A basic packetfly

PacketFly.java

package demo.knight.twelvemod.module.modules.movement;

import demo.knight.twelvemod.event.MovePlayerEvent;
import demo.knight.twelvemod.event.PacketEvent;
import demo.knight.twelvemod.mixin.mixins.ISPacketPlayerPosLook;
import demo.knight.twelvemod.module.Category;
import demo.knight.twelvemod.module.Module;
import demo.knight.twelvemod.setting.settings.FloatSetting;
import net.minecraft.network.play.client.CPacketConfirmTeleport;
import net.minecraft.network.play.client.CPacketPlayer;
import net.minecraft.network.play.server.SPacketPlayerPosLook;
import net.minecraft.util.math.Vec3d;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;

/**
 * @author Doogie13
 * @since 26/06/2022
 */
@Module.Register(name = "PacketFly", description = "Allows you to fly with a 1.9+ packet exploit", category = Category.MOVEMENT)
public class PacketFly extends Module {

    // setting for Factor with bounds 0.1 to 5.0 and a precision of 0.1
    // for 2b2tpvp.net, default value of 1.3 is recommended when using this for flying
    // when phasing, you may wish to use something closer to 2 or 3
    final FloatSetting factor = register(new FloatSetting("Factor", 1.3f, 0.1, 5, 0.1));

    // current teleport ID
    int tpID = -1;

    // set of packets we allow
    Set<CPacketPlayer> allowedCPacketPlayers = new HashSet<>();

    // map of IDs and positions where we can ignore server rubberbands
    HashMap<Integer, Vec3d> allowedPositionsAndIDs = new HashMap<>();

    @Override
    public void onDisable() {
        // clear these so they don't take up memory
        allowedCPacketPlayers.clear();
        allowedPositionsAndIDs.clear();
    }

    @Override
    public void onEnable() {
        // we will not have been tracking tpID so we must reset it
        tpID = -1;
    }

    // this can be any event which will let us set player motion
    @SubscribeEvent
    public void onMotion(MovePlayerEvent event) {

        // first we must get motion
        double motionX, motionY = 0, motionZ;

        // store whether we are anti-kicking
        boolean antiKicking = false;

        // Handle motion Y
        // check if we need to do anti-kick
        // we do not need to anti-kick when inside blocks
        if (mc.player.ticksExisted % 10 == 0 && !mc.world.collidesWithAnyBlock(mc.player.getEntityBoundingBox())) {
            // 0.04 is the distance we must fall before being kicked for flying
            // net.minecraft.network.NetHandlerPlayServer line 182
            motionY = -.04;
            antiKicking = true;
        } else {

            // we MUST allow the player to prioritise going up as it allows us to manipulate our bounding box with sneaking
            // NCP will flag SurvivalFly for anything larger than 0.0625 so we use 0.0624 to be on the safe side
            // I believe this to be because the server doesn't process movement slower than 0.0625 in the same way but I can't find evidence for this
            if (mc.gameSettings.keyBindJump.isKeyDown())
                motionY = .0624;
            else if (mc.gameSettings.keyBindSneak.isKeyDown())
                motionY = -.0624;

        }

        // Handle Motion X, Z
        // we will handle them as one speed and split them into X and Z based on rotation and keys pressed
        double motionH;

        // If we are inside blocks, we must use speed slower than 0.0625 so vanilla doesn't set us back
        // net.minecraft.network.NetHandlerPlayServer line 560

        boolean walls = mc.world.collidesWithAnyBlock(mc.player.getEntityBoundingBox());

        if (walls) {

            motionH = .0624;

            if (motionY != 0) {

                // this means the hypotenuse of our position is always under .625;
                double multiply = 1 / Math.sqrt(2);

                motionY *= multiply;
                motionH *= multiply;

            }

        } else {

            // base air move speed
            motionH = .2873;

            // we cannot move up if we are moving horizontally since NCP will notice
            boolean movingHorizontally = mc.player.moveForward != 0 || mc.player.moveStrafing != 0;

            if (movingHorizontally)
                motionY = Math.min(0, motionY);

        }

        // we now split motionH into motionX and motionZ
        // this should really be in a util
        // we use dir because tradition
        double[] dir = new double[]{0,0};

        // if we aren't moving we can just use 0 motion
        if (!(mc.player.moveForward == 0 && mc.player.moveStrafing == 0)) {

            int strafing = 0;
            int forward = 0;

