946 lines
37 KiB
Rust
946 lines
37 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::{
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collections::{BTreeMap, HashSet},
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net::SocketAddr,
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sync::Arc,
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time::Duration,
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};
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use futures::{
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future::{self, FutureExt},
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sink::SinkExt,
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stream::{FuturesUnordered, StreamExt, TryStreamExt},
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TryFutureExt,
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};
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use rand::seq::SliceRandom;
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use tokio::{
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net::{TcpListener, TcpStream},
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sync::broadcast,
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time::{sleep, Instant},
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};
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use tokio_stream::wrappers::IntervalStream;
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use tower::{
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buffer::Buffer, discover::Change, layer::Layer, util::BoxService, Service, ServiceExt,
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};
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use tracing_futures::Instrument;
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use zebra_chain::chain_tip::ChainTip;
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use crate::{
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address_book_updater::AddressBookUpdater,
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constants,
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meta_addr::{MetaAddr, MetaAddrChange},
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peer::{
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self, address_is_valid_for_inbound_listeners, HandshakeRequest, MinimumPeerVersion,
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OutboundConnectorRequest, PeerPreference,
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},
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peer_cache_updater::peer_cache_updater,
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peer_set::{set::MorePeers, ActiveConnectionCounter, CandidateSet, ConnectionTracker, PeerSet},
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AddressBook, BoxError, Config, PeerSocketAddr, Request, Response,
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};
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#[cfg(test)]
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mod tests;
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/// The result of an outbound peer connection attempt or inbound connection
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/// handshake.
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///
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/// This result comes from the `Handshaker`.
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type DiscoveredPeer = Result<(PeerSocketAddr, peer::Client), BoxError>;
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/// Initialize a peer set, using a network `config`, `inbound_service`,
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/// and `latest_chain_tip`.
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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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/// Use [`NoChainTip`][1] to explicitly provide no chain tip receiver.
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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. The shared address book should be accessed using a
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/// [blocking thread](https://docs.rs/tokio/1.15.0/tokio/task/index.html#blocking-and-yielding),
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/// to avoid async task deadlocks.
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///
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/// # Panics
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///
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/// If `config.config.peerset_initial_target_size` is zero.
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/// (zebra-network expects to be able to connect to at least one peer.)
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///
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/// [1]: zebra_chain::chain_tip::NoChainTip
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pub async fn init<S, C>(
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config: Config,
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inbound_service: S,
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latest_chain_tip: C,
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user_agent: String,
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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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C: ChainTip + Clone + Send + 'static,
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{
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// If we want Zebra to operate with no network,
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// we should implement a `zebrad` command that doesn't use `zebra-network`.
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assert!(
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config.peerset_initial_target_size > 0,
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"Zebra must be allowed to connect to at least one peer"
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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, address_book_updater, address_metrics, address_book_updater_guard) =
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AddressBookUpdater::spawn(&config, listen_addr);
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// Create a broadcast channel for peer inventory advertisements.
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// If it reaches capacity, this channel drops older inventory advertisements.
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//
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// When Zebra is at the chain tip with an up-to-date mempool,
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// we expect to have at most 1 new transaction per connected peer,
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// and 1-2 new blocks across the entire network.
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// (The block syncer and mempool crawler handle bulk fetches of blocks and transactions.)
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let (inv_sender, inv_receiver) = broadcast::channel(config.peerset_total_connection_limit());
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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_address_book_updater(address_book_updater.clone())
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.with_advertised_services(PeerServices::NODE_NETWORK)
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.with_user_agent(user_agent)
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.with_latest_chain_tip(latest_chain_tip.clone())
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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,
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// based on the maximum number of inbound and outbound peers.
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let (peerset_tx, peerset_rx) =
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futures::channel::mpsc::channel::<DiscoveredPeer>(config.peerset_total_connection_limit());
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let discovered_peers = peerset_rx
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// Discover interprets an error as stream termination,
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// so discard any errored connections...
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.filter(|result| future::ready(result.is_ok()))
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.map_ok(|(address, client)| Change::Insert(address, client.into()));
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// Create an mpsc channel for peerset demand signaling,
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// based on the maximum number of outbound peers.
