I have an HttpHandler that is returning `HTTP 1 1 400 body b

Question

I have an HttpHandler that is returning `HTTP 1 1 400 body body must be object` This message is hiding an exception How can I get hold of it I have these filters ``` routes sgzr api v1 bind Api router productService orderService let DebuggingFilters PrintRequestAndResponse then ServerFilters Cors CorsPolicy UnsafeGlobalPermissive then ServerFilters CatchAll then ServerFilters CatchLensFailure then it ```

elifarley · Answer

I think it would be nice to have the exception message or even the stack trace included in the response body

elifarley · Answer

And does the order of CatchAll and CatchLensFailure matter

dave · Answer

the ordering does matter the CatchAll will turn any uncaught exception into a 500 The CatchLensFailure catches LensFailures and turns them into a 400

dave · Answer

the LensFailure DOES contain the exception that caused it so if you write you own CatchLensFailure implementation you can do as you please for the moment ``` object CatchLensFailure Filter override fun invoke next HttpHandler HttpHandler = try next it catch lensFailure LensFailure when lensFailure target is Response gt throw lensFailure lensFailure target is RequestContext gt throw lensFailure lensFailure overall == Failure Type Unsupported gt Response UNSUPPORTED MEDIA TYPE else gt Response BAD REQUEST description lensFailure failures joinToString ```

elifarley · Answer

It turns out I only needed to invert the order of the 2 catchers which now is ``` then ServerFilters CatchLensFailure then ServerFilters CatchAll ``` Before this only `HTTP 1 1 400 body body must be object` would appear By doing this a nice stack trace appears on stdout only

elifarley · Answer

Here s what I get now ``` HTTP 1 1 500 Internal Server Error org http4k lens LensFailure body body must be object at org http4k contract ContractRouteSpec$invoke$1 invoke routeSpec kt 31 at org http4k contract ContractRouteSpec$invoke$1 invoke routeSpec kt 11 at org http4k core Http4kKt$then$2 invoke Http4k kt 19 ```

elifarley · Answer

But your suggestion seems better

elifarley · Answer

The Lens Failure was caused by an `InvalidJSONException Could not convert to a JSON Object or Array` I want to have this information readily available I ll follow your suggestion of creating a custom CatchLensFailure

dave · Answer

yep it s a general failure are you using GSON

elifarley · Answer

yep

dave · Answer

ok currently we swallow the exception and it isn t passed to the InvalidJsonException I ll change that to add the cause

dave · Answer

which might give you a better example of what s going on and why your JSON is invalid

dave · Answer

actually it looks like that exception is directly caused by something in your code not being able to convert a string to an object or an array ``` override fun String asJsonObject JsonElement = JsonParser parse this let if it isJsonArray || it isJsonObject it else throw InvalidJsonException ```

elifarley · Answer

that would be great thanks

elifarley · Answer

in fact the problem is that the reference is null

dave · Answer

so there isn t currently a cause to display

elifarley · Answer

But at least there s the name of the exception to be shown InvalidJsonException

dave · Answer

yeah you can see that the parse doesn t fail it fails the test in the let

elifarley · Answer

Maybe ` throw InvalidJsonException Not an array nor an object $it `

elifarley · Answer

would it make sense

dave · Answer

yeah I ll change it to be a message

elifarley · Answer

Having more contextual information on the exception feels good

elifarley · Answer

Here s how I would change the LensFailure class ``` open class LensFailure val failures List lt Failure gt override val cause Exception = null val target Any = null Exception failures joinToString $it + cause let $it cause ```

elifarley · Answer

Does it look good

dave · Answer

no need to change the LensFailure we ve already got the cause as a field if we need it you can get the message from there

dave · Answer

Generally we use the message as a general purpose thing and then we can drill down to get the cause message if we need it

elifarley · Answer

got it

dave · Answer

so in your new CatchLensFailure filter you can just access the cause and then add it if required

elifarley · Answer

yep exactly