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//! An async task that regularly updates the peer cache on disk from the current address book.
use std::{
io,
sync::{Arc, Mutex},
};
use chrono::Utc;
use tokio::time::sleep;
use crate::{
constants::{DNS_LOOKUP_TIMEOUT, PEER_DISK_CACHE_UPDATE_INTERVAL},
meta_addr::MetaAddr,
AddressBook, BoxError, Config,
};
/// An ongoing task that regularly caches the current `address_book` to disk, based on `config`.
#[instrument(skip(config, address_book))]
pub async fn peer_cache_updater(
config: Config,
address_book: Arc<Mutex<AddressBook>>,
) -> Result<(), BoxError> {
// Wait until we've queried DNS and (hopefully) sent peers to the address book.
// Ideally we'd wait for at least one peer crawl, but that makes tests very slow.
//
// TODO: turn the initial sleep time into a parameter of this function,
// and allow it to be set in tests
sleep(DNS_LOOKUP_TIMEOUT * 4).await;
let mut wrote_cache = false;
loop {
// Ignore errors because updating the cache is optional.
// Errors are already logged by the functions we're calling.
wrote_cache |= update_peer_cache_once(&config, &address_book)
.await
.unwrap_or(false);
// Right after a cold start, the address book can still be empty at the first attempt,
// and the cache is only written once there are cacheable peers. Retry soon until the
// first write, so the cache exists shortly after the node finds its first peers.
let interval = if wrote_cache {
PEER_DISK_CACHE_UPDATE_INTERVAL
} else {
DNS_LOOKUP_TIMEOUT * 4
};
sleep(interval).await;
}
}
/// Caches peers from the current `address_book` to disk, based on `config`.
///
/// Returns `true` if the cache was written, and `false` if the cacheable peer list was empty,
/// keeping any previous cache.
pub async fn update_peer_cache_once(
config: &Config,
address_book: &Arc<Mutex<AddressBook>>,
) -> io::Result<bool> {
let peer_list: std::collections::HashSet<_> = cacheable_peers(address_book)
.iter()
.map(|meta_addr| meta_addr.addr)
.collect();
let has_peers = !peer_list.is_empty();
config.update_peer_cache(peer_list).await?;
Ok(has_peers)
}
/// Returns a list of cacheable peers, blocking for as short a time as possible.
fn cacheable_peers(address_book: &Arc<Mutex<AddressBook>>) -> Vec<MetaAddr> {
// TODO: use spawn_blocking() here, if needed to handle address book mutex load
let now = Utc::now();
// # Concurrency
//
// We return from this function immediately to make sure the address book is unlocked.
address_book
.lock()
.expect("unexpected panic in previous thread while accessing the address book")
.cacheable(now)
}