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let (mut demand_tx, demand_rx) =
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futures::channel::mpsc::channel::<MorePeers>(config.peerset_outbound_connection_limit());
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// Create a oneshot to send background task JoinHandles to the peer set
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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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&config,
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discovered_peers,
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demand_tx.clone(),
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handle_rx,
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inv_receiver,
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address_metrics,
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MinimumPeerVersion::new(latest_chain_tip, config.network),
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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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// Connect peerset_tx to the 3 peer sources:
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//
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// 1. Incoming peer connections, via a listener.
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let listen_fut = accept_inbound_connections(
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config.clone(),
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tcp_listener,
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constants::MIN_INBOUND_PEER_CONNECTION_INTERVAL,
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listen_handshaker,
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peerset_tx.clone(),
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);
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let listen_guard = tokio::spawn(listen_fut.in_current_span());
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// 2. Initial peers, specified in the config and cached on disk.
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let initial_peers_fut = add_initial_peers(
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config.clone(),
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outbound_connector.clone(),
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peerset_tx.clone(),
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address_book_updater,
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);
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let initial_peers_join = tokio::spawn(initial_peers_fut.in_current_span());
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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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// Wait for the initial seed peer count
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let mut active_outbound_connections = initial_peers_join
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.await
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.expect("unexpected panic in spawned initial peers task")
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.expect("unexpected error connecting to initial peers");
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let active_initial_peer_count = active_outbound_connections.update_count();
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// We need to await candidates.update() here,
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// because zcashd rate-limits `addr`/`addrv2` messages per connection,
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// and if we only have one initial peer,
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// we need to ensure that its `Response::Addr` is used by the crawler.
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info!(
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?active_initial_peer_count,
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"sending initial request for peers"
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);
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let _ = candidates.update_initial(active_initial_peer_count).await;
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// Compute remaining connections to open.
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let demand_count = config
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.peerset_initial_target_size
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.saturating_sub(active_outbound_connections.update_count());
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for _ in 0..demand_count {
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let _ = demand_tx.try_send(MorePeers);
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}
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// Start the peer crawler
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let crawl_fut = crawl_and_dial(
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config.clone(),
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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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active_outbound_connections,
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);
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let crawl_guard = tokio::spawn(crawl_fut.in_current_span());
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// Start the peer disk cache updater
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let peer_cache_updater_fut = peer_cache_updater(config, address_book.clone());
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let peer_cache_updater_guard = tokio::spawn(peer_cache_updater_fut.in_current_span());
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handle_tx
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.send(vec![
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listen_guard,
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crawl_guard,
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address_book_updater_guard,
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peer_cache_updater_guard,
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])
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.unwrap();
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(peer_set, address_book)
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}
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/// Use the provided `outbound_connector` to connect to the configured DNS seeder and
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/// disk cache initial peers, then send the resulting peer connections over `peerset_tx`.
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///
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/// Also sends every initial peer address to the `address_book_updater`.
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#[instrument(skip(config, outbound_connector, peerset_tx, address_book_updater))]
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async fn add_initial_peers<S>(
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config: Config,
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outbound_connector: S,
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mut peerset_tx: futures::channel::mpsc::Sender<DiscoveredPeer>,
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address_book_updater: tokio::sync::mpsc::Sender<MetaAddrChange>,
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) -> Result<ActiveConnectionCounter, BoxError>
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where
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S: Service<
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OutboundConnectorRequest,
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Response = (PeerSocketAddr, peer::Client),
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Error = BoxError,
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> + Clone
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+ Send
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+ 'static,
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S::Future: Send + 'static,
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{
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let initial_peers = limit_initial_peers(&config, address_book_updater).await;
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let mut handshake_success_total: usize = 0;
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let mut handshake_error_total: usize = 0;
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let mut active_outbound_connections = ActiveConnectionCounter::new_counter_with(
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config.peerset_outbound_connection_limit(),
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"Outbound Connections",
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);
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// TODO: update when we add Tor peers or other kinds of addresses.
