Upgrade to Gradle 6.6 and use SpotBugs.

As a result, at least one real bug was fixed! Nice.

api/build.gradle

@@ -1,12 +1,10 @@
 plugins {
-    id 'java'
+    id 'java-library'
     id 'maven-publish'
     id 'checkstyle'
-    id "net.ltgt.errorprone" version "0.8"
 }
 
 apply from: '../gradle/checkstyle.gradle'
-apply from: '../gradle/errorprone.gradle'
 apply plugin: 'com.github.johnrengelman.shadow'
 
 sourceSets {
@@ -16,35 +14,35 @@ sourceSets {
 }
 
 dependencies {
-    compile 'com.google.code.gson:gson:2.8.6'
-    compile "com.google.guava:guava:${guavaVersion}"
+    api 'com.google.code.gson:gson:2.8.6'
+    api "com.google.guava:guava:${guavaVersion}"
 
     // DEPRECATED: Will be removed in Velocity 2.0.0
-    compile "net.kyori:text-api:${textVersion}"
-    compile "net.kyori:text-serializer-gson:${textVersion}"
-    compile "net.kyori:text-serializer-legacy:${textVersion}"
-    compile "net.kyori:text-serializer-plain:${textVersion}"
+    api "net.kyori:text-api:${textVersion}"
+    api "net.kyori:text-serializer-gson:${textVersion}"
+    api "net.kyori:text-serializer-legacy:${textVersion}"
+    api "net.kyori:text-serializer-plain:${textVersion}"
 
     // DEPRECATED: Will be removed in Velocity 2.0.0
-    compile 'com.moandjiezana.toml:toml4j:0.7.2'
+    api 'com.moandjiezana.toml:toml4j:0.7.2'
 
-    compile "net.kyori:adventure-api:${adventureVersion}"
-    compile "net.kyori:adventure-text-serializer-gson:${adventureVersion}"
-    compile "net.kyori:adventure-text-serializer-legacy:${adventureVersion}"
-    compile "net.kyori:adventure-text-serializer-plain:${adventureVersion}"
-    compile "net.kyori:adventure-text-serializer-legacy-text3:${adventureVersion}"
+    api "net.kyori:adventure-api:${adventureVersion}"
+    api "net.kyori:adventure-text-serializer-gson:${adventureVersion}"
+    api "net.kyori:adventure-text-serializer-legacy:${adventureVersion}"
+    api "net.kyori:adventure-text-serializer-plain:${adventureVersion}"
+    api "net.kyori:adventure-text-serializer-legacy-text3:${adventureVersion}"
 
-    compile "org.slf4j:slf4j-api:${slf4jVersion}"
-    compile 'com.google.inject:guice:4.2.3'
-    compile "org.checkerframework:checker-qual:${checkerFrameworkVersion}"
-    compile 'com.mojang:brigadier:1.0.17'
+    api "org.slf4j:slf4j-api:${slf4jVersion}"
+    api 'com.google.inject:guice:4.2.3'
+    api "org.checkerframework:checker-qual:${checkerFrameworkVersion}"
+    api 'com.mojang:brigadier:1.0.17'
 
-    compile "org.spongepowered:configurate-hocon:${configurateVersion}"
-    compile "org.spongepowered:configurate-yaml:${configurateVersion}"
-    compile "org.spongepowered:configurate-gson:${configurateVersion}"
+    api "org.spongepowered:configurate-hocon:${configurateVersion}"
+    api "org.spongepowered:configurate-yaml:${configurateVersion}"
+    api "org.spongepowered:configurate-gson:${configurateVersion}"
 
-    testCompile "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
-    testCompile "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
 }
 
 task javadocJar(type: Jar) {

build.gradle

@@ -9,9 +9,12 @@ buildscript {
 
 plugins {
     id 'java'
+    id "com.github.spotbugs" version "4.2.4" apply false
 }
 
 allprojects {
+    apply plugin: "com.github.spotbugs"
+
     group 'com.velocitypowered'
     version '1.1.0-SNAPSHOT'
 
