Net Handshake phase 1. Validates pairings on client and server.

build.gradle

@@ -87,6 +87,7 @@ project(':forge') {
                 target: 'fmldevserver'
             ]
         }
+        mcVersion = '1.13'
     }
     applyPatches {
         canonicalizeAccess true

patches/minecraft/net/minecraft/item/Item.java.patch

@@ -60,7 +60,7 @@
        float f7 = f2 * f4;
 -      double d3 = 5.0D;
 -      Vec3d vec3d1 = vec3d.add((double)f6 * 5.0D, (double)f5 * 5.0D, (double)f7 * 5.0D);
-+      double d3 = playerIn.getEntityAttribute(EntityPlayer.REACH_DISTANCE).getAttributeValue();
++      double d3 = 6;
 +      Vec3d vec3d1 = vec3d.add((double)f6 * d3, (double)f5 * d3, (double)f7 * d3);
        return worldIn.func_200259_a(vec3d, vec3d1, useLiquids ? RayTraceFluidMode.SOURCE_ONLY : RayTraceFluidMode.NEVER, false, false);
     }

src/main/java/net/minecraftforge/fml/network/FMLHandshakeMessage.java

@@ -0,0 +1,89 @@
+package net.minecraftforge.fml.network;
+
+import net.minecraft.nbt.INBTBase;
+import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.nbt.NBTTagList;
+import net.minecraft.nbt.NBTTagString;
+import net.minecraft.network.PacketBuffer;
+import net.minecraftforge.fml.ModList;
+import net.minecraftforge.fml.loading.moddiscovery.ModInfo;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+class FMLHandshakeMessage
+{
+    // Login index sequence number
+    private int index;
+    void setPacketIndexSequence(int i)
+    {
+        this.index = i;
+    }
+
+    int getPacketIndexSequence()
+    {
+        return index;
+    }
+
+    /**
+     * Server to client "list of mods". Always first handshake message.
+     */
+    static class S2CModList extends FMLHandshakeMessage
+    {
+        private NBTTagList channels;
+        private List<String> modList;
+
+        S2CModList() {
+            this.modList = ModList.get().getMods().stream().map(ModInfo::getModId).collect(Collectors.toList());
+        }
+
+        S2CModList(NBTTagCompound nbtTagCompound)
+        {
+            this.modList = nbtTagCompound.getTagList("modlist", 8).stream().map(INBTBase::getString).collect(Collectors.toList());
+            this.channels = nbtTagCompound.getTagList("channels", 10);
+        }
+
+        static S2CModList decode(PacketBuffer packetBuffer)
+        {
+            final NBTTagCompound nbtTagCompound = packetBuffer.readCompoundTag();
+            return new S2CModList(nbtTagCompound);
+        }
+
+        void encode(PacketBuffer packetBuffer)
+        {
+            NBTTagCompound tag = new NBTTagCompound();
+            tag.setTag("modlist",modList.stream().map(NBTTagString::new).collect(Collectors.toCollection(NBTTagList::new)));
+            tag.setTag("channels", NetworkRegistry.buildChannelVersions());
+            packetBuffer.writeCompoundTag(tag);
+        }
+
+        String getModList() {
+            return String.join(",", modList);
+        }
+
+        NBTTagList getChannels() {
+            return this.channels;
+        }
+    }
+
+    static class C2SModListReply extends S2CModList
+    {
+        C2SModListReply() {
+            super();
+        }
+
+        C2SModListReply(final NBTTagCompound buffer) {
+            super(buffer);
+        }
+
+        static C2SModListReply decode(PacketBuffer buffer)
+        {
+            return new C2SModListReply(buffer.readCompoundTag());
+        }
+
+        public void encode(PacketBuffer buffer)
+        {
+            super.encode(buffer);
+        }
+    }
+}

src/main/java/net/minecraftforge/fml/network/FMLNetworking.java

@@ -1,14 +1,9 @@
 package net.minecraftforge.fml.network;
 
 import io.netty.util.AttributeKey;
-import net.minecraft.nbt.INBTBase;
-import net.minecraft.nbt.NBTTagCompound;
-import net.minecraft.nbt.NBTTagList;
-import net.minecraft.nbt.NBTTagString;
 import net.minecraft.network.NetworkManager;
-import net.minecraft.network.PacketBuffer;
+import net.minecraft.util.text.ITextComponent;
-import net.minecraftforge.fml.ModList;
+import net.minecraft.util.text.TextComponentString;
-import net.minecraftforge.fml.loading.moddiscovery.ModInfo;
 import net.minecraftforge.fml.network.simple.SimpleChannel;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -19,7 +14,6 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
 
