Grab most of the low-hanging fruit.

api/src/test/java/com/velocitypowered/api/proxy/server/QueryResponseTest.java

@@ -1,6 +1,6 @@
 package com.velocitypowered.api.proxy.server;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.proxy.server.QueryResponse.PluginInformation;

api/src/test/java/com/velocitypowered/api/proxy/server/ServerPingTest.java

@@ -1,6 +1,6 @@
 package com.velocitypowered.api.proxy.server;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.proxy.server.ServerPing.Players;

gradle/checkstyle.gradle

@@ -1,4 +1,8 @@
 checkstyle {
     toolVersion '8.14'
     configFile new File(project.rootDir, ['config', 'checkstyle', 'checkstyle.xml'].join(File.separator))
+    
+    // The build should immediately fail if we have errors.
+    maxErrors = 0
+    maxWarnings = 0
 }

proxy/build.gradle

@@ -20,6 +20,10 @@ jar {
     }
 }
 
+tasks.withType(Checkstyle) {
+    exclude('**/com/velocitypowered/proxy/protocol/packet/*.java')
+}
+
 dependencies {
     // Note: we depend on the API twice, first the main sourceset, and then the annotation processor.
     compile project(':velocity-api')

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommandManager.java

@@ -123,6 +123,12 @@ public class VelocityCommandManager implements CommandManager {
     }
   }
 
+  /**
+   * Determines if the {@code source} has permission to run the {@code cmdLine}.
+   * @param source the source to check against
+   * @param cmdLine the command to run
+   * @return {@code true} if the command can be run, otherwise {@code false}
+   */
   public boolean hasPermission(CommandSource source, String cmdLine) {
     Preconditions.checkNotNull(source, "source");
     Preconditions.checkNotNull(cmdLine, "cmdLine");

proxy/src/main/java/com/velocitypowered/proxy/config/AnnotatedConfig.java

@@ -36,7 +36,10 @@ public abstract class AnnotatedConfig {
   @Retention(RetentionPolicy.RUNTIME)
   @Target({ElementType.FIELD, ElementType.TYPE})
   public @interface Table {
-
+    /**
+     * The table's name.
+     * @return the table's name
+     */
     String value();
   }
 
@@ -46,7 +49,10 @@ public abstract class AnnotatedConfig {
   @Retention(RetentionPolicy.RUNTIME)
   @Target({ElementType.FIELD, ElementType.TYPE})
   public @interface Comment {
-
+    /**
+     * The comments to include with this key. Each entry is considered a line.
+     * @return the comments
+     */
     String[] value();
   }
 
@@ -56,7 +62,10 @@ public abstract class AnnotatedConfig {
   @Retention(RetentionPolicy.RUNTIME)
   @Target({ElementType.FIELD, ElementType.TYPE})
   public @interface ConfigKey {
-
+    /**
+     * The name of this field in the configuration.
+     * @return the field's name
+     */
     String value();
   }
 

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -356,6 +356,12 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
         .toString();
   }
 
+  /**
+   * Reads the Velocity configuration from {@code path}.
+   * @param path the path to read from
+   * @return the deserialized Velocity configuration
+   * @throws IOException if we could not read from the {@code path}.
+   */
   public static VelocityConfiguration read(Path path) throws IOException {
     Toml toml;
     if (!path.toFile().exists()) {

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

@@ -5,8 +5,8 @@ import com.mojang.brigadier.builder.LiteralArgumentBuilder;
 import com.mojang.brigadier.builder.RequiredArgumentBuilder;
 import com.mojang.brigadier.tree.LiteralCommandNode;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
-import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;

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

@@ -53,6 +53,12 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
   private long lastPingId;
   private long lastPingSent;
 
+  /**
+   * Initializes a new server connection.
+   * @param registeredServer the server to connect to
+   * @param proxyPlayer the player connecting to the server
+   * @param server the Velocity proxy instance
+   */
   public VelocityServerConnection(VelocityRegisteredServer registeredServer,
       ConnectedPlayer proxyPlayer, VelocityServer server) {
     this.registeredServer = registeredServer;
@@ -60,6 +66,11 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
     this.server = server;
   }
 
