private void OnException()

in src/Activities/Internal/DiagnosticsListener/DiagnosticsObserversInitializer.cs [105:142]

• 28 lines of code
• 4 McCabe index (conditional complexity)

		private void OnException(string eventName, object? payload) =>
			m_logger.LogError(
				Tag.Create(),
				ExtractExceptionFromPayload(payload),
				"Exception diagnostic event '{0}' with payload '{1}'", eventName, payload);


		// Made internal for unit testing
		internal static Exception? ExtractExceptionFromPayload(object? payload)
		{
			if (payload == null)
			{
				return null;
			}
			else if (payload is Exception exception)
			{
				return exception;
			}
			else
			{
				// Attempting to find exception property since payload often use private classes,
				// It would be completely removed after .NET 5 release.
				// It's definitely not ideal identification
				// DataAdapters doing it by parameter name https://github.com/aspnet/EventNotification/blob/28b77e7fb51b30797ce34adf86748c98c040985e/src/Microsoft.Extensions.DiagnosticAdapter/Internal/ProxyMethodEmitter.cs#L69
				// Sample class with payload https://github.com/dotnet/runtime/blob/master/src/libraries/System.Net.Http/src/System/Net/Http/DiagnosticsHandler.cs#L181
				Type payloadType = payload.GetType();
				if (!s_exceptionProperties.TryGetValue(payloadType, out PropertyInfo? propertyInfo))
				{
					propertyInfo = payload.GetType()
						.GetProperties()
						.FirstOrDefault(p => typeof(Exception).IsAssignableFrom(p.PropertyType));

					s_exceptionProperties.TryAdd(payloadType, propertyInfo);
				}

				return propertyInfo?.GetValue(payload) as Exception;
			}
		}