            // make moveForward and moveStrafing rounded to the nearest 1
            if (mc.player.moveStrafing < 0)
                strafing = -1;
            else if (mc.player.moveStrafing > 0)
                strafing = 1;

            if (mc.player.moveForward < 0)
                forward = -1;
            else if (mc.player.moveForward > 0)
                forward = 1;

            float strafe = 90 * strafing;
            strafe *= (forward != 0F) ? forward * 0.5F : 1;

            float yaw = mc.player.rotationYaw - strafe;
            yaw -= (mc.player.moveForward < 0F) ? 180 : 0;

            // to radians
            yaw *= 1 / (180 / Math.PI);

            // get X and Z split
            double x = (-Math.sin(yaw) * motionH);
            double z = (Math.cos(yaw) * motionH);

            dir = new double[]{x, z};

        }

        motionX = dir[0];
        motionZ = dir[1];

        // get the lowest possible factor
        int factorInt = (int) Math.floor(factor.getValue());

        // check if we should send more packets
        // decimal place is how much we should factorise more
        if (mc.player.ticksExisted % 10 < 10 * (factor.getValue() - factorInt))
            factorInt++;

        // send packets
        Vec3d motion = send(motionX, motionY, motionZ, antiKicking, factorInt);

        event.setX(motion.x);
        event.setY(motion.y);
        event.setZ(motion.z);

        // allows us to phase
        mc.player.noClip = true;

    }

    // this can be repeated multiple times to move faster
    Vec3d send(double motionX, double motionY, double motionZ, boolean antiKick, int factor) {

        for (int i = 1; i < factor + 1; i++) {

            // only anti-kick once per loop as doing it multiple times is a waste of height
            if (antiKick && factor != 1)
                motionY = 0;

            // get the absolute position
            Vec3d pos = mc.player.getPositionVector().add(motionX * i, motionY * i, motionZ * i);

            // create a movement packet
            // we use onGround true to prevent fall damage on some servers
            CPacketPlayer.Position packet = new CPacketPlayer.Position(pos.x, pos.y, pos.z, true);

            // create a "bounds" packet
            // this is just any packet over 100 blocks away from current position or 300 when elytra is open
            // net.minecraft.network.NetHandlerPlayServer line 529
            CPacketPlayer.Position bounds = new CPacketPlayer.Position(pos.x, pos.y + 512, pos.z, true);

            // allow normal packet and "bounds" packet to be sent (handled later)
            allowedCPacketPlayers.add(packet);
            allowedCPacketPlayers.add(bounds);

            // send packets
            mc.player.connection.sendPacket(packet);
            mc.player.connection.sendPacket(bounds);

            // we must have a correct teleport ID to save, we use the "bounds" packet to get one anyways if not
            if (tpID < 0)
                break;

            // iterate tpID as bounds will have caused rubberband
            tpID++;

            // send a tpID packet confirming the bounds packet
            mc.player.connection.sendPacket(new CPacketConfirmTeleport(tpID));

            // add move vector and tpID to the map
            allowedPositionsAndIDs.put(tpID, pos);
        }

        // return a vec of our motion
        return new Vec3d(motionX * factor, motionY * (antiKick ? 1 : factor), motionZ * factor);

    }

    @SubscribeEvent
    public void onPacketSend(PacketEvent.Send event) {

        // we only cancel CPacketPlayers
        if (event.getPacket() instanceof CPacketPlayer)
            // check if we are allowing the packet through
            // cancel if not
            if (!allowedCPacketPlayers.contains((CPacketPlayer) event.getPacket()))
                event.setCanceled(true);

    }

    @SubscribeEvent
    public void onPacketReceive(PacketEvent.Receive event) {

        // check if the packet is a player pos look
        if (event.getPacket() instanceof SPacketPlayerPosLook) {

            SPacketPlayerPosLook packet = (SPacketPlayerPosLook) event.getPacket();
            int id = packet.getTeleportId();

            // check if saved history contains the packet ID
            if (allowedPositionsAndIDs.containsKey(id)) {

                // check if saved packet with that ID has the corresponding position
                // this would mean the packet lines up and we can ignore the packet
                if (allowedPositionsAndIDs.get(id).equals(new Vec3d(packet.getX(), packet.getY(), packet.getZ()))) {

                    // remove the entry
                    allowedPositionsAndIDs.remove(id);

                    // confirm the packet
                    mc.player.connection.sendPacket(new CPacketConfirmTeleport(id));

                    // cancel the event
                    event.setCanceled(true);
                    return;

                }

            }

            // update our teleport ID
            tpID = id;

            // prevent jittery rotation
            ((ISPacketPlayerPosLook) packet).setYaw(mc.player.rotationYaw);
            ((ISPacketPlayerPosLook) packet).setPitch(mc.player.rotationPitch);

            // we MUST confirm this packet
            mc.player.connection.sendPacket(new CPacketConfirmTeleport(id));

        }

    }

}

found this on internet :D