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C#: Sending typed exceptions to another process -> transform to base exception?

I'm working on a distributed system composed of multiple services (processes) working together orchestrated via message broker (service bus). Some of these service are very time sensitive, so we had the idea of using the bus the propagate exceptions to a service that would be used as a central point to log (to a database/on disk) the exceptions of all other services in order not to create latency in our services because we know sending a message is faster than writing on disk. So using NLog, I create a new target for sending exceptions on bus and redirect all service exception handling to it.
It works fine for basic framework exceptions, but of course some exceptions can be pretty complex objects. When using different libraries, not only are some exception not serializable (ex: IronPython), but more importantly our ExceptionLogger service don't have reference to every external dll used by every other endpoints, so it can't instantiate the typed exception.
Here's a few idea that I had to fix my problem, but none work:
Have the exception logger service reference every dlls used by the other services. In my opinion this is not clean, pretty overkill and still don't handle the case of exceptions that can't even be serialized and passed on the bus.
Creating a custom class that doesn't inherit from exception to pass only the data (as Antony Booth method here: How to serialize an Exception object in C#?). Problem with this is that when I receive an instance of this class on my exception logger endpoint and want to trigger a log, I can't create a new Exception() from it to create a NLog LogEventInfo object.
Transform the specially typed exception to a base native Exception type before sending it on the bus. This way, I lose some information, but I would keep the Message, Stacktrace and the InnerException stack, which is pretty much everything I need. Unfortunately, I did not find a way to do it and don't think it is possible.
That makes me question the relevance of the whole idea, am I simply going into a wrong path?

Option 4. Create an Exception assembly to store all of the custom exception types within your organization and reference that assembly in every other service. It's a centralized store of Exceptions.

[Serializable]
public sealed class SerializableException : Exception
{
public SerializableException()
{
}
public SerializableException(SerializationInfo info, StreamingContext context)
: base(info, context)
{
}
public SerializableException(Exception exception)
: base(exception.Message, exception.InnerException == null ? null : new SerializableException(exception.InnerException))
{
_data = exception.Data;
HelpLink = exception.HelpLink;
HResult = exception.HResult;
Source = exception.Source;
_stackTrace = exception.StackTrace;
}
public override IDictionary Data { get { return _data; } }
public override string StackTrace { get { return _stackTrace; } }
private readonly IDictionary _data;
private readonly string _stackTrace;
}

Throw or not throw the exception from the methods consumed by the ASP.NET Web API layer

Assume that I am building an ASP.NET Web API application and it has the following structure:
As you can see from the diagram, the ASP.NET Web API core will talk to domain service layer (e.g. MembershipService class which has methods such as GetUsers, CreateUser, etc.) and my service classes will talk to one or multiple repositories to handle the operations.
It's very obvious that a service operation (such as MembershipService.CreateUser method) would fail for several reasons (unmet conditions, an exception thrown by the repository, etc.) and this is the place where I have the doubts.
Do you think that service classes should handle exceptions and return some sort of result object such as the below one:
public class OperationResult {
public OperationResult(bool isSuccess) : this(isSuccess) {
IsSuccess = isSuccess;
}
public OperationResult(bool isSuccess, Exception exception) : this(isSuccess) {
Exception = exception;
}
public bool IsSuccess { get; private set; }
public Exception IsSuccess { get; private set; }
}
public class OperationResult<TEntity> : OperationResult {
public OperationResult(bool isSuccess)
: base(isSuccess) { }
public OperationResult(bool isSuccess, Exception exception)
: base(isSuccess, exception) { }
public TEntity Entity { get; set; }
}
Or do you think that the service methods shouldn't abstract the exception like that and should throw the exception directly or indirectly (creating a new meaningful exception type specific to operation and put the thrown exception as its inner exception)?

When you are in-process, use exceptions.

I don't see ANY point in avoiding exceptions. Exceptions are there for good reasons, mainly to be used!
Just try to look at the big picture: you are trying to change Exception mechanism with the old fashion way of error checking. This way you'll lose all the merits of Exceptions (like separation of the error-handling and regular code, CallStack, ...) and gain nothing in return.
What I usually do in this situation is to catch the exception in service layer and rewrap it into a custom exception (with the reference to the original exception in the InnerException field).

Taking a page from Microsoft's book, the implementation of the Membership API throws exceptions rather than handling them and returning a result object, so I would consider this a best practice as long as you don't control both the client and the API.
In the case where you do control both the client and the API, it is my personal preference to return a result object or an error message. The reason for this is that I want to log capture detailed information about the source of actual exceptions, but I don't want an exception for everything that could go wrong, such as the password being incorrect.
In this case, a simple error message to the user will be more than sufficient. From real-world experience, recording exceptions to the event log or log file every time a validation error occurs is a major burden on operations personnel that are trying to determine whether or not there is an actual fault occurring or whether it is just a user's typo.