+  /**
+   * Connects to the server.
+   * @return a {@link com.velocitypowered.api.proxy.ConnectionRequestBuilder.Result} representing
+   *         whether or not the connect succeeded
+   */
   public CompletableFuture<ConnectionRequestBuilder.Result> connect() {
     CompletableFuture<ConnectionRequestBuilder.Result> result = new CompletableFuture<>();
     server.initializeGenericBootstrap()
@@ -167,6 +178,9 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
     return proxyPlayer;
   }
 
+  /**
+   * Disconnects from the server.
+   */
   public void disconnect() {
     if (connection != null) {
       gracefulDisconnect = true;

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

@@ -188,7 +188,8 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
     MinecraftConnection backendConn = serverConn != null ? serverConn.getConnection() : null;
     if (serverConn != null && backendConn != null) {
       if (backendConn.getState() != StateRegistry.PLAY) {
-        logger.warn("Plugin message was sent while the backend was in PLAY. Channel: {}. Packet discarded.");
+        logger.warn("A plugin message was received while the backend server was not "
+            + "ready. Channel: {}. Packet discarded.", packet.getChannel());
       } else if (PluginMessageUtil.isRegister(packet)) {
         List<String> actuallyRegistered = new ArrayList<>();
         List<String> channels = PluginMessageUtil.getChannels(packet);

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

@@ -1,7 +1,7 @@
 package com.velocitypowered.proxy.connection.client;
 
-import com.velocitypowered.api.proxy.InboundConnection;
 import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.api.proxy.InboundConnection;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.MinecraftConnectionAssociation;
 import com.velocitypowered.proxy.protocol.packet.Disconnect;

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

@@ -2,10 +2,10 @@ package com.velocitypowered.proxy.connection.client;
 
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.event.proxy.ProxyPingEvent;
+import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.proxy.InboundConnection;
 import com.velocitypowered.api.proxy.server.ServerPing;
 import com.velocitypowered.api.util.ModInfo;
-import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.config.VelocityConfiguration;
 import com.velocitypowered.proxy.connection.MinecraftConnection;

proxy/src/main/java/com/velocitypowered/proxy/connection/forge/legacy/LegacyForgeConnectionType.java

@@ -14,7 +14,8 @@ public class LegacyForgeConnectionType extends ConnectionTypeImpl {
       new GameProfile.Property("forgeClient", "true", "");
 
   public LegacyForgeConnectionType() {
-    super(LegacyForgeHandshakeClientPhase.NOT_STARTED, LegacyForgeHandshakeBackendPhase.NOT_STARTED);
+    super(LegacyForgeHandshakeClientPhase.NOT_STARTED,
+        LegacyForgeHandshakeBackendPhase.NOT_STARTED);
   }
 
   @Override

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

@@ -7,7 +7,7 @@ import com.velocitypowered.proxy.connection.backend.BackendConnectionPhase;
 import com.velocitypowered.proxy.connection.client.ClientConnectionPhase;
 
 /**
- * Indicates the type of connection that has been made
+ * Indicates the type of connection that has been made.
  */
 public class ConnectionTypeImpl implements ConnectionType {
 

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

@@ -1,5 +1,7 @@
 package com.velocitypowered.proxy.console;
 
+import static com.velocitypowered.api.permission.PermissionFunction.*;
+
 import com.velocitypowered.api.event.permission.PermissionsSetupEvent;
 import com.velocitypowered.api.permission.PermissionFunction;
 import com.velocitypowered.api.permission.Tristate;
@@ -26,7 +28,7 @@ public final class VelocityConsole extends SimpleTerminalConsole implements Cons
   private static final Logger logger = LogManager.getLogger(VelocityConsole.class);
 
   private final VelocityServer server;
-  private PermissionFunction permissionFunction = PermissionFunction.ALWAYS_TRUE;
+  private PermissionFunction permissionFunction = ALWAYS_TRUE;
 
