Fix some low-hanging code smells using SonarLint.

api/src/main/java/com/velocitypowered/api/event/ResultedEvent.java

@@ -43,20 +43,20 @@ public interface ResultedEvent<R extends ResultedEvent.Result> {
         private static final GenericResult ALLOWED = new GenericResult(true);
         private static final GenericResult DENIED = new GenericResult(false);
 
-        private final boolean allowed;
+        private final boolean status;
 
         private GenericResult(boolean b) {
-            this.allowed = b;
+            this.status = b;
         }
 
         @Override
         public boolean isAllowed() {
-            return allowed;
+            return status;
         }
 
         @Override
         public String toString() {
-            return allowed ? "allowed" : "denied";
+            return status ? "allowed" : "denied";
         }
 
         public static GenericResult allowed() {
@@ -74,17 +74,17 @@ public interface ResultedEvent<R extends ResultedEvent.Result> {
     final class ComponentResult implements Result {
         private static final ComponentResult ALLOWED = new ComponentResult(true, null);
 
-        private final boolean allowed;
+        private final boolean status;
         private final @Nullable Component reason;
 
-        protected ComponentResult(boolean allowed, @Nullable Component reason) {
+        protected ComponentResult(boolean status, @Nullable Component reason) {
-            this.allowed = allowed;
+            this.status = status;
             this.reason = reason;
         }
 
         @Override
         public boolean isAllowed() {
-            return allowed;
+            return status;
         }
 
         public Optional<Component> getReason() {
@@ -93,7 +93,7 @@ public interface ResultedEvent<R extends ResultedEvent.Result> {
 
         @Override
         public String toString() {
-            if (allowed) {
+            if (status) {
                 return "allowed";
             }
             if (reason != null) {

api/src/main/java/com/velocitypowered/api/event/connection/PluginMessageEvent.java

@@ -78,20 +78,20 @@ public final class PluginMessageEvent implements ResultedEvent<PluginMessageEven
         private static final ForwardResult ALLOWED = new ForwardResult(true);
         private static final ForwardResult DENIED = new ForwardResult(false);
 
-        private final boolean allowed;
+        private final boolean status;
 
         private ForwardResult(boolean b) {
-            this.allowed = b;
+            this.status = b;
         }
 
         @Override
         public boolean isAllowed() {
-            return allowed;
+            return status;
         }
 
         @Override
         public String toString() {
-            return allowed ? "forward to sink" : "handled message at proxy";
+            return status ? "forward to sink" : "handled message at proxy";
         }
 
         public static ForwardResult forward() {

api/src/main/java/com/velocitypowered/api/event/player/PlayerChatEvent.java

@@ -58,21 +58,21 @@ public final class PlayerChatEvent implements ResultedEvent<PlayerChatEvent.Chat
 
         // The server can not accept formatted text from clients!
         private @Nullable String message;
-        private final boolean allowed;
+        private final boolean status;
 
-        protected ChatResult(boolean allowed, @Nullable String message) {
+        protected ChatResult(boolean status, @Nullable String message) {
-            this.allowed = allowed;
+            this.status = status;
             this.message = message;
         }
 
         @Override
         public boolean isAllowed() {
-            return allowed;
+            return status;
         }
 
         @Override
         public String toString() {
-            return allowed ? "allowed" : "denied";
+            return status ? "allowed" : "denied";
         }
 
         public static ChatResult allowed() {

api/src/main/java/com/velocitypowered/api/permission/Tristate.java

@@ -1,6 +1,5 @@
 package com.velocitypowered.api.permission;
 
-import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -52,7 +51,10 @@ public enum Tristate {
      *         is <code>null</code>, <code>true</code> or <code>false</code>, respectively.
      */
     public static Tristate fromNullableBoolean(@Nullable Boolean val) {
-        return val == null ? UNDEFINED : val ? TRUE : FALSE;
+        if (val == null) {
+            return UNDEFINED;
+        }
+        return val ? TRUE : FALSE;
     }
 
     private final boolean booleanValue;

api/src/main/java/com/velocitypowered/api/plugin/Dependency.java

@@ -18,8 +18,6 @@ public @interface Dependency {
      */
     String id();
 
-    // TODO Add required version field
-
     /**
      * If this dependency is optional for the plugin to work. By default
      * this is {@code false}.

api/src/main/java/com/velocitypowered/api/proxy/messages/LegacyChannelIdentifier.java

@@ -42,6 +42,6 @@ public final class LegacyChannelIdentifier implements ChannelIdentifier {
 
     @Override
     public String getId() {
-        return name;
+        return this.getName();
     }
 }

api/src/main/java/com/velocitypowered/api/proxy/player/SkinParts.java

@@ -8,7 +8,7 @@ public final class SkinParts {
     }
 
     public boolean hasCape() {
-        return ((bitmask >> 0) & 1) == 1;
+        return (bitmask & 1) == 1;
     }
 
     public boolean hasJacket() {

api/src/main/java/com/velocitypowered/api/scheduler/Scheduler.java

@@ -1,7 +1,6 @@
 package com.velocitypowered.api.scheduler;
 
 import org.checkerframework.common.value.qual.IntRange;
-import org.checkerframework.common.value.qual.IntRangeFromNonNegative;
 
 import java.util.concurrent.TimeUnit;
 

api/src/main/java/com/velocitypowered/api/util/GameProfile.java

@@ -56,7 +56,7 @@ public final class GameProfile {
                 '}';
     }
 
-    public final static class Property {
+    public static final class Property {
         private final String name;
         private final String value;
         private final String signature;

