Is the response body read async, even with the OkHttp engine (I'm currently interested in downloads)...

# ktor

[dave08]

Is the response body read async, even with the OkHttp engine (I'm currently interested in downloads) @orangy? How stable is CIO?

[thevery]

For okhttp it is probably easier to check sources :)

[dave08]

Ktor has byte channels that seem to be using Coroutines, the thing is whether that also needs a thread pool to run on, or is the implementation all async...

[jw]

OkHttp is all blocking I/O on its own pool

[dave08]

So it's not possible to read the response body async... the docs are a bit misleading then:

val readChannel = response.call.receive<ByteReadChannel>()
val inputStream = response.call.receive<InputStream>() Remember that InputStream API is synchronous!

Sounds like readChannel is async...

[jw]

I suspect the body is read on OkHttp's pool and sent over the channel to user code

[dave08]

https://github.com/ktorio/ktor/blob/e788f34b8a1de91253ed870bc510d3fa08dda5fc/ktor-client/ktor-client-okhttp/src/io/ktor/client/engine/okhttp/OkHttpEngine.kt#L48

[jw]

That's for sending the request, not reading the response

[dave08]

Oh, OutgoingContent... so there's still a bit of hope that it's async, I don't see the response code there...

[dave08]

Maybe it's there actually https://github.com/ktorio/ktor/blob/e788f34b8a1de91253ed870bc510d3fa08dda5fc/ktor-client/ktor-client-okhttp/src/io/ktor/client/engine/okhttp/OkHttpEngine.kt#L39

[gildor]

that it’s async

It is async of course.
Are you talking about syncronous/asyncronous or about blocking/non-blocking?
Because Ktor uses syncronous blocking API of OkHttp (it doesn’t have any non-blocking one) that blocking but on own thread pool, but this API wrapped to asyncronous coroutines

[dave08]

Thanks, I meant non-blocking, so even reading response content is done blocking? I'm not so familiar with Nio to know whether the fact they use it under the hood is also blocking. I knew for sure the request and initial response is blocking. @gildor