Pumpkin-MC/Pumpkin · error

duplicate player input flag

Error message

duplicate player input flag {flag}

What it means

This error is thrown while decoding the Bedrock PlayerAuthInput packet when the client's InputData bitfield repeats a PlayerInput flag that was already set in the same packet. The server rejects the packet as invalid data rather than tolerating redundant bits, because duplicated flags indicate a malformed or malicious packet.

Solutions

1. Update the client to a version matching the server's supported Bedrock protocol
2. Inspect the client's PlayerAuthInput serialization for duplicate flag emission
3. If you control middleware/proxies, re-encode InputData without duplicate flag bits
4. Kick the offending client; this is by-design rejection of malformed input

Example fix

// before (server-side strictness is correct; fix the sender)
input_data.set(flag as usize, true); // called twice for same flag
// after (sender must emit each flag once)
if !input_data.get(flag as usize) { input_data.set(flag as usize, true); }

// Cannot pre-validate raw wire input; on the server, ensure flags are set once:
if input_data.get(flag as usize) { /* already set -> skip or reject */ }

match decode_player_auth_input(buf) {
    Err(e) if e.kind() == std::io::ErrorKind::InvalidData => { disconnect(client, e); }
    Err(e) => propagate(e),
    Ok(p) => handle(p),
}

When it happens

Trigger: A client sends PlayerAuthInput whose InputData VarULong has a flag bit encoded more than once in the flag-listing sub-protocol (input_data.get(flag as usize) is already true when the flag is decoded).

Common situations: Bugged or modded Bedrock clients, custom/older protocol implementations, or crafted packets from untrusted clients probing the server.

Understand the failure class

Background: "unknown output mode", "invalid value for flag", "expects true/false": fixing invalid flag value errors in CLI tools — this error's family across 24 libraries.

Related errors

• item string array length out of bounds
• miss_count exceeds limit
• hit_count exceeds limit
• length exceeds
• missing inventory transaction type

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/000745402f54d0cc. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-protocol/src/bedrock/server/player_auth_input.rs:64

        let mut input_data = Bitset::<66>::default();
        if bool::read(reader)? {
            let count = VarUInt::read(reader)?.0;
            if count > 66 {
                return Err(Error::new(
                    ErrorKind::InvalidData,
                    format!("too many player input flags: {count}"),
                ));
            }
            for _ in 0..count {
                let flag = VarInt::read(reader)?.0;
                if !(0..66).contains(&flag) {
                    return Err(Error::new(
                        ErrorKind::InvalidData,
                        format!("invalid player input flag {flag}"),
                    ));
                }
                if input_data.get(flag as usize) {
                    return Err(Error::new(
                        ErrorKind::InvalidData,
                        format!("duplicate player input flag {flag}"),
                    ));
                }
                input_data.set(flag as usize, true);
            }
        }
        let input_mode = VarUInt::read(reader)?;
        let play_mode = VarUInt::read(reader)?;
        let interaction_model = VarInt::read(reader)?;
        let interact_pitch = f32::read(reader)?;
        let interact_yaw = f32::read(reader)?;
        let tick = VarULong::read(reader)?;
        let delta = Vector3::<f32>::read(reader)?;

        // 1. Perform Item Interaction
        let item_interaction = if bool::read(reader)? && bool::read(reader)? {
            Some(PlayerInventoryAction::read(reader)?)

View on GitHub (pinned to 8d4639e25a)