530 lines
20 KiB
Rust
530 lines
20 KiB
Rust
//! A peer set whose size is dynamically determined by resource constraints.
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// Portions of this submodule were adapted from tower-balance,
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// which is (c) 2019 Tower Contributors (MIT licensed).
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use std::{net::SocketAddr, sync::Arc};
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use futures::{
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channel::mpsc,
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future::{self, FutureExt},
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sink::SinkExt,
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stream::{FuturesUnordered, StreamExt},
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TryFutureExt,
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};
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use tokio::{net::TcpListener, sync::broadcast, time::Instant};
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use tower::{
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buffer::Buffer, discover::Change, layer::Layer, load::peak_ewma::PeakEwmaDiscover,
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util::BoxService, Service, ServiceExt,
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};
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use tracing::Span;
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use tracing_futures::Instrument;
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use crate::{
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constants, meta_addr::MetaAddr, peer, timestamp_collector::TimestampCollector, AddressBook,
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BoxError, Config, Request, Response,
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};
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use zebra_chain::parameters::Network;
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use super::CandidateSet;
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use super::PeerSet;
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use peer::Client;
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#[cfg(test)]
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mod tests;
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type PeerChange = Result<Change<SocketAddr, peer::Client>, BoxError>;
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/// Initialize a peer set.
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///
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/// The peer set abstracts away peer management to provide a
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/// [`tower::Service`] representing "the network" that load-balances requests
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/// over available peers. The peer set automatically crawls the network to
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/// find more peer addresses and opportunistically connects to new peers.
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///
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/// Each peer connection's message handling is isolated from other
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/// connections, unlike in `zcashd`. The peer connection first attempts to
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/// interpret inbound messages as part of a response to a previously-issued
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/// request. Otherwise, inbound messages are interpreted as requests and sent
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/// to the supplied `inbound_service`.
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///
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/// Wrapping the `inbound_service` in [`tower::load_shed`] middleware will
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/// cause the peer set to shrink when the inbound service is unable to keep up
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/// with the volume of inbound requests.
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///
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/// In addition to returning a service for outbound requests, this method
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/// returns a shared [`AddressBook`] updated with last-seen timestamps for
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/// connected peers.
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pub async fn init<S>(
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config: Config,
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inbound_service: S,
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) -> (
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Buffer<BoxService<Request, Response, BoxError>, Request>,
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Arc<std::sync::Mutex<AddressBook>>,
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)
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where
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S: Service<Request, Response = Response, Error = BoxError> + Clone + Send + 'static,
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S::Future: Send + 'static,
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{
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let (tcp_listener, listen_addr) = open_listener(&config.clone()).await;
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let (address_book, timestamp_collector) = TimestampCollector::spawn(listen_addr);
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let (inv_sender, inv_receiver) = broadcast::channel(100);
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// Construct services that handle inbound handshakes and perform outbound
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// handshakes. These use the same handshake service internally to detect
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// self-connection attempts. Both are decorated with a tower TimeoutLayer to
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// enforce timeouts as specified in the Config.
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let (listen_handshaker, outbound_connector) = {
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use tower::timeout::TimeoutLayer;
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let hs_timeout = TimeoutLayer::new(constants::HANDSHAKE_TIMEOUT);
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use crate::protocol::external::types::PeerServices;
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let hs = peer::Handshake::builder()
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.with_config(config.clone())
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.with_inbound_service(inbound_service)
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.with_inventory_collector(inv_sender)
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.with_timestamp_collector(timestamp_collector)
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.with_advertised_services(PeerServices::NODE_NETWORK)
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.with_user_agent(crate::constants::USER_AGENT.to_string())
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.want_transactions(true)
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.finish()
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.expect("configured all required parameters");
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(
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hs_timeout.layer(hs.clone()),
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hs_timeout.layer(peer::Connector::new(hs)),
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)
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};
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// Create an mpsc channel for peer changes, with a generous buffer.
