Pumpkin-MC/Pumpkin · error

Bitset too large

Error message

Bitset too large

What it means

Thrown when decoding a VarInt-encoded bitset that exceeds the maximum supported size of the u128 backing storage (more than 18 7-bit groups / 128 bits of data). The reader stops after the fixed loop bound and returns InvalidData rather than silently truncating.

Solutions

1. Confirm the client protocol version matches the pumpkin-protocol definitions; update if the field's bitset width changed.
2. Validate the bitset's length prefix before decoding; reject oversized inputs at the packet boundary.
3. Check for packet corruption — a missing terminator byte (0x80 flag never cleared) will also hit this limit.
4. If a wider bitset is genuinely required, widen the internal storage (e.g. to a larger integer or array) in the codec.

// Reject bitsets wider than u128 before decoding
if declared_len > 18 { return Err(Error::new(ErrorKind::InvalidData, "bitset too large")); }

match Bitset::read(reader) {
    Ok(b) => Ok(b),
    Err(e) if e.kind() == ErrorKind::InvalidData => {
        log::warn!("oversized bitset; likely corrupt stream");
        Err(DecodeError::Desync)
    }
    Err(e) => Err(e.into()),
}

When it happens

Trigger: Reading a bitset whose VarInt payload has more continuation groups than the read loop allows (a bitset larger than 128 bits, or a corrupted/missing terminator byte so the loop runs to exhaustion).

Common situations: Server/client disagreement on bitset width for a field (e.g. abilities or recipe flags); malicious or corrupt packets on the wire; a protocol version that widened the bitset.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• too many player input flags
• VarLong is too big (overflow)
• {0}
• extra_data_len exceeds 1MB limit
• extra_data length exceeds limit

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/6ee542eab5119c2d. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-protocol/src/codec/bitset.rs:46

impl<const N: usize> Default for Bitset<N> {
    fn default() -> Self {
        assert!(N <= 80,);
        Self { bits: 0 }
    }
}

impl<const N: usize> PacketRead for Bitset<N> {
    fn read<R: Read>(reader: &mut R) -> Result<Self, Error> {
        let mut bitset = Self::default();

        for i in 0..N.div_ceil(7) {
            let byte = u8::read(reader)?;
            bitset.bits |= (u128::from(byte) & 0x7F) << (i * 7);
            if byte & 0x80 == 0 {
                return Ok(bitset);
            }
        }
        Err(Error::new(ErrorKind::InvalidData, "Bitset too large"))
    }
}

View on GitHub (pinned to 8d4639e25a)