WCF web service call - which exception(s) to catch?

I have a program that calls an external web service, and I want to present the user with a friendly dialog if e.g. the server is down, someone cut the cable etc. Assuming the following code
try {
client.MyWebService()
}
catch(? ex)
{
// display friendly dialog explaining what went wrong
}
what exception(s) should I put in place of the question mark in the code? It is kind of hard to actually test situations like this when everything is working smoothly and I have no control over the external part, so some insight would be appreciated.
Thanks!

The first thing to do is take advantage of the .Faulted event on your proxy, which you can wire up like this:
((ICommunicationObject)client).Faulted += new EventHandler(client_Faulted);
In your client_Faulted event handler you can then try re-connecting, or shifting to a backup server, or disabling the UI, logging the error, or displaying a message there.
It's obviously still good practice to wrap each call in a try-catch as well, but the .Faulted event can let you deal with most channel problems even earlier.
As for the exception itself, you can have your service throw a FaultException that gets passed back to the client with the details you provide. See an example of its use at this blog posting.
You won't get a FaultException if the channel itself fails (FaultException is a way for the server to communicate its own internal faults to the client).
For channel faults, you may get a CommunicationException or TimeoutException.
Finally, take a look at this project on Codeplex for generating Exception Handling WCF proxies. It may give you a more flexible way of handing faults.

It's not really the client's job to provide as much detail as possible. The maximum amount you really have to provide at the client side is as much as you get back in your exception.
var userName = "bob";
try
{
client.MyWebService(userName);
}
catch(Exception ex)
{
//Maybe we know WellKnownExceptions and can provide Foo advice:
if (ex is WellKnownException)
{
Console.WriteLine("WellKnownException encountered, do Foo to fix Bar.");
}
//otherwise, this is the best you can do:
Console.WriteLine(string.Format(
"MyWebService call failed for {0}. Details: {1}", userName, ex));
}

I was asking the same question, as I have to implement some exception handling on web services calls at my client application, so I ended up here. Although it's an old question, I'd like to give my two cents, updating it a little bit.
The answer given by C. Lawrence Wenham was already very good and points to some interesting information, although the blog link is broken and Codeplex is now archived.
I found those articles very valuables:
Sending and Receiving Faults
https://learn.microsoft.com/en-us/dotnet/framework/wcf/sending-and-receiving-faults
Expected Exceptions
https://learn.microsoft.com/en-us/dotnet/framework/wcf/samples/expected-exceptions
And this article from Michèle Leroux Bustamante (apparently the creator of the Exception Handling WCF Proxy Generator CodePlex project) is very insighful also:
An Elegant Exception-Handling Proxy Solution
http://www.itprotoday.com/microsoft-visual-studio/elegant-exception-handling-proxy-solution
I'm still studying the subject but I guess I'll use a lot of ideias from Michèle. I'm just a little bit concerned about using reflection to call the web service's methods, but I wonder if this would have any impact in such kind of operation, that is inherently slow already.
Just to answer here explicitly what was asked originally, which are the exceptions that could be tested against a web service call:
string errorMessage = null;
// A class derived from System.ServiceModel.ClientBase.
MyWebService wcfClient = new MyWebService();
try
{
wcfClient.Open();
wcfClient.MyWebServiceMethod();
}
catch (TimeoutException timeEx)
{
// The service operation timed out.
errorMessage = timeEx.Message;
}
catch (FaultException<ExceptionDetail> declaredFaultEx)
{
// An error on the service, transmitted via declared SOAP
// fault (specified in the contract for an operation).
errorMessage = declaredFaultEx.Detail.Message;
}
catch (FaultException unknownFaultEx)
{
// An error on the service, transmitted via undeclared SOAP
// fault (not specified in the contract for an operation).
errorMessage = unknownFaultEx.Message;
}
catch (CommunicationException commEx)
{
// A communication error in either the service or client application.
errorMessage = commEx.Message;
}
finally
{
if (wcfClient.State == CommunicationState.Faulted)
wcfClient.Abort();
else
wcfClient.Close();
}
As stated by the articles, the order the exceptions are catched is important, since FaultException<TDetail> derives from FaultException, and FaultException derives from CommunicationException.

