Error when throwing an exception in a behavior.

[pborgmans]

Describe the bug

Description

When encountering an error in a behavior we're getting this exception:

System.ArgumentException: The value "False" is not of type "System.String" and cannot be used in this generic collection. (Parameter 'value')
   at System.Collections.Generic.Dictionary`2.System.Collections.IDictionary.set_Item(Object key, Object value) 
   at NServiceBus.MainPipelineExecutor.Invoke(MessageContext messageContext, CancellationToken cancellationToken) in /_/src/NServiceBus.Core/Pipeline/MainPipelineExecutor.cs:line 67
   at NServiceBus.MainPipelineExecutor.Invoke(MessageContext messageContext, CancellationToken cancellationToken) in /_/src/NServiceBus.Core/Pipeline/MainPipelineExecutor.cs:line 82
   at NServiceBus.Transport.AzureServiceBus.MessagePump.ProcessMessage(ServiceBusReceivedMessage message, ProcessMessageEventArgs processMessageEventArgs, String nativeMessageId, Dictionary`2 headers, BinaryData body, CancellationToken messageProcessingCancellationToken) in /_/src/Transport/Receiving/MessagePump.cs:line 263

This refers to this line of code: (https://github.com/Particular/NServiceBus/blob/master/src/NServiceBus.Core/Pipeline/MainPipelineExecutor.cs#L12)
ex.Data["Pipeline canceled"] = transportReceiveContext.CancellationToken.IsCancellationRequested;
So if I understand correctly it's not allowed to put a bool value into the dictionary, it expects a string value.

Expected behavior

Get the original exception that is failing in the pipeline, this exception hides the original error.

Actual behavior

An exception is happening in the MainPipelineExecutor which causes the original exception to not be shown.

Versions

10.1.4

Please list the version of the relevant packages or applications in which the bug exists.

Steps to reproduce

Add a behavior which throws an exception

Relevant log output

Additional Information

Workarounds

No blocker, just lack of information of what the original error was.

Possible solutions

.ToString() on the bool value.

Additional information

[helenktsai]

@pborgmans Could you please open a support case so you can send us the code that throws the exception and if you're using any custom exception type, the code for that as well?

[DavidBoike]

I believe the problem is a custom exception changing the contract of the Exception class's Data dictionary.

Exception.Data is defined as an IDictionary which supports Add(object key, object? value) and also the indexer object? this[Object key] { get; set; }. So this code works just fine:

try
{
    throw new Exception("Boom");
}
catch (Exception x)
{
    x.Data["Key"] = false;
}

But if a custom exception were to redefine the Data dictionary like this, then you'd get exactly the runtime problem described in this issue:

public class CustomException(string message) : Exception(message)
{
    private Dictionary<string, string> localData = new();

    public override IDictionary Data => localData;
}

try
{
    throw new Exception("Boom");
}
catch (CustomException x)
{
    // List<string, string> implements IDictionary but fails to insert a non-string at runtime
    x.Data["Key"] = false;
}

So the problem is a bug in the exception type that is violating the promise made by the contract of the Exception class.