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -51,7 +51,6 @@ import java.nio.file.Paths;
 import java.security.KeyPair;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 public class VelocityServer implements ProxyServer {
@@ -98,7 +97,9 @@ public class VelocityServer implements ProxyServer {
     @Override
     public ProxyVersion getVersion() {
         Package pkg = VelocityServer.class.getPackage();
-        String implName, implVersion, implVendor;
+        String implName;
+        String implVersion;
+        String implVendor;
         if (pkg != null) {
             implName = MoreObjects.firstNonNull(pkg.getImplementationTitle(), "Velocity");
             implVersion = MoreObjects.firstNonNull(pkg.getImplementationVersion(), "<unknown>");
@@ -148,7 +149,7 @@ public class VelocityServer implements ProxyServer {
 
             AnnotatedConfig.saveConfig(configuration.dumpConfig(), configPath); //Resave config to add new values
 
-        } catch (Throwable e) {
+        } catch (Exception e) {
             logger.error("Unable to read/load/save your velocity.toml. The server will shut down.", e);
             LogManager.shutdown();
             System.exit(1);
@@ -183,10 +184,10 @@ public class VelocityServer implements ProxyServer {
         try {
             Path pluginPath = Paths.get("plugins");
 
-            if (Files.notExists(pluginPath)) {
+            if (!pluginPath.toFile().exists()) {
                 Files.createDirectory(pluginPath);
             } else {
-                if (!Files.isDirectory(pluginPath)) {
+                if (!pluginPath.toFile().isDirectory()) {
                     logger.warn("Plugin location {} is not a directory, continuing without loading plugins", pluginPath);
                     return;
                 }
@@ -242,6 +243,7 @@ public class VelocityServer implements ProxyServer {
             }
         } catch (InterruptedException e) {
             // Not much we can do about this...
+            Thread.currentThread().interrupt();
         }
 
         shutdown = true;

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -1,7 +1,6 @@
 package com.velocitypowered.proxy.connection.backend;
 
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
-import com.velocitypowered.api.event.player.ServerConnectedEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
@@ -67,13 +66,10 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
 
     @Override
     public boolean handle(BossBar packet) {
-        switch (packet.getAction()) {
+        if (packet.getAction() == BossBar.ADD) {
-            case BossBar.ADD:
             playerSessionHandler.getServerBossBars().add(packet.getUuid());
-                break;
+        } else if (packet.getAction() == BossBar.REMOVE) {
-            case BossBar.REMOVE:
             playerSessionHandler.getServerBossBars().remove(packet.getUuid());
-                break;
         }
         return false; // forward
     }

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -1,7 +1,6 @@
 package com.velocitypowered.proxy.connection.backend;
 
 import com.google.common.base.Preconditions;
-import com.google.common.base.Verify;
 import com.google.common.base.VerifyException;
 import com.velocitypowered.api.proxy.ConnectionRequestBuilder;
 import com.velocitypowered.api.proxy.ServerConnection;
@@ -65,10 +64,10 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
                                 .addLast(MINECRAFT_DECODER, new MinecraftDecoder(ProtocolConstants.Direction.CLIENTBOUND))
                                 .addLast(MINECRAFT_ENCODER, new MinecraftEncoder(ProtocolConstants.Direction.SERVERBOUND));
 
-                        MinecraftConnection connection = new MinecraftConnection(ch, server);
+                        MinecraftConnection mc = new MinecraftConnection(ch, server);
-                        connection.setState(StateRegistry.HANDSHAKE);
+                        mc.setState(StateRegistry.HANDSHAKE);
-                        connection.setAssociation(VelocityServerConnection.this);
+                        mc.setAssociation(VelocityServerConnection.this);
-                        ch.pipeline().addLast(HANDLER, connection);
+                        ch.pipeline().addLast(HANDLER, mc);
                     }
                 })
                 .connect(registeredServer.getServerInfo().getAddress())

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -1,6 +1,5 @@
 package com.velocitypowered.proxy.connection.client;
 
-import com.google.common.base.Preconditions;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
 import com.velocitypowered.api.event.player.PlayerChatEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
@@ -57,14 +56,12 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
         VelocityServerConnection serverConnection = player.getConnectedServer();
         if (serverConnection != null && packet.getRandomId() == serverConnection.getLastPingId()) {
             MinecraftConnection smc = serverConnection.getConnection();
-            if (smc == null) {
+            if (smc != null) {
-                // eat the packet
-                return true;
-            }
                 player.setPing(System.currentTimeMillis() - serverConnection.getLastPingSent());
                 smc.write(packet);
                 serverConnection.resetLastPingId();
             }
+        }
         return true;
     }
 
@@ -122,7 +119,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                 String cmd = packet.getCommand().substring(1, spacePos);
                 if (server.getCommandManager().hasCommand(cmd)) {
                     List<String> suggestions = server.getCommandManager().offerSuggestions(player, packet.getCommand().substring(1));
-                    if (suggestions.size() > 0) {
+                    if (!suggestions.isEmpty()) {
                         TabCompleteResponse resp = new TabCompleteResponse();
                         resp.getOffers().addAll(suggestions);
                         player.getConnection().write(resp);
@@ -153,20 +150,17 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                     }
                 }
 
