decision/crates/ld-server/src/wot.rs

//! W — the size of the Ğ1 web of trust, the electorate of Monnaie libre.
//!
//! Read on chain first (`Membership.CounterForMembership`, JSON-RPC
//! `state_getStorage` on a Duniter v2s node), from an indexer otherwise, and
//! kept in `settings`. A failed refresh keeps the last known value; the very
//! first start falls back to `LD_WOT_FALLBACK`.

use crate::AppState;
use crate::util;
use serde_json::json;
use std::time::Duration;

/// W is read again this often.
pub const REFRESH: Duration = Duration::from_secs(6 * 3600);
const PLAUSIBLE: std::ops::RangeInclusive<u32> = 100..=10_000_000;

fn twox_128(data: &[u8]) -> [u8; 16] {
    let mut out = [0u8; 16];
    out[..8].copy_from_slice(&twox_hash::XxHash64::oneshot(0, data).to_le_bytes());
    out[8..].copy_from_slice(&twox_hash::XxHash64::oneshot(1, data).to_le_bytes());
    out
}

/// Storage key of a plain storage value: `twox_128(pallet) ++ twox_128(item)`.
pub fn storage_key(pallet: &str, item: &str) -> String {
    let mut key = Vec::with_capacity(32);
    key.extend_from_slice(&twox_128(pallet.as_bytes()));
    key.extend_from_slice(&twox_128(item.as_bytes()));
    format!("0x{}", hex::encode(key))
}

/// SCALE `u32`, little endian.
pub fn decode_u32(hex_value: &str) -> Option<u32> {
    let bytes = hex::decode(hex_value.trim_start_matches("0x")).ok()?;
    let arr: [u8; 4] = bytes.get(..4)?.try_into().ok()?;
    Some(u32::from_le_bytes(arr))
}

async fn from_chain(state: &AppState) -> Option<(u32, String)> {
    let key = storage_key("Membership", "CounterForMembership");
    for node in &state.cfg.rpc_endpoints {
        let body = json!({ "jsonrpc": "2.0", "id": 1, "method": "state_getStorage", "params": [key] });
        let res = state.http.post(node).json(&body).send().await;
        let value: Option<serde_json::Value> = match res {
            Ok(r) if r.status().is_success() => r.json().await.ok(),
            _ => None,
        };
        if let Some(n) = value.as_ref().and_then(|v| v["result"].as_str()).and_then(decode_u32)
            && PLAUSIBLE.contains(&n)
        {
            return Some((n, format!("chain:{node}")));
        }
    }
    None
}

async fn from_indexer(state: &AppState) -> Option<(u32, String)> {
    let query = json!({ "query": "{ identities(filter:{isMember:{equalTo:true}}) { totalCount } }" });
    for url in &state.cfg.indexers {
        let res = state.http.post(url).json(&query).send().await;
        let value: Option<serde_json::Value> = match res {
            Ok(r) if r.status().is_success() => r.json().await.ok(),
            _ => None,
        };
        let n = value
            .as_ref()
            .and_then(|v| v["data"]["identities"]["totalCount"].as_u64())
            .and_then(|n| u32::try_from(n).ok());
        if let Some(n) = n.filter(|n| PLAUSIBLE.contains(n)) {
            return Some((n, format!("indexer:{url}")));
        }
    }
    None
}

pub async fn refresh(state: &AppState) -> anyhow::Result<Option<u32>> {
    let found = match from_chain(state).await {
        Some(v) => Some(v),
        None => from_indexer(state).await,
    };
    let Some((n, source)) = found else {
        tracing::warn!("web of trust size: no node nor indexer answered, keeping the last value");
        return Ok(None);
    };
    let now = util::now();
    for (key, value) in [("wot_size", n.to_string()), ("wot_source", source.clone())] {
        sqlx::query(
            "INSERT INTO settings (key, value, updated_at) VALUES (?, ?, ?)
             ON CONFLICT(key) DO UPDATE SET value = excluded.value, updated_at = excluded.updated_at",
        )
        .bind(key)
        .bind(value)
        .bind(&now)
        .execute(&state.db)
        .await?;
    }
    tracing::info!(size = n, %source, "web of trust size");
    Ok(Some(n))
}

pub async fn refresher(state: AppState) {
    let mut tick = tokio::time::interval(REFRESH);
    loop {
        tick.tick().await;
        if let Err(e) = refresh(&state).await {
            tracing::warn!(error = %e, "web of trust refresh");
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn storage_keys_match_substrate() {
        // Well-known key of System.Number (block number) on any Substrate chain.
        assert_eq!(
            storage_key("System", "Number"),
            "0x26aa394eea5630e07c48ae0c9558cef702a5c1b19ab7a04f536c519aca4983ac"
        );
    }

    #[test]
    fn scale_u32() {
        assert_eq!(decode_u32("0x71160000"), Some(5745));
        assert_eq!(decode_u32("0x01"), None);
    }
}