   public VelocityConsole(VelocityServer server) {
     this.server = server;
@@ -43,20 +45,14 @@ public final class VelocityConsole extends SimpleTerminalConsole implements Cons
   }
 
   public void setupStreams() {
-    System.setOut(IoBuilder.forLogger(logger)
-        .setLevel(Level.INFO)
-        .buildPrintStream());
-    System.setErr(IoBuilder.forLogger(logger)
-        .setLevel(Level.ERROR)
-        .buildPrintStream());
+    System.setOut(IoBuilder.forLogger(logger).setLevel(Level.INFO).buildPrintStream());
+    System.setErr(IoBuilder.forLogger(logger).setLevel(Level.ERROR).buildPrintStream());
   }
 
   public void setupPermissions() {
-    PermissionsSetupEvent event = new PermissionsSetupEvent(this,
-        s -> PermissionFunction.ALWAYS_TRUE);
-    this.server.getEventManager().fire(event)
-        .join(); // this is called on startup, we can safely #join
-    this.permissionFunction = event.createFunction(this);
+    PermissionsSetupEvent event = new PermissionsSetupEvent(this, s -> ALWAYS_TRUE);
+    // we can safely block here, this is before any listeners fire
+    this.permissionFunction = this.server.getEventManager().fire(event).join().createFunction(this);
   }
 
   @Override

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

@@ -20,6 +20,11 @@ public class ServerChannelInitializerHolder implements Supplier<ChannelInitializ
     return this.initializer;
   }
 
+  /**
+   * Sets the channel initializer.
+   * @param initializer the new initializer to use
+   * @deprecated Internal implementation detail
+   */
   @Deprecated
   public void set(final ChannelInitializer<Channel> initializer) {
     LOGGER.warn("The server channel initializer has been replaced by {}",

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

@@ -8,7 +8,7 @@ import com.velocitypowered.api.plugin.PluginDescription;
 import com.velocitypowered.api.plugin.PluginManager;
 import com.velocitypowered.api.plugin.meta.PluginDependency;
 import com.velocitypowered.proxy.VelocityServer;
-import com.velocitypowered.proxy.plugin.loader.JavaPluginLoader;
+import com.velocitypowered.proxy.plugin.loader.java.JavaPluginLoader;
 import com.velocitypowered.proxy.plugin.util.PluginDependencyUtils;
 import java.io.IOException;
 import java.nio.file.DirectoryStream;

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

@@ -1,4 +1,4 @@
-package com.velocitypowered.proxy.plugin.loader;
+package com.velocitypowered.proxy.plugin.loader.java;
 
 import com.google.inject.Guice;
 import com.google.inject.Injector;
@@ -10,6 +10,9 @@ import com.velocitypowered.api.plugin.meta.PluginDependency;
 import com.velocitypowered.api.proxy.ProxyServer;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.plugin.PluginClassLoader;
+import com.velocitypowered.proxy.plugin.loader.PluginLoader;
+import com.velocitypowered.proxy.plugin.loader.VelocityPluginContainer;
+import com.velocitypowered.proxy.plugin.loader.VelocityPluginDescription;
 import com.velocitypowered.proxy.plugin.loader.java.JavaVelocityPluginDescription;
 import com.velocitypowered.proxy.plugin.loader.java.VelocityPluginModule;
 import java.io.BufferedInputStream;

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

@@ -9,11 +9,11 @@ import java.util.Collection;
 import java.util.List;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
-public class JavaVelocityPluginDescription extends VelocityPluginDescription {
+class JavaVelocityPluginDescription extends VelocityPluginDescription {
 
   private final Class<?> mainClass;
 
-  public JavaVelocityPluginDescription(String id, @Nullable String name, @Nullable String version,
+  JavaVelocityPluginDescription(String id, @Nullable String name, @Nullable String version,
       @Nullable String description, @Nullable String url,
       @Nullable List<String> authors, Collection<PluginDependency> dependencies, Path source,
       Class<?> mainClass) {
@@ -21,7 +21,7 @@ public class JavaVelocityPluginDescription extends VelocityPluginDescription {
     this.mainClass = checkNotNull(mainClass);
   }
 
