I am having trouble reproducing a few errors we are seeing in our error log.
It could be made a lot easier if I knew which record ID a specific method was using when it threw an exception.
All of our unhandled exceptions get handled by our global exception handler, which puts all the details of the exception, as well as all the details of the HTTP request, into a log table.
Is there a way to capture the values of all the parameters for the method that threw an exception? Or even better, all the values up the stack trace?
Unfortunately, this is not possible: at the time when you catch the exception in the handler, all the stack frames with the method parameters are gone. Once the control leaves your function, you can no longer access its parameter values.
Since you know the specific function where the crash happens, you could set up an exception handler there to collect all the parameters of interest, and re-throw a wrapped exception. Once the diagnostics is complete, you could revert the code back to normal:
void SuspiciousFunction(string name, long count) {
try {
// The code of your function goes here
} catch (Exception e) {
var args = new Dictionary<string,object> {
{ "name" , name }
, { "count", count }
};
throw new MySpecialException(e, args);
}
}
I would capture the exception in the method it's thrown, gather your parameters and any other needed info, then rethrow the error with a new ApplicationException or other custom Exception that contains your additional info.
From the documentation Environment.StackTrace i would say it is possible.
They say
The stack trace information for each method call is formatted as follows:
"at FullClassName. MethodName (MethodParams) in FileName :line LineNumber "
Related
I'm trying to invoke an instance using constructor.Invoke and also passing some parameters in it, but I'm getting
System.Reflection.TargetInvocationException: 'Exception has been thrown by the target of an invocation.'
Any inputs would be helpful
Thanks
TargetInvocationException basically means that the member could be invoked successfully and the exception occurred in the invoked member itself. To differentiate it from other issues (eg. wrong instance, invalid number or type of parameters, etc.) the exception thrown by the invoked member is wrapped into a TargetInvocationException. Just look at its InnerException to see what happened.
If you want to 'unwrap' such exceptions as if you called the constructor without reflection you can do something like this:
try
{
return myConstructorInfo.Invoke(parameters);
}
catch (TargetInvocationException e)
{
// we could just throw e.InnerException but that would corrupt the
// original stack trace, showing this line as the source of the exception
ExceptionDispatchInfo.Capture(e.InnerException).Throw();
throw; // unreachable, just to satisfy the compiler if there is no return later
}
Simply put, I don't expect this application to receive too many errors since it's a fairly controlled environment and the users are other developers.
Having said that, errors do happen sooner or later and I simply just want to keep a log of them and alert the user. I've got this method that tries to validate the information as best as it can, then it tries to copy a file from A to B.
try
{
File.Copy(source, destination, true);
return String.Empty;
}
catch (Exception ex)
{
logOp.AddLog(ex);
return string.Format("ERROR: {0}{1}{2}", ex.Message, Environment.NewLine, ex.StackTrace);
}
The method returns an empty string if it was successful, and if not it logs the exception and returns it to the calling method for presentation.
Do I need to catch each individual Exception type that File.Copy can throw if I want the most detailed Message / Stack trace, or will just catching Exception work? I tried hardcoding it to throw new instances of the various Exceptions and it seems OK but I wasn't sure if there was some programming principle I was missing/violating
Since all you're doing in exception handler is logging, then I'd say no, just take the Exception and log the message.
Catching individual exceptions would be useful if you attempted to recover from the error.
I would keep it as is and just catch the base class Exception.
Logging the ex.ToString() like you implicitly do in logOp.AddLog(ex) should write the actual type of the exception (which could be one of these that File.Copy method can throw in the Exceptions section here )
Based on that link, the name of the actual exception should be informative enough since you are not attempting to recover from the exceptions, just logging them.
I have the following code:
catch(Exception ex)
{
throw new FatalException("An error occurred while trying to load the XSLT file.", ex);
}
This unfortunately just swallows up the Exception. I can fix this by doing the following:
catch(Exception ex)
{
throw;
}
But I would still like to include the custom message for help with event logging.
How do I add this message to the exception without losing any information? (stack trace/debug symbols, etc.)
If you just need to add information to the original exception, such as a user-readable message or specific details that will be useful to you in tracking down the error but that won't be useful to the end user, you can make use of the Exception's Data property, which is a key/value pair dictionary.