@@ -70,4 +73,14 @@ allprojects {
             junitXml.enabled = true
         }
     }
+
+    tasks.withType(com.github.spotbugs.snom.SpotBugsTask) {
+        reports {
+            html {
+                enabled = true
+                destination = file("$buildDir/reports/spotbugs/main/spotbugs.html")
+                stylesheet = 'fancy-hist.xsl'
+            }
+        }
+    }
 }

gradle/errorprone.gradle

@@ -1,4 +0,0 @@
-dependencies {
-    errorprone("com.google.errorprone:error_prone_core:2.3.3")
-    errorproneJavac("com.google.errorprone:javac:9+181-r4173-1")
-}

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.6-all.zip

native/build.gradle

@@ -1,17 +1,15 @@
 plugins {
-    id 'java'
+    id 'java-library'
     id 'checkstyle'
-    id "net.ltgt.errorprone" version "0.8"
 }
 
 apply from: '../gradle/checkstyle.gradle'
-apply from: '../gradle/errorprone.gradle'
 
 dependencies {
-    compile "com.google.guava:guava:${guavaVersion}"
-    compile "io.netty:netty-handler:${nettyVersion}"
-    compile "org.checkerframework:checker-qual:${checkerFrameworkVersion}"
+    implementation "com.google.guava:guava:${guavaVersion}"
+    implementation "io.netty:netty-handler:${nettyVersion}"
+    implementation "org.checkerframework:checker-qual:${checkerFrameworkVersion}"
 
-    testCompile "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
-    testCompile "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
 }

proxy/build.gradle

@@ -3,11 +3,9 @@ import com.github.jengelman.gradle.plugins.shadow.transformers.Log4j2PluginsCach
 plugins {
     id 'java'
     id 'checkstyle'
-    id "net.ltgt.errorprone" version "0.8"
 }
 
 apply from: '../gradle/checkstyle.gradle'
-apply from: '../gradle/errorprone.gradle'
 apply plugin: 'com.github.johnrengelman.shadow'
 
 jar {
@@ -38,43 +36,43 @@ tasks.withType(Checkstyle) {
 
 dependencies {
     // Note: we depend on the API twice, first the main sourceset, and then the annotation processor.
-    compile project(':velocity-api')
-    compile project(':velocity-api').sourceSets.ap.output
-    compile project(':velocity-native')
+    implementation project(':velocity-api')
+    implementation project(':velocity-api').sourceSets.ap.output
+    implementation project(':velocity-native')
 
-    compile "io.netty:netty-codec:${nettyVersion}"
-    compile "io.netty:netty-codec-haproxy:${nettyVersion}"
-    compile "io.netty:netty-codec-http:${nettyVersion}"
-    compile "io.netty:netty-handler:${nettyVersion}"
-    compile "io.netty:netty-transport-native-epoll:${nettyVersion}"
-    compile "io.netty:netty-transport-native-epoll:${nettyVersion}:linux-x86_64"
-    compile "io.netty:netty-transport-native-epoll:${nettyVersion}:linux-aarch64"
-    compile "io.netty:netty-resolver-dns:${nettyVersion}"
+    implementation "io.netty:netty-codec:${nettyVersion}"
+    implementation "io.netty:netty-codec-haproxy:${nettyVersion}"
+    implementation "io.netty:netty-codec-http:${nettyVersion}"
+    implementation "io.netty:netty-handler:${nettyVersion}"
+    implementation "io.netty:netty-transport-native-epoll:${nettyVersion}"
+    implementation "io.netty:netty-transport-native-epoll:${nettyVersion}:linux-x86_64"
+    implementation "io.netty:netty-transport-native-epoll:${nettyVersion}:linux-aarch64"
+    implementation "io.netty:netty-resolver-dns:${nettyVersion}"
 
