Response validation

By default, Ktor doesn't validate a response depending on its status code. If required, you can use the following validation strategies:

Use the expectSuccess property to throw exceptions for non-2xx responses.
Add stricter validation of 2xx responses.
Customize validation of non-2xx responses.

Enable default validation

Ktor allows you to enable default validation by setting the expectSuccess property to true. This can be done on a client configuration level ...

import io.ktor.client.*
import io.ktor.client.engine.cio.*

val client = HttpClient(CIO) {
    expectSuccess = true
}

... or by using the same property on a request level. In this case, the following exceptions will be thrown for non-2xx error responses:

RedirectResponseException for 3xx responses.
ClientRequestException for 4xx responses.
ServerResponseException for 5xx responses.

Custom validation

You can add additional validation for 2xx responses or customize default validation by using the HttpCallValidator plugin. To install HttpCallValidator, call the HttpResponseValidator function inside a client configuration block:

val client = HttpClient(CIO) {
    HttpResponseValidator {
        // ...
    }
}

Validate 2xx responses

As mentioned above, default validation throws exceptions for non-2xx error responses. If you need to add stricter validation and check 2xx responses, use the validateResponse function available in HttpCallValidator.

In the example below, a client receives a 2xx response with error details in a JSON format. The validateResponse is used to raise a CustomResponseException:

        val client = HttpClient(CIO) {
            install(ContentNegotiation) { json() }
            HttpResponseValidator {
                validateResponse { response ->
                    val error: Error = response.body()
                    if (error.code != 0) {
                        throw CustomResponseException(response, "Code: ${error.code}, message: ${error.message}")
                    }
                }
            }
        }

Handle non-2xx exceptions

If you need to customize default validation and handle exceptions for non-2xx responses in a specific way, use handleResponseExceptionWithRequest. In the example below, a client raises a custom MissingPageException for 404 responses instead of the default ClientRequestException:

    val client = HttpClient(CIO) {
        expectSuccess = true
        HttpResponseValidator {
            handleResponseExceptionWithRequest { exception, request ->
                val clientException = exception as? ClientRequestException ?: return@handleResponseExceptionWithRequest
                val exceptionResponse = clientException.response
                if (exceptionResponse.status == HttpStatusCode.NotFound) {
                    val exceptionResponseText = exceptionResponse.bodyAsText()
                    throw MissingPageException(exceptionResponse, exceptionResponseText)
                }
            }
        }
    }

Last modified: 28 December 2022