Pumpkin-MC/Pumpkin · error · Error

Failed to decode varint - value too large

Error message

Failed to decode varint - value too large

What it means

NBT decode guard for Bedrock variable-length integers: a VarInt in the stream kept setting continuation bits past its maximum encoded size (5 bytes), so decoding aborted. The offending input is a length/varint field inside the NBT payload whose encoding runs longer than allowed — a sign of corrupted or truncated/misaligned data rather than a legitimate value.

Solutions

1. Reject the containing packet as invalid data
2. Cap varint reads to the maximum encoded length
3. Log the oversized varint at debug level

fn varint_len_ok(bytes: &[u8]) -> bool { bytes.iter().take(5).position(|b| b & 0x80 == 0).is_some() }

if let Err(Error::VarIntTooLarge) = result { mark_source_corrupt(); }

When it happens

Trigger: Reading Bedrock-format NBT where a varint never terminates within its maximum byte limit (e.g. continuation bits set past the 5-byte cap).

Common situations: Parsing corrupted Bedrock level data, desynced buffer offsets when reading NBT embedded in packets, or feeding Java-format NBT to the Bedrock reader.

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.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to decode varlong - value too large
• Nbt read error
• Serde error
• Length too large
• unexpected EOF

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/4d907fc630fbfb49. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-nbt/src/lib.rs:101

    #[error("Failed to UTF-8 Decode")]
    Utf8DecodingError,
    /// Serde reported an invalid value or serializer state.
    #[error("Serde error: {0}")]
    SerdeError(String),
    /// The requested Rust type has no NBT representation.
    #[error("NBT doesn't support this type: {0}")]
    UnsupportedType(String),
    /// The underlying reader or writer returned an I/O error.
    #[error("NBT reading was cut short: {0}")]
    Incomplete(io::Error),
    /// A list or array declared a negative element count.
    #[error("Negative list length: {0}")]
    NegativeLength(i32),
    /// A string, list, or array exceeded the supported length.
    #[error("Length too large: {0}")]
    LargeLength(usize),
    /// A Bedrock variable-length integer exceeded its maximum encoded size.
    #[error("Failed to decode varint - value too large")]
    VarIntTooLarge,
    /// A Bedrock variable-length long exceeded its maximum encoded size.
    #[error("Failed to decode varlong - value too large")]
    VarLongTooLarge,
    /// NBT nesting depth exceeded the maximum allowed limit.
    #[error("NBT depth exceeded maximum allowed limit")]
    MaxDepthExceeded,
    /// A list tag specified an invalid element tag type.
    #[error("Invalid element tag type for list: {0}")]
    InvalidListTag(u8),
}

/// A complete NBT document containing a named root compound.
#[derive(Clone, Debug, Default, PartialEq)]
pub struct Nbt {
    /// Name stored alongside the root compound.
    pub name: String,
    /// Root compound containing the document's tags.

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