Enough of the Login protocol to display a message upon connect

src/main/java/io/minimum/minecraft/velocity/protocol/ProtocolUtils.java

@@ -6,7 +6,7 @@ import io.netty.buffer.ByteBuf;
 import java.nio.charset.StandardCharsets;
 
 public enum ProtocolUtils { ;
-    private static final int DEFAULT_MAX_STRING_SIZE = 1024 * 1024; // 1MB
+    private static final int DEFAULT_MAX_STRING_SIZE = 65536; // 64KiB
 
     public static int readVarInt(ByteBuf buf) {
         int numRead = 0;

src/main/java/io/minimum/minecraft/velocity/protocol/StateRegistry.java

@@ -1,9 +1,6 @@
 package io.minimum.minecraft.velocity.protocol;
 
-import io.minimum.minecraft.velocity.protocol.packets.Handshake;
-import io.minimum.minecraft.velocity.protocol.packets.Ping;
-import io.minimum.minecraft.velocity.protocol.packets.StatusRequest;
-import io.minimum.minecraft.velocity.protocol.packets.StatusResponse;
+import io.minimum.minecraft.velocity.protocol.packets.*;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -23,6 +20,15 @@ public enum StateRegistry {
             TO_CLIENT.register(0x00, StatusResponse.class, StatusResponse::new);
             TO_CLIENT.register(0x01, Ping.class, Ping::new);
         }
+    },
+    PLAY {
+
+    },
+    LOGIN {
+        {
+            TO_SERVER.register(0x00, ServerLogin.class, ServerLogin::new);
+            TO_CLIENT.register(0x00, Disconnect.class, Disconnect::new);
+        }
     };
 
     public final ProtocolMappings TO_CLIENT = new ProtocolMappings(ProtocolConstants.Direction.TO_CLIENT, this);

src/main/java/io/minimum/minecraft/velocity/protocol/packets/Disconnect.java

@@ -0,0 +1,35 @@
+package io.minimum.minecraft.velocity.protocol.packets;
+
+import io.minimum.minecraft.velocity.protocol.MinecraftPacket;
+import io.minimum.minecraft.velocity.protocol.ProtocolConstants;
+import io.minimum.minecraft.velocity.protocol.ProtocolUtils;
+import io.netty.buffer.ByteBuf;
+
+public class Disconnect implements MinecraftPacket {
+    private String reason;
+
+    public String getReason() {
+        return reason;
+    }
+
+    public void setReason(String reason) {
+        this.reason = reason;
+    }
+
+    @Override
+    public String toString() {
+        return "Disconnect{" +
+                "reason='" + reason + '\'' +
+                '}';
+    }
+
+    @Override
+    public void decode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
+        reason = ProtocolUtils.readString(buf);
+    }
+
+    @Override
+    public void encode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
+        ProtocolUtils.writeString(buf, reason);
+    }
+}

src/main/java/io/minimum/minecraft/velocity/protocol/packets/ServerLogin.java

@@ -0,0 +1,35 @@
+package io.minimum.minecraft.velocity.protocol.packets;
+
+import io.minimum.minecraft.velocity.protocol.MinecraftPacket;
+import io.minimum.minecraft.velocity.protocol.ProtocolConstants;
+import io.minimum.minecraft.velocity.protocol.ProtocolUtils;
+import io.netty.buffer.ByteBuf;
+
+public class ServerLogin implements MinecraftPacket {
+    private String username;
+
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    @Override
+    public String toString() {
+        return "ServerLogin{" +
+                "username='" + username + '\'' +
+                '}';
+    }
+
+    @Override
+    public void decode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
+        username = ProtocolUtils.readString(buf, 16);
+    }
+
+    @Override
+    public void encode(ByteBuf buf, ProtocolConstants.Direction direction, int protocolVersion) {
+        ProtocolUtils.writeString(buf, username);
+    }
+}

src/main/java/io/minimum/minecraft/velocity/proxy/InboundMinecraftConnection.java

@@ -6,6 +6,7 @@ import io.minimum.minecraft.velocity.protocol.netty.MinecraftDecoder;
 import io.minimum.minecraft.velocity.protocol.netty.MinecraftEncoder;
 import io.minimum.minecraft.velocity.protocol.packets.Handshake;
 import io.minimum.minecraft.velocity.proxy.handler.HandshakeSessionHandler;
+import io.minimum.minecraft.velocity.proxy.handler.LoginSessionHandler;
 import io.minimum.minecraft.velocity.proxy.handler.StatusSessionHandler;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
@@ -66,7 +67,9 @@ public class InboundMinecraftConnection {
                 this.sessionHandler = new StatusSessionHandler(this);
                 break;
             default:
-                throw new UnsupportedOperationException("Unsupported next protocol state " + handshake.getNextStatus());
+                this.setStatus(StateRegistry.LOGIN);
+                this.sessionHandler = new LoginSessionHandler(this);
+                break;
         }
     }
 

src/main/java/io/minimum/minecraft/velocity/proxy/MinecraftClientSessionHandler.java

@@ -55,6 +55,5 @@ public class MinecraftClientSessionHandler extends ChannelInboundHandlerAdapter
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         cause.printStackTrace();
-        ctx.close();
     }
 }

src/main/java/io/minimum/minecraft/velocity/proxy/handler/LoginSessionHandler.java

@@ -0,0 +1,28 @@
+package io.minimum.minecraft.velocity.proxy.handler;
+
+import com.google.common.base.Preconditions;
+import io.minimum.minecraft.velocity.protocol.MinecraftPacket;
+import io.minimum.minecraft.velocity.protocol.packets.Disconnect;
+import io.minimum.minecraft.velocity.protocol.packets.ServerLogin;
+import io.minimum.minecraft.velocity.proxy.InboundMinecraftConnection;
+import io.minimum.minecraft.velocity.proxy.MinecraftSessionHandler;
+import net.kyori.text.TextComponent;
+import net.kyori.text.serializer.ComponentSerializers;
+
+public class LoginSessionHandler implements MinecraftSessionHandler {
+    private final InboundMinecraftConnection connection;
+
+    public LoginSessionHandler(InboundMinecraftConnection connection) {
+        this.connection = Preconditions.checkNotNull(connection, "connection");
+    }
+
+    @Override
+    public void handle(MinecraftPacket packet) {
+        Preconditions.checkArgument(packet instanceof ServerLogin, "Expected a ServerLogin packet, not " + packet.getClass().getName());
+
+        // Disconnect with test message
+        Disconnect disconnect = new Disconnect();
+        disconnect.setReason(ComponentSerializers.JSON.serialize(TextComponent.of("Hi there!")));
+        connection.closeWith(disconnect);
+    }
+}