Large responses are not completely sent with 'Connection: close'

When a ktor server sends a large amount of data over the network and the client specified Connection: close, the transfer will not complete.

curl http://poseidon:2000/ -H 'Connection: close' > /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  8 1000k    8 85432    0     0  3776k      0 --:--:-- --:--:-- --:--:-- 3792k
curl: (18) transfer closed with 938568 bytes remaining to read

This doesn’t happen on localhost connections, only on those going over at least a LAN (maybe VMs too).

The following code in combination with the curl command reproduces the problem:

import io.ktor.application.call
import io.ktor.response.respond
import io.ktor.routing.get
import io.ktor.routing.routing
import io.ktor.server.engine.embeddedServer
import io.ktor.server.netty.Netty
import java.io.File

fun main(args: Array<String>) {
  val server = embeddedServer(Netty, 2000) {
    routing {
      get("/") {
        val data = ByteArray(1024 * 1024)
        File("/dev/urandom").inputStream().read(data)
        call.respond(data)
      }
    }
  }
  server.start()
}

[jonstacks]

We just hit this as well in production when trying to transfer a payload of about 1M. We are using nginx with the proxy_pass directive and by default it sets the header Connection: close. We will mostly likely be adding this in the nginx config as a workaround:

proxy_set_header Connection "keep-alive";

We ended up trying things like turning off proxy_buffering and that seemed to work as well. Hope this helps someone else.

Edit:

We ended up using this in our config:

proxy_http_version 1.1;
proxy_set_header Connection "";

The nginx docs have this to say:

Alternatively, HTTP/1.0 persistent connections can be used by passing the “Connection: Keep-Alive” header field to an upstream server, though this method is not recommended.

[rvadim]

Same problem on io.ktor.server.tomcat and maybe other:

~$ curl -H "Connection: close" localhost:8080 -v
* Rebuilt URL to: localhost:8080/
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET / HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.52.1
> Accept: */*
> Connection: close
> 
< HTTP/1.1 200 
< Transfer-Encoding: chunked
< Connection: close
< Content-Type: text/html;charset=UTF-8
< Date: Thu, 22 Nov 2018 03:11:58 GMT
< 
* Illegal or missing hexadecimal sequence in chunked-encoding
* Curl_http_done: called premature == 1
* stopped the pause stream!
* Closing connection 0
curl: (56) Illegal or missing hexadecimal sequence in chunked-encoding