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let ipv4_peer_count = initial_peers.iter().filter(|ip| ip.is_ipv4()).count();
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let ipv6_peer_count = initial_peers.iter().filter(|ip| ip.is_ipv6()).count();
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info!(
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?ipv4_peer_count,
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?ipv6_peer_count,
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"connecting to initial peer set"
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);
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// # Security
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//
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// Resists distributed denial of service attacks by making sure that
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// new peer connections are initiated at least `MIN_OUTBOUND_PEER_CONNECTION_INTERVAL` apart.
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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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.enumerate()
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.map(|(i, addr)| {
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let connection_tracker = active_outbound_connections.track_connection();
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let req = OutboundConnectorRequest {
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addr,
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connection_tracker,
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};
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let outbound_connector = outbound_connector.clone();
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// Spawn a new task to make the outbound connection.
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tokio::spawn(
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async move {
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// Only spawn one outbound connector per
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// `MIN_OUTBOUND_PEER_CONNECTION_INTERVAL`,
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// by sleeping for the interval multiplied by the peer's index in the list.
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sleep(
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constants::MIN_OUTBOUND_PEER_CONNECTION_INTERVAL.saturating_mul(i as u32),
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)
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.await;
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// As soon as we create the connector future,
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// the handshake starts running as a spawned task.
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outbound_connector
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.oneshot(req)
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.map_err(move |e| (addr, e))
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.await
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}
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.in_current_span(),
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)
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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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let handshake_result =
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handshake_result.expect("unexpected panic in initial peer handshake");
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match handshake_result {
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Ok(ref change) => {
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handshake_success_total += 1;
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debug!(
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?handshake_success_total,
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?handshake_error_total,
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?change,
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"an initial peer handshake succeeded"
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);
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}
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Err((addr, ref e)) => {
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handshake_error_total += 1;
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// this is verbose, but it's better than just hanging with no output when there are errors
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let mut expected_error = false;
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if let Some(io_error) = e.downcast_ref::<tokio::io::Error>() {
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// Some systems only have IPv4, or only have IPv6,
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// so these errors are not particularly interesting.
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if io_error.kind() == tokio::io::ErrorKind::AddrNotAvailable {
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expected_error = true;
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}
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}
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if expected_error {
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debug!(
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successes = ?handshake_success_total,
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errors = ?handshake_error_total,
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?addr,
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?e,
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"an initial peer connection failed"
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);
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} else {
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info!(
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successes = ?handshake_success_total,
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errors = ?handshake_error_total,
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?addr,
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%e,
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"an initial peer connection failed"
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);
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}
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}
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}
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peerset_tx
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.send(handshake_result.map_err(|(_addr, e)| e))
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.await?;
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// Security: Let other tasks run after each connection is processed.
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//
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// Avoids remote peers starving other Zebra tasks using initial connection successes or errors.
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tokio::task::yield_now().await;
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}
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let outbound_connections = active_outbound_connections.update_count();
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info!(
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?handshake_success_total,
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?handshake_error_total,
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?outbound_connections,
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"finished connecting to initial seed and disk cache peers"
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);
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Ok(active_outbound_connections)
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}
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/// Limit the number of `initial_peers` addresses entries to the configured
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/// `peerset_initial_target_size`.
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///
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/// Returns randomly chosen entries from the provided set of addresses,
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/// in a random order.
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///
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/// Also sends every initial peer to the `address_book_updater`.
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async fn limit_initial_peers(
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config: &Config,
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address_book_updater: tokio::sync::mpsc::Sender<MetaAddrChange>,
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) -> HashSet<PeerSocketAddr> {
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let all_peers: HashSet<PeerSocketAddr> = config.initial_peers().await;
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let mut preferred_peers: BTreeMap<PeerPreference, Vec<PeerSocketAddr>> = BTreeMap::new();
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let all_peers_count = all_peers.len();
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if all_peers_count > config.peerset_initial_target_size {
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info!(
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"limiting the initial peers list from {} to {}",
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all_peers_count, config.peerset_initial_target_size,
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);
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}
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|
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// Filter out invalid initial peers, and prioritise valid peers for initial connections.
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// (This treats initial peers the same way we treat gossiped peers.)