-                if (actuallyRegistered.size() > 0) {
+                if (!actuallyRegistered.isEmpty()) {
                     PluginMessage newRegisterPacket = PluginMessageUtil.constructChannelsPacket(backendConn
                             .getProtocolVersion(), actuallyRegistered);
                     backendConn.write(newRegisterPacket);
                 }
-                return true;
             } else if (PluginMessageUtil.isMCUnregister(packet)) {
                 List<String> channels = PluginMessageUtil.getChannels(packet);
                 clientPluginMsgChannels.removeAll(channels);
                 backendConn.write(packet);
-                return true;
             } else if (PluginMessageUtil.isMCBrand(packet)) {
                 backendConn.write(PluginMessageUtil.rewriteMCBrand(packet));
-                return true;
             } else if (backendConn.isLegacyForge() && !serverConn.hasCompletedJoin()) {
                 if (packet.getChannel().equals(ForgeConstants.FORGE_LEGACY_HANDSHAKE_CHANNEL)) {
                     if (!player.getModInfo().isPresent()) {
@@ -184,17 +178,14 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                     // be sent once the JoinGame packet has been received by the proxy.
                     loginPluginMessages.add(packet);
                 }
-                return true;
             } else {
                 ChannelIdentifier id = server.getChannelRegistrar().getFromId(packet.getChannel());
                 if (id == null) {
                     backendConn.write(packet);
                 } else {
                     PluginMessageEvent event = new PluginMessageEvent(player, serverConn, id, packet.getData());
-                    server.getEventManager().fire(event)
+                    server.getEventManager().fire(event).thenAcceptAsync(pme -> backendConn.write(packet),
-                            .thenAcceptAsync(pme -> {
+                            backendConn.eventLoop());
-                                backendConn.write(packet);
-                            }, backendConn.eventLoop());
                 }
             }
         }
@@ -246,10 +237,10 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
     @Override
     public void writabilityChanged() {
-        VelocityServerConnection server = player.getConnectedServer();
+        VelocityServerConnection serverConn = player.getConnectedServer();
-        if (server != null) {
+        if (serverConn != null) {
             boolean writable = player.getConnection().getChannel().isWritable();
-            MinecraftConnection smc = server.getConnection();
+            MinecraftConnection smc = serverConn.getConnection();
             if (smc != null) {
                 smc.getChannel().config().setAutoRead(writable);
             }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientSettingsWrapper.java

@@ -8,7 +8,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 import java.util.Locale;
 
 public class ClientSettingsWrapper implements PlayerSettings {
-    static PlayerSettings DEFAULT = new ClientSettingsWrapper(new ClientSettings("en_US", (byte) 10, 0, true, (short)127, 1));
+    static final PlayerSettings DEFAULT = new ClientSettingsWrapper(new ClientSettings("en_US", (byte) 10, 0, true, (short)127, 1));
     
     private final ClientSettings settings;
     private final SkinParts parts;
@@ -21,7 +21,10 @@ public class ClientSettingsWrapper implements PlayerSettings {
 
     @Override
     public Locale getLocale() {
-        return locale == null ? locale = Locale.forLanguageTag(settings.getLocale().replaceAll("_", "-")) : locale; //Will throw error if locale not found
+        if (locale == null) {
+            locale = Locale.forLanguageTag(settings.getLocale().replaceAll("_", "-"));
+        }
+        return locale;
     }
 
     @Override

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -43,27 +43,24 @@ import net.kyori.text.serializer.PlainComponentSerializer;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
-import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.net.InetSocketAddress;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
-import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
 
 public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
-    private static final PlainComponentSerializer PASS_THRU_TRANSLATE = new PlainComponentSerializer((c) -> "", TranslatableComponent::key);
+    private static final PlainComponentSerializer PASS_THRU_TRANSLATE = new PlainComponentSerializer(c -> "", TranslatableComponent::key);
     static final PermissionProvider DEFAULT_PERMISSIONS = s -> PermissionFunction.ALWAYS_UNDEFINED;
 
     private static final Logger logger = LogManager.getLogger(ConnectedPlayer.class);
 
     private final MinecraftConnection connection;
-    private @Nullable final InetSocketAddress virtualHost;
+    private final @Nullable InetSocketAddress virtualHost;
     private GameProfile profile;
     private PermissionFunction permissionFunction;
     private int tryIndex = 0;
@@ -84,7 +81,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
         this.profile = profile;
         this.connection = connection;
         this.virtualHost = virtualHost;
-        this.permissionFunction = (permission) -> Tristate.UNDEFINED;
+        this.permissionFunction = PermissionFunction.ALWAYS_UNDEFINED;
     }
 
