Merge pull request #115 from Cu3PO42/feat/inherited-sockets

Add support for inherited sockets

gradle/libs.versions.toml

@@ -5,7 +5,7 @@ kotlin = "2.1.0"
 gson = "2.11.0"
 gson-extras = "1.3.0"
 jansi = "2.4.1"
-java-websocket = "1.5.7"
+java-websocket = "1.6.0"
 json = "20240303"
 jsonschema2pojo = "1.2.2"
 kotlinx-serialization-json = "1.7.3"

server/src/main/kotlin/Server.kt

@@ -8,6 +8,7 @@ import org.fusesource.jansi.AnsiConsole
 import picocli.CommandLine
 import picocli.CommandLine.*
 import picocli.CommandLine.Model.CommandSpec
+import java.nio.channels.ServerSocketChannel
 import java.util.*
 import kotlin.system.exitProcess
 
@@ -51,6 +52,8 @@ class Server : Runnable {
         private const val MIN_PORT = 1000
         private const val MAX_PORT = 65535
 
+        const val INHERIT = "inherit"
+
         @Option(names = ["-v", "--version"], description = ["Display version info"])
         private var isVersionInfoRequested = false
 
@@ -59,10 +62,16 @@ class Server : Runnable {
 
         @Option(
             names = ["-p", "--port"],
-            type = [Int::class],
-            description = ["Port number (default: $DEFAULT_PORT)"]
+            type = [String::class],
+            description = ["Port number (default: $DEFAULT_PORT) or '$INHERIT' to use socket activation (if supported by the system)"]
         )
-        var port: Int = DEFAULT_PORT
+        private var port: String = DEFAULT_PORT.toString()
+
+        val useInheritedChannel: Boolean
+            get() = port.equals(INHERIT, ignoreCase = true)
+
+        val portNumber: Int
+            get() = if (useInheritedChannel) getInheritedPort() else port.toIntOrNull() ?: DEFAULT_PORT
 
         @Option(
             names = ["-g", "--games"],
@@ -99,6 +108,11 @@ class Server : Runnable {
         var tps: Int = DEFAULT_TURNS_PER_SECOND
 
         val cmdLine = CommandLine(Server())
+
+        private fun getInheritedPort(): Int {
+            val channel = System.inheritedChannel() as? ServerSocketChannel
+            return channel?.socket()?.localPort ?: -1
+        }
     }
 
     @Spec
@@ -145,7 +159,7 @@ class Server : Runnable {
     }
 
     private fun validatePort() {
-        if (port !in MIN_PORT..MAX_PORT) {
+        if (!useInheritedChannel && portNumber !in MIN_PORT..MAX_PORT) {
             reportInvalidPort()
             exitProcess(1) // general error
         }
@@ -154,13 +168,17 @@ class Server : Runnable {
     private fun reportInvalidPort() {
         System.err.println(
             """
-            Port must be between $MIN_PORT and $MAX_PORT.
-            Default port $DEFAULT_PORT will be used for HTTP.
+                Port must be either 'inherit' or a number between $MIN_PORT and $MAX_PORT.
+                Default port is $DEFAULT_PORT used for http.
             """.trimIndent()
         )
     }
 
     private fun startExitInputMonitorThread() {
+        // When inheriting a channel, it is passed as FD3, i.e. stdin. In this case, it does not
+        // make sense to monitor for an exit command.
+        if (useInheritedChannel) return
+
         Thread {
             monitorStandardInputForExit()
         }.apply {

server/src/main/kotlin/dev/robocode/tankroyale/server/connection/MultiServerWebSocketObserver.kt