-    compile "org.apache.logging.log4j:log4j-api:${log4jVersion}"
-    compile "org.apache.logging.log4j:log4j-core:${log4jVersion}"
-    compile "org.apache.logging.log4j:log4j-slf4j-impl:${log4jVersion}"
-    compile "org.apache.logging.log4j:log4j-iostreams:${log4jVersion}"
+    implementation "org.apache.logging.log4j:log4j-api:${log4jVersion}"
+    implementation "org.apache.logging.log4j:log4j-core:${log4jVersion}"
+    implementation "org.apache.logging.log4j:log4j-slf4j-impl:${log4jVersion}"
+    implementation "org.apache.logging.log4j:log4j-iostreams:${log4jVersion}"
 
-    compile 'net.sf.jopt-simple:jopt-simple:5.0.4' // command-line options
-    compile 'net.minecrell:terminalconsoleappender:1.2.0'
-    runtime 'org.jline:jline-terminal-jansi:3.12.1' // Needed for JLine
-    runtime 'com.lmax:disruptor:3.4.2' // Async loggers
+    implementation 'net.sf.jopt-simple:jopt-simple:5.0.4' // command-line options
+    implementation 'net.minecrell:terminalconsoleappender:1.2.0'
+    runtimeOnly 'org.jline:jline-terminal-jansi:3.12.1' // Needed for JLine
+    runtimeOnly 'com.lmax:disruptor:3.4.2' // Async loggers
 
-    compile 'it.unimi.dsi:fastutil:8.2.3'
-    compile 'net.kyori:event-method-asm:4.0.0-SNAPSHOT'
-    compile 'net.kyori:adventure-nbt:4.0.0-SNAPSHOT'
+    implementation 'it.unimi.dsi:fastutil:8.2.3'
+    implementation 'net.kyori:event-method-asm:4.0.0-SNAPSHOT'
+    implementation 'net.kyori:adventure-nbt:4.0.0-SNAPSHOT'
 
-    compile 'com.mojang:brigadier:1.0.17'
+    implementation 'org.asynchttpclient:async-http-client:2.10.4'
 
-    compile 'org.asynchttpclient:async-http-client:2.10.4'
+    implementation 'com.spotify:completable-futures:0.3.2'
 
-    compile 'com.spotify:completable-futures:0.3.2'
+    implementation 'com.electronwill.night-config:toml:3.6.3'
 
-    compile 'com.electronwill.night-config:toml:3.6.3'
+    compileOnly 'com.github.spotbugs:spotbugs-annotations:4.1.2'
 
-    testCompile "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
-    testCompile "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
+    testImplementation "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
 }
 
 shadowJar {

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

@@ -39,12 +39,12 @@ public class Metrics {
   // The url to which the data is sent
   private static final String URL = "https://bstats.org/submitData/server-implementation";
 
-  // Should failed requests be logged?
-  private static boolean logFailedRequests = false;
-
   // The logger for the failed requests
   private static final Logger logger = LogManager.getLogger(Metrics.class);
 
+  // Should failed requests be logged?
+  private boolean logFailedRequests = false;
+
   // The name of the server software
   private final String name;
 
@@ -72,7 +72,7 @@ public class Metrics {
     this.name = name;
     this.pluginId = pluginId;
     this.serverUuid = serverUuid;
-    Metrics.logFailedRequests = logFailedRequests;
+    this.logFailedRequests = logFailedRequests;
     this.server = server;
 
     // Start submitting the data
@@ -262,9 +262,6 @@ public class Metrics {
         }
         chart.add("data", data);
       } catch (Throwable t) {
-        if (logFailedRequests) {
-          logger.warn("Failed to get data for custom chart with id {}", chartId, t);
-        }
         return null;
       }
       return chart;