     @Override
@@ -364,8 +361,8 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
 
     Optional<RegisteredServer> getNextServerToTry() {
         if (serversToTry == null) {
-            String virtualHost = getVirtualHost().map(InetSocketAddress::getHostString).orElse("");
+            String virtualHostStr = getVirtualHost().map(InetSocketAddress::getHostString).orElse("");
-            serversToTry = server.getConfiguration().getForcedHosts().getOrDefault(virtualHost, Collections.emptyList());
+            serversToTry = server.getConfiguration().getForcedHosts().getOrDefault(virtualHostStr, Collections.emptyList());
         }
 
         if (serversToTry.isEmpty()) {
@@ -401,7 +398,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
         // Otherwise, initiate the connection.
         ServerPreConnectEvent event = new ServerPreConnectEvent(this, request.getServer());
         return server.getEventManager().fire(event)
-                .thenCompose((newEvent) -> {
+                .thenCompose(newEvent -> {
                     Optional<RegisteredServer> connectTo = newEvent.getResult().getServer();
                     if (!connectTo.isPresent()) {
                         return CompletableFuture.completedFuture(
@@ -431,10 +428,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
 
     public void sendLegacyForgeHandshakeResetPacket() {
         if (connection.canSendLegacyFMLResetPacket()) {
-            PluginMessage resetPacket = new PluginMessage();
+            connection.write(ForgeConstants.resetPacket());
-            resetPacket.setChannel(ForgeConstants.FORGE_LEGACY_HANDSHAKE_CHANNEL);
-            resetPacket.setData(ForgeConstants.FORGE_LEGACY_HANDSHAKE_RESET_DATA);
-            connection.write(resetPacket);
             connection.setCanSendLegacyFMLResetPacket(false);
         }
     }
@@ -534,6 +528,9 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
                             case SERVER_DISCONNECTED:
                                 handleConnectionException(server, Disconnect.create(status.getReason().orElse(ConnectionMessages.INTERNAL_SERVER_CONNECTION_ERROR)));
                                 break;
+                            default:
+                                // The only remaining value is successful (no need to do anything!)
+                                break;
                         }
                     }, connection.eventLoop())
                     .thenApply(Result::isSuccessful);

proxy/src/main/java/com/velocitypowered/proxy/connection/client/HandshakeSessionHandler.java

@@ -48,7 +48,8 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
         server.getEventManager().fire(event)
                 .thenRunAsync(() -> {
                     // The disconnect packet is the same as the server response one.
-                    connection.closeWith(LegacyDisconnect.fromPingResponse(LegacyPingResponse.from(event.getPing())));
+                    LegacyPingResponse response = LegacyPingResponse.from(event.getPing());
+                    connection.closeWith(LegacyDisconnect.fromPingResponse(response));
                 }, connection.eventLoop());
         return true;
     }
@@ -116,12 +117,13 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
 
     @Override
     public void handleGeneric(MinecraftPacket packet) {
-
+        // Unknown packet received. Better to close the connection.
+        connection.close();
     }
 
     @Override
     public void handleUnknown(ByteBuf buf) {
-        // what even is going on?
+        // Unknown packet received. Better to close the connection.
         connection.close();
     }
 

proxy/src/main/java/com/velocitypowered/proxy/connection/client/StatusSessionHandler.java

@@ -48,9 +48,8 @@ public class StatusSessionHandler implements MinecraftSessionHandler {
 
         ProxyPingEvent event = new ProxyPingEvent(inboundWrapper, initialPing);
         server.getEventManager().fire(event)
-                .thenRunAsync(() -> {
+                .thenRunAsync(() -> connection.write(new StatusResponse(VelocityServer.GSON.toJson(event.getPing()))),
-                    connection.write(new StatusResponse(VelocityServer.GSON.toJson(event.getPing())));
+                        connection.eventLoop());
-                }, connection.eventLoop());
         return true;
     }
 

proxy/src/main/java/com/velocitypowered/proxy/connection/forge/ForgeConstants.java

@@ -1,12 +1,21 @@
 package com.velocitypowered.proxy.connection.forge;
 
+import com.velocitypowered.proxy.protocol.packet.PluginMessage;
+
 public class ForgeConstants {
     public static final String FORGE_LEGACY_HANDSHAKE_CHANNEL = "FML|HS";
     public static final String FORGE_LEGACY_CHANNEL = "FML";
     public static final String FORGE_MULTIPART_LEGACY_CHANNEL = "FML|MP";
-    public static final byte[] FORGE_LEGACY_HANDSHAKE_RESET_DATA = new byte[] { -2, 0 };
+    private static final byte[] FORGE_LEGACY_HANDSHAKE_RESET_DATA = new byte[] { -2, 0 };
 
     private ForgeConstants() {
         throw new AssertionError();
     }
+
+    public static PluginMessage resetPacket() {
+        PluginMessage msg = new PluginMessage();
+        msg.setChannel(FORGE_LEGACY_HANDSHAKE_CHANNEL);
+        msg.setData(FORGE_LEGACY_HANDSHAKE_RESET_DATA.clone());
+        return msg;
+    }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/util/ConnectionRequestResults.java

@@ -3,7 +3,6 @@ package com.velocitypowered.proxy.connection.util;
 import com.velocitypowered.api.proxy.ConnectionRequestBuilder;
 import com.velocitypowered.proxy.protocol.packet.Disconnect;
 import net.kyori.text.Component;
-import net.kyori.text.TextComponent;
 import net.kyori.text.serializer.ComponentSerializers;
 
 import java.util.Optional;

proxy/src/main/java/com/velocitypowered/proxy/console/VelocityConsole.java

@@ -18,7 +18,6 @@ import org.jline.reader.LineReader;
 import org.jline.reader.LineReaderBuilder;
 
 import java.util.List;
-import java.util.Optional;
 
 public final class VelocityConsole extends SimpleTerminalConsole implements CommandSource {
     private static final Logger logger = LogManager.getLogger(VelocityConsole.class);