 public class FMLNetworking
 {
@@ -49,24 +43,24 @@ public class FMLNetworking
 
     public static class FMLHandshake {
         private static SimpleChannel channel;
-        private static List<Supplier<HandshakeMessage>> messages = Arrays.asList(HandshakeMessage.S2CModList::new);
+        private static List<Supplier<FMLHandshakeMessage>> messages = Arrays.asList(FMLHandshakeMessage.S2CModList::new);
-        private List<HandshakeMessage> sentMessages = new ArrayList<>();
+        private List<FMLHandshakeMessage> sentMessages = new ArrayList<>();
         static {
             channel = NetworkRegistry.ChannelBuilder.named(NetworkHooks.FMLHANDSHAKE).
                     clientAcceptedVersions(a -> true).
                     serverAcceptedVersions(a -> true).
                     networkProtocolVersion(() -> NetworkHooks.NETVERSION).
                     simpleChannel();
-            channel.messageBuilder(HandshakeMessage.S2CModList.class, 1).
+            channel.messageBuilder(FMLHandshakeMessage.S2CModList.class, 1).
-                    decoder(HandshakeMessage.S2CModList::decode).
+                    decoder(FMLHandshakeMessage.S2CModList::decode).
-                    encoder(HandshakeMessage.S2CModList::encode).
+                    encoder(FMLHandshakeMessage.S2CModList::encode).
-                    loginIndex(HandshakeMessage.S2CModList::setPacketIndexSequence).
+                    loginIndex(FMLHandshakeMessage::getPacketIndexSequence, FMLHandshakeMessage::setPacketIndexSequence).
                     consumer((m,c)->getHandshake(c).handleServerModListOnClient(m, c)).
                     add();
-            channel.messageBuilder(HandshakeMessage.C2SModListReply.class, 2).
+            channel.messageBuilder(FMLHandshakeMessage.C2SModListReply.class, 2).
-                    loginIndex(HandshakeMessage::setPacketIndexSequence).
+                    loginIndex(FMLHandshakeMessage::getPacketIndexSequence, FMLHandshakeMessage::setPacketIndexSequence).
-                    decoder(HandshakeMessage.C2SModListReply::decode).
+                    decoder(FMLHandshakeMessage.C2SModListReply::decode).
-                    encoder(HandshakeMessage.C2SModListReply::encode).
+                    encoder(FMLHandshakeMessage.C2SModListReply::encode).
                     consumer((m,c) -> getHandshake(c).handleClientModListOnServer(m,c)).
                     add();
         }
@@ -82,30 +76,63 @@ public class FMLNetworking
             this.manager = networkManager;
         }
 
-        public void handleServerModListOnClient(HandshakeMessage.S2CModList serverModList, Supplier<NetworkEvent.Context> c)
+        private void handleServerModListOnClient(FMLHandshakeMessage.S2CModList serverModList, Supplier<NetworkEvent.Context> c)
         {
-            LOGGER.debug(FMLHSMARKER, "Received S2CModList packet with index {}", serverModList.getPacketIndexSequence());
+            LOGGER.debug(FMLHSMARKER, "Logging into server with mod list [{}]", serverModList.getModList());
+            boolean accepted = NetworkRegistry.validateClientChannels(serverModList.getChannels());
             c.get().setPacketHandled(true);
-            final HandshakeMessage.C2SModListReply reply = new HandshakeMessage.C2SModListReply();
+            if (!accepted) {
-            channel.sendLogin(reply, c.get().getNetworkManager(), c.get().getDirection().reply(), reply.getPacketIndexSequence());
+                LOGGER.error(FMLHSMARKER, "Terminating connection with server, mismatched mod list");
+                c.get().getNetworkManager().closeChannel(new TextComponentString("Connection closed - mismatched mod channel list"));
+                return;
+            }
+            final FMLHandshakeMessage.C2SModListReply reply = new FMLHandshakeMessage.C2SModListReply();
+            reply.setPacketIndexSequence(serverModList.getPacketIndexSequence());
+            channel.reply(reply, c.get());
             LOGGER.debug(FMLHSMARKER, "Sent C2SModListReply packet with index {}", reply.getPacketIndexSequence());
         }
 
