Add Control transport diagnostics and safe proxy method switching

VotingPlugin/src/main/java/com/bencodez/votingplugin/backendproxy/messaging/BackendProxyMessageRouter.java

@@ -72,11 +72,13 @@ public void register(GlobalMessageHandler messages, BungeeMethod method) {
 		messages.addListener(new GlobalMessageListener(VotingPluginWire.SUB_VOTE_BROADCAST) {
 			@Override public void onReceive(JsonEnvelope msg) { handleVoteBroadcast(msg); }
 		});
-		messages.addListener(new GlobalMessageListener("Status") {
+		messages.addListener(new GlobalMessageListener(VotingPluginWire.SUB_STATUS) {
 			@Override public void onReceive(JsonEnvelope msg) {
 				HashMap<String, Object> out = new HashMap<>();
-				out.put("server", nvl(msg.getFields().get("server")));
-				sendSubChannel(messages, "statusokay", out);
+				out.put(VotingPluginWire.K_SERVER, nvl(plugin.getOptions().getServer()));
+				String requestId = nvl(msg.getFields().get(VotingPluginWire.K_REQUEST_ID));
+				if (!requestId.isEmpty()) out.put(VotingPluginWire.K_REQUEST_ID, requestId);
+				sendSubChannel(messages, VotingPluginWire.SUB_STATUS_OKAY, out);
 			}
 		});
 		messages.addListener(new GlobalMessageListener("ServerName") {

VotingPlugin/src/main/java/com/bencodez/votingplugin/control/BackendConfigurationService.java

@@ -228,7 +228,8 @@ private String quickSetupRevision(String preset, String current) throws IOExcept
 	}
 
 	private static String quickSetupFile(String preset) {
-		if ("standalone".equals(preset) || "proxy-backend".equals(preset)) return "BungeeSettings.yml";
+		if ("standalone".equals(preset) || "proxy-backend".equals(preset)
+				|| "proxy-method".equals(preset)) return "BungeeSettings.yml";
 		if ("vote-site".equals(preset) || "easy-reward".equals(preset)
 				|| "sync-vote-sites".equals(preset)) return "VoteSites.yml";
 		if ("common-settings".equals(preset)) return "Config.yml";
@@ -258,6 +259,13 @@ private QuickProposal quickProposal(String preset, Map<String, String> options,
 			}
 			return new QuickProposal(fileName, yaml.saveToString());
 		}
+		if ("proxy-method".equals(preset)) {
+			BungeeMethod method = BungeeMethod.valueOf(bungeeMethodOption(options));
+			validateProxyMethod(method, yaml);
+			yaml.set("UseBungeecord", true);
+			yaml.set("BungeeMethod", method.name());
+			return new QuickProposal(fileName, yaml.saveToString());
+		}
 		if ("vote-site".equals(preset)) {
 			String name = option(options, "name", "[A-Za-z0-9_-]{1,64}");
 			String root = "VoteSites." + name;
@@ -322,6 +330,65 @@ private boolean caseInsensitiveYmlFiles() throws IOException {
 		return key != null && settings.getBoolean(key, false);
 	}
 