-  public Class<?> getMainClass() {
+  Class<?> getMainClass() {
     return mainClass;
   }
 }

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

@@ -12,13 +12,13 @@ import java.nio.file.Path;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class VelocityPluginModule implements Module {
+class VelocityPluginModule implements Module {
 
   private final ProxyServer server;
   private final JavaVelocityPluginDescription description;
   private final Path basePluginPath;
 
-  public VelocityPluginModule(ProxyServer server, JavaVelocityPluginDescription description,
+  VelocityPluginModule(ProxyServer server, JavaVelocityPluginDescription description,
       Path basePluginPath) {
     this.server = server;
     this.description = description;

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

@@ -83,6 +83,11 @@ public enum ProtocolUtils {
     return str;
   }
 
+  /**
+   * Writes the specified {@code str} to the {@code buf} with a VarInt prefix.
+   * @param buf the buffer to write to
+   * @param str the string to write
+   */
   public static void writeString(ByteBuf buf, String str) {
     int size = ByteBufUtil.utf8Bytes(str);
     writeVarInt(buf, size);
@@ -93,6 +98,13 @@ public enum ProtocolUtils {
     return readByteArray(buf, DEFAULT_MAX_STRING_SIZE);
   }
 
+  /**
+   * Reads a VarInt length-prefixed byte array from the {@code buf}, making sure to not go over
+   * {@code cap} size.
+   * @param buf the buffer to read from
+   * @param cap the maximum size of the string, in UTF-8 character length
+   * @return the byte array
+   */
   public static byte[] readByteArray(ByteBuf buf, int cap) {
     int length = readVarInt(buf);
     checkArgument(length <= cap, "Bad string size (got %s, maximum is %s)", length, cap);
@@ -109,6 +121,11 @@ public enum ProtocolUtils {
     buf.writeBytes(array);
   }
 
+  /**
+   * Reads an VarInt-prefixed array of VarInt integers from the {@code buf}.
+   * @param buf the buffer to read from
+   * @return an array of integers
+   */
   public static int[] readIntegerArray(ByteBuf buf) {
     int len = readVarInt(buf);
     int[] array = new int[len];
@@ -118,13 +135,11 @@ public enum ProtocolUtils {
     return array;
   }
 
-  public static void writeIntegerArray(ByteBuf buf, int[] array) {
-    writeVarInt(buf, array.length);
-    for (int i : array) {
-      writeVarInt(buf, i);
-    }
-  }
-
+  /**
+   * Reads an UUID from the {@code buf}.
+   * @param buf the buffer to read from
+   * @return the UUID from the buffer
+   */
   public static UUID readUuid(ByteBuf buf) {
     long msb = buf.readLong();
     long lsb = buf.readLong();
@@ -136,6 +151,11 @@ public enum ProtocolUtils {
     buf.writeLong(uuid.getLeastSignificantBits());
   }
 
+  /**
+   * Writes a list of {@link com.velocitypowered.api.util.GameProfile.Property} to the buffer.
+   * @param buf the buffer to write to
+   * @param properties the properties to serialize
+   */
   public static void writeProperties(ByteBuf buf, List<GameProfile.Property> properties) {
     writeVarInt(buf, properties.size());
     for (GameProfile.Property property : properties) {
@@ -151,6 +171,11 @@ public enum ProtocolUtils {
     }
   }
 
+  /**
+   * Reads a list of {@link com.velocitypowered.api.util.GameProfile.Property} from the buffer.
+   * @param buf the buffer to read from
+   * @return the read properties
+   */
   public static List<GameProfile.Property> readProperties(ByteBuf buf) {
     List<GameProfile.Property> properties = new ArrayList<>();
     int size = readVarInt(buf);
@@ -172,9 +197,9 @@ public enum ProtocolUtils {
     CLIENTBOUND;
 
     public StateRegistry.PacketRegistry.ProtocolRegistry getProtocolRegistry(StateRegistry state,
-                                                                    ProtocolVersion protocolVersion) {
+                                                                    ProtocolVersion version) {
       return (this == SERVERBOUND ? state.serverbound : state.clientbound)
-              .getProtocolRegistry(protocolVersion);
+          .getProtocolRegistry(version);
     }
   }
 }