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for peer_addr in all_peers {
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let preference = PeerPreference::new(peer_addr, config.network);
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|
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match preference {
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Ok(preference) => preferred_peers
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.entry(preference)
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.or_default()
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.push(peer_addr),
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Err(error) => info!(
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?peer_addr,
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?error,
|
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"invalid initial peer from DNS seeder, configured IP address, or disk cache",
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),
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}
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}
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|
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// Send every initial peer to the address book, in preferred order.
|
|
// (This treats initial peers the same way we treat gossiped peers.)
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//
|
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// # Security
|
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//
|
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// Initial peers are limited because:
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// - the number of initial peers is limited
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// - this code only runs once at startup
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for peer in preferred_peers.values().flatten() {
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let peer_addr = MetaAddr::new_initial_peer(*peer);
|
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// `send` only waits when the channel is full.
|
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// The address book updater runs in its own thread, so we will only wait for a short time.
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let _ = address_book_updater.send(peer_addr).await;
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}
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|
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// Split out the `initial_peers` that will be shuffled and returned,
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// choosing preferred peers first.
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let mut initial_peers: HashSet<PeerSocketAddr> = HashSet::new();
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for better_peers in preferred_peers.values() {
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let mut better_peers = better_peers.clone();
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let (chosen_peers, _unused_peers) = better_peers.partial_shuffle(
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&mut rand::thread_rng(),
|
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config.peerset_initial_target_size - initial_peers.len(),
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);
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|
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initial_peers.extend(chosen_peers.iter());
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|
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if initial_peers.len() >= config.peerset_initial_target_size {
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break;
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}
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}
|
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|
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initial_peers
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}
|
|
|
|
/// Open a peer connection listener on `config.listen_addr`,
|
|
/// returning the opened [`TcpListener`], and the address it is bound to.
|
|
///
|
|
/// 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.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// If opening the listener fails.
|
|
#[instrument(skip(config), fields(addr = ?config.listen_addr))]
|
|
pub(crate) async fn open_listener(config: &Config) -> (TcpListener, SocketAddr) {
|
|
// Warn if we're configured using the wrong network port.
|
|
if let Err(wrong_addr) =
|
|
address_is_valid_for_inbound_listeners(config.listen_addr, config.network)
|
|
{
|
|
warn!(
|
|
"We are configured with address {} on {:?}, but it could cause network issues. \
|
|
The default port for {:?} is {}. Error: {wrong_addr:?}",
|
|
config.listen_addr,
|
|
config.network,
|
|
config.network,
|
|
config.network.default_port(),
|
|
);
|
|
}
|
|
|
|
info!(
|
|
"Trying to open Zcash protocol endpoint at {}...",
|
|
config.listen_addr
|
|
);
|
|
let listener_result = TcpListener::bind(config.listen_addr).await;
|
|
|
|
let listener = match listener_result {
|
|
Ok(l) => l,
|
|
Err(e) => panic!(
|
|
"Opening Zcash network protocol listener {:?} failed: {e:?}. \
|
|
Hint: Check if another zebrad or zcashd process is running. \
|
|
Try changing the network listen_addr in the Zebra config.",
|
|
config.listen_addr,
|
|
),
|
|
};
|
|
|
|
let local_addr = listener
|
|
.local_addr()
|
|
.expect("unexpected missing local addr for open listener");
|
|
info!("Opened Zcash protocol endpoint at {}", local_addr);
|
|
|
|
(listener, local_addr)
|
|
}
|
|
|
|
/// Listens for peer connections on `addr`, then sets up each connection as a
|
|
/// Zcash peer.
|
|
///
|
|
/// Uses `handshaker` to perform a Zcash network protocol handshake, and sends
|
|
/// the [`peer::Client`] result over `peerset_tx`.
|
|
///
|
|
/// Limits the number of active inbound connections based on `config`,
|
|
/// and waits `min_inbound_peer_connection_interval` between connections.
