How to suppress 'An unhandled exception has occurred while executing the request.' log message with Serilog

Question

When implementing my own Exception handler using app.UseExceptionHandler with an exception handler lambda / delegate (Documentation) I do not want Microsofts Exception handler middleware to log this error:

An unhandled exception has occurred while executing the request.

This exception message clutters my log file because I take care of logging the exception with an appropriate LogLevel by myself.

This is how I register my own ErrorHandler:

app.UseExceptionHandler(errorApp =>
                errorApp.Run(ErrorHandler));

As described in this issue filtering this exact message and nothing else is not possible in a simple way.

How do I filter this exact log message and nothing else from the middleware?

I am using:

• ASP.NET Core 3.1
• Serilog 3.4.0

Answer 1

As described in the issue mentioned above, we can use a Filter expression for this. Unfortunately the issue only describes a solution for a deprecated package and is filtering all messages from the Middleware, not only the mentioned message.

1. Install the Serilog.Expressions package
2. Update the matching appsettings.json with this configuration:

  "Serilog": {
    "Using": [ "Serilog.Expressions" ],
    "Filter": [
      {
        "Name": "ByExcluding",
        "Args": {
          "expression": "@l='Error' and SourceContext='Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware' and @mt='An unhandled exception has occurred while executing the request.'"
        }
      }
    ]
  }

3. Make sure you have matching code that loads the configuration from appsettings.json as documented, e.g.:

Log.Logger = new LoggerConfiguration()
                .ReadFrom.Configuration(configuration)
                .CreateLogger();

This way you can keep all other messages from the ExceptionHandlerMiddleware and just disable the redundant error log message.

Side note: In case the response already has started, our custom exception handler will not be executed - but a warning will be logged and the exception will be rethrown and later logged by another application layer - at least in the application I tested. You can test this behavior by adding this code somewhere before the exception is thrown (context is the current HttpContext):

 await context.Response.WriteAsync("fish");