An Easter basket bearing gifts! (PaperMC#191)

* Delay switch to new server until after JoinGame is sent.

Unfortunately, in some cases (especially vanilla Minecraft) some login
disconnects are sent after ServerLoginSuccess but before JoinGame.
We've been using ServerLoginSuccess but it has caused too many problems.
Now Velocity will switch to a stripped-down version of the play session
handler until JoinGame is received. This handler does very little by
itself: it simply forwards plugin messages (for Forge) and waits for the
JoinGame packet from the server.

This is an initial version: only vanilla Minecraft 1.12.2 was tested.
However this is the way Waterfall without entity rewriting does server
switches (which, in turn, is inherited from BungeeCord).

* Move to Gradle 5 and Error Prone.

Author: astei

api/build.gradle

@@ -2,10 +2,11 @@ plugins {
     id 'java'
     id 'maven-publish'
     id 'checkstyle'
+    id "net.ltgt.errorprone" version "0.8"
 }
 
-apply from: '../gradle/checkerframework.gradle'
 apply from: '../gradle/checkstyle.gradle'
+apply from: '../gradle/errorprone.gradle'
 apply plugin: 'com.github.johnrengelman.shadow'
 
 sourceSets {

api/src/ap/java/com/velocitypowered/api/plugin/ap/PluginAnnotationProcessor.java

@@ -38,7 +38,8 @@ public SourceVersion getSupportedSourceVersion() {
   }
 
   @Override
-  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
+  public synchronized boolean process(Set<? extends TypeElement> annotations,
+      RoundEnvironment roundEnv) {
     if (roundEnv.processingOver()) {
       return false;
     }

api/src/ap/java/com/velocitypowered/api/plugin/ap/SerializedPluginDescription.java

@@ -12,7 +12,7 @@
 import java.util.stream.Collectors;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
-public class SerializedPluginDescription {
+public final class SerializedPluginDescription {
 
   public static final Pattern ID_PATTERN = Pattern.compile("[a-z][a-z0-9-_]{0,63}");
 
@@ -123,7 +123,7 @@ public String toString() {
         + '}';
   }
 
-  public static class Dependency {
+  public static final class Dependency {
 
     private final String id;
     private final boolean optional;

api/src/main/java/com/velocitypowered/api/proxy/Player.java

@@ -70,6 +70,7 @@ public interface Player extends CommandSource, InboundConnection, ChannelMessage
    *
    * @param component the chat message to send
    */
+  @Override
   default void sendMessage(Component component) {
     sendMessage(component, MessagePosition.CHAT);
   }

api/src/main/java/com/velocitypowered/api/proxy/server/QueryResponse.java

@@ -3,6 +3,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.proxy.config.ProxyConfig;
 import java.util.ArrayList;
@@ -26,14 +27,14 @@ public final class QueryResponse {
   private final int maxPlayers;
   private final String proxyHost;
   private final int proxyPort;
-  private final Collection<String> players;
+  private final ImmutableCollection<String> players;
   private final String proxyVersion;
-  private final Collection<PluginInformation> plugins;
+  private final ImmutableCollection<PluginInformation> plugins;
 
   @VisibleForTesting
   QueryResponse(String hostname, String gameVersion, String map, int currentPlayers,
-      int maxPlayers, String proxyHost, int proxyPort, Collection<String> players,
-      String proxyVersion, Collection<PluginInformation> plugins) {
+      int maxPlayers, String proxyHost, int proxyPort, ImmutableCollection<String> players,
+      String proxyVersion, ImmutableCollection<PluginInformation> plugins) {
     this.hostname = hostname;
     this.gameVersion = gameVersion;
     this.map = map;
@@ -403,7 +404,7 @@ public QueryResponse build() {
   /**
    * Represents a plugin in the query response.
    */
-  public static class PluginInformation {
+  public static final class PluginInformation {
 
     private final String name;
     private final @Nullable String version;

gradle/checkerframework.gradle

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

gradle/errorprone.gradle

@@ -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-4.10-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.4-all.zip

gradle/wrapper/gradle-wrapper.properties

@@ -1,10 +1,11 @@
 plugins {
     id 'java'
     id 'checkstyle'
+    id "net.ltgt.errorprone" version "0.8"
 }
 
-apply from: '../gradle/checkerframework.gradle'
 apply from: '../gradle/checkstyle.gradle'
+apply from: '../gradle/errorprone.gradle'
 
 dependencies {
     compile "com.google.guava:guava:${guavaVersion}"

native/build.gradle

@@ -21,13 +21,13 @@ public class NativeConstraints {
     return NATIVES_ENABLED
         && CAN_GET_MEMORYADDRESS
         && System.getProperty("os.name", "").equalsIgnoreCase("Mac OS X")
-        && System.getProperty("os.arch").equals("x86_64");
+        && System.getProperty("os.arch", "").equals("x86_64");
   };
 
   static final BooleanSupplier LINUX = () -> {
     return NATIVES_ENABLED
         && CAN_GET_MEMORYADDRESS
         && System.getProperty("os.name", "").equalsIgnoreCase("Linux")
-        && System.getProperty("os.arch").equals("amd64");
+        && System.getProperty("os.arch", "").equals("amd64");
   };
 }

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

@@ -1,10 +1,13 @@
+import com.github.jengelman.gradle.plugins.shadow.transformers.Log4j2PluginsCacheFileTransformer
+
 plugins {
     id 'java'
     id 'checkstyle'
+    id "net.ltgt.errorprone" version "0.8"
 }
 
