I am trying to extract better error message from Jackson deserialization of request Body - within `F...

# http4k

[Vojtěch Knyttl]

I am trying to extract better error message from Jackson deserialization of request Body - within Filter implemented in the example I am only getting 400 BAD REQUEST whereas Jackson provides a nice error description. Is it possible to get this very description to log within the logging filter?

https://gist.github.com/knyttl/bd0ffe5474e14a9e64f71d78249bac5b

[dave]

Yep. Catch the LensFailure that is thrown and you will be able to get the message from there. You'll have to wrap the handler that is returned in the bindContract call instead of wrapping the contract itself. (Because the contract handler also contains a catch filter)

[Vojtěch Knyttl]

I tried googling and find this:

val jsonResultLens = Body.json().toLens().asResult()
    val jsonResult: Result<JsonNode, LensFailure> = jsonResultLens(Request(GET, "/foo"))
    println(jsonResult)

is this what you meant? using jsonResultLens within the filter? however the method .asResult() seems to be missing - hasn't it been removed?

[dave]

Result wasn't removed. but you do need to include result4k manually. However, this will do what you want: https://gist.github.com/daviddenton/49d397479f2bf7e3ba48182d0a783483

[dave]

also - one more thing - when you're posting Gists, please include an entire runnable example including imports so that it's easy for everyone to run exactly the same thing instead of having to rewrite it. 🙂

[Vojtěch Knyttl]

okay, will do next time

[Vojtěch Knyttl]

hm in fact - i don't get any exception

[Vojtěch Knyttl]

no lensfailure

[Vojtěch Knyttl]

just response=400, message "400 BAD REQUEST"

[Vojtěch Knyttl]

val loggingFilter = Filter { next: HttpHandler ->
            { request: Request ->
                val response = next(request)
                <http://log.info|log.info>(response.status.description)
                // 400 BAD_REQUEST, no error details
                response
            }
        }

you can see here, that this is just response.status, no LensFailure exception

[Vojtěch Knyttl]

I think your example throws LensFailure on response.body, i have issues with request.body

[dave]

Set the pre extraction to no body. It's not getting to the handler (my example didn't declare the input lens)

[dave]

And yes - another reason to always use full examples. 😉

[Vojtěch Knyttl]

updated: https://gist.github.com/knyttl/2f380a060e3cf4f86baeecab5ce24096

however still no exception, only 400 BAD REQUEST

[Vojtěch Knyttl]

(I also tried PreFlightExtraction.Companion.None, but still no exception within the logging filter)

[dave]

that's because you're still not trapping the error. look again at the Gist I sent. 🙂

[Vojtěch Knyttl]

trapping the erorr you mean the exception catching here:

try {
                next(it)
            } catch( e: LensFailure){
                Response(BAD_REQUEST).body(e.cause?.localizedMessage ?: "")
            }

?

[Vojtěch Knyttl]

there is no exception thrown

[dave]

The output of: https://gist.github.com/daviddenton/49d397479f2bf7e3ba48182d0a783483 on my machine is:

HTTP/1.1 400 Bad Request


Unexpected end-of-input: was expecting closing quote for a string value
 at [Source: (String)"{"name":"}"; line: 1, column: 11] (through reference chain: Blob["name"])

[Vojtěch Knyttl]

fun CatchLensFailure(failResponseFn: (LensFailure) -> Response = {
        Response(BAD_REQUEST.description(it.failures.joinToString("; ")))
    }) = Filter { next ->
        {
            try {
                next(it)
            } catch (lensFailure: LensFailure) {
                when {
                    lensFailure.target is Response -> throw lensFailure
                    lensFailure.target is RequestContext -> throw lensFailure
                    lensFailure.overall() == Failure.Type.Unsupported -> Response(UNSUPPORTED_MEDIA_TYPE)
                    else -> failResponseFn(lensFailure)
                }
            }
        }
    }

It seems it ends here in the else branch - it catches the exception and retruns response

[Vojtěch Knyttl]

in your gist you do it differently - i need the filter to be out of the handler (i want to have it general for all handlers), note I have loggingFilter.then(handler)(request)

[dave]

yes. that's not supported

[dave]

because you can't override the CatchLensFailure inside the contract handler

[Vojtěch Knyttl]

sso basically i cannot have general filter which would look after all lensexceptions

[dave]

basically

[Vojtěch Knyttl]

and there is no way to overcome this?

[dave]

not at the moment

[Vojtěch Knyttl]

does it make sense to you if I create an issue for it?

[dave]

Actually - I'm being an idiot. There is a way to customise it - you need to provide your own ErrorResponsrRenderer - https://github.com/http4k/http4k/blob/55ae8008df9500203fc1bfe05f244c3da58992c1/http4k-contract/src/main/kotlin/org/http4k/contract/openapi/v3/OpenApi3.kt#L54

[dave]

Completely forgot about that. 🤣

[dave]

(But it won’t work in any example where you don’t set the renderer up)

[Vojtěch Knyttl]

hmm, but doesn't this seem to work only for OpenApi? does it mean, that once I setup OpenApi, this will start to work?

[Vojtěch Knyttl]

🙂 thanks, will try