CrispyWaffle.Elmah

CrispyWaffle.Elmah provides an exception handler that sends exceptions handled by CrispyWaffle to ELMAH, through the ElmahCore library for ASP.NET Core. Use it when your web application already uses ElmahCore and you want exceptions passed to LogConsumer.Handle to show up in the ELMAH error log.
Package CrispyWaffle.Elmah
Namespace CrispyWaffle.Elmah
Install dotnet add package CrispyWaffle.Elmah
Depends on CrispyWaffle, ElmahCore

How it works

ElmahExceptionHandler implements IExceptionHandler. Set it as the handler with LogConsumer.SetHandler; after that, every LogConsumer.Handle(...) call goes to it.

For each exception the handler:

  1. Works out a category by walking the call stack and taking the full name of the first declaring type whose namespace does not start with CrispyWaffle.
  2. Builds one text block with the message, type name and stack trace of the exception and of each inner exception. While doing so, it calls Error(category, message) on every provider added with ExceptionLogType.Message, once per exception in the chain.
  3. Writes the combined messages with Error(category, ...) to every provider added with ExceptionLogType.Full.
  4. Calls ElmahCore's ElmahExtensions.RaiseError(exception).

ElmahCore must be configured in your host (services.AddElmah(...) and app.UseElmah(), following the ElmahCore documentation) for the raised errors to be stored.

The list of additional providers is static. Providers added through one ElmahExceptionHandler instance are used by every instance, and there is no way to remove them.

Logging pipeline

Getting started

using CrispyWaffle.Elmah;
using CrispyWaffle.Log;
using ElmahCore.Mvc;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddElmah();

var app = builder.Build();
app.UseElmah();

LogConsumer.SetHandler(new ElmahExceptionHandler());

app.MapGet("/fail", () =>
{
    try
    {
        throw new InvalidOperationException("Something failed");
    }
    catch (Exception e)
    {
        LogConsumer.Handle(e);
        return Results.Problem();
    }
});

app.Run();

Reference

ElmahExceptionHandler

public sealed class ElmahExceptionHandler : IExceptionHandler — exception handler that raises exceptions in ELMAH and optionally copies them to other log providers.

Member Description
ElmahExceptionHandler() Implicit parameterless constructor.
Handle(Exception exception) Processes exception as described in How it works.
Handle(object sender, UnhandledExceptionEventArgs args) Casts args.ExceptionObject to Exception and processes it. Suitable for AppDomain.CurrentDomain.UnhandledException.
Handle(object sender, ThreadExceptionEventArgs args) Processes args.Exception.
AddLogProvider<TLogProvider>(ExceptionLogType type) Resolves TLogProvider through ServiceLocator.Resolve<TLogProvider>(), adds it to the shared provider list with type, and returns it. TLogProvider must implement ILogProvider.

ExceptionLogType is defined in the core package (CrispyWaffle.Log.Handlers): Message and Full. See Logging.

Examples

Copy exceptions to a text file log

Exceptions still go to ELMAH, and the full exception text is also written to the text file provider. TextFileLogProvider and its adapter must be resolvable through ServiceLocator.

using CrispyWaffle.Elmah;
using CrispyWaffle.Log;
using CrispyWaffle.Log.Handlers;
using CrispyWaffle.Log.Providers;

var handler = new ElmahExceptionHandler();
handler.AddLogProvider<TextFileLogProvider>(ExceptionLogType.Full).SetLevel(LogLevel.All);

LogConsumer.SetHandler(handler);

AppDomain.CurrentDomain.UnhandledException += handler.Handle;

See also