nautechsystems/nautilus_trader · error

Invalid currency0 topic length

Error message

Invalid currency0 topic length

What it means

parse_initialize_event_hypersync for Uniswap V4 throws this when topics[2] exists but is shorter than 32 bytes, so slicing the low 20 bytes (12..32) that hold the 160-bit currency0 address fails. Ethereum topics are fixed 32-byte words; a shorter value means the payload is malformed. The library checks the slice instead of panicking on an out-of-range index.

Source

Thrown at crates/adapters/blockchain/src/exchanges/parsing/uniswap_v4/initialize.rs:111

            "Initialize event missing topics: expected 4, was {}",
            topics.len()
        );
    }

    // Extract Pool ID from topics[1] - this is the unique identifier for V4 pools
    let pool_id_bytes = topics[1]
        .as_ref()
        .ok_or_else(|| anyhow::anyhow!("Missing poolId topic"))?
        .as_ref();
    let pool_identifier = Ustr::from(&hex::encode_prefixed(pool_id_bytes));

    let currency0 = Address::from_slice(
        topics[2]
            .as_ref()
            .ok_or_else(|| anyhow::anyhow!("Missing currency0 topic"))?
            .as_ref()
            .get(12..32)
            .ok_or_else(|| anyhow::anyhow!("Invalid currency0 topic length"))?,
    );

    let currency1 = Address::from_slice(
        topics[3]
            .as_ref()
            .ok_or_else(|| anyhow::anyhow!("Missing currency1 topic"))?
            .as_ref()
            .get(12..32)
            .ok_or_else(|| anyhow::anyhow!("Invalid currency1 topic length"))?,
    );

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

        // Validate minimum data length (5 fields × 32 bytes = 160 bytes)
        if data_bytes.len() < 160 {
            anyhow::bail!(
                "Initialize event data too short: expected at least 160 bytes, was {}",

View on GitHub (pinned to 18893faf8b)

Solutions

1. Ensure topics are represented as fixed 32-byte words; left-pad the currency0 address with zeros before parsing.
2. Check the log source/provider is not truncating topics (compare against the raw transaction receipt).
3. Validate topic byte length (>= 32) before calling the parser and reject/short-circuit malformed logs.
4. Fix test fixtures to use full 32-byte topic values (e.g. 0x000...<20-byte address>).

Example fix

// before
let topic = hex::decode(short_hex)?; // e.g. 20 bytes
// after
let mut topic = [0u8; 32];
topic[12..].copy_from_slice(&hex::decode(addr_hex)?); // left-pad to 32 bytes
let event = parse_initialize_event_hypersync(&log)?;

fn topic_is_word(t: &Option<FixedBytes<32>>) -> bool {
    t.as_ref().map(|b| b.len() == 32).unwrap_or(false)
}
// require topic_is_word(&log.topics[2]) before parsing

fn is_full_word_topic(topic: &Option<FixedBytes<32>>) -> bool {
    topic.as_ref().is_some_and(|t| t.len() == 32)
}

match parse_initialize_event_hypersync(&log) {
    Ok(event) => handle(event),
    Err(e) if e.to_string().contains("Invalid currency0 topic length") => {
        tracing::warn!("short currency0 topic; skipping log");
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Calling parse_initialize_event_hypersync (v4) with a log whose topics[2] contains fewer than 32 bytes — e.g. a provider returning a stripped/truncated topic, a hand-built fixture with a short byte array, or a binary serializer dropping leading zero bytes.

Common situations: Custom RPC/indexer clients that trim topics instead of left-padding addresses to 32 bytes; fixtures built from hex strings parsed without padding; forked contracts emitting non-standard topic widths.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Missing poolId topic
• Missing currency0 topic
• Missing data in burn event log
• Missing data in collect event log
• Missing data in initialize event log

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/b7cd49c7ea23ca8c. Report an issue: GitHub.