add whacky protocol version negotiation

Author: Skidamek

core/src/main/java/pl/skidam/automodpack_core/protocol/DownloadClient.java

@@ -282,7 +282,7 @@ protected SSLSocket getSocket() {
  */
 class Connection implements AutoCloseable {
 
-    private byte protocolVersion = PROTOCOL_VERSION;
+    private byte protocolVersion = LATEST_SUPPORTED_PROTOCOL_VERSION;
     private byte compressionType = COMPRESSION_ZSTD;
     private int chunkSize = DEFAULT_CHUNK_SIZE;
     private final byte[] secretBytes;
@@ -513,6 +513,10 @@ private byte sendCompressionConfig(byte desiredCompression) throws IOException {
         out.flush();
 
         byte version = in.readByte();
+        if (version >= 1 && version < protocolVersion) {
+            protocolVersion = version;
+        }
+
         byte type = in.readByte();
         if (type != CONFIGURATION_COMPRESSION_TYPE) throw new IOException("Unexpected response: " + type);
 
@@ -534,6 +538,10 @@ private int sendChunkSizeConfig(int desiredChunkSize) throws IOException {
         out.flush();
 
         byte version = in.readByte();
+        if (version >= 1 && version < protocolVersion) {
+            protocolVersion = version;
+        }
+
         byte type = in.readByte();
         if (type != CONFIGURATION_CHUNK_SIZE_TYPE) throw new IOException("Unexpected response: " + type);
 

core/src/main/java/pl/skidam/automodpack_core/protocol/NetUtils.java

@@ -30,7 +30,7 @@ public class NetUtils {
     public static final int MAGIC_AMOK = 0x414D4F4B;
 
     // Protocol versions
-    public static final byte PROTOCOL_VERSION = 0x01;
+    public static final byte LATEST_SUPPORTED_PROTOCOL_VERSION = 0x01;
 
     // Compression types
     public static final byte COMPRESSION_NONE = 0x00;

core/src/main/java/pl/skidam/automodpack_core/protocol/netty/handler/ConfigurationHandler.java

@@ -31,6 +31,14 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
         LOGGER.debug("Message version: {}, type: {}, readable bytes: {}", version, type, in.readableBytes());
         if ((type & 0xF0) == 0x40) {
             if (type == CONFIGURATION_ECHO_TYPE) {
+                if (version > LATEST_SUPPORTED_PROTOCOL_VERSION || version <= 0) {
+                    LOGGER.debug("Failed to negotatie protocol version with client");
+                    ctx.close();
+                    return;
+                }
+                ctx.channel().attr(NettyServer.PROTOCOL_VERSION).set(version);
+                LOGGER.debug("Negotiated {} protocol version with the client", version);
+
                 // remove this channel from pipeline
                 ctx.pipeline().remove(this);
                 LOGGER.debug("Removed ConfigurationHandler from pipeline after receiving echo configuration message.");
@@ -54,7 +62,7 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
                 ctx.channel().attr(NettyServer.COMPRESSION_TYPE).set(negotiatedCompressionType);
 
                 // Send negotiated values back to client
-                ConfigurationCompressionMessage responseMsg = new ConfigurationCompressionMessage(PROTOCOL_VERSION, negotiatedCompressionType);
+                ConfigurationCompressionMessage responseMsg = new ConfigurationCompressionMessage(LATEST_SUPPORTED_PROTOCOL_VERSION, negotiatedCompressionType);
                 ctx.writeAndFlush(responseMsg.toByteBuf());
 
                 LOGGER.debug("Negotiated configuration: compression {}", negotiatedCompressionType);
@@ -78,13 +86,13 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
                 ctx.channel().attr(NettyServer.CHUNK_SIZE).set(negotiatedChunkSize);
 
                 // Send negotiated values back to client
-                ConfigurationChunkSizeMessage responseMsg = new ConfigurationChunkSizeMessage(PROTOCOL_VERSION, negotiatedChunkSize);
+                ConfigurationChunkSizeMessage responseMsg = new ConfigurationChunkSizeMessage(LATEST_SUPPORTED_PROTOCOL_VERSION, negotiatedChunkSize);
                 ctx.writeAndFlush(responseMsg.toByteBuf());
 
