Is it possible to upload large files to Ktor & Netty server? - kotlin

Question

I was making a simple file upload&download service and found out that, as far as I understand, Netty doesn't release direct buffers until request processing is over. As a result, I can't upload bigger files.
I was trying to make sure that the problem is not inside my code, so I created the most simple tiny Ktor application:
routing {
post("upload") {
call.receiveMultipart().forEachPart {}
call.respond(HttpStatusCode.OK)
}
}
The default direct memory size is about 3Gb, to make test simpler I limit it with:
System.setProperty("io.netty.maxDirectMemory", (10 * 1024 * 1024).toString())
before starting the NettyApplicationEngine.
Now if I upload a large file, for example with httpie, I got "Connection reset":
http -v --form POST http://localhost:42195/upload file#/tmp/FileStorageLoadTest-test-data1.tmp
http: error: ConnectionError: ('Connection aborted.', ConnectionResetError(104, 'Connection reset by peer')) while doing POST request to URL: http://localhost:42195/upload
On the server side there is no information about the problem except for the "java.io.IOException: Broken delimiter occurred" exception. But if I put the breakpoint in NettyResponsePipeline#processCallFailed, the real exception is:
io.netty.util.internal.OutOfDirectMemoryError: failed to allocate 65536 byte(s) of direct memory (used: 10420231, max: 10485760)
It is a pity that this exception is not logged.
Also, I found out that the same code works without problems if I use Jetty engine instead.
Environment:
Ubuntu Linux
Java 8
Ktor=1.2.5
netty-transport-native-epoll=4.1.43.Final
(but if Netty started without native-epoll support, the problem is the same)