ViaMCP

ViaVersion VersionSwitcher for Minecraft Coder Pack (MCP)

About

If you are interested in the project, or you have issues / suggestions, feel free to join our discord!

Content

• ViaMCP
  • Setup
    • Main-Class
    • NetworkManager
  • Version Control
    • Version Slider
  • Clientside Fixes
    • Attack Order Fixes
    • Block Sound Fixes
    • Transaction Fixes for 1.17+
    • SequenceId Fixes for 1.19+
    • Client Tick Fixes for 1.21.2+
    • New Attributes Fixes for 26.2+
    • Hypixel Join Fix
  • Sending raw packets (e.g 1.9 interactions)
  • Exporting Without JAR Files

Updating notice for the latest version (if you are on ViaVersion 5.9.x or above)

ViaVersion 5.9.0 did some changes to the packet registrations and Protocol API, you need to make sure your codes are being loaded after Via* platforms initiated.

For example

Like you do as this do, after that you need delay the registration or replacement you have implemented.

try {
ViaMCP.create();
// In case you want a version slider like in the Minecraft options, you can use this code here, please choose one of those:ViaMCP.INSTANCE.initAsyncSlider(); // For top left aligned sliderViaMCP.INSTANCE.initAsyncSlider(x, y, width (min. 110), height (recommended20)); // For custom position and size slider// herenewThread(() -> {
try {
Thread.sleep(1000); // Just make sure the viaversions are fully loaded, adjust it depend on your device.
} catch (Throwableignored) {}
ViaMCP.INSTANCE.applyFix(); // Check the bugs you want to fix.
}).start();
} catch (Exceptione) {
e.printStackTrace();
}

Moreover, you have to update your registration code if you ever overrided packets which are already registered in Via* libraries:

// OldfinalProtocol1_17To1_16_4protocol = Via.getManager().getProtocolManager().getProtocol(Protocol1_17To1_16_4.class);
protocol.registerClientbound(ClientboundPackets1_17.PING, ClientboundPackets1_16_2.CONTAINER_ACK, wrapper -> {}, true);
protocol.registerServerbound(ServerboundPackets1_16_2.CONTAINER_ACK, ServerboundPackets1_17.PONG, wrapper -> {}, true);
// NewfinalProtocol1_17To1_16_4protocol = Via.getManager().getProtocolManager().getProtocol(Protocol1_17To1_16_4.class);
protocol.replaceClientbound(ClientboundPackets1_17.PING, wrapper -> {});
protocol.replaceServerbound(ServerboundPackets1_16_2.CONTAINER_ACK, wrapper -> {});

Otherwise, your registration code may be forcely overrided by ViaVersion itself or result in a failure (not working or crash).

Updating notice for existing users (if you are new to ViaMCP, you can ignore this)

ViaVersion 4.10.0 did some changes to the ProtocolVersion API, you have to update your own code if you ever used the ViaLoadingBase class:

// OldViaLoadingBase.getInstance().getTargetVersion().isOlderThan(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().isNewerThan(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().isNewerThanOrEqualTo(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().isOlderThanOrEqualTo(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().getIndex();
// NewViaLoadingBase.getInstance().getTargetVersion().olderThan(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().newerThan(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_8);
ViaLoadingBase.getInstance().getTargetVersion().olderThanOrEqualTo(ProtocolVersion.v1_8);
ViaLoadingBase.PROTOCOLS.indexOf(ViaLoadingBase.getInstance().getTargetVersion());

In addition to that, the ComparableProtocolVersion class has been removed and it's methods have been moved to the ProtocolVersion class.

Setup

Firstly, you will need to add the listed libraries into your dependencies in IntelliJ or Eclipse

Dependencies (Included inside libraries folder)

ViaVersion-[ver]-downgraded.jar > ViaVersion > https://github.com/ViaVersion/ViaVersion
ViaBackwards-[ver]-downgraded.jar > ViaBackwards > https://github.com/ViaVersion/ViaBackwards
ViaRewind-[ver]-downgraded.jar > ViaRewind > https://github.com/ViaVersion/ViaRewind

Secondly, you need to add code that allows you to actually use ViaMCP (Choose the version folder that corresponds with your client version)

For other versions than 1.8.x and 1.12.2, you will need to modify the code to fit your client version. You can see namings for other major versions here

NOTE: ViaVersion 5.0.0+ doesn't support Java 8 anymore, therefore when updating the libraries yourself, you need to download the -Java8 jar files from the ci server or generate them yourself using this tool. If you find the java source files lacking imports, fix it yourself.

