In the Ktor Client is there any reasonable way of handling a kotlinlang #ktor

In the Ktor Client, is there any reasonable way of...

phldavies

09/04/2025, 5:42 PM

In the Ktor Client, is there any reasonable way of handling a

response as

null

without either losing the default response validation (i.e

expectSuccess = false

) or intercepting

ClientRequestException

Aleksei Tirman [JB]

09/05/2025, 7:59 AM

Do you mean to return

null

when calling the

body

method with a nullable type?

phldavies

09/05/2025, 8:31 AM

That would be simplest - or be able to permit certain non-success statuses so one could handle them directly, but still raise exceptions for any unexpected statuses

Aleksei Tirman [JB]

09/05/2025, 8:51 AM

You can modify the default response validation logic by defining another response validator with the code copied from the default one. Here is an example:

Copy code

val client = HttpClient(CIO) {
    HttpResponseValidator {
        validateResponse { response ->
            val statusCode = response.status.value
            val originCall = response.call

            if (statusCode == HttpStatusCode.NotFound.value) { // Skip 404
                return@validateResponse
            }

            val exceptionCall = if (!originCall.response.isSaved) {
                originCall.save()
            } else {
                originCall
            }

            val exceptionResponse = exceptionCall.response
            val exceptionResponseText = try {
                exceptionResponse.bodyAsText()
            } catch (_: MalformedInputException) {
                "<body failed decoding>"
            }
            val exception = when (statusCode) {
                in 300..399 -> RedirectResponseException(exceptionResponse, exceptionResponseText)
                in 400..499 -> ClientRequestException(exceptionResponse, exceptionResponseText)
                in 500..599 -> ServerResponseException(exceptionResponse, exceptionResponseText)
                else -> ResponseException(exceptionResponse, exceptionResponseText)
            }
            throw exception
        }
    }
}

phldavies

09/05/2025, 9:27 AM

that's effectively what we've ended up with (albeit with the validation logic wrapped in a

.requireSuccess()

extension rather than the plugin along with a

.onStatus

extension) allowing for this kind of usage:

Copy code

return get("api/config/id") { url.appendPathSegments("$configId") }
        .onStatus(NotFound) { return null }
        .requireSuccess()
        .body<T>()

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