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

@@ -45,6 +45,7 @@ import com.velocitypowered.proxy.util.bossbar.AdventureBossBarManager;
 import com.velocitypowered.proxy.util.bossbar.VelocityBossBar;
 import com.velocitypowered.proxy.util.ratelimit.Ratelimiter;
 import com.velocitypowered.proxy.util.ratelimit.Ratelimiters;
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelInitializer;
@@ -54,7 +55,9 @@ import java.net.InetSocketAddress;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.security.AccessController;
 import java.security.KeyPair;
+import java.security.PrivilegedAction;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Locale;
@@ -75,7 +78,6 @@ import net.kyori.adventure.audience.Audience;
 import net.kyori.adventure.audience.ForwardingAudience;
 import net.kyori.adventure.text.TextComponent;
 import net.kyori.adventure.text.TranslatableComponent;
-import net.kyori.adventure.text.serializer.gson.GsonComponentSerializer;
 import net.kyori.text.Component;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -198,21 +200,7 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     commandManager.register("shutdown", new ShutdownCommand(this),"end");
     new GlistCommand(this).register();
 
-    try {
-      Path configPath = Paths.get("velocity.toml");
-      configuration = VelocityConfiguration.read(configPath);
-
-      if (!configuration.validate()) {
-        logger.error("Your configuration is invalid. Velocity will not start up until the errors "
-            + "are resolved.");
-        LogManager.shutdown();
-        System.exit(1);
-      }
-    } catch (Exception e) {
-      logger.error("Unable to read/load/save your velocity.toml. The server will shut down.", e);
-      LogManager.shutdown();
-      System.exit(1);
-    }
+    this.doStartupConfigLoad();
 
     for (Map.Entry<String, String> entry : configuration.getServers().entrySet()) {
       servers.register(new ServerInfo(entry.getKey(), AddressUtil.parseAddress(entry.getValue())));
@@ -243,6 +231,25 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     Metrics.VelocityMetrics.startMetrics(this, configuration.getMetrics());
   }
 
+  @SuppressFBWarnings("DM_EXIT")
+  private void doStartupConfigLoad() {
+    try {
+      Path configPath = Paths.get("velocity.toml");
+      configuration = VelocityConfiguration.read(configPath);
+
+      if (!configuration.validate()) {
+        logger.error("Your configuration is invalid. Velocity will not start up until the errors "
+            + "are resolved.");
+        LogManager.shutdown();
+        System.exit(1);
+      }
+    } catch (Exception e) {
+      logger.error("Unable to read/load/save your velocity.toml. The server will shut down.", e);
+      LogManager.shutdown();
+      System.exit(1);
+    }
+  }
+
   private void loadPlugins() {
     logger.info("Loading plugins...");
 
@@ -438,7 +445,14 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
       shutdown = true;
 
       if (explicitExit) {
-        System.exit(0);
+        AccessController.doPrivileged(new PrivilegedAction<Void>() {
+          @Override
+          @SuppressFBWarnings("DM_EXIT")
+          public Void run() {
+            System.exit(0);
+            return null;
+          }
+        });
       }
     };
 

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

@@ -276,7 +276,7 @@ public class VelocityConfiguration implements ProxyConfig {
   }
 
   public byte[] getForwardingSecret() {
-    return forwardingSecret;
+    return forwardingSecret.clone();
   }
 
   @Override

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

@@ -13,6 +13,7 @@ import com.velocitypowered.proxy.protocol.packet.PluginMessage;
 import com.velocitypowered.proxy.protocol.util.ByteBufDataInput;
 import com.velocitypowered.proxy.protocol.util.ByteBufDataOutput;
 import com.velocitypowered.proxy.server.VelocityRegisteredServer;
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import java.util.Optional;
@@ -23,6 +24,9 @@ import net.kyori.adventure.text.serializer.ComponentSerializer;
 import net.kyori.adventure.text.serializer.gson.GsonComponentSerializer;
 import net.kyori.adventure.text.serializer.legacy.LegacyComponentSerializer;
 