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -12,7 +12,6 @@ import io.netty.channel.EventLoopGroup;
 import io.netty.channel.WriteBufferWaterMark;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.checkerframework.checker.initialization.qual.UnderInitialization;
 
 import java.net.InetSocketAddress;
 import java.util.HashSet;
@@ -94,6 +93,7 @@ public final class ConnectionManager {
                 endpoint.close().sync();
             } catch (final InterruptedException e) {
                 LOGGER.info("Interrupted whilst closing endpoint", e);
+                Thread.currentThread().interrupt();
             }
         }
     }

proxy/src/main/java/com/velocitypowered/proxy/network/Connections.java

@@ -1,16 +1,20 @@
 package com.velocitypowered.proxy.network;
 
-public interface Connections {
+public class Connections {
-    String CIPHER_DECODER = "cipher-decoder";
+    public static final String CIPHER_DECODER = "cipher-decoder";
-    String CIPHER_ENCODER = "cipher-encoder";
+    public static final String CIPHER_ENCODER = "cipher-encoder";
-    String COMPRESSION_DECODER = "compression-decoder";
+    public static final String COMPRESSION_DECODER = "compression-decoder";
-    String COMPRESSION_ENCODER = "compression-encoder";
+    public static final String COMPRESSION_ENCODER = "compression-encoder";
-    String FRAME_DECODER = "frame-decoder";
+    public static final String FRAME_DECODER = "frame-decoder";
-    String FRAME_ENCODER = "frame-encoder";
+    public static final String FRAME_ENCODER = "frame-encoder";
-    String HANDLER = "handler";
+    public static final String HANDLER = "handler";
-    String LEGACY_PING_DECODER = "legacy-ping-decoder";
+    public static final String LEGACY_PING_DECODER = "legacy-ping-decoder";
-    String LEGACY_PING_ENCODER = "legacy-ping-encoder";
+    public static final String LEGACY_PING_ENCODER = "legacy-ping-encoder";
-    String MINECRAFT_DECODER = "minecraft-decoder";
+    public static final String MINECRAFT_DECODER = "minecraft-decoder";
-    String MINECRAFT_ENCODER = "minecraft-encoder";
+    public static final String MINECRAFT_ENCODER = "minecraft-encoder";
-    String READ_TIMEOUT = "read-timeout";
+    public static final String READ_TIMEOUT = "read-timeout";
+
+    private Connections() {
+        throw new AssertionError();
+    }
 }

proxy/src/main/java/com/velocitypowered/proxy/network/http/NettyHttpClient.java

@@ -31,6 +31,8 @@ public class NettyHttpClient {
 
                     @Override
                     public void channelAcquired(Channel channel) throws Exception {
+                        // We don't do anything special when acquiring channels. The channel handler cleans up after
+                        // each connection is used.
                     }
 
                     @Override
@@ -72,10 +74,8 @@ public class NettyHttpClient {
                         request.headers().add(HttpHeaderNames.USER_AGENT, "Velocity");
                         channel.writeAndFlush(request);
 
-                        reply.whenComplete((resp, err) -> {
                         // Make sure to release this connection
-                            poolMap.get(address).release(channel, channel.voidPromise());
+                        reply.whenComplete((resp, err) -> poolMap.get(address).release(channel));
-                        });
                     } else {
                         reply.completeExceptionally(future.cause());
                     }

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityEventManager.java

@@ -55,11 +55,15 @@ public class VelocityEventManager implements EventManager {
                 .setNameFormat("Velocity Event Executor - #%d").setDaemon(true).build());
     }
 
+    private void ensurePlugin(Object plugin) {
+        Preconditions.checkNotNull(plugin, "plugin");
+        Preconditions.checkArgument(pluginManager.fromInstance(plugin).isPresent(), "Specified plugin is not loaded");
+    }
+
     @Override
     public void register(Object plugin, Object listener) {
-        Preconditions.checkNotNull(plugin, "plugin");
+        ensurePlugin(plugin);
         Preconditions.checkNotNull(listener, "listener");
-        Preconditions.checkArgument(pluginManager.fromInstance(plugin).isPresent(), "Specified plugin is not loaded");
         if (plugin == listener && registeredListenersByPlugin.containsEntry(plugin, plugin)) {
             throw new IllegalArgumentException("Trying to register the plugin main instance. Velocity already takes care of this for you.");
         }
@@ -70,7 +74,7 @@ public class VelocityEventManager implements EventManager {
     @Override
     @SuppressWarnings("type.argument.type.incompatible")
     public <E> void register(Object plugin, Class<E> eventClass, PostOrder postOrder, EventHandler<E> handler) {
-        Preconditions.checkNotNull(plugin, "plugin");
+        ensurePlugin(plugin);
         Preconditions.checkNotNull(eventClass, "eventClass");
         Preconditions.checkNotNull(postOrder, "postOrder");
         Preconditions.checkNotNull(handler, "listener");
@@ -108,8 +112,7 @@ public class VelocityEventManager implements EventManager {
 