-        private void handleClientModListOnServer(HandshakeMessage.C2SModListReply m, Supplier<NetworkEvent.Context> c)
+        private void handleClientModListOnServer(FMLHandshakeMessage.C2SModListReply clientModList, Supplier<NetworkEvent.Context> c)
         {
-            LOGGER.debug(FMLHSMARKER, "Received C2SModListReply with index {}", m.getPacketIndexSequence());
+            LOGGER.debug(FMLHSMARKER, "Received client connection with modlist [{}]", clientModList.getModList());
-            final HandshakeMessage message = this.sentMessages.stream().filter(ob -> ob.getPacketIndexSequence() == m.getPacketIndexSequence()).findFirst().orElseThrow(() -> new RuntimeException("Unexpected reply from client"));
+            final FMLHandshakeMessage message = this.sentMessages.stream().filter(ob -> ob.getPacketIndexSequence() == clientModList.getPacketIndexSequence()).findFirst().orElseThrow(() -> new RuntimeException("Unexpected reply from client"));
             boolean removed = this.sentMessages.remove(message);
+            boolean accepted = NetworkRegistry.validateServerChannels(clientModList.getChannels());
             c.get().setPacketHandled(true);
+            if (!accepted) {
+                LOGGER.error(FMLHSMARKER, "Terminating connection with client, mismatched mod list");
+                c.get().getNetworkManager().closeChannel(new TextComponentString("Connection closed - mismatched mod channel list"));
+                return;
+            }
             LOGGER.debug(FMLHSMARKER, "Cleared original message {}", removed);
         }
 
+        /**
+         * Design of handshake.
+         *
+         * After {@link net.minecraft.server.network.NetHandlerLoginServer} enters the {@link net.minecraft.server.network.NetHandlerLoginServer.LoginState#NEGOTIATING}
+         * state, this will be ticked once per server tick.
+         *
+         * FML will send packets, from Server to Client, from the messages queue until the queue is drained. Each message
+         * will be indexed, and placed into the "pending acknowledgement" queue.
+         *
+         * The client should send an acknowledgement for every packet that has a positive index, containing
+         * that index (and maybe other data as well).
+         *
+         * As indexed packets are received at the server, they will be removed from the "pending acknowledgement" queue.
+         *
+         * Once the pending queue is drained, this method returns true - indicating that login processing can proceed to
+         * the next step.
+         *
+         * @return true if there is no more need to tick this login connection.
+         */
         public boolean tickServer()
         {
             if (packetPosition < messages.size()) {
-                final HandshakeMessage message = messages.get(packetPosition).get();
+                final FMLHandshakeMessage message = messages.get(packetPosition).get();
+                message.setPacketIndexSequence(packetPosition);
                 LOGGER.debug(FMLHSMARKER, "Sending ticking packet {} index {}", message.getClass().getName(), message.getPacketIndexSequence());
-                channel.sendLogin(message, this.manager, this.direction, packetPosition);
+                channel.sendTo(message, this.manager, this.direction);
                 sentMessages.add(message);
                 packetPosition++;
             }
@@ -121,57 +148,4 @@ public class FMLNetworking
     }
 
 
-    static class HandshakeMessage
-    {
-        private int index;
-        public void setPacketIndexSequence(int i)
-        {
-            this.index = i;
-        }
-
-        public int getPacketIndexSequence()
-        {
-            return index;
-        }
-
-        static class S2CModList extends HandshakeMessage
-        {
-            private List<String> modList;
-
-            S2CModList() {
-                this.modList = ModList.get().getMods().stream().map(ModInfo::getModId).collect(Collectors.toList());
-            }
-
-            S2CModList(NBTTagCompound nbtTagCompound)
-            {
-                this.modList = nbtTagCompound.getTagList("list", 8).stream().map(INBTBase::getString).collect(Collectors.toList());
-            }
-
-            public static S2CModList decode(PacketBuffer packetBuffer)
-            {
-                final NBTTagCompound nbtTagCompound = packetBuffer.readCompoundTag();
-                return new S2CModList(nbtTagCompound);
-            }
-
-            public void encode(PacketBuffer packetBuffer)
-            {
-                NBTTagCompound tag = new NBTTagCompound();
-                tag.setTag("list",modList.stream().map(NBTTagString::new).collect(Collectors.toCollection(NBTTagList::new)));
-                packetBuffer.writeCompoundTag(tag);
-            }
-        }
-
-        static class C2SModListReply extends HandshakeMessage
-        {
-            public static C2SModListReply decode(PacketBuffer buffer)
-            {
-                return new C2SModListReply();
-            }
-
-            public void encode(PacketBuffer buffer)
-            {
-
-            }
-        }
-    }
 }

src/main/java/net/minecraftforge/fml/network/NetworkDirection.java

@@ -29,6 +29,7 @@ import net.minecraft.network.play.server.SPacketCustomPayload;
 import net.minecraft.util.ResourceLocation;
 import net.minecraftforge.fml.LogicalSide;
 import net.minecraftforge.fml.UnsafeHacks;
+import org.apache.commons.lang3.tuple.Pair;
 
 import java.util.function.BiFunction;
 import java.util.function.Function;
@@ -84,12 +85,12 @@ public enum NetworkDirection
     }
 