Main-Class

Add this to the main class of your client (aka injection function)

try {
ViaMCP.create();
// In case you want a version slider like in the Minecraft options, you can use this code here, please choose one of those:ViaMCP.INSTANCE.initAsyncSlider(); // For top left aligned sliderViaMCP.INSTANCE.initAsyncSlider(x, y, width (min. 110), height (recommended20)); // For custom position and size slider
} catch (Exceptione) {
e.printStackTrace();
}

NetworkManager

You will need to modify 2 methods inside NetworkManager.java

1. Hook ViaVersion into the Netty Pipeline

Find the method, that is func_181124_a, createNetworkManagerAndConnect or contains (Bootstrap)((Bootstrap)((Bootstrap)(new Bootstrap()).group((EventLoopGroup)lazyloadbase.getValue())

Find the vanilla network pipeline call:

// 1.8.x clientp_initChannel_1_.pipeline().addLast((String)"timeout", (ChannelHandler)(newReadTimeoutHandler(30))).addLast((String)"splitter", (ChannelHandler)(newMessageDeserializer2())).addLast((String)"decoder", (ChannelHandler)(newMessageDeserializer(EnumPacketDirection.CLIENTBOUND))).addLast((String)"prepender", (ChannelHandler)(newMessageSerializer2())).addLast((String)"encoder", (ChannelHandler)(newMessageSerializer(EnumPacketDirection.SERVERBOUND))).addLast((String)"packet_handler", (ChannelHandler)networkmanager);
// 1.12.x clientp_initChannel_1_.pipeline().addLast("timeout", newReadTimeoutHandler(30)).addLast("splitter", newNettyVarint21FrameDecoder()).addLast("decoder", newNettyPacketDecoder(EnumPacketDirection.CLIENTBOUND)).addLast("prepender", newNettyVarint21FrameEncoder()).addLast("encoder", newNettyPacketEncoder(EnumPacketDirection.SERVERBOUND)).addLast("packet_handler", networkmanager);

After the vanilla network pipeline call, add the ViaMCP protocol pipeline hook:

if (p_initChannel_1_instanceofSocketChannel && ViaLoadingBase.getInstance().getTargetVersion().getVersion() != ViaMCP.NATIVE_VERSION) {
finalUserConnectionuser = newUserConnectionImpl(p_initChannel_1_, true);
newProtocolPipelineImpl(user);
p_initChannel_1_.pipeline().addLast(newMCPVLBPipeline(user));
}

Your code should look like this afterwards (1.8.x for example), the vanilla network pipeline call should not be commented out and the ViaMCP protocol pipeline hook should be after the vanilla network pipeline call:

p_initChannel_1_.pipeline().addLast((String)"timeout", (ChannelHandler)(newReadTimeoutHandler(30))).addLast((String)"splitter", (ChannelHandler)(newMessageDeserializer2())).addLast((String)"decoder", (ChannelHandler)(newMessageDeserializer(EnumPacketDirection.CLIENTBOUND))).addLast((String)"prepender", (ChannelHandler)(newMessageSerializer2())).addLast((String)"encoder", (ChannelHandler)(newMessageSerializer(EnumPacketDirection.SERVERBOUND))).addLast((String)"packet_handler", (ChannelHandler)networkmanager);
if (p_initChannel_1_instanceofSocketChannel && ViaLoadingBase.getInstance().getTargetVersion().getVersion() != ViaMCP.NATIVE_VERSION) {
finalUserConnectionuser = newUserConnectionImpl(p_initChannel_1_, true);
newProtocolPipelineImpl(user);
p_initChannel_1_.pipeline().addLast(newMCPVLBPipeline(user));
}

Side note: If you want to send custom packets, you have to store the UserConnection instance in a variable for later, it's important that this variable is NOT STATIC since it's also used for pinging servers!