     @Override
     public void unregisterListeners(Object plugin) {
-        Preconditions.checkNotNull(plugin, "plugin");
+        ensurePlugin(plugin);
-        Preconditions.checkArgument(pluginManager.fromInstance(plugin).isPresent(), "Specified plugin is not loaded");
         Collection<Object> listeners = registeredListenersByPlugin.removeAll(plugin);
         listeners.forEach(methodAdapter::unregister);
         Collection<EventHandler<?>> handlers = registeredHandlersByPlugin.removeAll(plugin);
@@ -118,16 +121,15 @@ public class VelocityEventManager implements EventManager {
 
     @Override
     public void unregisterListener(Object plugin, Object listener) {
-        Preconditions.checkNotNull(plugin, "plugin");
+        ensurePlugin(plugin);
         Preconditions.checkNotNull(listener, "listener");
-        Preconditions.checkArgument(pluginManager.fromInstance(plugin).isPresent(), "Specified plugin is not loaded");
         registeredListenersByPlugin.remove(plugin, listener);
         methodAdapter.unregister(listener);
     }
 
     @Override
     public <E> void unregister(Object plugin, EventHandler<E> handler) {
-        Preconditions.checkNotNull(plugin, "plugin");
+        ensurePlugin(plugin);
         Preconditions.checkNotNull(handler, "listener");
         registeredHandlersByPlugin.remove(plugin, handler);
         bus.unregister(new KyoriToVelocityHandler<>(handler, PostOrder.LAST));

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java

@@ -9,7 +9,6 @@ import com.velocitypowered.proxy.plugin.loader.JavaPluginLoader;
 import com.velocitypowered.proxy.plugin.util.PluginDependencyUtils;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.checkerframework.checker.nullness.qual.NonNull;
 
 import java.io.IOException;
 import java.nio.file.DirectoryStream;
@@ -41,12 +40,12 @@ public class VelocityPluginManager implements PluginManager {
 
     public void loadPlugins(Path directory) throws IOException {
         checkNotNull(directory, "directory");
-        checkArgument(Files.isDirectory(directory), "provided path isn't a directory");
+        checkArgument(directory.toFile().isDirectory(), "provided path isn't a directory");
 
         List<PluginDescription> found = new ArrayList<>();
         JavaPluginLoader loader = new JavaPluginLoader(server, directory);
 
-        try (DirectoryStream<Path> stream = Files.newDirectoryStream(directory, p -> Files.isRegularFile(p) && p.toString().endsWith(".jar"))) {
+        try (DirectoryStream<Path> stream = Files.newDirectoryStream(directory, p -> p.toFile().isFile() && p.toString().endsWith(".jar"))) {
             for (Path path : stream) {
                 try {
                     found.add(loader.loadPlugin(path));
@@ -79,7 +78,7 @@ public class VelocityPluginManager implements PluginManager {
 
             try {
                 pluginObject = loader.createPlugin(plugin);
-            } catch (Throwable e) {
+            } catch (Exception e) {
                 logger.error("Can't create plugin {}", plugin.getId(), e);
                 continue;
             }

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/JavaPluginLoader.java

@@ -12,7 +12,6 @@ import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.plugin.PluginClassLoader;
 import com.velocitypowered.proxy.plugin.loader.java.JavaVelocityPluginDescription;
 import com.velocitypowered.proxy.plugin.loader.java.VelocityPluginModule;
-import org.checkerframework.checker.nullness.qual.NonNull;
 
 import java.io.BufferedInputStream;
 import java.io.InputStreamReader;

proxy/src/main/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtils.java

@@ -13,6 +13,10 @@ import org.checkerframework.checker.nullness.qual.NonNull;
 import java.util.*;
 
 public class PluginDependencyUtils {
+    private PluginDependencyUtils() {
+        throw new AssertionError();
+    }
+
     public static List<PluginDescription> sortCandidates(List<@NonNull PluginDescription> candidates) {
         // Create our graph, we're going to be using this for Kahn's algorithm.
         MutableGraph<PluginDescription> graph = GraphBuilder.directed().allowsSelfLoops(false).build();

proxy/src/main/java/com/velocitypowered/proxy/protocol/StateRegistry.java

@@ -217,12 +217,12 @@ public enum StateRegistry {
         }
 
         public class ProtocolVersion {
-            public final int id;
+            public final int version;
             final IntObjectMap<Supplier<? extends MinecraftPacket>> packetIdToSupplier = new IntObjectHashMap<>(16, 0.5f);
             final Object2IntMap<Class<? extends MinecraftPacket>> packetClassToId = new Object2IntOpenHashMap<>(16, 0.5f);
 
-            ProtocolVersion(final int id) {
+            ProtocolVersion(final int version) {
-                this.id = id;
+                this.version = version;
                 this.packetClassToId.defaultReturnValue(Integer.MIN_VALUE);
             }
 
@@ -239,7 +239,7 @@ public enum StateRegistry {
                 if (id == Integer.MIN_VALUE) {
                     throw new IllegalArgumentException(String.format(
                             "Unable to find id for packet of type %s in %s protocol %s",
-                            packet.getClass().getName(), PacketRegistry.this.direction, this.id
+                            packet.getClass().getName(), PacketRegistry.this.direction, this.version
                     ));
                 }
                 return id;

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/GS4QueryHandler.java

@@ -35,15 +35,15 @@ import static com.velocitypowered.api.event.query.ProxyQueryEvent.QueryType.FULL
 public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket> {
     private static final Logger logger = LogManager.getLogger(GS4QueryHandler.class);
 
