static string GetLocalizedDescriptionStringForError(AppVerifierErrorCode errorCode) {
 572             return FormatErrorString(_errorStringMappings[errorCode]);
 573         }
 574
 575         // We use InstalledUICulture rather than CurrentCulture / CurrentUICulture since these strings will
 576         // be stored in the system event log.
 577         [SuppressMessage("Microsoft.Globalization", "CA1305:SpecifyIFormatProvider", MessageId = "System.String.Format(System.IFormatProvider,System.String,System.Object[])",
 578             Justification = "Matches culture specified in Misc.WriteUnhandledExceptionToEventLog.")]
 579         internal static string FormatErrorString(string name, params object[] args) {
 580             return String.Format(CultureInfo.InstalledUICulture, SR.Resources.GetString(name, CultureInfo.InstalledUICulture), args);
 581         }
 582
 583         // contains a counter and invocation information for an AsyncCallback delegate
 584         private sealed class AsyncCallbackInvocationHelper {
 585             private InvocationInfo _firstInvocationInfo;
 586             private int _totalInvocationCount;
 587
 588             public int TotalInvocations {
 589                 [MethodImpl(MethodImplOptions.Synchronized)]
 590                 get { return _totalInvocationCount; }
 591             }
 592
 593             [MethodImpl(MethodImplOptions.Synchronized)]
 594             public InvocationInfo GetFirstInvocationInfo(out int totalInvocationCount) {
 595                 totalInvocationCount = _totalInvocationCount;
 596                 return _firstInvocationInfo;
 597             }
 598
 599             [MethodImpl(MethodImplOptions.Synchronized)]
 600             public int RecordInvocation(bool captureCallStack) {
 601                 _totalInvocationCount++;
 602                 if (_firstInvocationInfo == null) {
 603                     _firstInvocationInfo = InvocationInfo.Capture(captureCallStack);
 604                 }
 605                 return _totalInvocationCount;
 606             }
 607         }
 608
 609         // We use a special class for holding data so that we can store the local's
 610         // intended type alongside its real value. Prevents us from misinterpreting
 611         // the degenerate case of "----CustomType : Exception, IAsyncResult" so that
 612         // we know whether it was returned as an IAsyncResult or thrown as an Exception.
 613         private sealed class Holder<T> {
 614             public readonly T Value;
 615
 616             public Holder(T value) {
 617                 Value = value;
 618             }
 619         }
 620
 621         // holds diagnostic information about a particular invocation
 622         private sealed class InvocationInfo {
 623             public readonly int ThreadId;
 624             public readonly DateTimeOffset Timestamp;
 625             public readonly string StackTrace;
 626
 627             private InvocationInfo(bool captureStack) {
 628                 ThreadId = Thread.CurrentThread.ManagedThreadId;
 629                 Timestamp = DateTimeOffset.UtcNow; // UTC is faster, will convert to local on error
 630                 StackTrace = captureStack? CaptureStackTrace(): "n/a";
 631             }
 632
 633             public static InvocationInfo Capture(bool captureStack) {
 634                 return new InvocationInfo(captureStack);
 635             }
 636
 637             // captures a stack trace, removing AppVerifier.* frames from the top of the stack to minimize noise
 638             private static string CaptureStackTrace() {
 639                 StackTrace fullStackTrace = new StackTrace(fNeedFileInfo: true);
 640                 string[] traceLines = fullStackTrace.ToString().Split(new string[] { Environment.NewLine }, StringSplitOptions.None);
 641                 for (int i = 0; i < fullStackTrace.FrameCount && i < traceLines.Length; i++) {
 642                     StackFrame thisFrame = fullStackTrace.GetFrame(i);
 643                     if (thisFrame.GetMethod().Module == typeof(AppVerifier).Module
 644                         && thisFrame.GetMethod().DeclaringType.FullName.StartsWith("System.Web.Util.AppVerifier", StringComparison.Ordinal)) {
 645                         // we want to skip this frame since it's an AppVerifier.* frame
 646                         continue;
 647                     }
 648                     else {
 649                         // this is the first frame that is not an AppVerifier.* frame, so start the stack trace from here
 650                         return String.Join(Environment.NewLine, traceLines.Skip(i));
 651                     }
 652                 }
 653
 654                 // if we reached this point, not sure what happened, so just return the original stack trace
 655                 return fullStackTrace.ToString();
 656             }
 657         }
 658
 659         [SuppressUnmanagedCodeSecurityAttribute]
 660         private static class NativeMethods {
 661             [DllImport("kernel32.dll")]
 662             internal extern static void DebugBreak();
 663         }
 664
 665     }
 666 }