2. Fix the compression in the NetworkManager#setCompressionTreshold function

Simply call the following code at the end of the method in Minecraft:

this.channel.pipeline().fireUserEventTriggered(newCompressionReorderEvent());

Version Control

You will need to add a button to access the protocol switcher (or alternatively use the version slider under this section)
In addSingleplayerMultiplayerButtons() function add (if in GuiMainMenu):

this.buttonList.add(newGuiButton(69, 5, 5, 90, 20, "Version"));

In actionPerformed() function add:

if (button.id == 69)
{
this.mc.displayGuiScreen(newGuiProtocolSelector(this));
}

Version Slider

You can also use a version slider to control ViaMCP versions

this.buttonList.add(ViaMCP.INSTANCE.getAsyncVersionSlider());

Clientside Fixes

Attack Order Fixes

Class: Minecraft.java
Function: clickMouse()

1.8.x
Replace this.thePlayer.swingItem(); on the 1st line in the if-clause with:

AttackOrder.sendConditionalSwing(this.objectMouseOver);

Replace this.playerController.attackEntity(this.thePlayer, this.objectMouseOver.entityHit); in the switch in case ENTITY with:

AttackOrder.sendFixedAttack(this.thePlayer, this.objectMouseOver.entityHit);

Class: EntityPlayerSP.java
Function: swingItem()
Replace this.sendQueue.addToSendQueue(new C0APacketAnimation()); with:

if (ViaLoadingBase.getInstance().getTargetVersion().olderThanOrEqualTo(ProtocolVersion.v1_8)) {
this.sendQueue.addToSendQueue(newC0APacketAnimation());
} else {
AttackOrder.send1_9Animation();
}

1.12.2
Replace this.player.swingArm(EnumHand.MAIN_HAND); at the last line in the else if-clause with:

AttackOrder.sendConditionalSwing(this.objectMouseOver, EnumHand.MAIN_HAND);

Replace this.playerController.attackEntity(this.player, this.objectMouseOver.entityHit); in the switch in case ENTITY with:

AttackOrder.sendFixedAttack(this.thePlayer, this.objectMouseOver.entityHit, EnumHand.MAIN_HAND);

Block Sound Fixes

Block Placement

Replace all code in onItemUse function in the ItemBlock class with:

returnFixedSoundEngine.onItemUse(this, stack, playerIn, worldIn, pos, side, hitX, hitY, hitZ);

Block Breaking

Replace all code in destroyBlock function in the World class with:

returnFixedSoundEngine.destroyBlock(this, pos, dropBlock);

Transaction Fixes for 1.17+

Call the fixTransactions(); in the ViaMCP class file so ViaVersion doesn't remap anything in transaction packets. After that, you need to do some changes in the Game code:

Class: S32PacketConfirmTransaction.java
Function: readPacketData()

Replace the code with this method:

publicvoidreadPacketData(PacketBufferbuf) throwsIOException {
if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_17)) {
this.windowId = buf.readInt();
} else {
this.windowId = buf.readUnsignedByte();
this.actionNumber = buf.readShort();
this.accepted = buf.readBoolean();
}
}

Class: C0FPacketConfirmTransaction.java
Function: writePacketData()

Replace the code with this method:

publicvoidwritePacketData(PacketBufferbuf) throwsIOException {
if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_17)) {
buf.writeInt(this.windowId);
} else {
buf.writeByte(this.windowId);
buf.writeShort(this.uid);
buf.writeByte(this.accepted ? 1 : 0);
}
}

Note: this code can be different depending on your mappings and game version, you just need to make sure it only reads the window id and doesn't read the rest of the packet because we previously removed the ViaVersion handlers which would have handled the rest of the packet.

Class: NetHandlerPlayClient.java
Function: handleConfirmTransaction()

Add this code after the checkThreadAndEnqueue function call:

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_17)) {
this.addToSendQueue(newC0FPacketConfirmTransaction(packetIn.getWindowId(), 0, false));
return;
}

SequenceId Fix for 1.19+

Add the code below to the class PlayerControllerMP / GameMode:

privateintsequenceId;
publicintgetSequenceId() {
return ++this.sequenceId;
}

Then replace the packet code in the functions below:

Function: clickBlock(BlockPos loc, EnumFacing face)
Replace: C07/CPacketPlayerDigging packet on action START_DESTROY_BLOCK