+	private void validateProxyMethod(BungeeMethod method, YamlConfiguration settings) {
+		String server = settings.getString("Server", "").trim();
+		if (server.isEmpty() || "PleaseSet".equalsIgnoreCase(server)) {
+			throw new IllegalArgumentException("Server must be set to this backend's unique proxy server name");
+		}
+		switch (method) {
+		case PLUGINMESSAGING:
+			if (settings.getString("PluginMessageChannel", "vp:vp").isBlank()) {
+				throw new IllegalArgumentException("PluginMessageChannel must be set");
+			}
+			break;
+		case REDIS:
+			configuredHostAndPort(settings, "Redis.Host", "Redis.Port", 6379, "Redis");
+			break;
+		case MQTT:
+			validBroker(settings.getString("MQTT.BrokerURL", "tcp://localhost:1883"));
+			String clientId = settings.getString("MQTT.ClientID", server);
+			if (clientId == null || clientId.isBlank()) throw new IllegalArgumentException("MQTT.ClientID must be set");
+			break;
+		case SOCKETS:
+			configuredHostAndPort(settings, "BungeeServer.Host", "BungeeServer.Port", 1297, "BungeeServer");
+			break;
+		case MYSQL:
+			try {
+				YamlConfiguration main = parse(readRaw(resolve("Config.yml"), false));
+				if (!"MYSQL".equalsIgnoreCase(main.getString("DataStorage", ""))
+						|| main.getString("Database.Host", "").isBlank()
+						|| main.getString("Database.Database", "").isBlank()) {
+					throw new IllegalArgumentException("Config.yml DataStorage must be MYSQL with Database.Host and Database.Database set");
+				}
+			} catch (IOException e) {
+				throw new IllegalArgumentException("Config.yml could not be checked for MYSQL settings");
+			}
+			break;
+		default:
+			throw new IllegalArgumentException("BungeeMethod is unsupported");
+		}
+	}
+
+	private static void configuredHostAndPort(YamlConfiguration yaml, String hostPath, String portPath,
+			int defaultPort, String label) {
+		String host = yaml.getString(hostPath, "");
+		int port = yaml.getInt(portPath, defaultPort);
+		if (host == null || host.isBlank() || port < 1 || port > 65535) {
+			throw new IllegalArgumentException(label + " host and port must be set");
+		}
+	}
+
+	private static void validBroker(String value) {
+		try {
+			java.net.URI broker = java.net.URI.create(value == null ? "" : value.trim());
+			if (!Set.of("tcp", "ssl", "ws", "wss").contains(broker.getScheme()) || broker.getHost() == null) {
+				throw new IllegalArgumentException();
+			}
+		} catch (RuntimeException e) {
+			throw new IllegalArgumentException("MQTT.BrokerURL must be a valid tcp, ssl, ws, or wss endpoint");
+		}
+	}
+
 	private static void mergeVoteSites(YamlConfiguration source, YamlConfiguration target, boolean ignoreCase) {
 		List<String> targetSecretValues = commentSecretReplacements(target);
 		String sourceRootKey = matchingKey(source, "VoteSites", true);

VotingPlugin/src/main/java/com/bencodez/votingplugin/control/BackendControlConnector.java

@@ -45,7 +45,7 @@ public final class BackendControlConnector implements AutoCloseable {
 	private static final long SHUTDOWN_TIMEOUT_SECONDS = 65;
 	private static final Pattern NODE_ID = Pattern.compile("[A-Za-z0-9][A-Za-z0-9._-]{0,63}");
 	private static final Set<String> CAPABILITIES = Set.of("config.files.v1", "config.file-comments.v1",
-			"config.quick-setup.v1", "config.vote-sites-sync.v1");
+			"config.quick-setup.v1", "config.vote-sites-sync.v1", "config.proxy-method.v1");
 
 	private final VotingPluginMain plugin;
 	private final Path dataDirectory;

VotingPlugin/src/main/java/com/bencodez/votingplugin/proxy/VotingPluginProxy.java

@@ -26,6 +26,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -171,6 +172,7 @@ public abstract class VotingPluginProxy {
 	private final Map<UUID, PendingPresenceHandoff> pendingPresenceHandoffs = new HashMap<>();
 	private final Set<String> pendingBackendRecoverySnapshots = ConcurrentHashMap.newKeySet();
 	private final Map<String, Long> controlEnrollmentNextAllowed = new ConcurrentHashMap<>();
+	private final Map<UUID, PendingCommunicationTest> pendingCommunicationTests = new ConcurrentHashMap<>();
 	private volatile ControlConnector controlConnector;
 	private volatile HostedControlManager hostedControlManager;
 	private final Object controlLifecycleLock = new Object();
@@ -1521,11 +1523,10 @@ && isPresenceGenerationValid(snapshot.backendIncarnationId, snapshot.backendStar
 			}
 		});
 
-		globalMessageProxyHandler.addListener(new GlobalMessageListener("statusokay") {
+		globalMessageProxyHandler.addListener(new GlobalMessageListener(VotingPluginWire.SUB_STATUS_OKAY) {
 			@Override
 			public void onReceive(JsonEnvelope message) {
-				String server = message.getFields().getOrDefault("server", "");
-				log("Status okay for " + server);
+				handleStatusOkay(message);
 			}
 		});
 