                 LOGGER.debug("Negotiated configuration: chunk size {}", negotiatedChunkSize);
             } else {
                 LOGGER.debug("Received unknown configuration message type: {} version: {}", type, version);
-                UnknownConfigurationMessage responseMsg = new UnknownConfigurationMessage(PROTOCOL_VERSION);
+                UnknownConfigurationMessage responseMsg = new UnknownConfigurationMessage(LATEST_SUPPORTED_PROTOCOL_VERSION);
                 ctx.writeAndFlush(responseMsg.toByteBuf());
             }
             in.release(); // Release the buffer after processing configuration message

core/src/main/java/pl/skidam/automodpack_core/protocol/netty/handler/ProtocolServerHandler.java

@@ -189,7 +189,7 @@ private void setupPipeline(ChannelHandlerContext ctx) {
         }
 
         ctx.channel().attr(NettyServer.REAL_REMOTE_ADDR).set(remoteAddress);
-        ctx.channel().attr(NettyServer.PROTOCOL_VERSION).set(PROTOCOL_VERSION);
+        ctx.channel().attr(NettyServer.PROTOCOL_VERSION).set(LATEST_SUPPORTED_PROTOCOL_VERSION);
         ctx.channel().attr(NettyServer.COMPRESSION_TYPE).set(COMPRESSION_ZSTD);
         ctx.channel().attr(NettyServer.CHUNK_SIZE).set(DEFAULT_CHUNK_SIZE);
 

core/src/main/java/pl/skidam/automodpack_core/protocol/netty/handler/ServerMessageHandler.java

@@ -40,24 +40,29 @@ public void handlerRemoved(ChannelHandlerContext ctx) {
 
     @Override
     protected void channelRead0(ChannelHandlerContext ctx, ProtocolMessage msg) throws Exception {
+        this.protocolVersion = ctx.pipeline().channel().attr(NettyServer.PROTOCOL_VERSION).get();
+        this.chunkSize = ctx.pipeline().channel().attr(NettyServer.CHUNK_SIZE).get();
+
         byte clientProtocolVersion = msg.getVersion();
+
+        if (protocolVersion != clientProtocolVersion) {
+            sendError(ctx, protocolVersion, "Protocol version mismatch");
+            return;
+        }
+
         SocketAddress address = ctx.channel().attr(NettyServer.REAL_REMOTE_ADDR).get();
 
         // Validate the secret
         if (!validateSecret(ctx, address, msg.getSecret())) {
-            sendError(ctx, clientProtocolVersion, "Authentication failed");
+            sendError(ctx, protocolVersion, "Authentication failed");
             return;
         }
 
-        // reassign channel attributes
-        this.protocolVersion = ctx.pipeline().channel().attr(NettyServer.PROTOCOL_VERSION).get();
-        this.chunkSize = ctx.pipeline().channel().attr(NettyServer.CHUNK_SIZE).get();
-
         switch (msg.getType()) {
             case ECHO_TYPE:
                 EchoMessage echoMsg = (EchoMessage) msg;
                 ByteBuf echoBuf = ctx.alloc().buffer(1 + 1 + msg.getSecret().length + echoMsg.getData().length);
-                echoBuf.writeByte(clientProtocolVersion);
+                echoBuf.writeByte(protocolVersion);
                 echoBuf.writeByte(ECHO_TYPE);
                 echoBuf.writeBytes(echoMsg.getSecret());
                 echoBuf.writeBytes(echoMsg.getData());
@@ -73,7 +78,7 @@ protected void channelRead0(ChannelHandlerContext ctx, ProtocolMessage msg) thro
                 refreshModpackFiles(ctx, refreshRequest.getFileHashesList());
                 break;
             default:
-                sendError(ctx, clientProtocolVersion, "Unknown message type");
+                sendError(ctx, protocolVersion, "Unknown message type");
         }
     }