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_19)) {
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_19.PLAYER_ACTION, Via.getManager().getConnectionManager().getConnections().iterator().next());
packet.write(Types.VAR_INT, C07PacketPlayerDigging.Action.START_DESTROY_BLOCK.ordinal());
packet.write(Types.BLOCK_POSITION1_14, newBlockPosition(loc.getX(), loc.getY(), loc.getZ()));
packet.write(Types.BYTE, (byte) face.getIndex());
packet.write(Types.VAR_INT, this.getSequenceId());
packet.sendToServer(Protocol1_19To1_18_2.class);
}

Function: onPlayerDamageBlock(BlockPos posBlock, EnumFacing directionFacing)
Replace: C07/CPacketPlayerDigging packet on action START_DESTROY_BLOCK

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_19)) {
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_19.PLAYER_ACTION, Via.getManager().getConnectionManager().getConnections().iterator().next());
packet.write(Types.VAR_INT, C07PacketPlayerDigging.Action.START_DESTROY_BLOCK.ordinal());
packet.write(Types.BLOCK_POSITION1_14, newBlockPosition(posBlock.getX(), posBlock.getY(), posBlock.getZ()));
packet.write(Types.BYTE, (byte) directionFacing.getIndex());
packet.write(Types.VAR_INT, this.getSequenceId());
packet.sendToServer(Protocol1_19To1_18_2.class);
}

Replace: C07/CPacketPlayerDigging packet on action STOP_DESTROY_BLOCK

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_19)) {
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_19.PLAYER_ACTION, Via.getManager().getConnectionManager().getConnections().iterator().next());
packet.write(Types.VAR_INT, C07PacketPlayerDigging.Action.STOP_DESTROY_BLOCK.ordinal());
packet.write(Types.BLOCK_POSITION1_14, newBlockPosition(posBlock.getX(), posBlock.getY(), posBlock.getZ()));
packet.write(Types.BYTE, (byte) directionFacing.getIndex());
packet.write(Types.VAR_INT, this.getSequenceId());
packet.sendToServer(Protocol1_19To1_18_2.class);
}

Function: onPlayerRightClick(EntityPlayerSP player, WorldClient worldIn, ItemStack heldStack, BlockPos hitPos, EnumFacing side, Vec3 hitVec)
Replace: C08PacketPlayerBlockPlacement/CPacketPlayerBlockPlacement packet send code

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_19)) {
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_19.USE_ITEM_ON, Via.getManager().getConnectionManager().getConnections().iterator().next());
packet.write(Types.VAR_INT, 0);
packet.write(Types.BLOCK_POSITION1_14, newBlockPosition(hitPos.getX(), hitPos.getY(), hitPos.getZ()));
packet.write(Types.VAR_INT, side.ordinal());
packet.write(Types.FLOAT, Float.valueOf(f)); // Change the arg according to your client code.packet.write(Types.FLOAT, Float.valueOf(f1));
packet.write(Types.FLOAT, Float.valueOf(f2));
packet.write(Types.BOOLEAN, false);
packet.write(Types.VAR_INT, this.getSequenceId());
packet.sendToServer(Protocol1_19To1_18_2.class);
}

Function: sendUseItem(EntityPlayer playerIn, World worldIn, ItemStack itemStackIn)
Replace: C08PacketPlayerBlockPlacement/CPacketPlayerBlockPlacement packet send code

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_19)) {
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_19.USE_ITEM, Via.getManager().getConnectionManager().getConnections().iterator().next());
packet.write(Types.VAR_INT, 0);
packet.write(Types.VAR_INT, this.getSequenceId());
packet.sendToServer(Protocol1_19To1_18_2.class);
}

Client Tick Fixes for 1.21.2+

Insert the code below in the end of function runTick() in the class Minecraft:

if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_21_2)) {
UserConnectionconnection = Via.getManager().getConnectionManager().getConnections().iterator().next();
PacketWrapperpacket = PacketWrapper.create(ServerboundPackets1_21_2.CLIENT_TICK_END, null, connection);
packet.sendToServer(Protocol1_21_2To1_21.class);
}

New Attributes Fix for 26.2+

Since it's not allowed to share any minecraft source code, I have to make the attributes update independent from MCP.

Please follow the steps below to apply the fix if you want :)

AIR_DRAG_MODIFIER: The origin minecraft's air friction is 0.98, check your LocalPlayer.java(for modern version) / EntityPlayerSP.java(for legacy version), LivingEntity.java(modern) / EntityLivingBase.java(legacy), Entity.java,then replace all 0.98 to the new air friction.

