Connection refused when connecting to localhost's port 9999

Question

I am trying to understand some example Kotlin code that connects to http://127.0.0.1 using sockets, and I have IIS enabled and running it on 127.0.0.1. However, when I run the code, I get:

"C:\Program Files\Microsoft\jdk-11.0.12.7-hotspot\bin\java.exe" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:52769,suspend=y,server=n -javaagent:C:/Users/ivlat/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlinx/kotlinx-coroutines-core-jvm/1.5.0/d8cebccdcddd029022aa8646a5a953ff88b13ac8/kotlinx-coroutines-core-jvm-1.5.0.jar -javaagent:C:\Users\ivlat\AppData\Local\JetBrains\IdeaIC2022.2\captureAgent\debugger-agent.jar=file:/C:/Users/ivlat/AppData/Local/Temp/capture.props -Dfile.encoding=UTF-8 -classpath "C:\Dev\KotlinProjects\7_08_Echo\client\build\classes\kotlin\main;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-jdk8\1.5.21\6b3de2a43405a65502728047db37a98a0c7e72f0\kotlin-stdlib-jdk8-1.5.21.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\ch.qos.logback\logback-classic\1.2.3\7c4f3c474fb2c041d8028740440937705ebb473a\logback-classic-1.2.3.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\ch.qos.logback\logback-core\1.2.3\864344400c3d4d92dfeb0a305dc87d953677c03c\logback-core-1.2.3.jar;C:\Dev\KotlinProjects\7_08_Echo\shared\build\classes\kotlin\main;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-core-jvm\1.5.0\d8cebccdcddd029022aa8646a5a953ff88b13ac8\kotlinx-coroutines-core-jvm-1.5.0.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-jdk7\1.5.21\f059658740a4b3a3461aba9681457615332bae1c\kotlin-stdlib-jdk7-1.5.21.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib\1.5.21\2f537cad7e9eeb9da73738c8812e1e4cf9b62e4e\kotlin-stdlib-1.5.21.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.slf4j\slf4j-api\1.7.25\da76ca59f6a57ee3102f8f9bd9cee742973efa8a\slf4j-api-1.7.25.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-common\1.5.21\cc8bf3586fd2ebcf234058b9440bb406e62dfacb\kotlin-stdlib-common-1.5.21.jar;C:\Users\ivlat\.gradle\caches\modules-2\files-2.1\org.jetbrains\annotations\13.0\919f0dfe192fb4e063e7dacadee7f8bb9a2672a9\annotations-13.0.jar;C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2022.2.3\lib\idea_rt.jar" com.knowledgespike.client.ApplicationKt
Connected to the target VM, address: '127.0.0.1:52769', transport: 'socket'
Exception in thread "main" java.io.IOException: The remote computer refused the network connection.

    at java.base/sun.nio.ch.Iocp.translateErrorToIOException(Iocp.java:299)
    at java.base/sun.nio.ch.Iocp$EventHandlerTask.run(Iocp.java:389)
    at java.base/sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:829)
Disconnected from the target VM, address: '127.0.0.1:52769', transport: 'socket'

Process finished with exit code 1

Apparently, my IIS isn't really set up for the port 9999, as I am getting the error below when I type localhost/127.0.0.1:9999

HTTP Error 404.0 - Not Found
The resource you are looking for has been removed, had its name changed, or is temporarily unavailable.

The connection string that the Kotlin code is also using is localhost/127.0.0.1:9999

How would I go about getting the IIS recognize this request/let it through? It really doesn't even have to be IIS. I just want to understand this sample code better, and any sort of sandbox/test web server that allows for this request would more than suffice at this point.

This is the Kotlin code that's throwing the exception when trying to connect:

fun main() = runBlocking {

    val client: AsynchronousSocketChannel = AsynchronousSocketChannel.open()
    val hostAddress = InetSocketAddress("localhost", PORT)
    val tcpSocket = TcpSocket(client)
    tcpSocket.connect(hostAddress)

    val br = BufferedReader(InputStreamReader(System.`in`))
    var line: String
    println("Main name is: \t\t\t\t\t${Thread.currentThread().name}")
    println("Message to server:")
    while (br.readLine().also { line = it } != null) {
        val result = async {
            println("while:async name is: \t\t\t${Thread.currentThread().name}")
            sendMessage(tcpSocket, line)
        }
        println("while: name is: \t\t\t\t${Thread.currentThread().name}")
        if (line == "bye") {
            println("End")
            break
        }
        val response: String = result.await()
        withContext(Dispatchers.Default) {
            println("withContext[Default] name is: \t${Thread.currentThread().name}")
            println("response from server: $response")
            println("Message to server:")
        }
    }
}

Answer 1

1. A webserver listens on a particular port, the default is port 80 for HTTP. Unless you go out of your way to configure it, I expect that's where IIS will be listening
2. I would start by taking Kotlin out of the question and establish you have a webserver listening on a particular port. Just use a regular web browser to check. Beware the browsers handle comms fails in nice friendly ways, hiding the real issues. Better to use a more technical tool like
   1. curl
   2. Postman
3. If IIS is suspect, then what IDE are you using? If you are using IntelliJ
   1. find yourself an HTML file,
   2. open it up, then notice in the Top Right several however icons will show up
   3. pick the IntelliJ one, this will start an internal web server and then a web browser will launch to connect to it
   4. try this web server for your tests

Answer 2

I was able to circumvent the error by going to bindings for the default web site in the IIS Manager UI and then adding the port 9999. The Kotlin code connects fine now. I'm pretty sure there are better ways of solving this IRL, but I think it's good enough, as I am just learning Kotlin at this point.