     @SuppressWarnings("unchecked")
-    public <T extends Packet<?>> ICustomPacket<T> buildPacket(PacketBuffer packetBuffer, ResourceLocation channelName, int index)
+    public <T extends Packet<?>> ICustomPacket<T> buildPacket(Pair<PacketBuffer,Integer> packetData, ResourceLocation channelName)
     {
         ICustomPacket<T> packet = (ICustomPacket<T>)UnsafeHacks.newInstance(getPacketClass());
         packet.setName(channelName);
-        packet.setData(packetBuffer);
+        packet.setData(packetData.getLeft());
-        packet.setIndex(index);
+        packet.setIndex(packetData.getRight());
         return packet;
     }
 }

src/main/java/net/minecraftforge/fml/network/NetworkEvent.java

@@ -32,10 +32,13 @@ public class NetworkEvent extends Event
 {
     private final PacketBuffer payload;
     private final Supplier<Context> source;
-    private NetworkEvent(ICustomPacket<?> payload, Supplier<Context> source)
+    private final int loginIndex;
+
+    private NetworkEvent(final ICustomPacket<?> payload, final Supplier<Context> source)
     {
         this.payload = payload.getData();
         this.source = source;
+        this.loginIndex = payload.getIndex();
     }
 
     public PacketBuffer getPayload()
@@ -48,9 +51,13 @@ public class NetworkEvent extends Event
         return source;
     }
 
+    public int getLoginIndex()
+    {
+        return loginIndex;
+    }
+
     public static class ServerCustomPayloadEvent extends NetworkEvent
     {
-
         ServerCustomPayloadEvent(final ICustomPacket<?> payload, final Supplier<Context> source) {
             super(payload, source);
         }
@@ -61,39 +68,20 @@ public class NetworkEvent extends Event
             super(payload, source);
         }
     }
-    public static class ServerCustomPayloadLoginEvent extends ServerCustomPayloadEvent implements ILoginIndex {
+    public static class ServerCustomPayloadLoginEvent extends ServerCustomPayloadEvent {
-        private final int index;
-
         ServerCustomPayloadLoginEvent(ICustomPacket<?> payload, Supplier<Context> source)
         {
             super(payload, source);
-            this.index = payload.getIndex();
-        }
-
-        public int getIndex()
-        {
-            return index;
         }
     }
 
-    public static class ClientCustomPayloadLoginEvent extends ClientCustomPayloadEvent implements ILoginIndex {
+    public static class ClientCustomPayloadLoginEvent extends ClientCustomPayloadEvent {
-        private final int index;
-
         ClientCustomPayloadLoginEvent(ICustomPacket<?> payload, Supplier<Context> source)
         {
             super(payload, source);
-            this.index = payload.getIndex();
-        }
-
-        public int getIndex()
-        {
-            return index;
         }
     }
 
-    public interface ILoginIndex {
-        int getIndex();
-    }
     /**
      * Context for {@link NetworkEvent}
      */

src/main/java/net/minecraftforge/fml/network/NetworkInstance.java

@@ -19,6 +19,7 @@
 
 package net.minecraftforge.fml.network;
 
+import net.minecraft.nbt.INBTBase;
 import net.minecraft.network.NetworkManager;
 import net.minecraft.network.PacketBuffer;
 import net.minecraft.util.ResourceLocation;
@@ -38,7 +39,7 @@ public class NetworkInstance
     }
 
     private final ResourceLocation channelName;
-    private final Supplier<String> networkProtocolVersion;
+    private final String networkProtocolVersion;
     private final Predicate<String> clientAcceptedVersions;
     private final Predicate<String> serverAcceptedVersions;
     private final IEventBus networkEventBus;
@@ -46,7 +47,7 @@ public class NetworkInstance
     NetworkInstance(ResourceLocation channelName, Supplier<String> networkProtocolVersion, Predicate<String> clientAcceptedVersions, Predicate<String> serverAcceptedVersions)
     {
         this.channelName = channelName;
-        this.networkProtocolVersion = networkProtocolVersion;
+        this.networkProtocolVersion = networkProtocolVersion.get();
         this.clientAcceptedVersions = clientAcceptedVersions;
         this.serverAcceptedVersions = serverAcceptedVersions;
         this.networkEventBus = IEventBus.create(this::handleError);
@@ -78,4 +79,15 @@ public class NetworkInstance
     }
 