+@SuppressFBWarnings(value = "OS_OPEN_STREAM", justification = "Most methods in this class open "
+    + "instances of ByteBufDataOutput backed by heap-allocated ByteBufs. Closing them does "
+    + "nothing.")
 class BungeeCordMessageResponder {
 
   private static final MinecraftChannelIdentifier MODERN_CHANNEL = MinecraftChannelIdentifier

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

@@ -305,7 +305,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
     TitlePacket subtitlePkt = new TitlePacket();
     subtitlePkt.setAction(TitlePacket.SET_SUBTITLE);
     subtitlePkt.setComponent(serializer.serialize(title.subtitle()));
-    connection.delayedWrite(titlePkt);
+    connection.delayedWrite(subtitlePkt);
 
     TitlePacket timesPkt = TitlePacket.timesForProtocolVersion(this.getProtocolVersion());
     net.kyori.adventure.title.Title.Times times = title.times();

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

@@ -1,6 +1,7 @@
 package com.velocitypowered.proxy.connection.forge.legacy;
 
 import com.velocitypowered.proxy.connection.ConnectionTypes;
+import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.backend.BackendConnectionPhase;
 import com.velocitypowered.proxy.connection.backend.BackendConnectionPhases;
 import com.velocitypowered.proxy.connection.backend.VelocityServerConnection;
@@ -38,8 +39,9 @@ public enum LegacyForgeHandshakeBackendPhase implements BackendConnectionPhase {
     void onTransitionToNewPhase(VelocityServerConnection connection) {
       // We must always reset the handshake before a modded connection is established if
       // we haven't done so already.
-      if (connection.getConnection() != null) {
-        connection.getConnection().setType(ConnectionTypes.LEGACY_FORGE);
+      MinecraftConnection mc = connection.getConnection();
+      if (mc != null) {
+        mc.setType(ConnectionTypes.LEGACY_FORGE);
       }
       connection.getPlayer().sendLegacyForgeHandshakeResetPacket();
     }

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

@@ -2,6 +2,7 @@ package com.velocitypowered.proxy.connection.forge.legacy;
 
 import com.velocitypowered.api.util.ModInfo;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
+import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
 import com.velocitypowered.proxy.connection.backend.VelocityServerConnection;
 import com.velocitypowered.proxy.connection.client.ClientConnectionPhase;
 import com.velocitypowered.proxy.connection.client.ClientPlaySessionHandler;
@@ -153,8 +154,9 @@ public enum LegacyForgeHandshakeClientPhase implements ClientConnectionPhase {
       // just in case the timing is awful
       player.sendKeepAlive();
 
-      if (backendConn.getSessionHandler() instanceof ClientPlaySessionHandler) {
-        ((ClientPlaySessionHandler) backendConn.getSessionHandler()).flushQueuedMessages();
+      MinecraftSessionHandler handler = backendConn.getSessionHandler();
+      if (handler instanceof ClientPlaySessionHandler) {
+        ((ClientPlaySessionHandler) handler).flushQueuedMessages();
       }
 
       return true;

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

@@ -12,6 +12,8 @@ import com.velocitypowered.api.event.proxy.ProxyShutdownEvent;
 import com.velocitypowered.api.plugin.PluginManager;
 import java.lang.reflect.Method;
 import java.net.URL;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.IdentityHashMap;
@@ -51,7 +53,8 @@ public class VelocityEventManager implements EventManager {
   public VelocityEventManager(PluginManager pluginManager) {
     // Expose the event executors to the plugins - required in order for the generated ASM classes
     // to work.
-    PluginClassLoader cl = new PluginClassLoader(new URL[0]);
+    PluginClassLoader cl = AccessController.doPrivileged(
+        (PrivilegedAction<PluginClassLoader>) () -> new PluginClassLoader(new URL[0]));
     cl.addToClassloaders();
 
     // Initialize the event bus.

