Reading <the docs> for “Response validation” for ktor client, it implies that using `expectSuccess =...

# ktor

[Stylianos Gakis]

Reading the docs for “Response validation” for ktor client, it implies that using expectSuccess = true will mean that all non 200 responses will throw their respective error.
If however one does not add expectSuccess, and then they just try to do response.body<SomeType>() directly, what is the exception they are supposed to be receiving?
Will it simply throw an NoTransformationFoundException directly, since it failed to transform to that new type? Since in a non 200 response it anyway had 0 chance it would’ve been transformed to our type anyway.

[Aleksei Tirman [JB]]

When expectSuccess is set to true and the status code indicates an error, the exception is thrown when retrieving a response from the server, occurring before the response body is received. In other words, the exception is thrown before the body method is called.

[Stylianos Gakis]

Right, sorry I probably wasn't clear about my question. When expectSuccess is set it makes sense. When it is not set I wonder what is the behavior.

[Stylianos Gakis]

I went on these docs trying to find out about the behavior without expectSuccess and I feel like I haven't gotten my answer. Perhaps there is another page I should be looking at instead?

[Aleksei Tirman [JB]]

As you correctly guessed, the NoTransformationFoundException is thrown when the response body cannot be transformed into the specified type.

[Stylianos Gakis]

Alright great, I was just missing some reassurance on the docs basically. Thanks a lot for the help here!
And then I guess inside the exception itself I can take the response: HttpResponse to log the status code and whatever, so this should work for me!
Is it that I am missing something in the docs btw around this, or could there be some addition to mention that scenario?

[Aleksei Tirman [JB]]

> And then I guess inside the exception itself I can take the response: HttpResponse to log the status code and whatever, so this should work for me!
No, you would already have the HttpResponse object because the NoTransformationFoundException may be thrown when calling the body method.

[Aleksei Tirman [JB]]

Is it that I am missing something in the docs btw around this, or could there be some addition to mention that scenario?

I think this information is missing in the docs.

[Stylianos Gakis]

Right, but since my function looks smth like this:

suspend fun foo(): MyResponse {
    val response =  <http://ktorClient.post|ktorClient.post>("...") {
        contentType(ContentType.Application.Json)
        setBody(...)
    }
    return response.body<MyResponse>()
}

I should either be getting MyResponse if it was a 200 and I manage to map it to the right type, and in all other scenarios I should be expecting a NoTransformationFoundException, is that not the case?
What else should I be catching here instead?

[Stylianos Gakis]

Call site would look like

try {
  val myResponse: MyResponse = foo()
  myResponse...
} catch (e: NoTransformationFoundException) {
  e.response.statusCode // here I have the code
  ... here log, fallback to some error type, whatever
}

[Aleksei Tirman [JB]]

I should either be getting MyResponse if it was a 200 and I manage to map it to the right type, and in all other scenarios I should be expecting a NoTransformationFoundException, is that not the case?

Yes, if the expectSuccess is false

[Stylianos Gakis]

Yeah I am planning to keep it false indeed

[Stylianos Gakis]

It’s already false and I do not want to flip it and have other consequences in places I do not expect, hence me trying make sure I am not missing something here

[Stylianos Gakis]

I see that body() also might throw DoubleReceiveException, but with this approach I really don’t think I need to catch that. And from my understanding I also don’t need to be catching anything like IOException etc since I do not see that I am calling any function that indicates that it would throw it. I only call <http://HttpClient.post|HttpClient.post> and then HttpResponse.body

[Aleksei Tirman [JB]]

Those methods could throw the IOException .

[Stylianos Gakis]

That's not documented in the documentation above the function 😬

Okay I feel like we need to take a step back. How do I make sure when using ktor client that I don't just crash my app by trying to do a normal request? Are there some docs that just cover this in its entirety without me having to be worried or having to ask you? 😕

[Aleksei Tirman [JB]]

Also, the ConnectException may be thrown. The set of potential exception depend on the client engine.

[Aleksei Tirman [JB]]

If you don't want your app to crash, you should catch every exception (the Throwable type). Also, there's a feature request to group all Ktor exceptions into one type."

Are there some docs that just cover this in its entirety without me having to be worried or having to ask you?

Unfortunately, there is no such docs.

[Stylianos Gakis]

Okay so I think I got this:
I catch first NoTransformationFoundException and I log more specifically from the information I have here.
I then catch Throwable, and log that as a more generic error.
I also make sure in the catch that catches Throwable that I rethrow specifically CancellationException so as not to break structured concurrency.

This plan should cover me 100% I think. How does it sound?

[Aleksei Tirman [JB]]

Sounds good.