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:

Handler	Action	Transition
Rethrow	Apply ReThrow transition	ReThrow
NextPolicy	Try to execute next policy suitable for given exception	NextPolicy
Handled	Mark exception as handled to prevent it from bein re thrown	Handled
Retry	Execute aspnetcore pipeline again if retry count not exceed limit	Retry (if retry limit not exceeded) or NextHandler
Log	Log exception	NextHandler
DisableFurtherLog	Prevent exception from being logged again in current middleware (for current request only)	NextHandler
Response	Modify response (set status code, headers and body) depending on further response builder configuration	NextHandler

Sample of transitions:

Nuget

Package	Comments
Community.AspNetCore.ExceptionHandling	Main functionality
Community.AspNetCore.ExceptionHandling.Mvc	Allow to use MVC IActionResult (including ObjectResult) in 'Response' handler
Community.AspNetCore.ExceptionHandling.NewtonsoftJson	Allow to set Json serialized object as a response body in 'Response' handler. Use it only if 'Community.AspNetCore.ExceptionHandling.Mvc' usage not possible