Allow serializing legacy hover events

Should fix #349

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

@@ -32,6 +32,7 @@ import com.velocitypowered.proxy.console.VelocityConsole;
 import com.velocitypowered.proxy.network.ConnectionManager;
 import com.velocitypowered.proxy.plugin.VelocityEventManager;
 import com.velocitypowered.proxy.plugin.VelocityPluginManager;
+import com.velocitypowered.proxy.protocol.ProtocolUtils;
 import com.velocitypowered.proxy.protocol.packet.Chat;
 import com.velocitypowered.proxy.protocol.util.FaviconSerializer;
 import com.velocitypowered.proxy.protocol.util.GameProfileSerializer;
@@ -91,13 +92,14 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
       .registerTypeHierarchyAdapter(Favicon.class, new FaviconSerializer())
       .registerTypeHierarchyAdapter(GameProfile.class, new GameProfileSerializer())
       .create();
-  private static final Gson PRE_1_16_PING_SERIALIZER = GsonComponentSerializer
+  private static final Gson PRE_1_16_PING_SERIALIZER = ProtocolUtils
-      .colorDownsamplingGson()
+      .getJsonChatSerializer(ProtocolVersion.MINECRAFT_1_15_2)
       .serializer()
       .newBuilder()
       .registerTypeHierarchyAdapter(Favicon.class, new FaviconSerializer())
       .create();
-  private static final Gson POST_1_16_PING_SERIALIZER = GsonComponentSerializer.gson()
+  private static final Gson POST_1_16_PING_SERIALIZER = ProtocolUtils
+      .getJsonChatSerializer(ProtocolVersion.MINECRAFT_1_16)
       .serializer()
       .newBuilder()
       .registerTypeHierarchyAdapter(Favicon.class, new FaviconSerializer())

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

@@ -3,10 +3,10 @@ package com.velocitypowered.proxy.protocol;
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.velocitypowered.proxy.protocol.util.NettyPreconditions.checkFrame;
 
-import com.google.common.base.Preconditions;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
+import com.velocitypowered.proxy.protocol.util.VelocityLegacyHoverEventSerializer;
 import com.velocitypowered.proxy.util.except.QuietDecoderException;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufInputStream;
@@ -28,6 +28,18 @@ import net.kyori.adventure.text.serializer.gson.GsonComponentSerializer;
 
 public enum ProtocolUtils {
   ;
+
+  private static final GsonComponentSerializer PRE_1_16_SERIALIZER =
+      GsonComponentSerializer.builder()
+          .downsampleColors()
+          .emitLegacyHoverEvent()
+          .legacyHoverEventSerializer(VelocityLegacyHoverEventSerializer.INSTANCE)
+          .build();
+  private static final GsonComponentSerializer MODERN_SERIALIZER =
+      GsonComponentSerializer.builder()
+          .legacyHoverEventSerializer(VelocityLegacyHoverEventSerializer.INSTANCE)
+          .build();
+
   private static final int DEFAULT_MAX_STRING_SIZE = 65536; // 64KiB
   private static final QuietDecoderException BAD_VARINT_CACHED =
       new QuietDecoderException("Bad varint decoded");
@@ -468,9 +480,9 @@ public enum ProtocolUtils {
    */
   public static GsonComponentSerializer getJsonChatSerializer(ProtocolVersion version) {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_16) >= 0) {
-      return GsonComponentSerializer.gson();
+      return MODERN_SERIALIZER;
     }
-    return GsonComponentSerializer.colorDownsamplingGson();
+    return PRE_1_16_SERIALIZER;
   }
 
   public enum Direction {

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

@@ -0,0 +1,96 @@
+package com.velocitypowered.proxy.protocol.util;
+
+import java.io.IOException;
+import java.util.UUID;
+import net.kyori.adventure.key.Key;
+import net.kyori.adventure.nbt.CompoundBinaryTag;
+import net.kyori.adventure.nbt.TagStringIO;
+import net.kyori.adventure.nbt.api.BinaryTagHolder;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.TextComponent;
+import net.kyori.adventure.text.event.HoverEvent;
+import net.kyori.adventure.text.event.HoverEvent.ShowEntity;
+import net.kyori.adventure.text.event.HoverEvent.ShowItem;
+import net.kyori.adventure.text.serializer.gson.LegacyHoverEventSerializer;
+import net.kyori.adventure.text.serializer.plain.PlainComponentSerializer;
+import net.kyori.adventure.util.Codec.Decoder;
+import net.kyori.adventure.util.Codec.Encoder;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * An implementation of {@link LegacyHoverEventSerializer} that implements the interface in the
+ * most literal, albeit "incompatible" way possible.
+ */
+public class VelocityLegacyHoverEventSerializer implements LegacyHoverEventSerializer {
+
+  public static final LegacyHoverEventSerializer INSTANCE =
+      new VelocityLegacyHoverEventSerializer();
+
+  private VelocityLegacyHoverEventSerializer() {
+
+  }
+
+  private static Key legacyIdToFakeKey(byte id) {
+    return Key.of("velocity", "legacy_hover/id_" + id);
+  }
+
+  @Override
+  public HoverEvent.@NonNull ShowItem deserializeShowItem(@NonNull Component input)
+      throws IOException {
+    String snbt = PlainComponentSerializer.plain().serialize(input);
+    CompoundBinaryTag item = TagStringIO.get().asCompound(snbt);
+
+    Key key;
+    String idIfString = item.getString("id", "");
+    if (idIfString.isEmpty()) {
+      key = legacyIdToFakeKey(item.getByte("id"));
+    } else {
+      key = Key.of(idIfString);
+    }
+
+    byte count = item.getByte("Count", (byte) 1);
+    return new ShowItem(key, count, BinaryTagHolder.of(snbt));
+  }
+
+  @Override
+  public HoverEvent.@NonNull ShowEntity deserializeShowEntity(@NonNull Component input,
+      Decoder<Component, String, ? extends RuntimeException> componentDecoder) throws IOException {
+    String snbt = PlainComponentSerializer.plain().serialize(input);
+    CompoundBinaryTag item = TagStringIO.get().asCompound(snbt);
+    return new ShowEntity(Key.of(item.getString("type")),
+        UUID.fromString(item.getString("id")),
+        componentDecoder.decode(item.getString("name")));
+  }
+
+  @Override
+  public @NonNull Component serializeShowItem(HoverEvent.@NonNull ShowItem input)
+      throws IOException {
+    final CompoundBinaryTag.Builder builder = CompoundBinaryTag.builder()
+        .putByte("Count", (byte) input.count());
+
+    String keyAsString = input.item().asString();
+    if (keyAsString.startsWith("velocity:legacy_hover/id_")) {
+      builder.putByte("id", Byte.parseByte(keyAsString
+          .substring("velocity:legacy_hover/id_".length())));
+    } else {
+      builder.putString("id", keyAsString);
+    }
+    if (input.nbt() != null) {
+      builder.put("tag", TagStringIO.get().asCompound(input.nbt().string()));
+    }
+
+    return TextComponent.of(TagStringIO.get().asString(builder.build()));
+  }
+
+  @Override
+  public @NonNull Component serializeShowEntity(HoverEvent.@NonNull ShowEntity input,
+      Encoder<Component, String, ? extends RuntimeException> componentEncoder) throws IOException {
+    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()));
+    }
+    return TextComponent.of(TagStringIO.get().asString(tag.build()));
+  }
+}