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let (peerset_tx, peerset_rx) = mpsc::channel::<PeerChange>(100);
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// Create an mpsc channel for peerset demand signaling.
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let (mut demand_tx, demand_rx) = mpsc::channel::<()>(100);
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let (handle_tx, handle_rx) = tokio::sync::oneshot::channel();
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// Connect the rx end to a PeerSet, wrapping new peers in load instruments.
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let peer_set = PeerSet::new(
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PeakEwmaDiscover::new(
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// Discover interprets an error as stream termination,
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// so discard any errored connections...
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peerset_rx.filter(|result| future::ready(result.is_ok())),
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constants::EWMA_DEFAULT_RTT,
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constants::EWMA_DECAY_TIME,
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tower::load::CompleteOnResponse::default(),
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),
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demand_tx.clone(),
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handle_rx,
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inv_receiver,
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address_book.clone(),
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);
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let peer_set = Buffer::new(BoxService::new(peer_set), constants::PEERSET_BUFFER_SIZE);
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// 1. Incoming peer connections, via a listener.
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let listen_guard = tokio::spawn(
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accept_inbound_connections(tcp_listener, listen_handshaker, peerset_tx.clone())
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.instrument(Span::current()),
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);
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// 2. Initial peers, specified in the config.
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let (initial_peer_count_tx, initial_peer_count_rx) = tokio::sync::oneshot::channel();
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let initial_peers_fut = {
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let config = config.clone();
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let outbound_connector = outbound_connector.clone();
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let peerset_tx = peerset_tx.clone();
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async move {
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let initial_peers = config.initial_peers().await;
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let _ = initial_peer_count_tx.send(initial_peers.len());
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// Connect the tx end to the 3 peer sources:
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add_initial_peers(initial_peers, outbound_connector, peerset_tx).await
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}
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.boxed()
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};
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let add_guard = tokio::spawn(initial_peers_fut.instrument(Span::current()));
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// 3. Outgoing peers we connect to in response to load.
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let mut candidates = CandidateSet::new(address_book.clone(), peer_set.clone());
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// We need to await candidates.update() here, because zcashd only sends one
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// `addr` message per connection, and if we only have one initial peer we
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// need to ensure that its `addr` message is used by the crawler.
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info!("Sending initial request for peers");
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let _ = candidates
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.update_initial(initial_peer_count_rx.await.expect("value sent before drop"))
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.await;
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for _ in 0..config.peerset_initial_target_size {
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let _ = demand_tx.try_send(());
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}
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let crawl_guard = tokio::spawn(
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crawl_and_dial(
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config.crawl_new_peer_interval,
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demand_tx,
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demand_rx,
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candidates,
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outbound_connector,
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peerset_tx,
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)
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.instrument(Span::current()),
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);
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handle_tx
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.send(vec![add_guard, listen_guard, crawl_guard])
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.unwrap();
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(peer_set, address_book)
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}
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/// Use the provided `handshaker` to connect to `initial_peers`, then send
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/// the results over `tx`.
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#[instrument(skip(initial_peers, outbound_connector, tx))]
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async fn add_initial_peers<S>(
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initial_peers: std::collections::HashSet<SocketAddr>,
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outbound_connector: S,
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mut tx: mpsc::Sender<PeerChange>,
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) -> Result<(), BoxError>
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where
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S: Service<SocketAddr, Response = Change<SocketAddr, peer::Client>, Error = BoxError> + Clone,
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S::Future: Send + 'static,
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{
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info!(?initial_peers, "connecting to initial peer set");
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// # Security
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//
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// TODO: rate-limit initial seed peer connections (#2326)
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//
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// # Correctness
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//
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// Each `FuturesUnordered` can hold one `Buffer` or `Batch` reservation for
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// an indefinite period. We can use `FuturesUnordered` without filling
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// the underlying network buffers, because we immediately drive this
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// single `FuturesUnordered` to completion, and handshakes have a short timeout.