 
+    String getNetworkProtocolVersion() {
+        return networkProtocolVersion;
+    }
+
+    boolean tryServerVersionOnClient(final String serverVersion) {
+        return this.clientAcceptedVersions.test(serverVersion);
+    }
+
+    boolean tryClientVersionOnServer(final String clientVersion) {
+        return this.serverAcceptedVersions.test(clientVersion);
+    }
 }

src/main/java/net/minecraftforge/fml/network/NetworkRegistry.java

@@ -19,10 +19,12 @@
 
 package net.minecraftforge.fml.network;
 
-import io.netty.util.AttributeKey;
+import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.nbt.NBTTagList;
 import net.minecraft.util.ResourceLocation;
 import net.minecraftforge.fml.network.event.EventNetworkChannel;
 import net.minecraftforge.fml.network.simple.SimpleChannel;
+import org.apache.commons.lang3.tuple.Pair;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.Marker;
@@ -35,6 +37,7 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 public class NetworkRegistry
 {
@@ -71,6 +74,53 @@ public class NetworkRegistry
         return Optional.ofNullable(instances.get(resourceLocation));
     }
 
+    static NBTTagList buildChannelVersions() {
+        return instances.entrySet().stream().map(e-> {
+            final NBTTagCompound tag = new NBTTagCompound();
+            tag.setString("name", e.getKey().toString());
+            tag.setString("version", e.getValue().getNetworkProtocolVersion());
+            return tag;
+        }).collect(Collectors.toCollection(NBTTagList::new));
+    }
+
+    static boolean validateClientChannels(final NBTTagList channels) {
+        final List<Pair<ResourceLocation, Boolean>> results = channels.stream().map(t -> {
+            NBTTagCompound tag = (NBTTagCompound) t;
+            final ResourceLocation rl = new ResourceLocation(tag.getString("name"));
+            final String serverVersion = tag.getString("version");
+            boolean test = instances.get(rl).tryServerVersionOnClient(serverVersion);
+            LOGGER.debug(NETREGISTRY, "Channel {} : Client version test of ''{}'' from server : {}", rl, serverVersion, test);
+            return Pair.of(rl, test);
+        }).filter(p->!p.getRight()).collect(Collectors.toList());
+
+        if (!results.isEmpty()) {
+            LOGGER.error(NETREGISTRY, "Channels [{}] rejected their server side version number",
+                    results.stream().map(Pair::getLeft).map(Object::toString).collect(Collectors.joining(",")));
+            return false;
+        }
+        LOGGER.debug(NETREGISTRY, "Accepting channel list from server");
+        return true;
+    }
+
+    static boolean validateServerChannels(final NBTTagList channels) {
+        final List<Pair<ResourceLocation, Boolean>> results = channels.stream().map(t -> {
+            NBTTagCompound tag = (NBTTagCompound) t;
+            final ResourceLocation rl = new ResourceLocation(tag.getString("name"));
+            final String clientVersion = tag.getString("version");
+            boolean test = instances.get(rl).tryClientVersionOnServer(clientVersion);
+            LOGGER.debug(NETREGISTRY, "Channel {} : Server version test of ''{}'' from client : {}", rl, clientVersion, test);
+            return Pair.of(rl, test);
+        }).filter(p->!p.getRight()).collect(Collectors.toList());
+
+        if (!results.isEmpty()) {
+            LOGGER.error(NETREGISTRY, "Channels [{}] rejected their client side version number",
+                    results.stream().map(Pair::getLeft).map(Object::toString).collect(Collectors.joining(",")));
+            return false;
+        }
+        LOGGER.debug(NETREGISTRY, "Accepting channel list from client");
+        return true;
+    }
+
     public static class ChannelBuilder {
         private ResourceLocation channelName;
         private Supplier<String> networkProtocolVersion;

src/main/java/net/minecraftforge/fml/network/simple/IndexedMessageCodec.java

@@ -21,9 +21,7 @@ package net.minecraftforge.fml.network.simple;
 
 import it.unimi.dsi.fastutil.objects.Object2ObjectArrayMap;
 import it.unimi.dsi.fastutil.shorts.Short2ObjectArrayMap;
-import net.minecraft.network.Packet;
 import net.minecraft.network.PacketBuffer;
-import net.minecraftforge.fml.network.ICustomPacket;
 import net.minecraftforge.fml.network.NetworkEvent;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -32,7 +30,6 @@ import org.apache.logging.log4j.MarkerManager;
 
 import java.util.Optional;
 import java.util.function.BiConsumer;
-import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.function.Supplier;
 
