Turn off Nagle's algorithm on TCP connections

src/main/scala/io/stepfunc/dnp3c/protocol/channel/TcpClientChannelFactory.scala

@@ -46,10 +46,14 @@ object TcpClientChannelFactory {
     }
 
   // connects the socket; a failure to use its local address, e.g. one whose port is still held by a connection to the
-  // same remote address and port that closed moments ago, is LocalBindException
+  // same remote address and port that closed moments ago, is LocalBindException. Nagle's algorithm is off, as in DNP3
+  // stacks, so a small write goes out at once rather than waiting for the previous one to be acknowledged, which would
+  // shift the timing the procedures check
   def connect(socket: SocketChannel, remote: SocketAddress, local: Option[InetSocketAddress], timeoutMs: Int): Unit =
-    try socket.socket().connect(remote, timeoutMs)
-    catch {
+    try {
+      socket.setOption(StandardSocketOptions.TCP_NODELAY, java.lang.Boolean.TRUE)
+      socket.socket().connect(remote, timeoutMs)
+    } catch {
       case ex: java.net.BindException =>
         throw new LocalBindException(local.getOrElse(new InetSocketAddress(0)), ex)
     }

src/test/scala/io/stepfunc/dnp3c/protocol/channel/TcpClientChannelFactoryTest.scala

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-3.0-only
+// Copyright Step Function I/O LLC
+
+package io.stepfunc.dnp3c.protocol.channel
+
+import java.net.{ InetAddress, InetSocketAddress, ServerSocket, StandardSocketOptions }
+import java.nio.channels.SocketChannel
+
+import scala.util.Using
+
+import org.junit.runner.RunWith
+import org.scalatestplus.junit.JUnitRunner
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.funsuite.AnyFunSuite
+
+@RunWith(classOf[JUnitRunner])
+class TcpClientChannelFactoryTest extends AnyFunSuite with Matchers {
+
+  test("a connection has Nagle's algorithm off, so each write goes out at once") {
+    Using.resource(new ServerSocket(0, 1, InetAddress.getLoopbackAddress)) { server =>
+      Using.resource(SocketChannel.open()) { socket =>
+        TcpClientChannelFactory.connect(socket, server.getLocalSocketAddress, None, 1000)
+        socket.getOption(StandardSocketOptions.TCP_NODELAY) should equal(true)
+      }
+    }
+  }
+}