|
|
#[instrument(skip(config, listener, handshaker, peerset_tx), fields(listener_addr = ?listener.local_addr()))]
|
|
async fn accept_inbound_connections<S>(
|
|
config: Config,
|
|
listener: TcpListener,
|
|
min_inbound_peer_connection_interval: Duration,
|
|
mut handshaker: S,
|
|
peerset_tx: futures::channel::mpsc::Sender<DiscoveredPeer>,
|
|
) -> Result<(), BoxError>
|
|
where
|
|
S: Service<peer::HandshakeRequest<TcpStream>, Response = peer::Client, Error = BoxError>
|
|
+ Clone,
|
|
S::Future: Send + 'static,
|
|
{
|
|
let mut active_inbound_connections = ActiveConnectionCounter::new_counter_with(
|
|
config.peerset_inbound_connection_limit(),
|
|
"Inbound Connections",
|
|
);
|
|
|
|
let mut handshakes = FuturesUnordered::new();
|
|
// Keeping an unresolved future in the pool means the stream never terminates.
|
|
handshakes.push(future::pending().boxed());
|
|
|
|
loop {
|
|
// Check for panics in finished tasks, before accepting new connections
|
|
let inbound_result = tokio::select! {
|
|
biased;
|
|
next_handshake_res = handshakes.next() => match next_handshake_res {
|
|
// The task has already sent the peer change to the peer set.
|
|
Some(Ok(_)) => continue,
|
|
Some(Err(task_panic)) => panic!("panic in inbound handshake task: {task_panic:?}"),
|
|
None => unreachable!("handshakes never terminates, because it contains a future that never resolves"),
|
|
},
|
|
|
|
inbound_result = listener.accept() => inbound_result,
|
|
};
|
|
|
|
if let Ok((tcp_stream, addr)) = inbound_result {
|
|
let addr: PeerSocketAddr = addr.into();
|
|
|
|
if active_inbound_connections.update_count()
|
|
>= config.peerset_inbound_connection_limit()
|
|
{
|
|
// Too many open inbound connections or pending handshakes already.
|
|
// Close the connection.
|
|
std::mem::drop(tcp_stream);
|
|
continue;
|
|
}
|
|
|
|
// The peer already opened a connection to us.
|
|
// So we want to increment the connection count as soon as possible.
|
|
let connection_tracker = active_inbound_connections.track_connection();
|
|
debug!(
|
|
inbound_connections = ?active_inbound_connections.update_count(),
|
|
"handshaking on an open inbound peer connection"
|
|
);
|
|
|
|
let connected_addr = peer::ConnectedAddr::new_inbound_direct(addr);
|
|
let accept_span = info_span!("listen_accept", peer = ?connected_addr);
|
|
let _guard = accept_span.enter();
|
|
|
|
debug!("got incoming connection");
|
|
handshaker.ready().await?;
|
|
// TODO: distinguish between proxied listeners and direct listeners
|
|
let handshaker_span = info_span!("listen_handshaker", peer = ?connected_addr);
|
|
|
|
// Construct a handshake future but do not drive it yet....
|
|
let handshake = handshaker.call(HandshakeRequest {
|
|
data_stream: tcp_stream,
|
|
connected_addr,
|
|
connection_tracker,
|
|
});
|
|
// ... instead, spawn a new task to handle this connection
|
|
{
|
|
let mut peerset_tx = peerset_tx.clone();
|
|
|
|
let handshake_task = tokio::spawn(
|
|
async move {
|
|
let handshake_result = handshake.await;
|
|
|
|
if let Ok(client) = handshake_result {
|
|
let _ = peerset_tx.send(Ok((addr, client))).await;
|
|
} else {
|
|
debug!(?handshake_result, "error handshaking with inbound peer");
|
|
}
|
|
}
|
|
.instrument(handshaker_span),
|
|
);
|
|
|
|
handshakes.push(Box::pin(handshake_task));
|
|
}
|
|
|
|
// Rate-limit inbound connection handshakes.
|
|
// But sleep longer after a successful connection,
|
|
// so we can clear out failed connections at a higher rate.
|
|
//
|
|
// If there is a flood of connections,
|
|
// this stops Zebra overloading the network with handshake data.
|
|
//
|
|
// Zebra can't control how many queued connections are waiting,
|
|
// but most OSes also limit the number of queued inbound connections on a listener port.
|
|
tokio::time::sleep(min_inbound_peer_connection_interval).await;
|
|
} else {
|
|
// Allow invalid connections to be cleared quickly,
|
|
// but still put a limit on our CPU and network usage from failed connections.