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let mut handshakes: FuturesUnordered<_> = initial_peers
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.into_iter()
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.map(|addr| {
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outbound_connector
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.clone()
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.oneshot(addr)
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.map_err(move |e| (addr, e))
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})
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.collect();
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while let Some(handshake_result) = handshakes.next().await {
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// this is verbose, but it's better than just hanging with no output
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if let Err((addr, ref e)) = handshake_result {
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info!(?addr, ?e, "an initial peer connection failed");
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}
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tx.send(handshake_result.map_err(|(_addr, e)| e)).await?;
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}
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Ok(())
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}
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/// Open a peer connection listener on `config.listen_addr`,
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/// returning the opened [`TcpListener`], and the address it is bound to.
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///
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/// If the listener is configured to use an automatically chosen port (port `0`),
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/// then the returned address will contain the actual port.
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///
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/// # Panics
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///
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/// If opening the listener fails.
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#[instrument(skip(config), fields(addr = ?config.listen_addr))]
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async fn open_listener(config: &Config) -> (TcpListener, SocketAddr) {
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// Warn if we're configured using the wrong network port.
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use Network::*;
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let wrong_net = match config.network {
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Mainnet => Testnet,
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Testnet => Mainnet,
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};
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if config.listen_addr.port() == wrong_net.default_port() {
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warn!(
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"We are configured with port {} for {:?}, but that port is the default port for {:?}",
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config.listen_addr.port(),
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config.network,
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wrong_net
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);
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}
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info!(
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"Trying to open Zcash protocol endpoint at {}...",
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config.listen_addr
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);
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let listener_result = TcpListener::bind(config.listen_addr).await;
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let listener = match listener_result {
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Ok(l) => l,
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Err(e) => panic!(
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"Opening Zcash network protocol listener {:?} failed: {:?}. \
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Hint: Check if another zebrad or zcashd process is running. \
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Try changing the network listen_addr in the Zebra config.",
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config.listen_addr, e,
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),
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};
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let local_addr = listener
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.local_addr()
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.expect("unexpected missing local addr for open listener");
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info!("Opened Zcash protocol endpoint at {}", local_addr);
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(listener, local_addr)
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}
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/// Listens for peer connections on `addr`, then sets up each connection as a
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/// Zcash peer.
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///
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/// Uses `handshaker` to perform a Zcash network protocol handshake, and sends
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/// the [`Client`][peer::Client] result over `tx`.
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#[instrument(skip(listener, handshaker, tx), fields(listener_addr = ?listener.local_addr()))]
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async fn accept_inbound_connections<S>(
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listener: TcpListener,
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mut handshaker: S,
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tx: mpsc::Sender<PeerChange>,
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) -> Result<(), BoxError>
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where
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S: Service<peer::HandshakeRequest, Response = peer::Client, Error = BoxError> + Clone,
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S::Future: Send + 'static,
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{
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loop {
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if let Ok((tcp_stream, addr)) = listener.accept().await {
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let connected_addr = peer::ConnectedAddr::new_inbound_direct(addr);
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let accept_span = info_span!("listen_accept", peer = ?connected_addr);
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let _guard = accept_span.enter();
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debug!("got incoming connection");
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handshaker.ready_and().await?;
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// TODO: distinguish between proxied listeners and direct listeners
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let handshaker_span = info_span!("listen_handshaker", peer = ?connected_addr);
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// Construct a handshake future but do not drive it yet....
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let handshake = handshaker.call((tcp_stream, connected_addr));
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// ... instead, spawn a new task to handle this connection
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let mut tx2 = tx.clone();
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tokio::spawn(
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async move {
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if let Ok(client) = handshake.await {
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let _ = tx2.send(Ok(Change::Insert(addr, client))).await;
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}
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}
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.instrument(handshaker_span),
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);
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}
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}
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}
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/// An action that the peer crawler can take.
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#[allow(dead_code)]
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enum CrawlerAction {
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/// Drop the demand signal because there are too many pending handshakes.