@@ -40,69 +37,86 @@ public class IndexedMessageCodec
 {
     private static final Logger LOGGER = LogManager.getLogger();
     private static final Marker SIMPLENET = MarkerManager.getMarker("SIMPLENET");
-    private final Short2ObjectArrayMap<CodecIndex<?>> indicies = new Short2ObjectArrayMap<>();
+    private final Short2ObjectArrayMap<MessageHandler<?>> indicies = new Short2ObjectArrayMap<>();
-    private final Object2ObjectArrayMap<Class<?>, CodecIndex<?>> types = new Object2ObjectArrayMap<>();
+    private final Object2ObjectArrayMap<Class<?>, MessageHandler<?>> types = new Object2ObjectArrayMap<>();
+
+    @SuppressWarnings("unchecked")
+    public <MSG> MessageHandler<MSG> findMessageType(final MSG msgToReply) {
+        return (MessageHandler<MSG>) types.get(msgToReply.getClass());
+    }
 
     @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
-    public class CodecIndex<MSG>
+    class MessageHandler<MSG>
     {
-
         private final Optional<BiConsumer<MSG, PacketBuffer>> encoder;
         private final Optional<Function<PacketBuffer, MSG>> decoder;
         private final int index;
         private final BiConsumer<MSG,Supplier<NetworkEvent.Context>> messageConsumer;
         private final Class<MSG> messageType;
-        private Optional<BiConsumer<MSG, Integer>> loginIndexFunction;
+        private Optional<BiConsumer<MSG, Integer>> loginIndexSetter;
+        private Optional<Function<MSG, Integer>> loginIndexGetter;
 
-        public CodecIndex(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer)
+        public MessageHandler(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer)
         {
             this.index = index;
             this.messageType = messageType;
             this.encoder = Optional.ofNullable(encoder);
             this.decoder = Optional.ofNullable(decoder);
             this.messageConsumer = messageConsumer;
-            this.loginIndexFunction = Optional.empty();
+            this.loginIndexGetter = Optional.empty();
+            this.loginIndexSetter = Optional.empty();
             indicies.put((short)(index & 0xff), this);
             types.put(messageType, this);
         }
 
-        public void setLoginIndexFunction(BiConsumer<MSG, Integer> loginIndexFunction)
+        void setLoginIndexSetter(BiConsumer<MSG, Integer> loginIndexSetter)
         {
-            this.loginIndexFunction = Optional.of(loginIndexFunction);
+            this.loginIndexSetter = Optional.of(loginIndexSetter);
         }
 
-        public Optional<BiConsumer<MSG, Integer>> getLoginIndexFunction() {
+        Optional<BiConsumer<MSG, Integer>> getLoginIndexSetter() {
-            return this.loginIndexFunction;
+            return this.loginIndexSetter;
+        }
+
+        void setLoginIndexGetter(Function<MSG, Integer> loginIndexGetter) {
+            this.loginIndexGetter = Optional.of(loginIndexGetter);
+        }
+
+        public Optional<Function<MSG, Integer>> getLoginIndexGetter() {
+            return this.loginIndexGetter;
         }
     }
-    private static <M> void tryDecode(PacketBuffer payload, Supplier<NetworkEvent.Context> context, CodecIndex<M> codec)
-    {
-        codec.decoder.map(d->d.apply(payload)).ifPresent(m->codec.messageConsumer.accept(m, context));
-    }
 
-    private static <M> void tryDecode(PacketBuffer payload, Supplier<NetworkEvent.Context> context, int payloadIndex, CodecIndex<M> codec)
+    private static <M> void tryDecode(PacketBuffer payload, Supplier<NetworkEvent.Context> context, int payloadIndex, MessageHandler<M> codec)
     {
         codec.decoder.map(d->d.apply(payload)).
-                map(p->{ codec.getLoginIndexFunction().ifPresent(f-> f.accept(p, payloadIndex)); return p; }).
+                map(p->{
-                ifPresent(m->codec.messageConsumer.accept(m, context));
+                    // Only run the loginIndex function for payloadIndexed packets (login)
+                    if (payloadIndex != Integer.MIN_VALUE)
+                    {
+                        codec.getLoginIndexSetter().ifPresent(f-> f.accept(p, payloadIndex));
+                    }
+                    return p;
+                }).ifPresent(m->codec.messageConsumer.accept(m, context));
     }
 
