Add support to send older version packets to servers

README.md

@@ -33,6 +33,9 @@ Server developers are welcome to submit additional patches they need, however al
 
 # For developers
 
+Any developers interested in writing code that interacts with Noxesium should have a look at the `api` module which contains various structures useful for setting up a server-side implementation that interacts with Noxesium. This modules
+does not have a dependency on fabric and can thus be used as a dependency in server software.
+
 ## Player Heads
 
 Noxesium supports rendering player heads into text through a custom skull component. The details of which can be found by looking into the contents

fabric/src/main/java/com/noxcrew/noxesium/NoxesiumMod.java

@@ -1,13 +1,11 @@
 package com.noxcrew.noxesium;
 
 import com.noxcrew.noxesium.feature.rule.ServerRuleModule;
-import com.noxcrew.noxesium.feature.skull.CustomSkullFont;
 import com.noxcrew.noxesium.feature.skull.SkullFontModule;
 import com.noxcrew.noxesium.network.NoxesiumPackets;
 import com.noxcrew.noxesium.network.serverbound.ServerboundClientInformationPacket;
 import com.noxcrew.noxesium.network.serverbound.ServerboundClientSettingsPacket;
 import net.fabricmc.api.ClientModInitializer;
-import net.fabricmc.fabric.api.client.event.lifecycle.v1.ClientTickEvents;
 import net.fabricmc.fabric.api.client.networking.v1.ClientPlayConnectionEvents;
 import net.minecraft.client.Minecraft;
 import net.minecraft.resources.ResourceLocation;
@@ -39,6 +37,11 @@ public class NoxesiumMod implements ClientModInitializer {
             SkullFontModule.getInstance()
     ));
 
+    /**
+     * The current maximum supported protocol version.
+     */
+    private static int currentMaxProtocol = VERSION;
+
     /**
      * Adds a new module to the list of modules that should have
      * their hooks called. Available for other mods to use.
@@ -47,6 +50,20 @@ public static void registerModule(NoxesiumModule module) {
         modules.add(module);
     }
 
+    /**
+     * Returns the latest protocol version that is currently supported.
+     */
+    public static int getMaxProtocolVersion() {
+         return currentMaxProtocol;
+    }
+
+    /**
+     * Stores the maximum protocol version of the current server.
+     */
+    public static void setServerVersion(int maxProtocolVersion) {
+        currentMaxProtocol = maxProtocolVersion;
+    }
+
     @Override
     public void onInitializeClient() {
         // Every time the client joins a server we send over information on the version being used
@@ -66,6 +83,9 @@ public void onInitializeClient() {
         // Call disconnection hooks
         ClientPlayConnectionEvents.DISCONNECT.register((ignored1, ignored2) -> {
             modules.forEach(NoxesiumModule::onQuitServer);
+
+            // Reset the current max protocol version
+            currentMaxProtocol = VERSION;
         });
 
         // Register all universal messaging channels

fabric/src/main/java/com/noxcrew/noxesium/mixin/music/SoundSourceMixin.java

@@ -13,6 +13,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Collectors;
 
 /**
  * Hooks into the SoundSource enum to add additional custom values.
@@ -36,9 +37,15 @@ private static SoundSource createNewCategory(String fieldName, int ordinal, Stri
             at = @At(value = "FIELD", target = "Lnet/minecraft/sounds/SoundSource;$VALUES:[Lnet/minecraft/sounds/SoundSource;", opcode = Opcodes.PUTSTATIC, shift = At.Shift.AFTER)
     )
     private static void modifyValues(CallbackInfo ci) {
+        // Avoid conflicts by checking if they already exist
         var newValues = new ArrayList<>(List.of($VALUES));
-        newValues.add(createNewCategory("CORE_MUSIC", newValues.size(), "core_music"));
-        newValues.add(createNewCategory("GAME_MUSIC", newValues.size(), "game_music"));
+        var existingValues = newValues.stream().map(Enum::name).toList();
+        if (!existingValues.contains("CORE_MUSIC")) {
+            newValues.add(createNewCategory("CORE_MUSIC", newValues.size(), "core_music"));
+        }
+        if (!existingValues.contains("GAME_MUSIC")) {
+            newValues.add(createNewCategory("GAME_MUSIC", newValues.size(), "game_music"));
+        }
         $VALUES = newValues.toArray(new SoundSource[0]);
     }
 }

fabric/src/main/java/com/noxcrew/noxesium/network/NoxesiumPackets.java

@@ -7,6 +7,7 @@
 import com.noxcrew.noxesium.network.clientbound.ClientboundNoxesiumPacket;
 import com.noxcrew.noxesium.network.clientbound.ClientboundResetPacket;
 import com.noxcrew.noxesium.network.clientbound.ClientboundResetServerRulesPacket;
+import com.noxcrew.noxesium.network.clientbound.ClientboundServerInformationPacket;
 import com.noxcrew.noxesium.network.serverbound.ServerboundClientInformationPacket;
 import com.noxcrew.noxesium.network.serverbound.ServerboundNoxesiumPacket;
 import net.fabricmc.fabric.api.client.networking.v1.ClientPlayNetworking;
@@ -39,6 +40,7 @@ public class NoxesiumPackets {
     public static final PacketType<ClientboundChangeServerRulesPacket> CLIENT_CHANGE_SERVER_RULES = client("change_server_rules", ClientboundChangeServerRulesPacket::new);
     public static final PacketType<ClientboundResetServerRulesPacket> CLIENT_RESET_SERVER_RULES = client("reset_server_rules", ClientboundResetServerRulesPacket::new);
     public static final PacketType<ClientboundResetPacket> CLIENT_RESET = client("reset", ClientboundResetPacket::new);
+    public static final PacketType<ClientboundServerInformationPacket> CLIENT_SERVER_INFO = client("server_info", ClientboundServerInformationPacket::new);
 
     public static final PacketType<ServerboundClientInformationPacket> SERVER_CLIENT_INFO = server("client_info");
     public static final PacketType<ServerboundClientInformationPacket> SERVER_CLIENT_SETTINGS = server("client_settings");

fabric/src/main/java/com/noxcrew/noxesium/network/clientbound/ClientboundServerInformationPacket.java

