Code/net/minecraft/network/chat/LastSeenMessagesValidator.java

package net.minecraft.network.chat;

import it.unimi.dsi.fastutil.objects.ObjectArrayList;
import it.unimi.dsi.fastutil.objects.ObjectList;
import javax.annotation.Nullable;

public class LastSeenMessagesValidator {
    private final int lastSeenCount;
    private final ObjectList<LastSeenTrackedEntry> trackedMessages = new ObjectArrayList<>();
    @Nullable
    private MessageSignature lastPendingMessage;

    public LastSeenMessagesValidator(int p_249951_) {
        this.lastSeenCount = p_249951_;

        for (int i = 0; i < p_249951_; i++) {
            this.trackedMessages.add(null);
        }
    }

    public void addPending(MessageSignature p_248841_) {
        if (!p_248841_.equals(this.lastPendingMessage)) {
            this.trackedMessages.add(new LastSeenTrackedEntry(p_248841_, true));
            this.lastPendingMessage = p_248841_;
        }
    }

    public int trackedMessagesCount() {
        return this.trackedMessages.size();
    }

    public void applyOffset(int p_251273_) throws LastSeenMessagesValidator.ValidationException {
        int i = this.trackedMessages.size() - this.lastSeenCount;
        if (p_251273_ >= 0 && p_251273_ <= i) {
            this.trackedMessages.removeElements(0, p_251273_);
        } else {
            throw new LastSeenMessagesValidator.ValidationException("Advanced last seen window by " + p_251273_ + " messages, but expected at most " + i);
        }
    }

    public LastSeenMessages applyUpdate(LastSeenMessages.Update p_248868_) throws LastSeenMessagesValidator.ValidationException {
        this.applyOffset(p_248868_.offset());
        ObjectList<MessageSignature> objectlist = new ObjectArrayList<>(p_248868_.acknowledged().cardinality());
        if (p_248868_.acknowledged().length() > this.lastSeenCount) {
            throw new LastSeenMessagesValidator.ValidationException(
                "Last seen update contained " + p_248868_.acknowledged().length() + " messages, but maximum window size is " + this.lastSeenCount
            );
        } else {
            for (int i = 0; i < this.lastSeenCount; i++) {
                boolean flag = p_248868_.acknowledged().get(i);
                LastSeenTrackedEntry lastseentrackedentry = this.trackedMessages.get(i);
                if (flag) {
                    if (lastseentrackedentry == null) {
                        throw new LastSeenMessagesValidator.ValidationException(
                            "Last seen update acknowledged unknown or previously ignored message at index " + i
                        );
                    }

                    this.trackedMessages.set(i, lastseentrackedentry.acknowledge());
                    objectlist.add(lastseentrackedentry.signature());
                } else {
                    if (lastseentrackedentry != null && !lastseentrackedentry.pending()) {
                        throw new LastSeenMessagesValidator.ValidationException(
                            "Last seen update ignored previously acknowledged message at index " + i + " and signature " + lastseentrackedentry.signature()
                        );
                    }

                    this.trackedMessages.set(i, null);
                }
            }

            LastSeenMessages lastseenmessages = new LastSeenMessages(objectlist);
            if (!p_248868_.verifyChecksum(lastseenmessages)) {
                throw new LastSeenMessagesValidator.ValidationException("Checksum mismatch on last seen update: the client and server must have desynced");
            } else {
                return lastseenmessages;
            }
        }
    }

    public static class ValidationException extends Exception {
        public ValidationException(String p_394588_) {
            super(p_394588_);
        }
    }
}