nautechsystems/nautilus_trader · error

Initialize event missing topics: expected 4, was {log_topics

Error message

Initialize event missing topics: expected 4, was {log_topics_len}

What it means

parse_initialize_event_rpc mirrors the hypersync parser: it requires 4 topics (event signature, poolId, currency0, currency1) on the RPC log before extracting V4 pool parameters. Fewer topics means the log cannot be a V4 Initialize event and the parser bails.

Source

Thrown at crates/adapters/blockchain/src/exchanges/parsing/uniswap_v4/initialize.rs:176

/// # Errors
///
/// Returns an error if the log parsing fails or if the event data is invalid.
pub fn parse_initialize_event_rpc(log: &RpcLog) -> anyhow::Result<PoolCreatedEvent> {
    rpc_log::validate_event_signature(log, INITIALIZE_EVENT_SIGNATURE_HASH, "InitializeEvent")?;

    let block_number = rpc_log::extract_block_number(log)?;

    // Pool address is the PoolManager contract (event emitter)
    let pool_manager_bytes = rpc_log::decode_hex(&log.address)?;
    let pool_manager_address = Address::from_slice(&pool_manager_bytes);

    // Extract currency0 and currency1 from topics
    // topics[0] = event signature
    // topics[1] = poolId (bytes32)
    // topics[2] = currency0 (indexed)
    // topics[3] = currency1 (indexed)
    if log.topics.len() < 4 {
        anyhow::bail!(
            "Initialize event missing topics: expected 4, was {}",
            log.topics.len()
        );
    }

    // Extract Pool ID from topics[1] - this is the unique identifier for V4 pools
    let pool_id_bytes = rpc_log::decode_hex(&log.topics[1])?;
    let pool_identifier = Ustr::from(&hex::encode_prefixed(pool_id_bytes));

    let currency0_bytes = rpc_log::decode_hex(&log.topics[2])?;
    let currency0 = Address::from_slice(&currency0_bytes[12..32]);

    let currency1_bytes = rpc_log::decode_hex(&log.topics[3])?;
    let currency1 = Address::from_slice(&currency1_bytes[12..32]);

    // Extract and decode event data
    let data_bytes = rpc_log::extract_data_bytes(log)?;

View on GitHub (pinned to 18893faf8b)

Solutions

1. Pass topic0 (exact V4 Initialize signature) in the eth_getLogs filter so only matching logs are fetched
2. Check log.topics.len() >= 4 in the caller before invoking the parser and skip otherwise
3. Verify the emitting contract is the chain's V4 PoolManager
4. Route non-V4 logs to the correct version-specific parser

Example fix

// before
if log.topics.len() < 4 {
    anyhow::bail!("Initialize event missing topics: expected 4, was {}", log.topics.len());
}
// after
if log.topics.len() < 4 {
    tracing::debug!(n = log.topics.len(), "skipping non-V4 initialize log");
    return Ok(None); // or continue
}

fn is_v4_initialize_rpc_log(log: &RpcLog) -> bool {
    log.topics.len() >= 4 && log.topics[0] == INITIALIZE_V4_TOPIC0
}
if !is_v4_initialize_rpc_log(&log) { skip_or_log(); }

match parse_initialize_event_rpc(&log, &dex) {
    Ok(ev) => handle(ev),
    Err(e) => { tracing::debug!(%e, "non-V4 initialize log skipped"); Ok(None) }
}

When it happens

Trigger: Calling parse_initialize_event_rpc with an RPC log having fewer than 4 topics — non-V4 contract logs, a filter without topic0 constraint, or logs from a V3 pool whose Initialize has different indexed layout.

Common situations: get_logs calls scoped by address but not by topics, pulling in every event the contract emits; decoding logs from unrelated protocols; re-indexing forks with different event definitions.

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

• Initialize event missing topics: expected 4, was {topics_len
• Missing fee in topic3 when parsing pool created event
• Initialize event data too short: expected at least 160 bytes
• Profiler log has no block hash
• Finalized Swap log has no block hash

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/56e9f071240200b8. Report an issue: GitHub.