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

@@ -17,10 +17,13 @@ import com.velocitypowered.proxy.plugin.loader.VelocityPluginDescription;
 import java.io.BufferedInputStream;
 import java.io.InputStreamReader;
 import java.io.Reader;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.HashSet;
 import java.util.Optional;
 import java.util.Set;
@@ -58,9 +61,10 @@ public class JavaPluginLoader implements PluginLoader {
     if (!(source instanceof JavaVelocityPluginDescriptionCandidate)) {
       throw new IllegalArgumentException("Description provided isn't of the Java plugin loader");
     }
-    PluginClassLoader loader = new PluginClassLoader(
-        new URL[]{source.getSource().get().toUri().toURL()}
-    );
+
+    URL pluginJarUrl = source.getSource().get().toUri().toURL();
+    PluginClassLoader loader = AccessController.doPrivileged(
+        (PrivilegedAction<PluginClassLoader>) () -> new PluginClassLoader(new URL[]{pluginJarUrl}));
     loader.addToClassloaders();
 
     JavaVelocityPluginDescriptionCandidate candidate =

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

@@ -135,7 +135,7 @@ public enum ProtocolUtils {
   public static void writeString(ByteBuf buf, CharSequence str) {
     int size = ByteBufUtil.utf8Bytes(str);
     writeVarInt(buf, size);
-    ByteBufUtil.writeUtf8(buf, str);
+    buf.writeCharSequence(str, StandardCharsets.UTF_8);
   }
 
   public static byte[] readByteArray(ByteBuf buf) {
@@ -230,12 +230,6 @@ public enum ProtocolUtils {
    * @return {@link net.kyori.adventure.nbt.CompoundBinaryTag} the CompoundTag from the buffer
    */
   public static CompoundBinaryTag readCompoundTag(ByteBuf buf) {
-    int indexBefore = buf.readerIndex();
-    byte startType = buf.readByte();
-    if (startType == 0) {
-      throw new DecoderException("Invalid NBT start-type (end/empty)");
-    }
-    buf.readerIndex(indexBefore);
     try {
       return BinaryTagIO.readDataInput(new ByteBufInputStream(buf));
     } catch (IOException thrown) {
@@ -250,10 +244,6 @@ public enum ProtocolUtils {
    * @param compoundTag the CompoundTag to write
    */
   public static void writeCompoundTag(ByteBuf buf, CompoundBinaryTag compoundTag) {
-    if (compoundTag == null) {
-      buf.writeByte(0);
-      return;
-    }
     try {
       BinaryTagIO.writeDataOutput(compoundTag, new ByteBufOutputStream(buf));
     } catch (IOException e) {

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

@@ -36,6 +36,8 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class AvailableCommands implements MinecraftPacket {
+  private static final Command<CommandSource> PLACEHOLDER_COMMAND = source -> 0;
+
   private static final byte NODE_TYPE_ROOT = 0x00;
   private static final byte NODE_TYPE_LITERAL = 0x01;
   private static final byte NODE_TYPE_ARGUMENT = 0x02;
@@ -121,16 +123,14 @@ public class AvailableCommands implements MinecraftPacket {
       flags |= FLAG_EXECUTABLE;
     }
 
-    if (node instanceof RootCommandNode<?>) {
-      flags |= NODE_TYPE_ROOT;
-    } else if (node instanceof LiteralCommandNode<?>) {
+    if (node instanceof LiteralCommandNode<?>) {
       flags |= NODE_TYPE_LITERAL;
     } else if (node instanceof ArgumentCommandNode<?, ?>) {
       flags |= NODE_TYPE_ARGUMENT;
       if (((ArgumentCommandNode<CommandSource, ?>) node).getCustomSuggestions() != null) {
         flags |= FLAG_HAS_SUGGESTIONS;
       }
-    } else {
+    } else if (!(node instanceof RootCommandNode<?>)) {
       throw new IllegalArgumentException("Unknown node type " + node.getClass().getName());
     }
 
