Get line number where exception occurred in ASP.NET Core

Question

I've implemented a custom exception filter based on this blog post https://blog.kloud.com.au/2016/03/23/aspnet-core-tips-and-tricks-global-exception-handling/ .

I now noticed that I cannot get the file name or the line number where the exception occurred from StackFrame; the value for method GetFileLineNumber is always 0.

A quick example of what I tried:

StackTrace trace = new StackTrace(exception, true);
StackFrame[] stackFrames = trace.GetFrames();
if (stackFrames != null) {
 foreach (StackFrame traceFrame in stackFrames) {
   sourceFile = traceFrame.GetFileName();
   sourceLineNumber = traceFrame.GetFileLineNumber();
  }
}

Just to mention: GetFileName returns also null, but I can get the namespace and class name from various locations, so it's not a problem.

Noticed somewhere that I should have the PDB file on the folder for this to work and I checked that I already have it. And even if it worked, this should work in production environment as well.

Tried also using Caller Information (https://msdn.microsoft.com/en-us/library/mt653988.aspx) but there's a bit different problem. The exception filter has to implement IExceptionFilter interface and use it's method. Therefore I cannot add the attributes even if they are optional.

Here's the code part from Startup.cs:

public void ConfigureServices(IServiceCollection services) {
 ...
 services.AddMvc(config => {
  config.Filters.Add(new ApplicationExceptionFilter());
 });
}

And here's the custom Filter

public class ApplicationExceptionFilter : IExceptionFilter {
 public void OnException(ExceptionContext context) {
  ApplicationExceptionHandler.handleException(context.HttpContext, context.Exception);
 }
}

And what I tried for getting the Caller Information was:

public void OnException(ExceptionContext context,
 [System.Runtime.CompilerServices.CallerLineNumber] int sourceLineNumber = 0) {

But that will not work since it doesn't implement the interface anymore.

How can I get the line number while still handling the exceptions in a single place?

---

Assumed that my problem is the fact that I'm not getting line number from stack trace and reproduced the problem with:

public ActionResult ServerError() {
 Int32 x = 0;
 try {
  return Content((1 / x).ToString());
 } catch (Exception ex) {
  StackTrace trace = new StackTrace(ex, true);
  StackFrame[] stackFrames = trace.GetFrames();
  if (stackFrames != null) {
   foreach (StackFrame traceFrame in stackFrames) {
    String sourceFile = traceFrame.GetFileName();
    int sourceLineNumber = traceFrame.GetFileLineNumber();
   }
  }
 }
 return Content("");
}

Still not getting values for sourceFile (it's null) or sourceLineNumber (it's 0).

Answer 1

Take a look at the DeveloperErrorPageMiddleware implementation:

    private IEnumerable<ErrorDetails> GetErrorDetails(Exception ex)
    {
        for (var scan = ex; scan != null; scan = scan.InnerException)
        {
            var stackTrace = ex.StackTrace;
            yield return new ErrorDetails
            {
                Error = scan,
                StackFrames = StackTraceHelper.GetFrames(ex)
                    .Select(frame => GetStackFrame(frame.MethodDisplayInfo.ToString(), frame.FilePath, frame.LineNumber))
            };
        };
    }

    // make it internal to enable unit testing
    internal StackFrame GetStackFrame(string method, string filePath, int lineNumber)
    {
        var stackFrame = new StackFrame
        {
            Function = method,
            File = filePath,
            Line = lineNumber
        };

        if (string.IsNullOrEmpty(stackFrame.File))
        {
            return stackFrame;
        }

        IEnumerable<string> lines = null;
        if (File.Exists(stackFrame.File))
        {
            lines = File.ReadLines(stackFrame.File);
        }
        else
        {
            // Handle relative paths and embedded files
            var fileInfo = _fileProvider.GetFileInfo(stackFrame.File);
            if (fileInfo.Exists)
            {
                // ReadLines doesn't accept a stream. Use ReadLines as its more efficient
                // relative to reading lines via stream reader
                if (!string.IsNullOrEmpty(fileInfo.PhysicalPath))
                {
                    lines = File.ReadLines(fileInfo.PhysicalPath);
                }
                else
                {
                    lines = ReadLines(fileInfo);
                }
            }
        }

        if (lines != null)
        {
            ReadFrameContent(stackFrame, lines, stackFrame.Line, stackFrame.Line);
        }

        return stackFrame;
    }