@@ -2402,6 +2403,7 @@ public void prepareForRuntimeReplacement() {
 
 	/** Best-effort remainder of runtime teardown after the Control overlap gate has succeeded. */
 	public void completeRuntimeReplacementShutdown() {
+		cancelCommunicationTests("Proxy runtime stopped before the backend replied");
 		runCleanup("vote cache", () -> getVoteCacheHandler().saveVoteCache());
 		runCleanup("proxy MySQL messenger", () -> {
 			if (getProxyMysqlMessenger() != null) getProxyMysqlMessenger().shutdown();
@@ -2891,6 +2893,100 @@ public void status() {
 		}
 	}
 
+	/** Runs a correlated, non-vote round trip over the active backend transport. */
+	public CompletableFuture<CommunicationTestResult> testBackendCommunication(String requestedServer,
+			long timeoutMillis) {
+		String server = requestedServer == null ? "" : requestedServer.trim();
+		BungeeMethod activeMethod = method;
+		if (server.isEmpty() || !getAllAvailableServers().contains(server)) {
+			return CompletableFuture.completedFuture(CommunicationTestResult.failure(server, activeMethod,
+					"UNKNOWN_BACKEND", "The backend is not configured on this proxy"));
+		}
+		if (activeMethod == null || globalMessageProxyHandler == null) {
+			return CompletableFuture.completedFuture(CommunicationTestResult.failure(server, activeMethod,
+					"TRANSPORT_UNAVAILABLE", "The proxy communication transport is not running"));
+		}
+		if (activeMethod == BungeeMethod.PLUGINMESSAGING && !isSomeoneOnlineServerForVoteRouting(server)) {
+			return CompletableFuture.completedFuture(CommunicationTestResult.failure(server, activeMethod,
+					"PLAYER_REQUIRED", "Plugin messaging requires an online player on the selected backend"));
+		}
+		ScheduledExecutorService scheduler = getScheduler();
+		if (scheduler == null) {
+			return CompletableFuture.completedFuture(CommunicationTestResult.failure(server, activeMethod,
+					"TRANSPORT_UNAVAILABLE", "The proxy scheduler is not running"));
+		}
+		long boundedTimeout = Math.max(500L, Math.min(timeoutMillis, 30000L));
+		UUID requestId = UUID.randomUUID();
+		CompletableFuture<CommunicationTestResult> result = new CompletableFuture<>();
+		PendingCommunicationTest pending = new PendingCommunicationTest(server, activeMethod, System.nanoTime(), result);
+		pendingCommunicationTests.put(requestId, pending);
+		result.whenComplete((ignored, failure) -> pendingCommunicationTests.remove(requestId, pending));
+		try {
+			if (!sendCommunicationTestEnvelopeNow(server, VotingPluginWire.status(server, requestId))) {
+				result.complete(CommunicationTestResult.failure(server, activeMethod, "TRANSPORT_UNAVAILABLE",
+						"The active transport could not accept the communication test"));
+				return result;
+			}
+			scheduler.schedule(() -> result.complete(CommunicationTestResult.failure(server, activeMethod,
+					"TIMEOUT", "No correlated reply arrived before the timeout")), boundedTimeout, TimeUnit.MILLISECONDS);
+		} catch (RuntimeException failure) {
+			result.complete(CommunicationTestResult.failure(server, activeMethod, "SEND_FAILED",
+					"The proxy could not send the communication test"));
+		}
+		return result;
+	}
+
+	/** Sends a diagnostic immediately and reports whether the active transport accepted it. */
+	protected boolean sendCommunicationTestEnvelopeNow(String server, JsonEnvelope envelope) {
+		return sendProxyBroadcastEnvelopeNow(server, envelope);
+	}
+
+	protected void handleStatusOkay(JsonEnvelope message) {
+		String server = message.getFields().getOrDefault(VotingPluginWire.K_SERVER, "");
+		String request = message.getFields().getOrDefault(VotingPluginWire.K_REQUEST_ID, "");
+		if (request.isEmpty()) {
+			log("Status okay for " + server);
+			return;
+		}
+		UUID requestId;
+		try {
+			requestId = UUID.fromString(request);
+		} catch (IllegalArgumentException ignored) {
+			debug("Ignored status reply with an invalid request ID from " + server);
+			return;
+		}
+		PendingCommunicationTest pending = pendingCommunicationTests.get(requestId);
+		if (pending == null || !pending.server().equals(server)) {
+			debug("Ignored unexpected status reply from " + server);
+			return;
+		}
+		long roundTripMillis = Math.max(0L,
+				TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - pending.startedAtNanos()));
+		pending.result().complete(CommunicationTestResult.success(server, pending.method(), roundTripMillis));
+	}
+
+	private void cancelCommunicationTests(String message) {
+		pendingCommunicationTests.forEach((requestId, pending) -> pending.result().complete(
+				CommunicationTestResult.failure(pending.server(), pending.method(), "TRANSPORT_STOPPED", message)));
+		pendingCommunicationTests.clear();
+	}
+
+	public record CommunicationTestResult(boolean success, String code, String message, String server,
+			String method, long roundTripMillis) {
+		private static CommunicationTestResult success(String server, BungeeMethod method, long roundTripMillis) {
+			return new CommunicationTestResult(true, "OK", "Backend replied over the active transport", server,
+					method == null ? "" : method.name(), roundTripMillis);
+		}
+
+		private static CommunicationTestResult failure(String server, BungeeMethod method, String code, String message) {
+			return new CommunicationTestResult(false, code, message, server,
+					method == null ? "" : method.name(), -1L);
+		}
+	}
+
+	private record PendingCommunicationTest(String server, BungeeMethod method, long startedAtNanos,
+			CompletableFuture<CommunicationTestResult> result) { }
+
 	private void sendVoteDelayRejected(String player, String uuid, String service, boolean playerOnline,
 			String playerServer) {
 		if (!playerOnline || playerServer == null || !getAllAvailableServers().contains(playerServer)) {