@@ -238,8 +238,9 @@ public class AvailableCommands implements MinecraftPacket {
               throw new IllegalStateException("Node points to non-existent index " + redirectTo);
             }
 
-            if (wireNodes[redirectTo].built != null) {
-              args.redirect(wireNodes[redirectTo].built);
+            WireNode redirect = wireNodes[redirectTo];
+            if (redirect.built != null) {
+              args.redirect(redirect.built);
             } else {
               // Redirect node does not yet exist
               return false;
@@ -248,7 +249,7 @@ public class AvailableCommands implements MinecraftPacket {
 
           // If executable, add an empty command
           if ((flags & FLAG_EXECUTABLE) != 0) {
-            args.executes((Command<CommandSource>) context -> 0);
+            args.executes(PLACEHOLDER_COMMAND);
           }
 
           this.built = args.build();

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

@@ -16,19 +16,19 @@ public class EncryptionRequest implements MinecraftPacket {
   private byte[] verifyToken = EMPTY_BYTE_ARRAY;
 
   public byte[] getPublicKey() {
-    return publicKey;
+    return publicKey.clone();
   }
 
   public void setPublicKey(byte[] publicKey) {
-    this.publicKey = publicKey;
+    this.publicKey = publicKey.clone();
   }
 
   public byte[] getVerifyToken() {
-    return verifyToken;
+    return verifyToken.clone();
   }
 
   public void setVerifyToken(byte[] verifyToken) {
-    this.verifyToken = verifyToken;
+    this.verifyToken = verifyToken.clone();
   }
 
   @Override

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

@@ -15,19 +15,11 @@ public class EncryptionResponse implements MinecraftPacket {
   private byte[] verifyToken = EMPTY_BYTE_ARRAY;
 
   public byte[] getSharedSecret() {
-    return sharedSecret;
-  }
-
-  public void setSharedSecret(byte[] sharedSecret) {
-    this.sharedSecret = sharedSecret;
+    return sharedSecret.clone();
   }
 
   public byte[] getVerifyToken() {
-    return verifyToken;
-  }
-
-  public void setVerifyToken(byte[] verifyToken) {
-    this.verifyToken = verifyToken;
+    return verifyToken.clone();
   }
 
   @Override

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

@@ -99,7 +99,10 @@ public class PlayerListItem implements MinecraftPacket {
       ProtocolUtils.writeVarInt(buf, action);
       ProtocolUtils.writeVarInt(buf, items.size());
       for (Item item : items) {
-        ProtocolUtils.writeUuid(buf, item.getUuid());
+        UUID uuid = item.getUuid();
+        assert uuid != null : "UUID-less entry serialization attempt - 1.7 component!";
+
+        ProtocolUtils.writeUuid(buf, uuid);
         switch (action) {
           case ADD_PLAYER:
             ProtocolUtils.writeString(buf, item.getName());
@@ -127,9 +130,10 @@ public class PlayerListItem implements MinecraftPacket {
       }
     } else {
       Item item = items.get(0);
-      if (item.getDisplayName() != null) {
+      Component displayNameComponent = item.getDisplayName();
+      if (displayNameComponent != null) {
         String displayName = LegacyComponentSerializer.legacySection()
-            .serialize(item.getDisplayName());
+            .serialize(displayNameComponent);
         ProtocolUtils.writeString(buf,
             displayName.length() > 16 ? displayName.substring(0, 16) : displayName);
       } else {

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

@@ -121,6 +121,25 @@ public class TabCompleteResponse implements MinecraftPacket {
       this.tooltip = tooltip;
     }
 
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+
+      Offer offer = (Offer) o;
+
+      return text.equals(offer.text);
+    }
+
+    @Override
+    public int hashCode() {
+      return text.hashCode();
+    }
+
     @Override
     public String toString() {
       return MoreObjects.toStringHelper(this)