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DemandDrop,
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/// Initiate a handshake to `candidate` in response to demand.
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DemandHandshake { candidate: MetaAddr },
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/// Crawl existing peers for more peers in response to demand, because there
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/// are no available candidates.
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DemandCrawl,
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/// Crawl existing peers for more peers in response to a timer `tick`.
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TimerCrawl { tick: Instant },
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/// Handle a successfully connected handshake `peer_set_change`.
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HandshakeConnected {
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peer_set_change: Change<SocketAddr, Client>,
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},
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/// Handle a handshake failure to `failed_addr`.
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HandshakeFailed { failed_addr: MetaAddr },
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}
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/// Given a channel `demand_rx` that signals a need for new peers, try to find
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/// and connect to new peers, and send the resulting `peer::Client`s through the
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/// `success_tx` channel.
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///
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/// Crawl for new peers every `crawl_new_peer_interval`, and whenever there is
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/// demand, but no new peers in `candidates`. After crawling, try to connect to
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/// one new peer using `outbound_connector`.
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///
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/// If a handshake fails, restore the unused demand signal by sending it to
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/// `demand_tx`.
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///
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/// The crawler terminates when `candidates.update()` or `success_tx` returns a
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/// permanent internal error. Transient errors and individual peer errors should
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/// be handled within the crawler.
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#[instrument(skip(demand_tx, demand_rx, candidates, outbound_connector, success_tx))]
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async fn crawl_and_dial<C, S>(
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crawl_new_peer_interval: std::time::Duration,
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mut demand_tx: mpsc::Sender<()>,
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mut demand_rx: mpsc::Receiver<()>,
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mut candidates: CandidateSet<S>,
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outbound_connector: C,
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mut success_tx: mpsc::Sender<PeerChange>,
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) -> Result<(), BoxError>
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where
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C: Service<SocketAddr, Response = Change<SocketAddr, peer::Client>, Error = BoxError>
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+ Clone
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+ Send
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+ 'static,
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C::Future: Send + 'static,
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S: Service<Request, Response = Response, Error = BoxError>,
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S::Future: Send + 'static,
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{
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use CrawlerAction::*;
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// CORRECTNESS
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//
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// To avoid hangs and starvation, the crawler must:
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// - spawn a separate task for each crawl and handshake, so they can make
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// progress independently (and avoid deadlocking each other)
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// - use the `select!` macro for all actions, because the `select` function
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// is biased towards the first ready future
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let mut handshakes = FuturesUnordered::new();
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// <FuturesUnordered as Stream> returns None when empty.
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// Keeping an unresolved future in the pool means the stream
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// never terminates.
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// We could use StreamExt::select_next_some and StreamExt::fuse, but `fuse`
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// prevents us from adding items to the stream and checking its length.
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handshakes.push(future::pending().boxed());
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let mut crawl_timer =
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tokio::time::interval(crawl_new_peer_interval).map(|tick| TimerCrawl { tick });
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loop {
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metrics::gauge!(
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"crawler.in_flight_handshakes",
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handshakes
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.len()
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.checked_sub(1)
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.expect("the pool always contains an unresolved future") as f64
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);
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let crawler_action = tokio::select! {
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next_handshake_res = handshakes.next() => next_handshake_res.expect(
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"handshakes never terminates, because it contains a future that never resolves"
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),
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next_timer = crawl_timer.next() => next_timer.expect("timers never terminate"),
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// turn the demand into an action, based on the crawler's current state
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_ = demand_rx.next() => {
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if handshakes.len() > 50 {
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// Too many pending handshakes already
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DemandDrop
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} else if let Some(candidate) = candidates.next().await {
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// candidates.next has a short delay, and briefly holds the address
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// book lock, so it shouldn't hang
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DemandHandshake { candidate }
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} else {
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DemandCrawl
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}
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}
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};
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match crawler_action {
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DemandDrop => {
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// This is set to trace level because when the peerset is
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// congested it can generate a lot of demand signal very
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// rapidly.