VotingPlugin/src/main/java/com/bencodez/votingplugin/proxy/VotingPluginProxyConfig.java

@@ -22,6 +22,22 @@ default void persistControlProxyRouting(boolean sendVotesToAllServers, List<Stri
 		persistControlProxyRouting(sendVotesToAllServers, blockedServers);
 	}
 
+	/** Atomically persists only the proxy communication method. */
+	default void persistControlProxyMethod(String method, String expectedRevision) throws IOException {
+		persistControlProxyMethod(method, expectedRevision, ignored -> { });
+	}
+
+	/** Atomically validates the freshly loaded file before persisting the proxy communication method. */
+	default void persistControlProxyMethod(String method, String expectedRevision,
+			ControlProxyMethodValidator validator) throws IOException {
+		throw new UnsupportedOperationException("Control proxy method writes are unavailable");
+	}
+
+	@FunctionalInterface
+	interface ControlProxyMethodValidator {
+		void validate(VotingPluginProxyConfig current);
+	}
+
 	/** Restores the most recent Control-created backup. */
 	default void rollbackControlProxyRouting() throws IOException {
 		throw new UnsupportedOperationException("Control configuration rollback is unavailable");

VotingPlugin/src/main/java/com/bencodez/votingplugin/proxy/VotingPluginWire.java

@@ -170,10 +170,20 @@ public static JsonEnvelope status(String server) {
 		return base(SUB_STATUS).put(K_SERVER, safe(server)).build();
 	}
 
+	public static JsonEnvelope status(String server, UUID requestId) {
+		return base(SUB_STATUS).put(K_SERVER, safe(server))
+				.put(K_REQUEST_ID, requestId == null ? "" : requestId.toString()).build();
+	}
+
 	public static JsonEnvelope statusOkay(String server) {
 		return base(SUB_STATUS_OKAY).put(K_SERVER, safe(server)).build();
 	}
 
+	public static JsonEnvelope statusOkay(String server, UUID requestId) {
+		return base(SUB_STATUS_OKAY).put(K_SERVER, safe(server))
+				.put(K_REQUEST_ID, requestId == null ? "" : requestId.toString()).build();
+	}
+
 	public static JsonEnvelope serverName(String server) {
 		return base(SUB_SERVER_NAME).put(K_SERVER, safe(server)).build();
 	}

VotingPlugin/src/main/java/com/bencodez/votingplugin/proxy/bungee/BungeeConfig.java

@@ -17,7 +17,9 @@
 import java.util.Map;
 import java.util.Set;
 
