nautechsystems/nautilus_trader · error

Failed to decode mint event data: {e}

Error message

Failed to decode mint event data: {e}

What it means

Thrown by parse_mint_event_hypersync when the data payload passes the 128-byte length check but alloy's abi_decode into MintEventData fails, with the underlying error embedded. Indicates the data words do not fit the expected Mint event layout (e.g. wrong word count, dynamic tails, or non-multiple-of-32 length).

Source

Thrown at crates/adapters/blockchain/src/exchanges/parsing/uniswap_v3/mint.rs:90

        Some(topic) => {
            let tick_upper_bytes: [u8; 32] = topic.as_ref().try_into()?;
            i32::from_be_bytes(tick_upper_bytes[28..32].try_into()?)
        }
        None => anyhow::bail!("Missing tickUpper in topic3 when parsing mint event"),
    };

    if let Some(data) = &log.data {
        let data_bytes = data.as_ref();

        // Validate if data contains 4 parameters of 32 bytes each
        if data_bytes.len() < 4 * 32 {
            anyhow::bail!("Mint event data is too short");
        }

        // Decode the data using the MintEventData struct
        let decoded = match <MintEventData as SolType>::abi_decode(data_bytes) {
            Ok(decoded) => decoded,
            Err(e) => anyhow::bail!("Failed to decode mint event data: {e}"),
        };

        let pool_address = Address::from_slice(
            log.address
                .clone()
                .expect("Contract address should be set in logs")
                .as_ref(),
        );
        let pool_identifier = PoolIdentifier::Address(Ustr::from(&pool_address.to_string()));
        Ok(MintEvent::new(
            dex,
            pool_identifier,
            extract_block_number(log)?,
            extract_transaction_hash(log)?,
            extract_transaction_index(log)?,
            extract_log_index(log)?,
            decoded.sender,
            owner,

View on GitHub (pinned to 18893faf8b)

Solutions

1. Require data_bytes.len() == 4 * 32 exactly rather than >= .
2. Manually decode the four words to inspect the layout against MintEventData.
3. Verify the pool contract is a standard Uniswap V3 deployment.
4. Check alloy-sol-types codegen matches the deployed Mint event ABI.

Example fix

// before
if data_bytes.len() < 4 * 32 { bail!("too short"); }
let decoded = <MintEventData as SolType>::abi_decode(data_bytes)?;
// after
if data_bytes.len() != 4 * 32 {
    anyhow::bail!("Mint data must be 128 bytes, got {}", data_bytes.len());
}
let decoded = <MintEventData as SolType>::abi_decode(data_bytes)?;

fn exact_mint_data(log: &HypersyncLog) -> bool {
    log.data.as_ref().map(|d| d.len() == 128).unwrap_or(false)
}
if !exact_mint_data(&log) { skip(&log); }

fn mint_data_words(log: &HypersyncLog) -> Option<&[u8; 128]> {
    let d = log.data.as_deref()?;
    (d.len() == 128).then_some(d.try_into().ok()?)
}

match parse_mint_event_hypersync(log, dex) {
    Ok(event) => process(event),
    Err(e) if e.to_string().contains("Failed to decode mint event data") => {
        log::warn!("non-canonical mint payload: {e}");
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Hypersync log data >= 128 bytes but not exactly four static words — extra trailing bytes, dynamic encoding, or data belonging to a different event with the same topic0.

Common situations: Forked V3 Mint events with modified parameters, corrupted payloads, mixing logs across event types with colliding signatures.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

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

Related errors

• Initialize event data is too short
• Failed to decode initialize event data: {e}
• Missing tickLower in topic2 when parsing mint event
• Missing tickUpper in topic3 when parsing mint event
• Mint event data is too short

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/7edc7deecc32966c. Report an issue: GitHub.