Make Velocity's server list ping behavior more conformant.

This fixes pinging with 1.7.x and with certain ping libraries that send
the -1 protocol version.

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

@@ -179,7 +179,7 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
 
     @Override
     public ProtocolVersion getProtocolVersion() {
-      return ProtocolVersion.UNKNOWN;
+      return ProtocolVersion.LEGACY;
     }
   }
 }

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

@@ -38,9 +38,8 @@ public class StatusSessionHandler implements MinecraftSessionHandler {
   public boolean handle(StatusRequest packet) {
     VelocityConfiguration configuration = server.getConfiguration();
 
-    ProtocolVersion shownVersion = ProtocolVersion.isSupported(connection.getProtocolVersion()) ? connection
+    ProtocolVersion shownVersion = ProtocolVersion.isSupported(connection.getProtocolVersion())
-        .getProtocolVersion() :
+        ? connection.getProtocolVersion() : ProtocolVersion.MAXIMUM_VERSION;
-        ProtocolVersion.MAXIMUM_VERSION;
     ServerPing initialPing = new ServerPing(
         new ServerPing.Version(shownVersion.getProtocol(),
             "Velocity " + ProtocolVersion.SUPPORTED_VERSION_STRING),

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

@@ -200,14 +200,18 @@ public enum StateRegistry {
 
   public static class PacketRegistry {
 
-    private static final EnumMap<ProtocolVersion, ImmutableList<ProtocolVersion>> LINKED_PROTOCOL_VERSIONS = new EnumMap(ProtocolVersion.class);
+    private static final Map<ProtocolVersion, List<ProtocolVersion>> LINKED_PROTOCOL_VERSIONS
+        = new EnumMap<>(ProtocolVersion.class);
 
     static {
-      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_9, ImmutableList.of(MINECRAFT_1_9_1, MINECRAFT_1_9_2, MINECRAFT_1_9_4));
+      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_9, ImmutableList.of(MINECRAFT_1_9_1, MINECRAFT_1_9_2,
-      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_9_4, ImmutableList.of(MINECRAFT_1_10, MINECRAFT_1_11, MINECRAFT_1_11_1));
+          MINECRAFT_1_9_4));
+      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_9_4, ImmutableList.of(MINECRAFT_1_10, MINECRAFT_1_11,
+          MINECRAFT_1_11_1));
       LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_12, ImmutableList.of(MINECRAFT_1_12_1));
       LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_12_1, ImmutableList.of(MINECRAFT_1_12_2));
-      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_13, ImmutableList.of(MINECRAFT_1_13_1, MINECRAFT_1_13_2));
+      LINKED_PROTOCOL_VERSIONS.put(MINECRAFT_1_13, ImmutableList.of(MINECRAFT_1_13_1,
+          MINECRAFT_1_13_2));
     }
 
     private final Direction direction;
@@ -217,9 +221,11 @@ public enum StateRegistry {
     PacketRegistry(Direction direction) {
       this.direction = direction;
 
-      EnumMap<ProtocolVersion, ProtocolRegistry> mutableVersions = new EnumMap(ProtocolVersion.class);
+      Map<ProtocolVersion, ProtocolRegistry> mutableVersions = new EnumMap<>(ProtocolVersion.class);
       for (ProtocolVersion version : ProtocolVersion.values()) {
-        mutableVersions.put(version, new ProtocolRegistry(version));
+        if (!version.isLegacy() && !version.isUnknown()) {
+          mutableVersions.put(version, new ProtocolRegistry(version));
+        }
       }
 
       this.versions = Collections.unmodifiableMap(mutableVersions);
@@ -252,7 +258,7 @@ public enum StateRegistry {
         }
         registry.packetClassToId.put(clazz, mapping.id);
 
-        ImmutableList<ProtocolVersion> linked = LINKED_PROTOCOL_VERSIONS.get(mapping.protocolVersion);
+        List<ProtocolVersion> linked = LINKED_PROTOCOL_VERSIONS.get(mapping.protocolVersion);
         if (linked != null) {
           links:
           for (int i = 0; i < linked.size(); i++) {

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

@@ -56,15 +56,16 @@ public class Handshake implements MinecraftPacket {
   }
 
   @Override
-  public void decode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion protocolVersion) {
+  public void decode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion ignored) {
-    this.protocolVersion = ProtocolVersion.getProtocolVersion(ProtocolUtils.readVarInt(buf));
+    int realProtocolVersion = ProtocolUtils.readVarInt(buf);
+    this.protocolVersion = ProtocolVersion.getProtocolVersion(realProtocolVersion);
     this.serverAddress = ProtocolUtils.readString(buf);
     this.port = buf.readUnsignedShort();
     this.nextStatus = ProtocolUtils.readVarInt(buf);
   }
 
   @Override
-  public void encode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion protocolVersion) {
+  public void encode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion ignored) {
     ProtocolUtils.writeVarInt(buf, this.protocolVersion.getProtocol());
     ProtocolUtils.writeString(buf, this.serverAddress);
     buf.writeShort(this.port);