-    private static <M> void tryEncode(PacketBuffer target, M message, CodecIndex<M> codec) {
+    private static <M> int tryEncode(PacketBuffer target, M message, MessageHandler<M> codec) {
         codec.encoder.ifPresent(encoder->{
             target.writeByte(codec.index & 0xff);
             encoder.accept(message, target);
         });
+        return codec.loginIndexGetter.orElse(m -> Integer.MIN_VALUE).apply(message);
     }
 
-    public <MSG> void build(MSG message, PacketBuffer target)
+    public <MSG> int build(MSG message, PacketBuffer target)
     {
         @SuppressWarnings("unchecked")
-        CodecIndex<MSG> codecIndex = (CodecIndex<MSG>)types.get(message.getClass());
+        MessageHandler<MSG> messageHandler = (MessageHandler<MSG>)types.get(message.getClass());
-        if (codecIndex == null) {
+        if (messageHandler == null) {
             LOGGER.error(SIMPLENET, "Received invalid message {}", message.getClass().getName());
             throw new IllegalArgumentException("Invalid message "+message.getClass().getName());
         }
-        tryEncode(target, message, codecIndex);
+        return tryEncode(target, message, messageHandler);
     }
 
     void consume(PacketBuffer payload, int payloadIndex, Supplier<NetworkEvent.Context> context) {
@@ -111,30 +125,15 @@ public class IndexedMessageCodec
             return;
         }
         short discriminator = payload.readUnsignedByte();
-        final CodecIndex<?> codecIndex = indicies.get(discriminator);
+        final MessageHandler<?> messageHandler = indicies.get(discriminator);
-        if (codecIndex == null) {
+        if (messageHandler == null) {
             LOGGER.error(SIMPLENET, "Received invalid discriminator byte {}", discriminator);
             return;
         }
-        tryDecode(payload, context, payloadIndex, codecIndex);
+        tryDecode(payload, context, payloadIndex, messageHandler);
     }
 
-    void consume(PacketBuffer payload, Supplier<NetworkEvent.Context> context) {
+    <MSG> MessageHandler<MSG> addCodecIndex(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer) {
-        // no data in empty payload
+        return new MessageHandler<>(index, messageType, encoder, decoder, messageConsumer);
-        if (payload == null) {
-            LOGGER.error(SIMPLENET, "Received empty payload");
-            return;
-        }
-        short discriminator = payload.readUnsignedByte();
-        final CodecIndex<?> codecIndex = indicies.get(discriminator);
-        if (codecIndex == null) {
-            LOGGER.error(SIMPLENET, "Received invalid discriminator byte {}", discriminator);
-            return;
-        }
-        tryDecode(payload, context, codecIndex);
-    }
-
-    <MSG> CodecIndex<MSG> addCodecIndex(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer) {
-        return new CodecIndex<>(index, messageType, encoder, decoder, messageConsumer);
     }
 }

src/main/java/net/minecraftforge/fml/network/simple/SimpleChannel.java

@@ -24,18 +24,14 @@ import net.minecraft.client.Minecraft;
 import net.minecraft.network.NetworkManager;
 import net.minecraft.network.Packet;
 import net.minecraft.network.PacketBuffer;
-import net.minecraft.network.play.client.CPacketCustomPayload;
 import net.minecraftforge.fml.network.ICustomPacket;
 import net.minecraftforge.fml.network.NetworkDirection;
 import net.minecraftforge.fml.network.NetworkEvent;
 import net.minecraftforge.fml.network.NetworkInstance;
+import org.apache.commons.lang3.tuple.Pair;
 
 import java.util.function.BiConsumer;
-import java.util.function.BinaryOperator;
 import java.util.function.Function;
-import java.util.function.IntBinaryOperator;
-import java.util.function.IntConsumer;
-import java.util.function.IntFunction;
 import java.util.function.Supplier;
 
 public class SimpleChannel
@@ -52,42 +48,38 @@ public class SimpleChannel
 
     private void networkEventListener(final NetworkEvent networkEvent)
     {
-        if (networkEvent instanceof NetworkEvent.ILoginIndex)
+        this.indexedCodec.consume(networkEvent.getPayload(), networkEvent.getLoginIndex(), networkEvent.getSource());
-        {
-            this.indexedCodec.consume(networkEvent.getPayload(), ((NetworkEvent.ILoginIndex)networkEvent).getIndex(), networkEvent.getSource());
-        }
-        else
-        {
-            this.indexedCodec.consume(networkEvent.getPayload(), networkEvent.getSource());
-        }
     }
 
