Separate protocol version for new proxy <-> server connections

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -37,6 +37,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
     private StateRegistry state;
     private MinecraftSessionHandler sessionHandler;
     private int protocolVersion;
+    private int nextProtocolVersion;
     private MinecraftConnectionAssociation association;
     private boolean isLegacyForge;
     private final VelocityServer server;
@@ -185,6 +186,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
 
     public void setProtocolVersion(int protocolVersion) {
         this.protocolVersion = protocolVersion;
+        this.nextProtocolVersion = protocolVersion;
         if (protocolVersion != ProtocolConstants.LEGACY) {
             this.channel.pipeline().get(MinecraftEncoder.class).setProtocolVersion(protocolVersion);
             this.channel.pipeline().get(MinecraftDecoder.class).setProtocolVersion(protocolVersion);
@@ -264,4 +266,12 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
     public void setCanSendLegacyFMLResetPacket(boolean canSendLegacyFMLResetPacket) {
         this.canSendLegacyFMLResetPacket = isLegacyForge && canSendLegacyFMLResetPacket;
     }
+
+    public int getNextProtocolVersion() {
+        return this.nextProtocolVersion;
+    }
+
+    public void setNextProtocolVersion(int nextProtocolVersion) {
+        this.nextProtocolVersion = nextProtocolVersion;
+    }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -98,7 +98,7 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
         // Initiate a handshake.
         Handshake handshake = new Handshake();
         handshake.setNextStatus(StateRegistry.LOGIN_ID);
-        handshake.setProtocolVersion(proxyPlayer.getConnection().getProtocolVersion());
+        handshake.setProtocolVersion(proxyPlayer.getConnection().getNextProtocolVersion());
         if (forwardingMode == PlayerInfoForwarding.LEGACY) {
             handshake.setServerAddress(createBungeeForwardingAddress());
         } else if (proxyPlayer.getConnection().isLegacyForge()) {
@@ -109,7 +109,7 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
         handshake.setPort(registeredServer.getServerInfo().getAddress().getPort());
         connection.write(handshake);
 
-        int protocolVersion = proxyPlayer.getConnection().getProtocolVersion();
+        int protocolVersion = proxyPlayer.getConnection().getNextProtocolVersion();
         connection.setProtocolVersion(protocolVersion);
         connection.setState(StateRegistry.LOGIN);