@@ -2,20 +2,46 @@ package dev.robocode.tankroyale.server.dev.robocode.tankroyale.server.connection
 
 import dev.robocode.tankroyale.server.Server
 import org.java_websocket.WebSocket
+import org.slf4j.LoggerFactory
 import java.net.InetAddress
 import java.net.InetSocketAddress
+import java.nio.channels.ServerSocketChannel
+import kotlin.system.exitProcess
 
 class MultiServerWebSocketObserver(observer: IClientWebSocketObserver) {
 
-    private val loopbackServerWebSocketObserver = ServerWebSocketObserver(InetSocketAddress(Server.port), observer)
-    private val localhostServerWebSocketObserver = ServerWebSocketObserver(InetSocketAddress(InetAddress.getLocalHost(), Server.port), observer)
+    private val log = LoggerFactory.getLogger(this::class.java)
+
+    private val webSocketServer = if (Server.useInheritedChannel) {
+        validateInheritedChannel()
+        arrayOf(ServerWebSocketObserver(observer))
+    } else {
+        arrayOf(
+            ServerWebSocketObserver(InetSocketAddress(Server.portNumber), observer),
+            ServerWebSocketObserver(InetSocketAddress(InetAddress.getLocalHost(), Server.portNumber), observer)
+        )
+    }
 
     fun start() {
-        loopbackServerWebSocketObserver.run()
-        localhostServerWebSocketObserver.run()
+        webSocketServer.forEach { it.run() }
     }
 
     fun broadcast(clientSockets: Collection<WebSocket>, message: String) {
-        localhostServerWebSocketObserver.broadcast(message, clientSockets)
+        webSocketServer.forEach { it.broadcast(message, clientSockets) }
+    }
+
+    private fun validateInheritedChannel() {
+        val inheritedChannel = System.inheritedChannel()
+        if (inheritedChannel == null) {
+            log.error(
+                "The '${Server.INHERIT}' mode require that a valid socket is passed to this server via file descriptor 3 (fd 3). " +
+                        "Make sure the socket was passed correctly"
+            )
+            exitProcess(2)
+        }
+        if (inheritedChannel !is ServerSocketChannel) {
+            log.error("The '${Server.INHERIT}' mode expects a server socket")
+            exitProcess(2)
+        }
     }
 }

server/src/main/kotlin/dev/robocode/tankroyale/server/connection/ServerWebSocketObserver.kt

@@ -5,21 +5,35 @@ import org.java_websocket.handshake.ClientHandshake
 import org.java_websocket.server.WebSocketServer
 import org.slf4j.LoggerFactory
 import java.net.InetSocketAddress
+import java.nio.channels.ServerSocketChannel
 
-class ServerWebSocketObserver(
-    address: InetSocketAddress,
-    private val observer: IClientWebSocketObserver
-) : WebSocketServer(address) {
-
+class ServerWebSocketObserver : WebSocketServer {
     private val log = LoggerFactory.getLogger(this::class.java)
+    private val observer: IClientWebSocketObserver
+    private val useInheritedChannel: Boolean
+
+    constructor(
+        address: InetSocketAddress,
+        observer: IClientWebSocketObserver
+    ) : super(address) {
+        this.observer = observer
+        this.useInheritedChannel = false
+        isTcpNoDelay = true
+    }
 
-    init {
-        // Disable Nagle's algorithm
+    constructor(
+        observer: IClientWebSocketObserver
+    ) : super(
+        (System.inheritedChannel() as? ServerSocketChannel)
+            ?: throw IllegalStateException("No inherited server socket channel available")
+    ) {
+        this.observer = observer
+        this.useInheritedChannel = true
         isTcpNoDelay = true
     }
 
     override fun onStart() {
-        log.debug("onStart()")
+        log.debug("onStart(){}", if (useInheritedChannel) " with inherited channel" else "")
     }
 
     override fun onOpen(clientSocket: WebSocket, handshake: ClientHandshake) {

server/src/main/kotlin/dev/robocode/tankroyale/server/core/GameServer.kt

@@ -86,7 +86,7 @@ class GameServer(
 
     /** Starts this server */
     fun start() {
-        log.info("Starting server on port ${Server.port} with supporting game type(s): ${gameTypes.joinToString()}")
+        log.info("Starting server on port ${Server.portNumber} with supporting game type(s): ${gameTypes.joinToString()}")
         connectionHandler.start()
     }