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trace!("too many in-flight handshakes, dropping demand signal");
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continue;
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}
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DemandHandshake { candidate } => {
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// spawn each handshake into an independent task, so it can make
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// progress independently of the crawls
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let hs_join = tokio::spawn(dial(candidate, outbound_connector.clone()))
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.map(move |res| match res {
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Ok(crawler_action) => crawler_action,
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Err(e) => {
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panic!("panic during handshaking with {:?}: {:?} ", candidate, e);
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}
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})
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.instrument(Span::current());
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handshakes.push(Box::pin(hs_join));
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}
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DemandCrawl => {
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debug!("demand for peers but no available candidates");
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// update has timeouts, and briefly holds the address book
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// lock, so it shouldn't hang
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//
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// TODO: refactor candidates into a buffered service, so we can
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// spawn independent tasks to avoid deadlocks
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candidates.update().await?;
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// Try to connect to a new peer.
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let _ = demand_tx.try_send(());
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}
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TimerCrawl { tick } => {
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debug!(
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?tick,
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"crawling for more peers in response to the crawl timer"
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);
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// TODO: spawn independent tasks to avoid deadlocks
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candidates.update().await?;
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// Try to connect to a new peer.
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let _ = demand_tx.try_send(());
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}
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HandshakeConnected { peer_set_change } => {
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if let Change::Insert(ref addr, _) = peer_set_change {
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debug!(candidate.addr = ?addr, "successfully dialed new peer");
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} else {
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unreachable!("unexpected handshake result: all changes should be Insert");
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}
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// successes are handled by an independent task, so they
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// shouldn't hang
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success_tx.send(Ok(peer_set_change)).await?;
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}
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HandshakeFailed { failed_addr } => {
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debug!(?failed_addr.addr, "marking candidate as failed");
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candidates.report_failed(&failed_addr);
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// The demand signal that was taken out of the queue
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// to attempt to connect to the failed candidate never
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// turned into a connection, so add it back:
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let _ = demand_tx.try_send(());
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}
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}
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}
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}
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/// Try to connect to `candidate` using `outbound_connector`.
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///
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/// Returns a `HandshakeConnected` action on success, and a
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/// `HandshakeFailed` action on error.
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#[instrument(skip(outbound_connector,))]
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|
async fn dial<C>(candidate: MetaAddr, mut outbound_connector: C) -> CrawlerAction
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|
where
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|
C: Service<SocketAddr, Response = Change<SocketAddr, peer::Client>, Error = BoxError>
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|
+ Clone
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|
+ Send
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|
+ 'static,
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|
C::Future: Send + 'static,
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|
{
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|
// CORRECTNESS
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|
//
|
|
// To avoid hangs, the dialer must only await:
|
|
// - functions that return immediately, or
|
|
// - functions that have a reasonable timeout
|
|
|
|
debug!(?candidate.addr, "attempting outbound connection in response to demand");
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|
|
|
// the connector is always ready, so this can't hang
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|
let outbound_connector = outbound_connector
|
|
.ready_and()
|
|
.await
|
|
.expect("outbound connector never errors");
|
|
|
|
// the handshake has timeouts, so it shouldn't hang
|
|
outbound_connector
|
|
.call(candidate.addr)
|
|
.map_err(|e| (candidate, e))
|
|
.map(Into::into)
|
|
.await
|
|
}
|
|
|
|
impl From<Result<Change<SocketAddr, Client>, (MetaAddr, BoxError)>> for CrawlerAction {
|
|
fn from(dial_result: Result<Change<SocketAddr, Client>, (MetaAddr, BoxError)>) -> Self {
|
|
use CrawlerAction::*;
|
|
match dial_result {
|
|
Ok(peer_set_change) => HandshakeConnected { peer_set_change },
|
|
Err((candidate, e)) => {
|
|
debug!(?candidate.addr, ?e, "failed to connect to candidate");
|
|
HandshakeFailed {
|
|
failed_addr: candidate,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|