Pumpkin-MC/Pumpkin · error

Nbt read error

Error message

Nbt read error

What it means

Thrown when parsing the NBT payload embedded in an item's user data fails. For version -1 user data the library reads a version byte and then Nbt::read via NbtReadHelperBedrock; any NBT parse error (bad tag, truncated data, unsupported version) is mapped to this InvalidData error.

Solutions

1. Verify client and server Bedrock protocol versions match (NBT encoding changed between versions).
2. Validate that the item's serialized NBT is well-formed using an NBT debugger on the sender side.
3. Check that the full packet was received; truncated user data leads to NBT read failures.
4. If a custom tool generates the item data, confirm it emits network little-endian NBT compatible with NbtReadHelperBedrock.

Example fix

// before: writing disk-format NBT into the packet
let nbt = Nbt::write_disk_format(&value);
// after
let nbt = Nbt::write_network_bedrock(&value); // network little-endian, headerless

fn nbt_version_is_supported(version: i16) -> bool {
    version == -1 // only -1 signals an embedded NBT payload; others default
}

match read_user_data(&mut cursor, is_shield) {
    Err(e) if e.to_string().contains("Nbt read error") => {
        log::warn!("malformed NBT in item user data: {e}; rejecting item");
        // fall back to a default item or disconnect the peer
    }
    other => other?,
}

When it happens

Trigger: Triggered in read_user_data when nbt_version == -1 and Nbt::read returns an error: malformed NBT tags, truncated compound data, or an unsupported NBT version byte.

Common situations: Third-party clients/tools producing non-standard NBT, corrupted packets, protocol version mismatch causing NBT version negotiation differences, network truncation of the item payload.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Failed to decode varint - value too large
• Failed to decode varlong - value too large
• user_data_len exceeds 1MB limit
• extra_data_len exceeds 1MB limit
• Invalid ContainerName ID

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/9e5bebc381f2caef. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-protocol/src/bedrock/network_item.rs:609

    }
    Ok(values)
}

fn read_user_data(
    user_data: Vec<u8>,
    is_shield: bool,
) -> Result<(Nbt, Vec<String>, Vec<String>, i64), Error> {
    if user_data.is_empty() {
        return Ok((Nbt::default(), Vec::new(), Vec::new(), 0));
    }

    let mut cursor = std::io::Cursor::new(user_data);
    let nbt_version = i16::read(&mut cursor)?;
    let nbt_data = if nbt_version == -1 {
        let _version = i8::read(&mut cursor)?;
        let mut nbt_reader = NbtReadHelperBedrock::new(&mut cursor);
        Nbt::read(&mut nbt_reader)
            .map_err(|error| Error::new(std::io::ErrorKind::InvalidData, error))?
    } else {
        Nbt::default()
    };
    let place_on_blocks = read_user_data_strings(&mut cursor)?;
    let destroy_blocks = read_user_data_strings(&mut cursor)?;
    let shield_blocking_tick = if is_shield {
        i64::read(&mut cursor)?
    } else {
        0
    };
    Ok((
        nbt_data,
        place_on_blocks,
        destroy_blocks,
        shield_blocking_tick,
    ))
}

View on GitHub (pinned to 8d4639e25a)