We're finding that slow HTTP POSTs into Ktor can block the server from responding to other connections until that request completes. Is that expected?

You should not block the thread in the request processing code.

It blocks in Ktor code, e.g.:

post("/login") {
            val credentials = call.receive<Credentials>()
            call.respond(credentials)
        }

Any idea why this POST request is slow?

We encounter it in our live web app, we haven't figured out exactly why it happens there, but we've can reproduce with slow POSTs manually with

telnet

From what I understand it looks like a bug. Try filling an issue with ktor.

👍 I've raised https://github.com/ktorio/ktor/issues/1001