What causes "Lighter candles only support EXTERNAL aggregation" in nautechsystems/nautilus_trader?

Create the BarType with `AggregationSource::External` (e.g. `BarType::new(instrument_id, BarAggregation::Minute, PriceType::Last, AggregationSource::External)`).

nautechsystems/nautilus_trader · error

Lighter candles only support EXTERNAL aggregation

Error message

Lighter candles only support EXTERNAL aggregation

What it means

Converting a Nautilus `BarType` into a `LighterCandleResolution` requires the bar's aggregation source to be `AggregationSource::External`, because Lighter provides candles directly and the adapter does not aggregate bars internally. `TryFrom<&BarType>` fails with this error for any internally-aggregated bar type.

Source

Thrown at crates/adapters/lighter/src/common/enums.rs:250

            Self::OneWeek => (1, BarAggregation::Week),
        };
        BarSpecification::new(step, aggregation, PriceType::Last)
    }

    /// Returns `true` when this resolution is offered on the candle WebSocket stream.
    ///
    /// `1w` is REST-only; the streaming channel only carries `1m`..=`1d`.
    #[must_use]
    pub const fn is_ws_streamable(self) -> bool {
        !matches!(self, Self::OneWeek)
    }
}

impl TryFrom<&BarType> for LighterCandleResolution {
    type Error = anyhow::Error;

    fn try_from(value: &BarType) -> Result<Self, Self::Error> {
        anyhow::ensure!(
            value.aggregation_source() == AggregationSource::External,
            "Lighter candles only support EXTERNAL aggregation",
        );

        let spec = value.spec();
        anyhow::ensure!(
            spec.price_type == PriceType::Last,
            "Lighter candles only support LAST price type",
        );

        let step = spec.step.get();
        match spec.aggregation {
            BarAggregation::Minute => match step {
                1 => Ok(Self::OneMinute),
                5 => Ok(Self::FiveMinute),
                15 => Ok(Self::FifteenMinute),
                30 => Ok(Self::ThirtyMinute),
                _ => anyhow::bail!("unsupported Lighter candle minute step: {step}"),

View on GitHub (pinned to 18893faf8b)

Solutions

Create the BarType with `AggregationSource::External` (e.g. `BarType::new(instrument_id, BarAggregation::Minute, PriceType::Last, AggregationSource::External)`).
Update any bar spec strings in config from `...-INTERNAL` to `...-EXTERNAL`.
If internal aggregation is required, aggregate locally from Lighter trades/ticks instead of using Lighter candles.

Example fix

// before
let bar_type = BarType::from("BTCUSDT-PERP.LIGHTER-1-MINUTE-LAST-INTERNAL");
// after
let bar_type = BarType::from("BTCUSDT-PERP.LIGHTER-1-MINUTE-LAST-EXTERNAL");

Defensive patterns

Strategy: validation

Validate before calling

if bar_type.aggregation_source() != AggregationSource::External {
    panic!("Lighter candles require EXTERNAL aggregation");
}

Type guard

fn is_external_bar(bar: &BarType) -> bool {
    bar.aggregation_source() == AggregationSource::External
}

Try / catch

let resolution = LighterCandleResolution::try_from(&bar_type)
    .map_err(|e| { eprintln!("bad bar type {bar_type}: {e:#}"); e })?;

Prevention

Always declare Lighter bar types with -EXTERNAL aggregation.
Validate bar spec strings in config at startup.
Never copy INTERNAL bar specs from other venues.

When it happens

Trigger: Requesting Lighter candle data with a BarType whose spec uses `AggregationSource::Internal` (e.g. bars aggregated by the Nautilus data engine from ticks).

Common situations: Subscribing to bars with the default internal aggregation instead of declaring EXTERNAL bars; copying BarType strings like `BTCUSDT-PERP.LIGHTER-*MINUTE-INTERNAL` from a config that targeted a different venue.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/245c627b9b9f67ce. Report an issue: GitHub.