ASP.NET Core Exception Handling Middleware

ASP.NET Core exception handling policies middleware. Allows to set a chain of exception handlers per exception type. OOTB handlers: log, retry, set responce headers and body

Code Sample

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddExceptionHandlingPolicies(options =>
    {
        options.For<InitializationException>().Rethrow();
                
        options.For<SomeTransientException>().Retry(ro => ro.MaxRetryCount = 2).NextPolicy();
                
        options.For<SomeBadRequestException>()
            .Response(e => 400)
                .Headers((h, e) => h["X-MyCustomHeader"] = e.Message)
				.WithBody((req,sw, exception) =>
                    {
                        byte[] array = Encoding.UTF8.GetBytes(exception.ToString());
                        return sw.WriteAsync(array, 0, array.Length);
                    })
            .NextPolicy();

        // Ensure that all exception types are handled by adding handler for generic exception at the end.
        options.For<Exception>()
            .Log(lo =>
                {
                    lo.LogAction = (l, c, e) => l.LogError(e,"UnhandledException");
                    lo.Category = (context, exception) => "MyCategory";
                })
            .Response(null, ResponseAlreadyStartedBehaviour.GoToNextHandler)
                .ClearCacheHeaders()
                .WithObjectResult((r, e) => new { msg = e.Message, path = r.Path })
            .Handled();
    });
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseExceptionHandlingPolicies();
    app.UseMvc();
}

Policy exception handler transitions

When exception catched in middleware it try to apply handlers from first registered policy suitable for given exception. Policy contains a chain of handlers. Each handler perform some action and apply transition. To prevent re throw of exception handlers chain MUST ends with "Handled" transition. Following handlers currently supported:

Sample of transitions:

Nuget