What is the preferred way of validating query, path and headers? Wrapping everything in try/catches is not really DRY in my opinion. For instance, I'd have a UUID as a path parameter. I use UUID.fromString which might fail. I can wrap that with a try/catch and send a response. What is the idiomatic thing of repeatedly handling validation of these parameters?

Maybe let it throw exception and handle that exception in StatusPages, responding bad request with explanatory body

For example, with query parameters you can retrieve them with:

val value = call.parameters.getOrFail("value")

And you can handle the specific exception with `StatusPages`:

install(StatusPages) {
    exception<MissingRequestParameterException> { call, cause ->
        call.respondText("Missing \"${cause.parameterName}\" parameter.", status = HttpStatusCode.BadRequest)
    }
}

maybe this will be useful https://ktor.io/docs/request-validation.html + RequestValidationException

install(RequestValidation) {
    validate<String> { bodyText ->
        if (!bodyText.startsWith("Hello"))
            ValidationResult.Invalid("Body text should start with 'Hello'")
        else ValidationResult.Valid
    }
}

install(StatusPages) {
    exception<RequestValidationException> { call, cause ->
        call.respond(HttpStatusCode.BadRequest, cause.reasons.joinToString())
    }
}

@Johann Pardanaud true, but that doesn’t validate the input. It just checks that there is an input but not that it is a good input. @Łukasz Nowakowski those are for bodies only right? Not for path, query and header parameters? I guess the best solution would be to create extension methods on the call object and have those throw Exceptions