nautechsystems/nautilus_trader · error

Flash event data is too short

Error message

Flash event data is too short

What it means

Thrown by parse_flash_event_hypersync when the hypersync log's data is present but shorter than 4 x 32 = 128 bytes, the minimum for the Flash event's four parameters (amount0, amount1, paid0, paid1). The library validates length before attempting abi_decode.

Source

Thrown at crates/adapters/blockchain/src/exchanges/parsing/uniswap_v3/flash.rs:70

///
/// # Panics
///
/// Panics if the contract address is not set in the log.
pub fn parse_flash_event_hypersync(
    dex: SharedDex,
    log: &HypersyncLog,
) -> anyhow::Result<FlashEvent> {
    validate_event_signature_hash("FlashEvent", FLASH_EVENT_SIGNATURE_HASH, log)?;

    let sender = extract_address_from_topic(log, 1, "sender")?;
    let recipient = extract_address_from_topic(log, 2, "recipient")?;

    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!("Flash event data is too short");
        }

        // Decode the data using the FlashEventData struct
        let decoded = match <FlashEventData as SolType>::abi_decode(data_bytes) {
            Ok(decoded) => decoded,
            Err(e) => anyhow::bail!("Failed to decode flash 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(FlashEvent::new(
            dex,

View on GitHub (pinned to 18893faf8b)

Solutions

1. Filter the hypersync query on the exact Flash event topic0.
2. Check log.data hex length >= 256 chars before parsing.
3. Ensure the log originates from a standard Uniswap V3 pool (Flash events only exist there).
4. Fix fixtures so data holds four 32-byte words.
5. If a variant event with fewer fields is expected, adjust FlashEventData and the length check together.

Example fix

// before
if data_bytes.len() < 4 * 32 {
    anyhow::bail!("Flash event data is too short");
}
// after
if data_bytes.len() != 4 * 32 {
    anyhow::bail!("Flash event data must be exactly 128 bytes, got {}", data_bytes.len());
}

fn is_valid_flash_data(data: Option<&[u8]>) -> bool {
    data.map(|d| d.len() == 4 * 32).unwrap_or(false)
}

fn has_flash_shape(log: &HypersyncLog) -> bool {
    log.data.as_ref().map(|d| d.len() >= 128).unwrap_or(false)
}

match parse_flash_event_hypersync(dex, &log) {
    Ok(event) => handle(event),
    Err(e) if e.to_string().contains("Flash event data") => {
        tracing::warn!("skipping malformed Flash log: {e}");
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: A hypersync log matching the Flash topic arrives with data < 128 bytes — empty data field, truncated hex, or data belonging to a different event.

Common situations: Hypersync queries not filtering on the Flash topic0; partial data returned by the provider; unit-test fixtures with short data (test_parse_flash_event_hypersync).

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.

Related errors

• SetFeeProtocol event data is too short
• Failed to decode SetFeeProtocol event data: {e}
• Failed to decode flash event data: {e}
• Missing tickLower in topic2 when parsing burn event
• Missing data in SetFeeProtocol event log

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/cc4dd8049dc26886. Report an issue: GitHub.