We use this extensively in order to record information such as the report being executed or file that is being processed so that operations can determine what exactly was happening at the time of the error. The user doesn't need this detail since they are working directly with the cause of the failure.
You could also use this to pass a plain text message that makes sense to the user. The only issue is that you will have to perform some additional work in your logging framework or end-user interface in order to extract the data and make it useful to the consumer.
For example, you could do:
catch (Exception ex)
{
ex.Data.Add("UserMessage", "An error occurred while trying to load the XSLT file.");
throw;
}
Then in the client-side code, you could test to see if UserMessage exists and, if so, present it to the user instead of the Exception:
catch (Exception ex)
{
if (ex.Data.Contains("UserMessage"))
{
MessageBox.Show(ex.Data["UserMessage"].ToString());
}
else
{
MessageBox.Show(ex.Message);
}
}
That original Exception is still there.
When you do your Exception logging, the Exception that you receive will be the FatalException that you made with your message. The original Exception is in ex.InnerException. You can continue to cycle through InnerException until it's null to get all of the Stack Trace information, etc.
In short, don't.
I'm sure you could find some way of getting around this with some reflection, but I would strongly caution you against this. It goes against the original design of exceptions in .NET. Exceptions are not just there to help with logging, they provide information about the original cause of an application failure.
Using the first option is generally preferred as it maintains the stack trace of the original exception but allows you to provide additional information by wrapping it in a separate exception. In my own code, whenever I log exceptions, my logging function will recurse through the InnerException property to find every bit of useful information possible about the error.
Just in case someone needs a good answer. The key is to use AppDomain.CurrentDomain.FirstChanceException
The you can create a custom object with IDisposable to put all info in it. And if exception happens then FirstChanceException handler gets that info and populate Exception.Data.
Use Local Thread Storage to make it thread safe. Then down the line the code that catches it will get the data and log it.
Example:
using(MyCustomMessage.EnterToLocalStorage("Info for logging"") )
{
...code
...exception thrown
.... FirstChanceException examines local thread storage and get's "info for logging" and puts into Exception.Data.
}
//Dispose is called and all messages that were put into LocalStorage are removed.
//So if exception was not thrown before then it like nothing happened.
Google AsyncDiagnosticStack for a good example. https://github.com/StephenCleary/AsyncDiagnostics/blob/master/src/Nito.AsyncEx.AsyncDiagnostics/AsyncDiagnosticStack.cs
I wanted to log the Exception details
Filename , FileLineNo, Method Name (where the exception occured)
This is working using the StackTrace class
But some times i am getting the File Line No and Method Name as null
How shall i track Exception Details all the time when an Exception occur
here is my code
Public Shared Sub LogException(ByVal ex As Exception)
Dim trace As Diagnostics.StackTrace = New Diagnostics.StackTrace(ex, True)
LogInfo(String.Format("Error Message :{0} => Error In :{1} => Line Number :{2} => Error Method:{3}",
ex.Message, trace.GetFrame(0).GetFileName(),
trace.GetFrame(0).GetFileLineNumber(),
trace.GetFrame(0).GetMethod().Name))
End Sub
So, the answer to probably all of your questions at once is: "The caught exception will have all of the details it can possibly have."
Your public shared sub LogException is getting an Exception object that is already going to have most of that information. So, you can just do...
LogInfo(ex.ToString())
...and get as much detail as possible.
There are going to be cases where you may not have file name or line numbers, and in some cases the LogInfo statement you have will throw an exception itself. This explains how to reliably get these details, though it comes with potential security risks.
I have found that the type of exception and the stack trace information contained in Exception.ToString() is usually enough to pinpoint the actual errors. When it isn't, its usually a problem with the structure of the code.
The exception already contains the full stack trace. You don't need to create a new one.
1) You can get the stack trace from inside the Exception object using Exception.StackTrace. You don't need to create a new one.
2) If the exception was thrown from somewhere you do not have debugging info (for example inside the framework), you may simply not have a line number or source filename to get.
Duplicate of: In C#, how can I rethrow InnerException without losing stack trace?
