Convert Velocity buildscripts to Kotlin DSL (#918)

Spiritually indebted to #518 and @alexstaeding.

There's a minor break - we're going up to 3.2.0-SNAPSHOT as the API now compiles against Java 11. But this is more academic in practice.

native/src/main/java/com/velocitypowered/natives/Native.java

@@ -19,6 +19,9 @@ package com.velocitypowered.natives;
 
 import com.velocitypowered.natives.util.BufferPreference;
 
+/**
+ * Generic interface for any Velocity native.
+ */
 public interface Native {
   BufferPreference preferredBufferType();
 }

native/src/main/java/com/velocitypowered/natives/NativeSetupException.java

@@ -17,6 +17,9 @@
 
 package com.velocitypowered.natives;
 
+/**
+ * Thrown when we cannot set up a variant of a native library.
+ */
 public class NativeSetupException extends RuntimeException {
 
   public NativeSetupException() {

native/src/main/java/com/velocitypowered/natives/compression/CompressorUtils.java

@@ -28,6 +28,7 @@ class CompressorUtils {
 
   /**
    * Ensures that the buffer does not go over {@code max}.
+   *
    * @param buf the buffer for check
    * @param max the maximum size for the buffer
    * @throws DataFormatException if the buffer becomes too bug

native/src/main/java/com/velocitypowered/natives/compression/JavaVelocityCompressor.java

@@ -28,6 +28,9 @@ import java.util.zip.DataFormatException;
 import java.util.zip.Deflater;
 import java.util.zip.Inflater;
 
+/**
+ * Implements deflate compression by wrapping {@link Deflater} and {@link Inflater}.
+ */
 public class JavaVelocityCompressor implements VelocityCompressor {
 
   public static final VelocityCompressorFactory FACTORY = JavaVelocityCompressor::new;

native/src/main/java/com/velocitypowered/natives/compression/LibdeflateVelocityCompressor.java

@@ -22,6 +22,9 @@ import com.velocitypowered.natives.util.BufferPreference;
 import io.netty.buffer.ByteBuf;
 import java.util.zip.DataFormatException;
 
+/**
+ * Implements deflate compression using the {@code libdeflate} native C library.
+ */
 public class LibdeflateVelocityCompressor implements VelocityCompressor {
 
   public static final VelocityCompressorFactory FACTORY = LibdeflateVelocityCompressor::new;

native/src/main/java/com/velocitypowered/natives/compression/VelocityCompressorFactory.java

@@ -17,6 +17,9 @@
 
 package com.velocitypowered.natives.compression;
 
+/**
+ * Factory for {@link VelocityCompressor}.
+ */
 public interface VelocityCompressorFactory {
 
   VelocityCompressor create(int level);

native/src/main/java/com/velocitypowered/natives/encryption/JavaVelocityCipher.java

@@ -26,6 +26,9 @@ import javax.crypto.SecretKey;
 import javax.crypto.ShortBufferException;
 import javax.crypto.spec.IvParameterSpec;
 
+/**
+ * Implements AES-CFB8 encryption/decryption using {@link Cipher}.
+ */
 public class JavaVelocityCipher implements VelocityCipher {
 
   public static final VelocityCipherFactory FACTORY = new VelocityCipherFactory() {

native/src/main/java/com/velocitypowered/natives/encryption/NativeVelocityCipher.java

@@ -23,6 +23,9 @@ import io.netty.buffer.ByteBuf;
 import java.security.GeneralSecurityException;
 import javax.crypto.SecretKey;
 
+/**
+ * Implements AES-CFB8 encryption/decryption using a native library.
+ */
 public class NativeVelocityCipher implements VelocityCipher {
 
   public static final VelocityCipherFactory FACTORY = new VelocityCipherFactory() {

native/src/main/java/com/velocitypowered/natives/encryption/VelocityCipher.java

@@ -21,6 +21,15 @@ import com.velocitypowered.natives.Disposable;
 import com.velocitypowered.natives.Native;
 import io.netty.buffer.ByteBuf;
 
+/**
+ * Implements an AES-CFB8 cipher that either encrypts or decrypts connection data.
+ */
 public interface VelocityCipher extends Disposable, Native {
+
+  /**
+   * Encrypts the given {@link ByteBuf} in-place.
+   *
+   * @param source the buffer to encrypt
+   */
   void process(ByteBuf source);
 }

native/src/main/java/com/velocitypowered/natives/encryption/VelocityCipherFactory.java

@@ -20,6 +20,9 @@ package com.velocitypowered.natives.encryption;
 import java.security.GeneralSecurityException;
 import javax.crypto.SecretKey;
 
+/**
+ * A factory interface for {@link VelocityCipher}.
+ */
 public interface VelocityCipherFactory {
 
   VelocityCipher forEncryption(SecretKey key) throws GeneralSecurityException;

native/src/main/java/com/velocitypowered/natives/util/BufferPreference.java

@@ -17,6 +17,9 @@
 
 package com.velocitypowered.natives.util;
 
+/**
+ * Emumerates Netty buffer preferences and requirements for use with Netty.
+ */
 public enum BufferPreference {
   /**
    * A heap buffer is required.

native/src/main/java/com/velocitypowered/natives/util/MoreByteBufUtils.java

@@ -21,6 +21,9 @@ import com.velocitypowered.natives.Native;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
 
+/**
+ * Additional utilities for {@link ByteBuf}.
+ */
 public class MoreByteBufUtils {
   private MoreByteBufUtils() {
     throw new AssertionError();

native/src/main/java/com/velocitypowered/natives/util/NativeCodeLoader.java

@@ -22,6 +22,11 @@ import java.util.function.BooleanSupplier;
 import java.util.function.Supplier;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
+/**
+ * A loader for native code.
+ *
+ * @param <T> the interface of the instance to load
+ */
 public final class NativeCodeLoader<T> implements Supplier<T> {
 
   private final Variant<T> selected;

native/src/main/java/com/velocitypowered/natives/util/NativeConstraints.java

@@ -21,6 +21,9 @@ import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import java.util.function.BooleanSupplier;
 
+/**
+ * Statically-computed constraints for native code.
+ */
 public class NativeConstraints {
   private static final boolean NATIVES_ENABLED = !Boolean.getBoolean("velocity.natives-disabled");
   private static final boolean IS_AMD64;

native/src/main/java/com/velocitypowered/natives/util/Natives.java

@@ -31,6 +31,9 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 
+/**
+ * Enumerates all supported natives for Velocity.
+ */
 public class Natives {
 
   private Natives() {