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

@@ -102,4 +102,8 @@ public class ByteBufDataOutput extends OutputStream implements ByteArrayDataOutp
       throw new IllegalStateException(e);
     }
   }
+
+  @Override
+  public void close() {
+  }
 }

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

@@ -83,8 +83,10 @@ public class VelocityLegacyHoverEventSerializer implements LegacyHoverEventSeria
     } else {
       builder.putString("id", keyAsString);
     }
-    if (input.nbt() != null) {
-      builder.put("tag", TagStringIO.get().asCompound(input.nbt().string()));
+
+    BinaryTagHolder nbt = input.nbt();
+    if (nbt != null) {
+      builder.put("tag", TagStringIO.get().asCompound(nbt.string()));
     }
 
     return TextComponent.of(TagStringIO.get().asString(builder.build()));
@@ -96,8 +98,9 @@ public class VelocityLegacyHoverEventSerializer implements LegacyHoverEventSeria
     CompoundBinaryTag.Builder tag = CompoundBinaryTag.builder()
         .putString("id", input.id().toString())
         .putString("type", input.type().asString());
-    if (input.name() != null) {
-      tag.putString("name", componentEncoder.encode(input.name()));
+    Component name = input.name();
+    if (name != null) {
+      tag.putString("name", componentEncoder.encode(name));
     }
     return TextComponent.of(TagStringIO.get().asString(tag.build()));
   }

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

@@ -1,6 +1,9 @@
 package com.velocitypowered.proxy.tablist;
 
+import static com.google.common.base.Verify.verify;
+
 import com.google.common.base.Preconditions;
+import com.google.common.base.Verify;
 import com.velocitypowered.api.proxy.player.TabList;
 import com.velocitypowered.api.proxy.player.TabListEntry;
 import com.velocitypowered.api.util.GameProfile;
@@ -121,6 +124,7 @@ public class VelocityTabList implements TabList {
     // Packets are already forwarded on, so no need to do that here
     for (PlayerListItem.Item item : packet.getItems()) {
       UUID uuid = item.getUuid();
+      assert uuid != null : "1.7 tab list entry given to modern tab list handler!";
 
       if (packet.getAction() != PlayerListItem.ADD_PLAYER && !entries.containsKey(uuid)) {
         // Sometimes UPDATE_GAMEMODE is sent before ADD_PLAYER so don't want to warn here

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

@@ -12,6 +12,12 @@ public class VelocityTabListEntryLegacy extends VelocityTabListEntry {
     super(tabList, profile, displayName, latency, gameMode);
   }
 
+  @Override
+  public TabListEntry setDisplayName(net.kyori.text.@Nullable Component displayName) {
+    getTabList().removeEntry(getProfile().getId()); // We have to remove first if updating
+    return super.setDisplayName(displayName);
+  }
+
   @Override
   public TabListEntry setDisplayName(@Nullable Component displayName) {
     getTabList().removeEntry(getProfile().getId()); // We have to remove first if updating

proxy/src/test/java/com/velocitypowered/proxy/command/MockCommandSource.java

@@ -6,7 +6,7 @@ import net.kyori.text.Component;
 
 public class MockCommandSource implements CommandSource {
 
-  public static CommandSource INSTANCE = new MockCommandSource();
+  public static final CommandSource INSTANCE = new MockCommandSource();
 
   @Override
   public void sendMessage(final Component component) {

proxy/src/test/java/com/velocitypowered/proxy/plugin/MockPluginManager.java

@@ -9,7 +9,7 @@ import java.util.Optional;
 
 public class MockPluginManager implements PluginManager {
 
-  public static PluginManager INSTANCE = new MockPluginManager();
+  public static final PluginManager INSTANCE = new MockPluginManager();
 
   @Override
   public Optional<PluginContainer> fromInstance(final Object instance) {