-    private final static short QUERY_MAGIC_FIRST = 0xFE;
+    private static final short QUERY_MAGIC_FIRST = 0xFE;
-    private final static short QUERY_MAGIC_SECOND = 0xFD;
+    private static final short QUERY_MAGIC_SECOND = 0xFD;
-    private final static byte QUERY_TYPE_HANDSHAKE = 0x09;
+    private static final byte QUERY_TYPE_HANDSHAKE = 0x09;
-    private final static byte QUERY_TYPE_STAT = 0x00;
+    private static final byte QUERY_TYPE_STAT = 0x00;
-    private final static byte[] QUERY_RESPONSE_FULL_PADDING = new byte[] { 0x73, 0x70, 0x6C, 0x69, 0x74, 0x6E, 0x75, 0x6D, 0x00, (byte) 0x80, 0x00 };
+    private static final byte[] QUERY_RESPONSE_FULL_PADDING = new byte[] { 0x73, 0x70, 0x6C, 0x69, 0x74, 0x6E, 0x75, 0x6D, 0x00, (byte) 0x80, 0x00 };
-    private final static byte[] QUERY_RESPONSE_FULL_PADDING2 = new byte[] { 0x01, 0x70, 0x6C, 0x61, 0x79, 0x65, 0x72, 0x5F, 0x00, 0x00 };
+    private static final byte[] QUERY_RESPONSE_FULL_PADDING2 = new byte[] { 0x01, 0x70, 0x6C, 0x61, 0x79, 0x65, 0x72, 0x5F, 0x00, 0x00 };
 
     // Contents to add into basic stat response. See ResponseWriter class below
-    private final static Set<String> QUERY_BASIC_RESPONSE_CONTENTS = ImmutableSet.of(
+    private static final Set<String> QUERY_BASIC_RESPONSE_CONTENTS = ImmutableSet.of(
             "hostname",
             "gametype",
             "map",
@@ -159,11 +159,9 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
 
                     break;
                 }
-
+                default:
-                default: {
                     throw new IllegalStateException("Invalid query type: " + type);
             }
-            }
         } catch (Exception e) {
             logger.warn("Error while trying to handle a query packet from {}", msg.sender(), e);
             // NB: Only need to explicitly release upon exception, writing the response out will decrement the reference

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftDecoder.java

@@ -38,14 +38,14 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
             out.add(slice.retain());
         } else {
             try {
-                packet.decode(msg, direction, protocolVersion.id);
+                packet.decode(msg, direction, protocolVersion.version);
             } catch (Exception e) {
                 throw new CorruptedFrameException("Error decoding " + packet.getClass() + " Direction " + direction
-                        + " Protocol " + protocolVersion.id + " State " + state + " ID " + Integer.toHexString(packetId), e);
+                        + " Protocol " + protocolVersion.version + " State " + state + " ID " + Integer.toHexString(packetId), e);
             }
             if (msg.isReadable()) {
                 throw new CorruptedFrameException("Did not read full packet for " + packet.getClass() + " Direction " + direction
-                        + " Protocol " + protocolVersion.id + " State " + state + " ID " + Integer.toHexString(packetId));
+                        + " Protocol " + protocolVersion.version + " State " + state + " ID " + Integer.toHexString(packetId));
             }
             out.add(packet);
         }
@@ -57,6 +57,6 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf> {
 
     public void setState(StateRegistry state) {
         this.state = state;
-        this.setProtocolVersion(protocolVersion.id);
+        this.setProtocolVersion(protocolVersion.version);
     }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftEncoder.java

@@ -24,7 +24,7 @@ public class MinecraftEncoder extends MessageToByteEncoder<MinecraftPacket> {
     protected void encode(ChannelHandlerContext ctx, MinecraftPacket msg, ByteBuf out) {
         int packetId = this.protocolVersion.getPacketId(msg);
         ProtocolUtils.writeVarInt(out, packetId);
-        msg.encode(out, direction, protocolVersion.id);
+        msg.encode(out, direction, protocolVersion.version);
     }
 
     public void setProtocolVersion(final int protocolVersion) {
@@ -33,6 +33,6 @@ public class MinecraftEncoder extends MessageToByteEncoder<MinecraftPacket> {
 
     public void setState(StateRegistry state) {
         this.state = state;
-        this.setProtocolVersion(protocolVersion.id);
+        this.setProtocolVersion(protocolVersion.version);
     }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/BossBar.java

@@ -123,6 +123,8 @@ public class BossBar implements MinecraftPacket {
             case UPDATE_PROPERTIES:
                 this.flags = buf.readUnsignedByte();
                 break;
+            default:
+                throw new UnsupportedOperationException("Unknown action " + action);
         }
     }
 
@@ -162,6 +164,8 @@ public class BossBar implements MinecraftPacket {
             case UPDATE_PROPERTIES:
                 buf.writeByte(flags);
                 break;
+            default:
+                throw new UnsupportedOperationException("Unknown action " + action);
         }
     }
 