I have some operations that I invoke asynchronously on a background thread. Sometimes, things go bad. When this happens, I tend to get a TargetInvocationException, which, while appropriate, is quite useless. What I really need is the TargetInvocationException's InnerException, like this:
try
{
ReturnValue = myFunctionCall.Invoke(Target, Parameters);
}
catch (TargetInvocationException err)
{
throw err.InnerException;
}
That way, my callers are served up with the REAL exception that occured. The problem is, that the throw statement seems to reset the stack trace. I'd like to basically rethrow the inner exception, but keep the stack trace it originally had. How do I do that?
CLARIFICATION:
The reason I want only the inner exception is that this class tries to 'abstract away' the whole fact that these functions (delegates supplied by caller) are run on other threads and whatnot. If there is an exception, then odds are it has nothing to do with being run on a background thread, and the caller would really like the stack trace that goes into their delegate and finds the real issue, not my call to invoke.
It is possible to preserve the stack trace before rethrowing without reflection:
static void PreserveStackTrace (Exception e)
{
var ctx = new StreamingContext (StreamingContextStates.CrossAppDomain) ;
var mgr = new ObjectManager (null, ctx) ;
var si = new SerializationInfo (e.GetType (), new FormatterConverter ()) ;
e.GetObjectData (si, ctx) ;
mgr.RegisterObject (e, 1, si) ; // prepare for SetObjectData
mgr.DoFixups () ; // ObjectManager calls SetObjectData
// voila, e is unmodified save for _remoteStackTraceString
}
This wastes a lot of cycles compared to InternalPreserveStackTrace, but has the advantage of relying only on public functionality. Here are a couple of common usage patterns for stack-trace preserving functions:
// usage (A): cross-thread invoke, messaging, custom task schedulers etc.
catch (Exception e)
{
PreserveStackTrace (e) ;
// store exception to be re-thrown later,
// possibly in a different thread
operationResult.Exception = e ;
}
// usage (B): after calling MethodInfo.Invoke() and the like
catch (TargetInvocationException tiex)
{
PreserveStackTrace (tiex.InnerException) ;
// unwrap TargetInvocationException, so that typed catch clauses
// in library/3rd-party code can work correctly;
// new stack trace is appended to existing one
throw tiex.InnerException ;
}
No, that isn't possible. Your only real opportunity is to follow the recommended pattern and throw your own exception with the appropriate InnerException.
Edit
If your concern is the presence of the TargetInvocationException and you want to disregard it (not that I recommend this, as it could very well have something to do with the fact that it's being run on another thread) then nothing is stopping you from throwing your own exception here and attaching the InnerException from the TargetInvocationException as your own InnerException. It's a little smelly, but it might accomplish what you want.
There is a way of "resetting" the stack trace on an exception by using the internal mechanism that is used to preserve server side stack traces when using remoting, but it is horrible:
try
{
// some code that throws an exception...
}
catch (Exception exception)
{
FieldInfo remoteStackTraceString = typeof(Exception).GetField("_remoteStackTraceString", BindingFlags.Instance | BindingFlags.NonPublic);
remoteStackTraceString.SetValue(exception, exception.StackTrace);
throw exception;
}
This puts the original stack trace in the _remoteStackTraceString field of the exception, which gets concatenated to the newly reset stack trace when the exception is re-thrown.
This is really a horrible hack, but it does achieve what you want. You are tinkering inside the System.Exception class though so this method may therefore break in subsequent releases of the framework.
Although you may feel that the TargetInvocationException is "useless", it's the reality. Don't try to pretend that .NET didn't take the original exception and wrap it with a TargetInvocationException and throw it. That really happened. Some day, you might even want some piece of information that comes from that wrapping - like maybe the location of the code that threw the TargetInvocationException.
You can't do that. throw always resets the stack trace, unless used without parameter. I'm afraid your callers will have to use the InnerException...
Using the "throw" keyword with an exception will always reset the stack trace.
The best thing to do is to catch the actual exception you want, and use "throw;" instead of "throw ex;". Or to throw your own exception, with the InnerException that you want to pass along.
I don't believe what you want to do is possible.
As others have said, use the "throw" keyword without adding to it to keep the exception chain intact. If you need that original exception (assuming that is what you mean) then you could call Exception.GetBaseException() at the end of your chain to get the Exception that started it all.
It is possible with .net 4.5:
catch(Exception e)
{
ExceptionDispatchInfo.Capture(e.InnerException).Throw();
}