|
|
debug!(?inbound_result, "error accepting inbound connection");
|
|
tokio::time::sleep(constants::MIN_INBOUND_PEER_FAILED_CONNECTION_INTERVAL).await;
|
|
}
|
|
|
|
// Security: Let other tasks run after each connection is processed.
|
|
//
|
|
// Avoids remote peers starving other Zebra tasks using inbound connection successes or
|
|
// errors.
|
|
//
|
|
// Preventing a denial of service is important in this code, so we want to sleep *and* make
|
|
// the next connection after other tasks have run. (Sleeps are not guaranteed to do that.)
|
|
tokio::task::yield_now().await;
|
|
}
|
|
}
|
|
|
|
/// An action that the peer crawler can take.
|
|
enum CrawlerAction {
|
|
/// Drop the demand signal because there are too many pending handshakes.
|
|
DemandDrop,
|
|
/// Initiate a handshake to `candidate` in response to demand.
|
|
DemandHandshake { candidate: MetaAddr },
|
|
/// Crawl existing peers for more peers in response to demand, because there
|
|
/// are no available candidates.
|
|
DemandCrawl,
|
|
/// Crawl existing peers for more peers in response to a timer `tick`.
|
|
TimerCrawl { tick: Instant },
|
|
/// Handle a successfully connected handshake `peer_set_change`.
|
|
HandshakeConnected {
|
|
address: PeerSocketAddr,
|
|
client: peer::Client,
|
|
},
|
|
/// Handle a handshake failure to `failed_addr`.
|
|
HandshakeFailed { failed_addr: MetaAddr },
|
|
}
|
|
|
|
/// Given a channel `demand_rx` that signals a need for new peers, try to find
|
|
/// and connect to new peers, and send the resulting `peer::Client`s through the
|
|
/// `peerset_tx` channel.
|
|
///
|
|
/// Crawl for new peers every `config.crawl_new_peer_interval`.
|
|
/// Also crawl whenever there is demand, but no new peers in `candidates`.
|
|
/// After crawling, try to connect to one new peer using `outbound_connector`.
|
|
///
|
|
/// If a handshake fails, restore the unused demand signal by sending it to
|
|
/// `demand_tx`.
|
|
///
|
|
/// The crawler terminates when `candidates.update()` or `peerset_tx` returns a
|
|
/// permanent internal error. Transient errors and individual peer errors should
|
|
/// be handled within the crawler.
|
|
///
|
|
/// Uses `active_outbound_connections` to limit the number of active outbound connections
|
|
/// across both the initial peers and crawler. The limit is based on `config`.
|
|
#[instrument(
|
|
skip(
|
|
config,
|
|
demand_tx,
|
|
demand_rx,
|
|
candidates,
|
|
outbound_connector,
|
|
peerset_tx,
|
|
active_outbound_connections,
|
|
),
|
|
fields(
|
|
new_peer_interval = ?config.crawl_new_peer_interval,
|
|
)
|
|
)]
|
|
async fn crawl_and_dial<C, S>(
|
|
config: Config,
|
|
mut demand_tx: futures::channel::mpsc::Sender<MorePeers>,
|
|
mut demand_rx: futures::channel::mpsc::Receiver<MorePeers>,
|
|
mut candidates: CandidateSet<S>,
|
|
outbound_connector: C,
|
|
mut peerset_tx: futures::channel::mpsc::Sender<DiscoveredPeer>,
|
|
mut active_outbound_connections: ActiveConnectionCounter,
|
|
) -> Result<(), BoxError>
|
|
where
|
|
C: Service<
|
|
OutboundConnectorRequest,
|
|
Response = (PeerSocketAddr, peer::Client),
|
|
Error = BoxError,
|
|
> + Clone
|
|
+ Send
|
|
+ 'static,
|
|
C::Future: Send + 'static,
|
|
S: Service<Request, Response = Response, Error = BoxError>,
|
|
S::Future: Send + 'static,
|
|
{
|
|
use CrawlerAction::*;
|
|
|
|
// CORRECTNESS
|
|
//
|
|
// To avoid hangs and starvation, the crawler must:
|
|
// - spawn a separate task for each crawl and handshake, so they can make
|
|
// progress independently (and avoid deadlocking each other)
|
|
// - use the `select!` macro for all actions, because the `select` function
|
|
// is biased towards the first ready future
|
|
|
|
info!(
|
|
crawl_new_peer_interval = ?config.crawl_new_peer_interval,
|
|
outbound_connections = ?active_outbound_connections.update_count(),
|
|
"starting the peer address crawler",
|
|
);
|
|
|
|
let mut handshakes = FuturesUnordered::new();
|
|
// <FuturesUnordered as Stream> returns None when empty.