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/Chat.java

@@ -11,7 +11,7 @@ import net.kyori.text.serializer.ComponentSerializers;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class Chat implements MinecraftPacket {
-    public static final byte CHAT = (byte) 0;
+    public static final byte CHAT_TYPE = (byte) 0;
     public static final int MAX_SERVERBOUND_MESSAGE_LENGTH = 256;
 
     private @Nullable String message;
@@ -77,7 +77,7 @@ public class Chat implements MinecraftPacket {
     }
 
     public static Chat createClientbound(Component component) {
-        return createClientbound(component, CHAT);
+        return createClientbound(component, CHAT_TYPE);
     }
 
     public static Chat createClientbound(Component component, byte type) {
@@ -86,6 +86,6 @@ public class Chat implements MinecraftPacket {
     }
 
     public static Chat createServerbound(String message) {
-        return new Chat(message, CHAT);
+        return new Chat(message, CHAT_TYPE);
     }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/PlayerListItem.java

@@ -54,10 +54,7 @@ public class PlayerListItem implements MinecraftPacket {
                     item.setProperties(ProtocolUtils.readProperties(buf));
                     item.setGameMode(ProtocolUtils.readVarInt(buf));
                     item.setLatency(ProtocolUtils.readVarInt(buf));
-                    boolean hasDisplayName = buf.readBoolean();
+                    item.setDisplayName(readOptionalComponent(buf));
-                    if (hasDisplayName) {
-                        item.setDisplayName(ComponentSerializers.JSON.deserialize(ProtocolUtils.readString(buf)));
-                    }
                     break;
                 }
                 case UPDATE_GAMEMODE:
@@ -66,19 +63,26 @@ public class PlayerListItem implements MinecraftPacket {
                 case UPDATE_LATENCY:
                     item.setLatency(ProtocolUtils.readVarInt(buf));
                     break;
-                case UPDATE_DISPLAY_NAME: {
+                case UPDATE_DISPLAY_NAME:
-                    boolean hasDisplayName = buf.readBoolean();
+                    item.setDisplayName(readOptionalComponent(buf));
-                    if (hasDisplayName) {
+                    break;
-                        item.setDisplayName(ComponentSerializers.JSON.deserialize(ProtocolUtils.readString(buf)));
-                    }
-                } break;
                 case REMOVE_PLAYER:
                     //Do nothing, all that is needed is the uuid
                     break;
+                default:
+                    throw new UnsupportedOperationException("Unknown action " + action);
             }
         }
     }
 
+    @Nullable
+    private static Component readOptionalComponent(ByteBuf buf) {
+        if (buf.readBoolean()) {
+            return ComponentSerializers.JSON.deserialize(ProtocolUtils.readString(buf));
+        }
+        return null;
+    }
+
     @Override
     public void encode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
         ProtocolUtils.writeVarInt(buf, action);
@@ -106,6 +110,8 @@ public class PlayerListItem implements MinecraftPacket {
                 case REMOVE_PLAYER:
                     //Do nothing, all that is needed is the uuid
                     break;
+                default:
+                    throw new UnsupportedOperationException("Unknown action " + action);
             }
         }
     }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/StatusRequest.java

@@ -14,12 +14,12 @@ public class StatusRequest implements MinecraftPacket {
 
     @Override
     public void decode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
-
+        // There is no additional data to decode.
     }
 
     @Override
     public void encode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
-
+        // There is no data to decode.
     }
 
     @Override

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/TitlePacket.java

@@ -51,6 +51,8 @@ public class TitlePacket implements MinecraftPacket {
                 case HIDE:
                 case RESET:
                     break;
+                default:
+                    throw new UnsupportedOperationException("Unknown action " + action);
             }
         } else {
             switch (action) {
@@ -69,6 +71,8 @@ public class TitlePacket implements MinecraftPacket {
                 case HIDE_OLD:
                 case RESET_OLD:
                     break;
+                default:
+                    throw new UnsupportedOperationException("Unknown action " + action);
             }
         }
     }

proxy/src/main/java/com/velocitypowered/proxy/protocol/util/FaviconSerializer.java

@@ -7,7 +7,7 @@ import java.lang.reflect.Type;
 
 public class FaviconSerializer implements JsonSerializer<Favicon>, JsonDeserializer<Favicon> {
     @Override
-    public Favicon deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
+    public Favicon deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) {
         return new Favicon(json.getAsString());
     }
 

proxy/src/main/java/com/velocitypowered/proxy/protocol/util/PluginMessageUtil.java

@@ -2,9 +2,6 @@ package com.velocitypowered.proxy.protocol.util;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Lists;
-import com.velocitypowered.api.util.ModInfo;
-import com.velocitypowered.proxy.connection.VelocityConstants;
 import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import com.velocitypowered.proxy.protocol.ProtocolUtils;
 import com.velocitypowered.proxy.protocol.packet.PluginMessage;
@@ -14,7 +11,6 @@ import io.netty.buffer.Unpooled;
 import java.nio.charset.StandardCharsets;
 import java.util.Collection;
 import java.util.List;
-import java.util.Optional;
 
 public class PluginMessageUtil {
     public static final String BRAND_CHANNEL_LEGACY = "MC|Brand";

proxy/src/main/java/com/velocitypowered/proxy/server/ping/PingSessionHandler.java

@@ -45,7 +45,7 @@ public class PingSessionHandler implements MinecraftSessionHandler {
         completed = true;
         connection.close();
 
-        ServerPing ping = VelocityServer.GSON.fromJson(((StatusResponse) packet).getStatus(), ServerPing.class);
+        ServerPing ping = VelocityServer.GSON.fromJson(packet.getStatus(), ServerPing.class);
         result.complete(ping);
         return true;
     }