ASP.Net Core 2.1 Issue

[jculverwell]

Just upgraded to ASP.Net Core 2.1 and got this error:

InvalidOperationException: An error occurred when configuring the exception handler middleware. Either the 'ExceptionHandlingPath' or the 'ExceptionHandler' option must be set in 'UseExceptionHandler()'.

My setup before was this:

 app.UseExceptionHandler().WithConventions(x => {
                x.ContentType = "application/json";
                x.MessageFormatter(s => JsonConvert.SerializeObject(new
                {
                    Message = "Internal Server Error"
                }));
                x.OnError((exception, httpContext) =>
                {
                    Log.Error(exception, "WebAPI Global Exception Handler");
                    return Task.CompletedTask;
                });
            });

Adding app.UseExceptionHandler("/error") as below seems to fix it.

app.UseExceptionHandler("/error").WithConventions(x => {
                x.ContentType = "application/json";
                x.MessageFormatter(s => JsonConvert.SerializeObject(new
                {
                    Message = "Internal Server Error"
                }));
                x.OnError((exception, httpContext) =>
                {
                    Log.Error(exception, "WebAPI Global Exception Handler");
                    return Task.CompletedTask;
                });
            });

Just wanted to give you a heads up and check the workaround makes sense. Thanks for a great repo.

[josephwoodward]

Great, thanks for reporting this @jculverwell, I'll take a look.

[alhardy]

Was curious about this also

[josephwoodward]

There's a bit more about why this was changed here.

I've come to the conclusion that this library's config should live separate to the UseExceptionHandler() endpoint. I've got a new release coming out in the next few days that doesn't change any behaviours, but it goes from:

app.UseExceptionHandler().WithConventions(...);

to

app.UseGlobalExceptionHandler(...);

It still uses the UseExceptionHandler under the hood, but now it's required to have a string passed to it, it feels very jarring and unclear.

[slang25]

It's worth noting that this was changed in 2.1 because leaving it empty is dangerous. By default in 2.0 and below it will use the current path as the error handler path, so for us we had POST requests being "replayed" and things getting saved to the database twice etc...

[josephwoodward]

so for us we had POST requests being "replayed" and things getting saved to the database twice etc...

Was GlobalExceptionHandler causing them to be posted twice?

[slang25]

No, just using using UseExceptionHandler with no parameter did it

[josephwoodward]

I've now released a beta package which resolves this (it's a major version bump as it includes some breaking changes, but they're just method renames). If you'd like to give it a try I'd love to hear how you get on with it.

The new version can be found here https://www.nuget.org/packages/GlobalExceptionHandler/4.0.0-beta1 and the release notes here.