Proper catching of specific exceptions through web service

I am currently using a C# .NET Service in our client program. As part of the server design, several custom made exceptions are thrown to indicate specific errors (as in any normal desktop program).
The problem is that the Web Service catches these errors and serializes them into a FaultException, with the actual exception (like NoRoomsAvailableException) written in the Message field.
My question is whether there is a best practice for handling these errors. We have just begun working on this, and we would probably do some text pattern matching to pull out the exception type and error message, but it seems like a hacky way to do it, so any "clean" way of doing it would be much appreciated.

The proper way would be to define fault contracts. For example in your web service you could do the following:
[DataContract]
public class NoRoomsAvailableFaultContract
{
[DataMember]
public string Message { get; set; }
}
Next you declare this contract for a given service operation
[ServiceContract]
public interface IMyServiceContract
{
[OperationContract]
[FaultContract(typeof(NoRoomsAvailableFaultContract))]
void MyOperation();
}
And you implement it like so:
public class MyService : IMyServiceContract
{
public void MyOperation()
{
if (somethingWentWrong)
{
var faultContract = new NoRoomsAvailableFaultContract()
{
Message = "ERROR MESSAGE"
};
throw new FaultException<NoRoomsAvailableFaultContract>(faultContract);
}
}
}
In this case the NoRoomsAvailableFaultContract will be exposed in the WSDL and svcutil.exe could generate a proxy class. Then you could catch this exception:
try
{
myServiceProxy.MyOperation();
}
catch (FaultException<NoRoomsAvailableFaultContract> ex)
{
Console.WriteLine(ex.Message);
}

darin has the correct answer. I'll only say explicitly what he implies: web services do not pass exceptions. They return SOAP Faults. If you define your faults properly, as he does, then you get to throw FaultException<fault>. This will become a SOAP Fault with fault in the detail element. In the case of a .NET client, this will then be turned into a FaultException<fault>, which you can catch.
Other platforms may handle this somewhat differently. I've seen IBM's Rational Web Developer generate Java proxy code that creates a separate exception for each declared fault. That was a version before Java generics, so maybe by now it does the same thing as .NET does.

Easy way to catch all unhandled exceptions in C#.NET

I have a website built in C#.NET that tends to produce a fairly steady stream of SQL timeouts from various user controls and I want to easily pop some code in to catch all unhandled exceptions and send them to something that can log them and display a friendly message to the user.
How do I, through minimal effort, catch all unhandled exceptions?
this question seems to say it's impossible, but that doesn't make sense to me (and it's about .NET 1.1 in windows apps):

All unhandled exceptions finally passed through Application_Error in global.asax. So, to give general exception message or do logging operations, see Application_Error.

If you need to catch exeptions in all threads the best aproach is to implement UnhandledExceptionModule and add it to you application look here
for an example

Use the Application_Error method in your Global.asax file. Inside your Application_Error method implementation call Server.GetLastError(), log the details of the exception returned by Server.GetLastError() however you wish.
e.g.
void Application_Error(object sender, EventArgs e)
{
// Code that runs when an unhandled error occurs
log4net.ILog log = log4net.LogManager.GetLogger(typeof(object));
using (log4net.NDC.Push(this.User.Identity.Name))
{
log.Fatal("Unhandled Exception", Server.GetLastError());
}
}
Don't pay too much attention to the log4net stuff, Server.GetLastError() is the most useful bit, log the details however you prefer.

The ELMAH project sounds worth a try, its list of features include:
ELMAH (Error Logging Modules and
Handlers) is an application-wide error
logging facility that is completely
pluggable. It can be dynamically added
to a running ASP.NET web application,
or even all ASP.NET web applications
on a machine, without any need for
re-compilation or re-deployment.
Logging of nearly all unhandled exceptions.
A web page to remotely view the entire log of recoded exceptions.
A web page to remotely view the full details of any one logged
exception.
In many cases, you can review the original yellow screen of death that
ASP.NET generated for a given
exception, even with customErrors mode
turned off.
An e-mail notification of each error at the time it occurs.
An RSS feed of the last 15 errors from the log.
A number of backing storage implementations for the log
More on using ELMAH from dotnetslackers

You can subscribe to the AppDomain.CurrentDomain.UnhandledException event.

It's probably important to note that you are not supposed to catch unhandled exceptions. If you are having SQL timeout issues, you should specifically catch those.

Do you mean handling it in all threads, including ones created by third-party code? Within "known" threads just catch Exception at the top of the stack.

I'd recommend looking at log4net and seeing if that's suitable for the logging part of the question.

