Cleanup, renames, check protocol version of client on handshake.

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

@@ -42,8 +42,7 @@ public class ConnectedPlayer {
 
     public void handleConnectionException(ServerInfo info, Throwable throwable) {
         String error = ThrowableUtils.briefDescription(throwable);
-        Disconnect disconnect = new Disconnect();
-        disconnect.setReason(ComponentSerializers.JSON.serialize(TextComponent.of(error, TextColor.RED)));
+        Disconnect disconnect = Disconnect.create(TextComponent.of(error, TextColor.RED));
         handleConnectionException(info, disconnect);
     }
 
@@ -56,9 +55,7 @@ public class ConnectedPlayer {
 
         if (connectedServer == null) {
             // The player isn't yet connected to a server - we should disconnect them.
-            Disconnect d = new Disconnect();
-            d.setReason(ComponentSerializers.JSON.serialize(component));
-            connection.closeWith(d);
+            connection.closeWith(Disconnect.create(component));
         } else {
             Chat chat = new Chat();
             chat.setMessage(ComponentSerializers.JSON.serialize(component));
@@ -71,8 +68,6 @@ public class ConnectedPlayer {
     }
 
     public void close(TextComponent reason) {
-        Disconnect disconnect = new Disconnect();
-        disconnect.setReason(ComponentSerializers.JSON.serialize(reason));
-        connection.closeWith(disconnect);
+        connection.closeWith(Disconnect.create(reason));
     }
 }

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

@@ -2,10 +2,13 @@ package com.velocitypowered.proxy.connection.client;
 
 import com.google.common.base.Preconditions;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
+import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import com.velocitypowered.proxy.protocol.StateRegistry;
+import com.velocitypowered.proxy.protocol.packets.Disconnect;
 import com.velocitypowered.proxy.protocol.packets.Handshake;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
+import net.kyori.text.TextComponent;
 
 public class HandshakeSessionHandler implements MinecraftSessionHandler {
     private final MinecraftConnection connection;
@@ -30,7 +33,12 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
                 break;
             case 2:
                 connection.setState(StateRegistry.LOGIN);
+                if (!ProtocolConstants.isSupported(handshake.getProtocolVersion())) {
+                    connection.closeWith(Disconnect.create(TextComponent.of("Unsupported client")));
+                    return;
+                } else {
                     connection.setSessionHandler(new LoginSessionHandler(connection));
+                }
                 break;
             default:
                 throw new IllegalArgumentException("Invalid state " + handshake.getNextStatus());

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

@@ -1,8 +1,18 @@
 package com.velocitypowered.proxy.protocol;
 
+import java.util.Arrays;
+
 public enum ProtocolConstants { ;
     public static final int MINECRAFT_1_12 = 340;
 
+    private static final int[] SUPPORTED_VERSIONS = new int[] {
+            MINECRAFT_1_12
+    };
+
+    public static boolean isSupported(int version) {
+        return Arrays.binarySearch(SUPPORTED_VERSIONS, version) >= 0;
+    }
+
     public enum Direction {
         TO_SERVER,
         TO_CLIENT

src/main/java/com/velocitypowered/proxy/protocol/packets/Disconnect.java

@@ -1,13 +1,23 @@
 package com.velocitypowered.proxy.protocol.packets;
 
+import com.google.common.base.Preconditions;
 import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.ProtocolUtils;
 import io.netty.buffer.ByteBuf;
+import net.kyori.text.TextComponent;
+import net.kyori.text.serializer.ComponentSerializers;
 
 public class Disconnect implements MinecraftPacket {
     private String reason;
 
+    public Disconnect() {
+    }
+
+    public Disconnect(String reason) {
+        this.reason = reason;
+    }
+
     public String getReason() {
         return reason;
     }
@@ -32,4 +42,9 @@ public class Disconnect implements MinecraftPacket {
     public void encode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
         ProtocolUtils.writeString(buf, reason);
     }
+
+    public static Disconnect create(TextComponent component) {
+        Preconditions.checkNotNull(component, "component");
+        return new Disconnect(ComponentSerializers.JSON.serialize(component));
+    }
 }

src/main/java/com/velocitypowered/proxy/util/EncryptionUtils.java

@@ -3,7 +3,7 @@ package com.velocitypowered.proxy.util;
 import java.math.BigInteger;
 
 public enum EncryptionUtils { ;
-    public static String twoComplementsSha1Digest(byte[] digest) {
+    public static String twosComplementSha1Digest(byte[] digest) {
         return new BigInteger(digest).toString(16);
     }
 }

src/test/java/com/velocitypowered/proxy/util/EncryptionUtilsTest.java

@@ -9,7 +9,7 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class EncryptionUtilsTest {
     @Test
-    void twoComplementsSha1Digest() throws Exception {
+    void twosComplementSha1Digest() throws Exception {
         String notchHash = hexDigest("Notch");
         assertEquals("4ed1f46bbe04bc756bcb17c0c7ce3e4632f06a48", notchHash);
 
@@ -21,6 +21,6 @@ class EncryptionUtilsTest {
         MessageDigest digest = MessageDigest.getInstance("SHA-1");
         digest.update(str.getBytes(StandardCharsets.UTF_8));
         byte[] digested = digest.digest();
-        return EncryptionUtils.twoComplementsSha1Digest(digested);
+        return EncryptionUtils.twosComplementSha1Digest(digested);
     }
 }