+import com.bencodez.votingplugin.proxy.BungeeMethod;
 import com.bencodez.votingplugin.proxy.VotingPluginProxyConfig;
+import com.bencodez.votingplugin.proxy.control.ProxyMethodConfiguration;
 import com.bencodez.votingplugin.proxy.control.ProxyRoutingConfiguration;
 import com.bencodez.votingplugin.util.DurableFiles;
 
@@ -579,6 +581,49 @@ private static ProxyRoutingConfiguration routing(Configuration configuration) {
 				configuration.getStringList("BlockedServers"));
 	}
 
+	@Override
+	public synchronized void persistControlProxyMethod(String method, String expectedRevision,
+			ControlProxyMethodValidator validator) throws IOException {
+		Path target = new File(bungee.getDataFolder(), "bungeeconfig.yml").toPath();
+		Path stage = Files.createTempFile(target.getParent(), target.getFileName().toString(), ".control-stage");
+		Path backupStage = null;
+		Path backup = target.resolveSibling(target.getFileName() + ".control-backup");
+		try {
+			backupStage = Files.createTempFile(target.getParent(), target.getFileName().toString(), ".control-backup-stage");
+			byte[] sourceSnapshot = Files.readAllBytes(target);
+			Configuration latest = ConfigurationProvider.getProvider(YamlConfiguration.class).load(target.toFile());
+			ProxyMethodConfiguration current = new ProxyMethodConfiguration(
+					BungeeMethod.getByName(latest.getString("BungeeMethod", "SOCKETS")));
+			if (!java.util.Arrays.equals(sourceSnapshot, Files.readAllBytes(target))
+					|| !current.revision().equals(expectedRevision)) throw new StaleControlRevisionException();
+			BungeeConfig fresh = new BungeeConfig(bungee);
+			fresh.loadControlConfiguration();
+			validator.validate(fresh);
+			if (!java.util.Arrays.equals(sourceSnapshot, Files.readAllBytes(target))) {
+				throw new StaleControlRevisionException();
+			}
+			latest.set("BungeeMethod", method);
+			ConfigurationProvider.getProvider(YamlConfiguration.class).save(latest, stage.toFile());
+			byte[] installedSnapshot = Files.readAllBytes(stage);
+			if (!java.util.Arrays.equals(sourceSnapshot, Files.readAllBytes(target))) throw new StaleControlRevisionException();
+			Files.write(backupStage, sourceSnapshot);
+			if (!java.util.Arrays.equals(sourceSnapshot, Files.readAllBytes(target))) throw new StaleControlRevisionException();
+			atomicReplace(backupStage, backup);
+			if (!java.util.Arrays.equals(sourceSnapshot, Files.readAllBytes(target))) throw new StaleControlRevisionException();
+			controlInstalledSnapshot = installedSnapshot;
+			try {
+				atomicReplace(stage, target);
+			} catch (IOException failure) {
+				if (!(failure instanceof DurableFiles.PublishedException)) controlInstalledSnapshot = null;
+				throw failure;
+			}
+			data = latest;
+		} finally {
+			Files.deleteIfExists(stage);
+			if (backupStage != null) Files.deleteIfExists(backupStage);
+		}
+	}
+
 	@Override
 	public synchronized void rollbackControlProxyRouting() throws IOException {
 		Path target = new File(bungee.getDataFolder(), "bungeeconfig.yml").toPath();
@@ -739,14 +784,14 @@ public Configuration sectionOrNull(Configuration root, String key) {
 	@Override
 	public boolean hasDatabaseConfigured() {
 		// New-style: Database: { Host: ..., ... }
-		Configuration db = sectionOrNull(data, "Database");
-		if (db != null) {
-			return db.getString("Host", "") != null && !db.getString("Host", "").isEmpty();
-		}
+		Configuration db = sectionOrNull(data, "Database");
+		if (db != null) {
+			return !db.getString("Host", "").isEmpty() && !db.getString("Database", "").isEmpty();
+		}
 
 		// Legacy-style: Host/Port/... at root
 		String host = data.getString("Host", "");
-		return host != null && !host.isEmpty();
+		return host != null && !host.isEmpty() && !data.getString("Database", "").isEmpty();
 	}
 
 }