-apply from: '../gradle/checkerframework.gradle'
 apply from: '../gradle/checkstyle.gradle'
+apply from: '../gradle/errorprone.gradle'
 apply plugin: 'com.github.johnrengelman.shadow'
 
 jar {
@@ -20,7 +23,7 @@ jar {
 }
 
 shadowJar {
-    transform(com.github.jengelman.gradle.plugins.shadow.transformers.Log4j2PluginsCacheFileTransformer)
+    transform(Log4j2PluginsCacheFileTransformer)
 }
 
 tasks.withType(Checkstyle) {

proxy/build.gradle

@@ -109,6 +109,7 @@ public KeyPair getServerKeyPair() {
     return ensureInitialized(serverKeyPair);
   }
 
+  @Override
   public VelocityConfiguration getConfiguration() {
     return ensureInitialized(this.configuration);
   }

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

@@ -93,14 +93,14 @@ public List<String> offerSuggestions(CommandSource source, String cmdLine) {
     String alias = split[0];
     if (split.length == 1) {
       // Offer to fill in commands.
-      List<String> availableCommands = new ArrayList<>();
+      ImmutableList.Builder<String> availableCommands = ImmutableList.builder();
       for (Map.Entry<String, Command> entry : commands.entrySet()) {
         if (entry.getKey().regionMatches(true, 0, alias, 0, alias.length())
             && entry.getValue().hasPermission(source, new String[0])) {
           availableCommands.add("/" + entry.getKey());
         }
       }
-      return availableCommands;
+      return availableCommands.build();
     }
 
     Command command = commands.get(alias.toLowerCase(Locale.ENGLISH));
@@ -116,7 +116,7 @@ public List<String> offerSuggestions(CommandSource source, String cmdLine) {
         return ImmutableList.of();
       }
 
-      return command.suggest(source, actualArgs);
+      return ImmutableList.copyOf(command.suggest(source, actualArgs));
     } catch (Exception e) {
       throw new RuntimeException(
           "Unable to invoke suggestions for command " + alias + " for " + source, e);

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

@@ -245,14 +245,17 @@ public InetSocketAddress getBind() {
     return AddressUtil.parseAddress(bind);
   }
 
+  @Override
   public boolean isQueryEnabled() {
     return query.isQueryEnabled();
   }
 
+  @Override
   public int getQueryPort() {
     return query.getQueryPort();
   }
 
+  @Override
   public String getQueryMap() {
     return query.getQueryMap();
   }
@@ -271,6 +274,7 @@ public String getMotd() {
    *
    * @return the MOTD
    */
+  @Override
   public Component getMotdComponent() {
     if (motdAsComponent == null) {
       if (motd.startsWith("{")) {
@@ -282,10 +286,12 @@ public Component getMotdComponent() {
     return motdAsComponent;
   }
 
+  @Override
   public int getShowMaxPlayers() {
     return showMaxPlayers;
   }
 
+  @Override
   public boolean isOnlineMode() {
     return onlineMode;
   }
@@ -298,42 +304,52 @@ public byte[] getForwardingSecret() {
     return forwardingSecret;
   }
 
+  @Override
   public Map<String, String> getServers() {
     return servers.getServers();
   }
 
+  @Override
   public List<String> getAttemptConnectionOrder() {
     return servers.getAttemptConnectionOrder();
   }
 
+  @Override
   public Map<String, List<String>> getForcedHosts() {
     return forcedHosts.getForcedHosts();
   }
 
+  @Override
   public int getCompressionThreshold() {
     return advanced.getCompressionThreshold();
   }
 
+  @Override
   public int getCompressionLevel() {
     return advanced.getCompressionLevel();
   }
 
+  @Override
   public int getLoginRatelimit() {
     return advanced.getLoginRatelimit();
   }
 
+  @Override
   public Optional<Favicon> getFavicon() {
     return Optional.ofNullable(favicon);
   }
 
+  @Override
   public boolean isAnnounceForge() {
     return announceForge;
   }
 
+  @Override
   public int getConnectTimeout() {
     return advanced.getConnectionTimeout();
   }
 
+  @Override
   public int getReadTimeout() {
     return advanced.getReadTimeout();
   }
@@ -402,15 +418,9 @@ public static VelocityConfiguration read(Path path) throws IOException {
         advanced,
         query
     );
-    upgradeConfig(configuration, toml);
     return configuration;
   }
 
-  private static void upgradeConfig(VelocityConfiguration configuration, Toml toml) {
-    // Will be implemented once there has been a backwards-incompatible change in the config file
-    // format.
-  }
-
   private static String generateRandomString(int length) {
     String chars = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz1234567890";
     StringBuilder builder = new StringBuilder();
@@ -547,7 +557,7 @@ private static class Advanced {
         "compress all packets, and setting it to -1 will disable compression entirely."
     })
     @ConfigKey("compression-threshold")
-    private int compressionThreshold = 1024;
+    private int compressionThreshold = 256;
 
     @Comment({"How much compression should be done (from 0-9). The default is -1, which uses the",
         "default level of 6."})
@@ -579,7 +589,7 @@ private Advanced() {
 
     private Advanced(Toml toml) {
       if (toml != null) {
-        this.compressionThreshold = toml.getLong("compression-threshold", 1024L).intValue();
+        this.compressionThreshold = toml.getLong("compression-threshold", 256L).intValue();
         this.compressionLevel = toml.getLong("compression-level", -1L).intValue();
         this.loginRatelimit = toml.getLong("login-ratelimit", 3000L).intValue();
         this.connectionTimeout = toml.getLong("connection-timeout", 5000L).intValue();