BOUNCINESS: Find the code that makes player stop(delta movement is 0.0) when collided horizontally, it's most probably in LocalPlayer.java / EntityPlayerSP.java, then rewrite the Vec3 delta movement / motionXZ which is 0.0 to the new attributes you got.

FRICTION_MODIFIER: Find the code that affects block friction, the origin minecraft's block friction is 0.91, and it's most probably in LivingEntity.java / EntityLivingBase.java, then replace them to the new attributes you got.

Hypixel Join Fix

Call the fixHypixelLogin(); in the ViaMCP class file

Then insert the code below in the head of runTick() function in the class Minecraft:

PacketWrapperImplpacket = null;
PacketWrapperImplpacketInfo = null;
intmodelParts = 0;
// Hypixel only allow 1.21.4+ client to login.if (ViaLoadingBase.getInstance().getTargetVersion().newerThanOrEqualTo(ProtocolVersion.v1_21_4)) {
packet = (PacketWrapperImpl) PacketWrapper.create(ServerboundConfigurationPackets1_20_2.CUSTOM_PAYLOAD, ViaMCP.INSTANCE.user);
packet.write(Types.STRING, "minecraft:brand");
packet.write(Types.STRING, "vanilla");
packet.sendToServer(Protocol1_20_3To1_20_2.class);
packetInfo = (PacketWrapperImpl) PacketWrapper.create(ServerboundConfigurationPackets1_20_2.CLIENT_INFORMATION, ViaMCP.INSTANCE.user);
packetInfo.write(Types.STRING, Minecraft.getMinecraft().gameSettings.language.toLowerCase());
packetInfo.write(Types.BYTE, (byte) Minecraft.getMinecraft().gameSettings.renderDistanceChunks);
packetInfo.write(Types.VAR_INT, Minecraft.getMinecraft().gameSettings.chatVisibility.ordinal());
packetInfo.write(Types.BOOLEAN, Minecraft.getMinecraft().gameSettings.chatColours);
for (EnumPlayerModelPartsparts : Minecraft.getMinecraft().gameSettings.getModelParts()) {
modelParts |= parts.getPartMask();
}
packetInfo.write(Types.UNSIGNED_BYTE, (short) modelParts);
packetInfo.write(Types.VAR_INT, 1);
packetInfo.write(Types.BOOLEAN, true);
packetInfo.write(Types.BOOLEAN, true);
packetInfo.sendToServer(Protocol1_20_3To1_20_2.class);
}

Sending raw packets (e.g 1.9 interactions)

You can send raw packets with ViaMCP, you can use the following code to send raw packets:

finalPacketWrapperblockPlace = PacketWrapper.create(ServerboundPackets1_9.PLAYER_BLOCK_PLACEMENT, null); // Replace null with your stored UserConnection, see NetworkManager tutorial aboveblockPlace.write(Type.POSITION1_8, newPosition(0, 0, 0)); // Replace with the block positionblockPlace.write(Type.VAR_INT, 0); // Replace with the block face, see https://wiki.vg/index.php?title=Protocol&oldid=7617#Player_DiggingblockPlace.write(Type.VAR_INT, 0); // Replace with the hand, 0 for main hand, 1 for off handblockPlace.write(Type.UNSIGNED_BYTE, (short) 0); // The x pos of the crosshair, from 0 to 15 increasing from west to eastblockPlace.write(Type.UNSIGNED_BYTE, (short) 0); // The y pos of the crosshair, from 0 to 15 increasing from bottom to topblockPlace.write(Type.UNSIGNED_BYTE, (short) 0); // The z pos of the crosshair, from 0 to 15 increasing from north to southtry {
blockPlace.sendToServer(Protocol1_9To1_8.class); // Protocol class names are: server -> client version
} catch (Exceptione) {
// Packet sending failedthrownewRuntimeException(e);
}

Exporting Without JAR Files

This should fix most peoples issues with dependencies (usually NoClassDefFoundError or ClassNotFoundException)

• First export your client normally
• Open your client .jar file with an archive program (winrar or 7zip for example)
• Also open all libraries with the selected archive program (ViaVersion, ViaBackwards, ViaRewind and SnakeYaml)
• From ViaVersion, ViaBackwards and ViaRewind drag and drop assets, com and us folders to your client .jar
• Then save and close, now your client should be working correctly ;)