I am trying to understand why I'm seeing TCP retransmissions on a simple program. I created a small program based on the 2.4.2 docs:
object HelloWorld { def main(args: Array[String]): Unit = { implicit val system = ActorSystem("Sys") implicit val materializer = ActorMaterializer() val connections: Source[IncomingConnection, Future[Tcp.ServerBinding]] = Tcp().bind("localhost", 8888) connections runForeach { connection => // server logic, parses incoming commands val commandParser = Flow[String].takeWhile(_ != "BYE").map(_ + "!") import connection._ val welcomeMsg = s"Welcome to: $localAddress, you are: $remoteAddress!" val welcome = Source.single(welcomeMsg) val serverLogic = Flow[ByteString] .via(Framing.delimiter( ByteString("\n"), 256 )) .map(_.utf8String) .via(commandParser) // merge in the initial banner after parser .merge(welcome) .map(_ + "\n") .map(ByteString(_)) connection.handleWith(serverLogic) } } } But when I connect to localhost/8888 via telnet, type in a few lines, and watch the traffic with wireshark, I'm seeing various retransmits and out of order: 46482→8888 [SYN] Seq=0 Win=43690 Len=0 MSS=65495 SACK_PERM=1 TSval=47383693 TSecr=0 WS=128 8888→46482 [SYN, ACK] Seq=0 Ack=1 Win=43690 Len=0 MSS=65495 SACK_PERM=1 TSval=47383693 TSecr=47383693 WS=128 46482→8888 [ACK] Seq=1 Ack=1 Win=43776 Len=0 TSval=47383693 TSecr=47383693 8888→46482 [PSH, ACK] Seq=1 Ack=1 Win=43776 Len=56 TSval=47383719 TSecr=47383693 46482→8888 [ACK] Seq=1 Ack=57 Win=43776 Len=0 TSval=47383719 TSecr=47383719 [TCP Out-Of-Order] 46482→8888 [SYN] Seq=0 Win=43690 Len=0 MSS=65495 SACK_PERM=1 TSval=47383693 TSecr=0 WS=128 [TCP Retransmission] 8888→46482 [SYN, ACK] Seq=0 Ack=1 Win=43690 Len=0 MSS=65495 SACK_PERM=1 TSval=47383693 TSecr=47383693 WS=128 46482→8888 [ACK] Seq=1 Ack=1 Win=43776 Len=0 TSval=47383693 TSecr=47383693 [TCP Retransmission] 8888→46482 [PSH, ACK] Seq=1 Ack=1 Win=43776 Len=56 TSval=47383719 TSecr=47383693 46482→8888 [ACK] Seq=1 Ack=57 Win=43776 Len=0 TSval=47383719 TSecr=47383719 46482→8888 [PSH, ACK] Seq=1 Ack=57 Win=43776 Len=6 TSval=47384746 TSecr=47383719 8888→46482 [ACK] Seq=57 Ack=7 Win=43776 Len=0 TSval=47384746 TSecr=47384746 8888→46482 [PSH, ACK] Seq=57 Ack=7 Win=43776 Len=7 TSval=47384747 TSecr=47384746 46482→8888 [ACK] Seq=7 Ack=64 Win=43776 Len=0 TSval=47384747 TSecr=47384747 [TCP Retransmission] 46482→8888 [PSH, ACK] Seq=1 Ack=57 Win=43776 Len=6 TSval=47384746 TSecr=47383719 8888→46482 [ACK] Seq=57 Ack=7 Win=43776 Len=0 TSval=47384746 TSecr=47384746 [TCP Retransmission] 8888→46482 [PSH, ACK] Seq=57 Ack=7 Win=43776 Len=7 TSval=47384747 TSecr=47384746 46482→8888 [ACK] Seq=7 Ack=64 Win=43776 Len=0 TSval=47384747 TSecr=47384747 46482→8888 [PSH, ACK] Seq=7 Ack=64 Win=43776 Len=6 TSval=47386128 TSecr=47384747 8888→46482 [PSH, ACK] Seq=64 Ack=13 Win=43776 Len=7 TSval=47386129 TSecr=47386128 46482→8888 [ACK] Seq=13 Ack=71 Win=43776 Len=0 TSval=47386129 TSecr=47386129 [TCP Retransmission] 46482→8888 [PSH, ACK] Seq=7 Ack=64 Win=43776 Len=6 TSval=47386128 TSecr=47384747 [TCP Retransmission] 8888→46482 [PSH, ACK] Seq=64 Ack=13 Win=43776 Len=7 TSval=47386129 TSecr=47386128 46482→8888 [ACK] Seq=13 Ack=71 Win=43776 Len=0 TSval=47386129 TSecr=47386129 Full trace at http://pastebin.com/09xi1kGa Could someone explain to me if I'm doing something wrong, or what's going on? -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. To unsubscribe from this group and stop receiving emails from it, send an email to akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at https://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.