@@ -0,0 +1,36 @@
+package com.noxcrew.noxesium.network.clientbound;
+
+import com.noxcrew.noxesium.NoxesiumMod;
+import com.noxcrew.noxesium.network.NoxesiumPackets;
+import com.noxcrew.noxesium.network.serverbound.ServerboundNoxesiumPacket;
+import net.fabricmc.fabric.api.networking.v1.PacketSender;
+import net.fabricmc.fabric.api.networking.v1.PacketType;
+import net.minecraft.client.player.LocalPlayer;
+import net.minecraft.network.FriendlyByteBuf;
+
+/**
+ * Sent to the client when the server is first informed of it existing, this contains information
+ * about what protocol version the server supports.
+ */
+public class ClientboundServerInformationPacket extends ClientboundNoxesiumPacket {
+
+    private final int maxProtocolVersion;
+
+    public ClientboundServerInformationPacket(FriendlyByteBuf buf) {
+        super(buf.readVarInt());
+        this.maxProtocolVersion = buf.readVarInt();
+    }
+
+    @Override
+    public void receive(LocalPlayer player, PacketSender responseSender) {
+        // Whenever the server sends information about the supported protocol version we store
+        // that and can use it to downgrade server-side packets based on the newest version
+        // that can be sent.
+        NoxesiumMod.setServerVersion(maxProtocolVersion);
+    }
+
+    @Override
+    public PacketType<?> getType() {
+        return NoxesiumPackets.CLIENT_SERVER_INFO;
+    }
+}

fabric/src/main/java/com/noxcrew/noxesium/network/serverbound/ServerboundNoxesiumPacket.java

@@ -1,5 +1,6 @@
 package com.noxcrew.noxesium.network.serverbound;
 
+import com.noxcrew.noxesium.NoxesiumMod;
 import com.noxcrew.noxesium.network.NoxesiumPacket;
 import com.noxcrew.noxesium.network.NoxesiumPackets;
 import net.fabricmc.fabric.api.client.networking.v1.ClientPlayNetworking;
@@ -12,21 +13,20 @@
 public abstract class ServerboundNoxesiumPacket extends NoxesiumPacket {
 
     /**
-     * Creates a new serverbound Noxesium packet with the given version.
+     * Creates a new serverbound Noxesium packet with the given latest version.
      *
-     * @param version The version of this packet, this is always
-     *                the first varint of any Noxesium packet and
-     *                allows the contents of packets to change
-     *                over time without much issue.
+     * @param latestVersion The latest version of this packet, this is always
+     *                      the first varint of any Noxesium packet and
+     *                      allows the contents of packets to change
+     *                      over time without much issue.
      */
-    public ServerboundNoxesiumPacket(int version) {
-        super(version);
+    public ServerboundNoxesiumPacket(int latestVersion) {
+        super(latestVersion);
     }
 
     @Override
     public final void write(FriendlyByteBuf buf) {
-        buf.writeVarInt(version);
-        serialize(buf);
+        throw new UnsupportedOperationException("Cannot directly write a ServerboundNoxesiumPacket, use send()");
     }
 
     /**
@@ -37,13 +37,23 @@ public final void write(FriendlyByteBuf buf) {
      */
     public abstract void serialize(FriendlyByteBuf buffer);
 
+    /**
+     * Returns the maximum packet version this packet should be serialized
+     * as based on the given protocol version. This is the protocol version
+     * used by the server, e.g. if this is 3 and the packet being serialized
+     * was v1 until protocol 4 and v2 after then this should return 1.
+     */
+    public int getVersion(int protocolVersion) {
+        return version;
+    }
+
     /**
      * Writes this packet into the given buffer as the selected legacy version.
      *
      * @param version The version to serialize this packet as, it is guaranteed to be
      *                below the version of the packet.
-     * @param buffer The buffer to serialize to, the intended version varint has already
-     *               been written.
+     * @param buffer  The buffer to serialize to, the intended version varint has already
+     *                been written.
      */
     public void legacySerialize(int version, FriendlyByteBuf buffer) {
         throw new UnsupportedOperationException("Packet " + getClass().getSimpleName() + " does not support legacy serialization as version version");
@@ -56,12 +66,17 @@ public void legacySerialize(int version, FriendlyByteBuf buffer) {
     public boolean send() {
         // We assume the server indicates which packets it wishes to receive, otherwise we do not send anything.
         if (ClientPlayNetworking.canSend(getType()) && NoxesiumPackets.canSend(getType())) {
-            // TODO Determine the latest protocol version the server has indicated it supports and
-            // possibly use legacy serialization!
+            var maxProtocol = NoxesiumMod.getMaxProtocolVersion();
+            var maxVersion = getVersion(maxProtocol);
 
             var buffer = PacketByteBufs.create();
-            buffer.writeVarInt(version);
-            serialize(buffer);
+            if (maxVersion >= version) {
+                buffer.writeVarInt(version);
+                serialize(buffer);
+            } else {
+                buffer.writeInt(maxVersion);
+                legacySerialize(maxVersion, buffer);
+            }
             ClientPlayNetworking.send(getType().getId(), buffer);
             return true;
         }