|
|
// Keeping an unresolved future in the pool means the stream
|
|
// never terminates.
|
|
// We could use StreamExt::select_next_some and StreamExt::fuse, but `fuse`
|
|
// prevents us from adding items to the stream and checking its length.
|
|
handshakes.push(future::pending().boxed());
|
|
|
|
let mut crawl_timer = tokio::time::interval(config.crawl_new_peer_interval);
|
|
// If the crawl is delayed, also delay all future crawls.
|
|
// (Shorter intervals just add load, without any benefit.)
|
|
crawl_timer.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);
|
|
|
|
let mut crawl_timer = IntervalStream::new(crawl_timer).map(|tick| TimerCrawl { tick });
|
|
|
|
loop {
|
|
metrics::gauge!(
|
|
"crawler.in_flight_handshakes",
|
|
handshakes
|
|
.len()
|
|
.checked_sub(1)
|
|
.expect("the pool always contains an unresolved future") as f64,
|
|
);
|
|
|
|
let crawler_action = tokio::select! {
|
|
next_handshake_res = handshakes.next() => next_handshake_res.expect(
|
|
"handshakes never terminates, because it contains a future that never resolves"
|
|
),
|
|
next_timer = crawl_timer.next() => next_timer.expect("timers never terminate"),
|
|
// turn the demand into an action, based on the crawler's current state
|
|
_ = demand_rx.next() => {
|
|
if active_outbound_connections.update_count() >= config.peerset_outbound_connection_limit() {
|
|
// Too many open outbound connections or pending handshakes already
|
|
DemandDrop
|
|
} else if let Some(candidate) = candidates.next().await {
|
|
// candidates.next has a short delay, and briefly holds the address
|
|
// book lock, so it shouldn't hang
|
|
DemandHandshake { candidate }
|
|
} else {
|
|
DemandCrawl
|
|
}
|
|
}
|
|
};
|
|
|
|
match crawler_action {
|
|
DemandDrop => {
|
|
// This is set to trace level because when the peerset is
|
|
// congested it can generate a lot of demand signal very
|
|
// rapidly.
|
|
trace!("too many open connections or in-flight handshakes, dropping demand signal");
|
|
}
|
|
DemandHandshake { candidate } => {
|
|
// Increment the connection count before we spawn the connection.
|
|
let outbound_connection_tracker = active_outbound_connections.track_connection();
|
|
debug!(
|
|
outbound_connections = ?active_outbound_connections.update_count(),
|
|
"opening an outbound peer connection"
|
|
);
|
|
|
|
// Spawn each handshake into an independent task, so it can make
|
|
// progress independently of the crawls.
|
|
let hs_join = tokio::spawn(dial(
|
|
candidate,
|
|
outbound_connector.clone(),
|
|
outbound_connection_tracker,
|
|
))
|
|
.map(move |res| match res {
|
|
Ok(crawler_action) => crawler_action,
|
|
Err(e) => {
|
|
panic!("panic during handshaking with {candidate:?}: {e:?} ");
|
|
}
|
|
})
|
|
.in_current_span();
|
|
|
|
handshakes.push(Box::pin(hs_join));
|
|
}
|
|
DemandCrawl => {
|
|
debug!("demand for peers but no available candidates");
|
|
// update has timeouts, and briefly holds the address book
|
|
// lock, so it shouldn't hang
|
|
//
|
|
// TODO: refactor candidates into a buffered service, so we can
|
|
// spawn independent tasks to avoid deadlocks
|
|
let more_peers = candidates.update().await?;
|
|
|
|
// If we got more peers, try to connect to a new peer.
|
|
//
|
|
// # Security
|
|
//
|
|
// Update attempts are rate-limited by the candidate set.