If using .net 2.0 framework, I use the built in Health Monitoring services. There's a nice article describing this method here: https://web.archive.org/web/20210305134220/https://aspnet.4guysfromrolla.com/articles/031407-1.aspx
If you're stuck with the 1.0 framework, I would use ELMAH:
http://msdn.microsoft.com/en-us/library/aa479332.aspx
hope this helps

There are 2 parts to this problem handling & identifying.
Identifying
This is what you do when the exception is finally caught, not necessarily where it is thrown. So the exception at that stage must have enough context information for you to idenitfy what the problem was
Handling
For handling, you can
a) add a HttpModeule. See
http://www.eggheadcafe.com/articles/20060305.asp
I would suggest this approach only when there is absolutely no context informaatn available and there might be issuus wiih IIS/aspnet, In short for catastrophic situations
b) Create a abstract class called AbstractBasePage which derives from Page class and have all your codebehind classes derive from AbstractBasePage
The AbstractBasePage can implement that Page.Error delegate so that all exceptions which percolate up through the n-tier architecture can be caught here(and possibly logged)
I would suggest this cause for the kind of exceptions you are talking about (SQlException) there is enough context information for you to identify that it was a timeout and take possible action. This action might include redirecting user to a custom error page with appropriate message for each different kind of exception (Sql, webservice, async call timeouts etc).
Thanks
RVZ

One short answer is to use (Anonymous) delegate methods with common handling code when the delegate is invoked.
Background: If you have targeted the weak points, or have some boilerplate error handling code you need to universally apply to a particular class of problem, and you don't want to write the same try..catch for every invocation location, (such as updating a specific control on every page, etc).
Case study: A pain point is web forms and saving data to the database. We have a control that displays the saved status to the user, and we wanted to have common error handling code as well as common display without copy-pasting-reuse in every page. Also, each page did it's own thing in it's own way, so the only really common part of the code was the error handling and display.
Now, before being slammed, this is no replacement for a data-access layer and data access code. That's all still assumed to exist, good n-tier separation, etc. This code is UI-layer specific to allow us to write clean UI code and not repeat ourselves. We're big believers in not quashing exceptions, but certain exceptions shouldn't necessitate the user getting a generic error page and losing their work. There will be sql timeouts, servers go down, deadlocks, etc.
A Solution: The way we did it was to pass an anonymous delegate to a method on a custom control and essentially inject the try block using anonymous delegates.
// normal form code.
private void Save()
{
// you can do stuff before and after. normal scoping rules apply
saveControl.InvokeSave(
delegate
{
// everywhere the save control is used, this code is different
// but the class of errors and the stage we are catching them at
// is the same
DataContext.SomeStoredProcedure();
DataContext.SomeOtherStoredProcedure();
DataContext.SubmitChanges();
});
}
The SaveControl itself has the method like:
public delegate void SaveControlDelegate();
public void InvokeSave(SaveControlDelegate saveControlDelegate)
{
// I've changed the code from our code.
// You'll have to make up your own logic.
// this just gives an idea of common handling.
retryButton.Visible = false;
try
{
saveControlDelegate.Invoke();
}
catch (SqlTimeoutException ex)
{
// perform other logic here.
statusLabel.Text = "The server took too long to respond.";
retryButton.Visible = true;
LogSqlTimeoutOnSave(ex);
}
// catch other exceptions as necessary. i.e.
// detect deadlocks
catch (Exception ex)
{
statusLabel.Text = "An unknown Error occurred";
LogGenericExceptionOnSave(ex);
}
SetSavedStatus();
}
There are other ways to achieve this (e.g. common base class, intefaces), but in our case this had the best fit.
This isn't a replacement to a great tool such as Elmah for logging all unhandled exceptions. This is a targeted approach to handling certain exceptions in a standard manner.

Timeout errors typically occur if you are not forcefully closing your sqlconnections.
so if you had a
try {
conn.Open();
cmd.ExecuteReader();
conn.Close();
} catch (SqlException ex) {
//do whatever
}
If anything goes wrong with that ExecuteReader your connection will not be closed. Always add a finally block.
try {
conn.Open();
cmd.ExecuteReader();
conn.Close();
} catch (SqlException ex) {
//do whatever
} finally {
if(conn.State != ConnectionState.Closed)
conn.Close();
}

This is old question, but the best method (for me) is not listed here. So here we are:
ExceptionFilterAttribute is nice and easy solution for me. Source: http://weblogs.asp.net/fredriknormen/asp-net-web-api-exception-handling.
public class ExceptionHandlingAttribute : ExceptionFilterAttribute
{
public override void OnException(HttpActionExecutedContext context)
{
var exception = context.Exception;
if(exception is SqlTimeoutException)
{
//do some handling for this type of exception
}
}
}
And attach it to f.e. HomeController:
[ExceptionHandling]
public class HomeController: Controller
{
}