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

@@ -50,7 +50,12 @@ import io.netty.util.collection.IntObjectMap;
 import it.unimi.dsi.fastutil.objects.Object2IntMap;
 import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
 
-import java.util.*;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.EnumMap;
+import java.util.EnumSet;
+import java.util.Map;
+import java.util.Objects;
 import java.util.function.Supplier;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -245,7 +250,7 @@ public enum StateRegistry {
       this.versions = Collections.unmodifiableMap(mutableVersions);
     }
 
-    public ProtocolRegistry getProtocolRegistry(final ProtocolVersion version) {
+    ProtocolRegistry getProtocolRegistry(final ProtocolVersion version) {
       ProtocolRegistry registry = versions.get(version);
       if (registry == null) {
         if (fallback) {
@@ -256,7 +261,7 @@ public enum StateRegistry {
       return registry;
     }
 
-    public <P extends MinecraftPacket> void register(Class<P> clazz, Supplier<P> packetSupplier,
+    <P extends MinecraftPacket> void register(Class<P> clazz, Supplier<P> packetSupplier,
         PacketMapping... mappings) {
       if (mappings.length == 0) {
         throw new IllegalArgumentException("At least one mapping must be provided.");
@@ -301,6 +306,11 @@ public enum StateRegistry {
         this.packetClassToId.defaultReturnValue(Integer.MIN_VALUE);
       }
 
+      /**
+       * Attempts to create a packet from the specified {@code id}.
+       * @param id the packet ID
+       * @return the packet instance, or {@code null} if the ID is not registered
+       */
       public @Nullable MinecraftPacket createPacket(final int id) {
         final Supplier<? extends MinecraftPacket> supplier = this.packetIdToSupplier.get(id);
         if (supplier == null) {
@@ -309,6 +319,12 @@ public enum StateRegistry {
         return supplier.get();
       }
 
+      /**
+       * Attempts to look up the packet ID for an {@code packet}.
+       * @param packet the packet to look up
+       * @return the packet ID
+       * @throws IllegalArgumentException if the packet ID is not found
+       */
       public int getPacketId(final MinecraftPacket packet) {
         final int id = this.packetClassToId.getInt(packet.getClass());
         if (id == Integer.MIN_VALUE) {
@@ -328,7 +344,7 @@ public enum StateRegistry {
     private final ProtocolVersion protocolVersion;
     private final boolean encodeOnly;
 
-    public PacketMapping(int id, ProtocolVersion protocolVersion, boolean packetDecoding) {
+    PacketMapping(int id, ProtocolVersion protocolVersion, boolean packetDecoding) {
       this.id = id;
       this.protocolVersion = protocolVersion;
       this.encodeOnly = packetDecoding;

proxy/src/main/java/com/velocitypowered/proxy/tablist/VelocityTabList.java

@@ -65,7 +65,12 @@ public class VelocityTabList implements TabList {
     return Optional.ofNullable(entry);
   }
 
-  public void clearAll() { // Note: this method is called upon server switch
+  /**
+   * Clears all entries from the tab list. Note that the entries are written with
+   * {@link MinecraftConnection#delayedWrite(Object)}, so make sure to do an explicit
+   * {@link MinecraftConnection#flush()}.
+   */
+  public void clearAll() {
     List<PlayerListItem.Item> items = new ArrayList<>();
     for (TabListEntry value : entries.values()) {
       items.add(PlayerListItem.Item.from(value));
@@ -85,6 +90,10 @@ public class VelocityTabList implements TabList {
     return new VelocityTabListEntry(this, profile, displayName, latency, gameMode);
   }
 
+  /**
+   * Processes a tab list entry packet from the backend.
+   * @param packet the packet to process
+   */
   public void processBackendPacket(PlayerListItem packet) {
     // Packets are already forwarded on, so no need to do that here
     for (PlayerListItem.Item item : packet.getItems()) {