|
|
//
|
|
// We only try peers if there was actually an update.
|
|
// So if all peers have had a recent attempt,
|
|
// and there was recent update with no peers,
|
|
// the channel will drain.
|
|
// This prevents useless update attempt loops.
|
|
if let Some(more_peers) = more_peers {
|
|
let _ = demand_tx.try_send(more_peers);
|
|
}
|
|
}
|
|
TimerCrawl { tick } => {
|
|
debug!(
|
|
?tick,
|
|
"crawling for more peers in response to the crawl timer"
|
|
);
|
|
// TODO: spawn independent tasks to avoid deadlocks
|
|
candidates.update().await?;
|
|
// Try to connect to a new peer.
|
|
let _ = demand_tx.try_send(MorePeers);
|
|
}
|
|
HandshakeConnected { address, client } => {
|
|
debug!(candidate.addr = ?address, "successfully dialed new peer");
|
|
// successes are handled by an independent task, except for `candidates.update` in
|
|
// this task, which has a timeout, so they shouldn't hang
|
|
peerset_tx.send(Ok((address, client))).await?;
|
|
}
|
|
HandshakeFailed { failed_addr } => {
|
|
// The connection was never opened, or it failed the handshake and was dropped.
|
|
|
|
debug!(?failed_addr.addr, "marking candidate as failed");
|
|
candidates.report_failed(&failed_addr).await;
|
|
// The demand signal that was taken out of the queue
|
|
// to attempt to connect to the failed candidate never
|
|
// turned into a connection, so add it back:
|
|
//
|
|
// Security: handshake failures are rate-limited by peer attempt timeouts.
|
|
let _ = demand_tx.try_send(MorePeers);
|
|
}
|
|
}
|
|
|
|
// Security: Let other tasks run after each crawler action is processed.
|
|
//
|
|
// Avoids remote peers starving other Zebra tasks using outbound connection errors.
|
|
tokio::task::yield_now().await;
|
|
}
|
|
}
|
|
|
|
/// Try to connect to `candidate` using `outbound_connector`.
|
|
/// Uses `outbound_connection_tracker` to track the active connection count.
|
|
///
|
|
/// Returns a `HandshakeConnected` action on success, and a
|
|
/// `HandshakeFailed` action on error.
|
|
#[instrument(skip(outbound_connector, outbound_connection_tracker))]
|
|
async fn dial<C>(
|
|
candidate: MetaAddr,
|
|
mut outbound_connector: C,
|
|
outbound_connection_tracker: ConnectionTracker,
|
|
) -> CrawlerAction
|
|
where
|
|
C: Service<
|
|
OutboundConnectorRequest,
|
|
Response = (PeerSocketAddr, peer::Client),
|
|
Error = BoxError,
|
|
> + Clone
|
|
+ Send
|
|
+ 'static,
|
|
C::Future: Send + 'static,
|
|
{
|
|
// CORRECTNESS
|
|
//
|
|
// 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");
|
|
|
|
// the connector is always ready, so this can't hang
|
|
let outbound_connector = outbound_connector
|
|
.ready()
|
|
.await
|
|
.expect("outbound connector never errors");
|
|
|
|
let req = OutboundConnectorRequest {
|
|
addr: candidate.addr,
|
|
connection_tracker: outbound_connection_tracker,
|
|
};
|
|
|
|
// the handshake has timeouts, so it shouldn't hang
|
|
outbound_connector
|
|
.call(req)
|
|
.map_err(|e| (candidate, e))
|
|
.map(Into::into)
|
|
.await
|
|
}
|
|
|
|
impl From<Result<(PeerSocketAddr, peer::Client), (MetaAddr, BoxError)>> for CrawlerAction {
|
|
fn from(dial_result: Result<(PeerSocketAddr, peer::Client), (MetaAddr, BoxError)>) -> Self {
|
|
use CrawlerAction::*;
|
|
match dial_result {
|
|
Ok((address, client)) => HandshakeConnected { address, client },
|
|
Err((candidate, e)) => {
|
|
debug!(?candidate.addr, ?e, "failed to connect to candidate");
|
|
HandshakeFailed {
|
|
failed_addr: candidate,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|