-    public <MSG> void encodeMessage(MSG message, final PacketBuffer target) {
+    public <MSG> int encodeMessage(MSG message, final PacketBuffer target) {
-        this.indexedCodec.build(message, target);
+        return this.indexedCodec.build(message, target);
     }
-    public <MSG> IndexedMessageCodec.CodecIndex<MSG> registerMessage(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer) {
+    public <MSG> IndexedMessageCodec.MessageHandler<MSG> registerMessage(int index, Class<MSG> messageType, BiConsumer<MSG, PacketBuffer> encoder, Function<PacketBuffer, MSG> decoder, BiConsumer<MSG, Supplier<NetworkEvent.Context>> messageConsumer) {
         return this.indexedCodec.addCodecIndex(index, messageType, encoder, decoder, messageConsumer);
     }
 
-    private <MSG> PacketBuffer toBuffer(MSG msg) {
+    private <MSG> Pair<PacketBuffer,Integer> toBuffer(MSG msg) {
         final PacketBuffer bufIn = new PacketBuffer(Unpooled.buffer());
-        encodeMessage(msg, bufIn);
+        int index = encodeMessage(msg, bufIn);
-        return bufIn;
+        return Pair.of(bufIn, index);
     }
+
     public <MSG> void sendToServer(MSG message)
     {
         sendTo(message, Minecraft.getMinecraft().getConnection().getNetworkManager(), NetworkDirection.PLAY_TO_SERVER);
     }
 
-    public <MSG> void sendTo(MSG message, NetworkManager manager, NetworkDirection direction) {
+    public <MSG> void sendTo(MSG message, NetworkManager manager, NetworkDirection direction)
-        ICustomPacket<Packet<?>> payload = direction.buildPacket(toBuffer(message), instance.getChannelName(), -1);
+    {
+        ICustomPacket<Packet<?>> payload = direction.buildPacket(toBuffer(message), instance.getChannelName());
         manager.sendPacket(payload.getThis());
     }
 
-    public <MSG> void sendLogin(MSG message, NetworkManager manager, NetworkDirection direction, int packetIndex) {
+    public <MSG> void reply(MSG msgToReply, NetworkEvent.Context context)
-        ICustomPacket<Packet<?>> payload = direction.buildPacket(toBuffer(message), instance.getChannelName(), packetIndex);
+    {
-        manager.sendPacket(payload.getThis());
+        sendTo(msgToReply, context.getNetworkManager(), context.getDirection().reply());
     }
+
     public <M> MessageBuilder<M> messageBuilder(final Class<M> type, int id) {
         return MessageBuilder.forType(this, type, id);
     }
@@ -99,7 +91,8 @@ public class SimpleChannel
         private BiConsumer<MSG, PacketBuffer> encoder;
         private Function<PacketBuffer, MSG> decoder;
         private BiConsumer<MSG, Supplier<NetworkEvent.Context>> consumer;
-        private BiConsumer<MSG, Integer> loginIndexFunction;
+        private Function<MSG, Integer> loginIndexGetter;
+        private BiConsumer<MSG, Integer> loginIndexSetter;
 
         private static <MSG> MessageBuilder<MSG> forType(final SimpleChannel channel, final Class<MSG> type, int id) {
             MessageBuilder<MSG> builder = new MessageBuilder<>();
@@ -119,8 +112,9 @@ public class SimpleChannel
             return this;
         }
 
-        public MessageBuilder<MSG> loginIndex(BiConsumer<MSG, Integer> loginIndexFunction) {
+        public MessageBuilder<MSG> loginIndex(Function<MSG, Integer> loginIndexGetter, BiConsumer<MSG, Integer> loginIndexSetter) {
-            this.loginIndexFunction = loginIndexFunction;
+            this.loginIndexGetter = loginIndexGetter;
+            this.loginIndexSetter = loginIndexSetter;
             return this;
         }
         public MessageBuilder<MSG> consumer(BiConsumer<MSG, Supplier<NetworkEvent.Context>> consumer) {
@@ -129,9 +123,12 @@ public class SimpleChannel
         }
 
         public void add() {
-            final IndexedMessageCodec.CodecIndex<MSG> message = this.channel.registerMessage(this.id, this.type, this.encoder, this.decoder, this.consumer);
+            final IndexedMessageCodec.MessageHandler<MSG> message = this.channel.registerMessage(this.id, this.type, this.encoder, this.decoder, this.consumer);
-            if (this.loginIndexFunction != null) {
+            if (this.loginIndexSetter != null) {
-                message.setLoginIndexFunction(this.loginIndexFunction);
+                message.setLoginIndexSetter(this.loginIndexSetter);
+            }
+            if (this.loginIndexGetter != null) {
+                message.setLoginIndexGetter(this.loginIndexGetter);
             }
         }
     }