nautechsystems/nautilus_trader · error

Missing event signature in topic0

Error message

Missing event signature in topic0

What it means

This error means a log entry had no topic0 value, so the event signature bytes cannot be extracted. The library requires topic0 because it is the keccak-256 hash of the event signature used to identify which event the log belongs to. It is thrown whenever `log.topics` is empty or the first element is null, rather than silently returning empty bytes that could cause false event matches.

Source

Thrown at crates/adapters/blockchain/src/hypersync/log.rs:106

/// Extracts the event signature from a log entry and returns it as a hex string
///
/// # Errors
///
/// Returns an error if the event signature (topic0) is not present in the log.
pub fn extract_event_signature(log: &HypersyncLog) -> anyhow::Result<String> {
    extract_event_signature_bytes(log).map(hex::encode)
}

/// Extracts the event signature from a log entry and returns it as raw bytes
///
/// # Errors
///
/// Returns an error if the event signature (topic0) is not present in the log.
pub fn extract_event_signature_bytes(log: &HypersyncLog) -> anyhow::Result<&[u8]> {
    if let Some(topic) = log.topics.first().and_then(|t| t.as_ref()) {
        Ok(topic.as_ref())
    } else {
        anyhow::bail!("Missing event signature in topic0");
    }
}

/// Validates that a log entry corresponds to the expected event by comparing its topic0 with the provided event signature hash.
///
/// # Errors
///
/// Returns an error if the event signature doesn't match or if topic0 is missing.
pub fn validate_event_signature_hash(
    event_name: &str,
    target_event_signature_hash: &str,
    log: &HypersyncLog,
) -> anyhow::Result<()> {
    let sig_bytes = extract_event_signature_bytes(log)?;
    core::validate_signature_bytes(sig_bytes, target_event_signature_hash, event_name)
}

#[cfg(test)]

View on GitHub (pinned to 18893faf8b)

Solutions

1. Check `log.topics.first()` is `Some` before calling, and skip anonymous logs (events declared with `anonymous` in Solidity have no topic0)
2. Filter your Hypersync query on topic0 so returned logs always carry an event signature
3. When decoding arbitrary logs, treat absence of topic0 as 'undecodable' and skip the log instead of erroring
4. If the log should always have topic0, verify the query/table mapping isn't dropping the topics column

Example fix

// before
let sig = extract_event_signature_bytes(&log)?;
// after
let sig = log.topics.first().and_then(|t| t.as_ref()).map(|t| t.as_ref());
match sig {
    Some(sig) => { /* use signature */ }
    None => { /* skip anonymous/unmatched log */ }
}

fn log_has_topic0(log: &HypersyncLog) -> bool {
    matches!(log.topics.first(), Some(Some(_)))
}
// call only if log_has_topic0(&log)

fn has_signature(log: &HypersyncLog) -> Option<&[u8]> {
    log.topics.first().and_then(|t| t.as_ref()).map(|t| t.as_ref())
}

match extract_event_signature_bytes(&log) {
    Ok(sig) => decode_with(sig),
    Err(_) => skip_log(), // anonymous or malformed log
}

When it happens

Trigger: Calling `extract_event_signature_bytes`, `extract_event_signature`, or `validate_event_signature_hash` with a `HypersyncLog` whose `topics` array is empty, or whose first entry is `None`/null (e.g. anonymous events or malformed log data).

Common situations: Querying logs for contracts that emit anonymous events (no topic0); fetching logs with a topic filter that does not constrain topic0; decoding raw logs from chain reorgs or partial data where the topics array was truncated; passing an artificially constructed log in tests.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Missing data in the pool created event log
• HyperSync parsing of pool created event is not defined in th
• HyperSync parsing of swap event is not defined in this dex:
• HyperSync parsing of mint event is not defined in this dex:
• HyperSync parsing of burn event is not defined in this dex:

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/f60970a889c870b7. Report an issue: GitHub.