lib.rs 17.2 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
// Copyright 2020 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! PoV Distribution Subsystem of Polkadot.
//!
//! This is a gossip implementation of code that is responsible for distributing PoVs
//! among validators.

22
23
24
#![deny(unused_crate_dependencies)]
#![warn(missing_docs)]

asynchronous rob's avatar
asynchronous rob committed
25
use polkadot_primitives::v1::{Hash, PoV, CandidateDescriptor};
26
use polkadot_subsystem::{
27
28
	ActiveLeavesUpdate, OverseerSignal, SubsystemContext, Subsystem, SubsystemResult, SubsystemError,
	FromOverseer, SpawnedSubsystem,
29
30
31
	messages::{
		PoVDistributionMessage, RuntimeApiMessage, RuntimeApiRequest, AllMessages, NetworkBridgeMessage,
	},
32
};
33
34
use polkadot_node_subsystem_util::{
	metrics::{self, prometheus},
35
36
37
};
use polkadot_node_network_protocol::{
	v1 as protocol_v1, ReputationChange as Rep, NetworkBridgeEvent, PeerId, View,
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
};

use futures::prelude::*;
use futures::channel::oneshot;

use std::collections::{hash_map::{Entry, HashMap}, HashSet};
use std::sync::Arc;

const COST_APPARENT_FLOOD: Rep = Rep::new(-500, "Peer appears to be flooding us with PoV requests");
const COST_UNEXPECTED_POV: Rep = Rep::new(-500, "Peer sent us an unexpected PoV");
const COST_AWAITED_NOT_IN_VIEW: Rep
	= Rep::new(-100, "Peer claims to be awaiting something outside of its view");

const BENEFIT_FRESH_POV: Rep = Rep::new(25, "Peer supplied us with an awaited PoV");
const BENEFIT_LATE_POV: Rep = Rep::new(10, "Peer supplied us with an awaited PoV, \
	but was not the first to do so");

/// The PoV Distribution Subsystem.
56
57
58
59
pub struct PoVDistribution {
	// Prometheus metrics
	metrics: Metrics,
}
60
61
62
63
64
65
66

impl<C> Subsystem<C> for PoVDistribution
	where C: SubsystemContext<Message = PoVDistributionMessage>
{
	fn start(self, ctx: C) -> SpawnedSubsystem {
		// Swallow error because failure is fatal to the node and we log with more precision
		// within `run`.
67
68
69
		let future = self.run(ctx)
			.map_err(|e| SubsystemError::with_origin("pov-distribution", e))
			.boxed();
70
71
		SpawnedSubsystem {
			name: "pov-distribution-subsystem",
72
			future,
73
		}
74
75
76
77
78
79
80
	}
}

struct State {
	relay_parent_state: HashMap<Hash, BlockBasedState>,
	peer_state: HashMap<PeerId, PeerState>,
	our_view: View,
81
	metrics: Metrics,
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
}

struct BlockBasedState {
	known: HashMap<Hash, Arc<PoV>>,
	/// All the PoVs we are or were fetching, coupled with channels expecting the data.
	///
	/// This may be an empty list, which indicates that we were once awaiting this PoV but have
	/// received it already.
	fetching: HashMap<Hash, Vec<oneshot::Sender<Arc<PoV>>>>,
	n_validators: usize,
}

#[derive(Default)]
struct PeerState {
	/// A set of awaited PoV-hashes for each relay-parent in the peer's view.
	awaited: HashMap<Hash, HashSet<Hash>>,
}

100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
fn awaiting_message(relay_parent: Hash, awaiting: Vec<Hash>)
	-> protocol_v1::ValidationProtocol
{
	protocol_v1::ValidationProtocol::PoVDistribution(
		protocol_v1::PoVDistributionMessage::Awaiting(relay_parent, awaiting)
	)
}

fn send_pov_message(relay_parent: Hash, pov_hash: Hash, pov: PoV)
	-> protocol_v1::ValidationProtocol
{
	protocol_v1::ValidationProtocol::PoVDistribution(
		protocol_v1::PoVDistributionMessage::SendPoV(relay_parent, pov_hash, pov)
	)
}

116
117
118
119
120
121
122
123
124
/// Handles the signal. If successful, returns `true` if the subsystem should conclude,
/// `false` otherwise.
async fn handle_signal(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	signal: OverseerSignal,
) -> SubsystemResult<bool> {
	match signal {
		OverseerSignal::Conclude => Ok(true),
125
126
127
128
129
130
131
132
		OverseerSignal::ActiveLeaves(ActiveLeavesUpdate { activated, deactivated }) => {
			for relay_parent in activated {
				let (vals_tx, vals_rx) = oneshot::channel();
				ctx.send_message(AllMessages::RuntimeApi(RuntimeApiMessage::Request(
					relay_parent,
					RuntimeApiRequest::Validators(vals_tx),
				))).await?;

133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
				let n_validators = match vals_rx.await? {
					Ok(v) => v.len(),
					Err(e) => {
						log::warn!(target: "pov_distribution",
							"Error fetching validators from runtime API for active leaf: {:?}",
							e
						);

						// Not adding bookkeeping here might make us behave funny, but we
						// shouldn't take down the node on spurious runtime API errors.
						//
						// and this is "behave funny" as in be bad at our job, but not in any
						// slashable or security-related way.
						continue;
					}
				};

150
151
152
				state.relay_parent_state.insert(relay_parent, BlockBasedState {
					known: HashMap::new(),
					fetching: HashMap::new(),
153
					n_validators: n_validators,
154
155
156
157
158
159
				});
			}

			for relay_parent in deactivated {
				state.relay_parent_state.remove(&relay_parent);
			}
160
161
162

			Ok(false)
		}
163
		OverseerSignal::BlockFinalized(_) => Ok(false),
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
	}
}

/// Notify peers that we are awaiting a given PoV hash.
///
/// This only notifies peers who have the relay parent in their view.
async fn notify_all_we_are_awaiting(
	peers: &mut HashMap<PeerId, PeerState>,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	relay_parent: Hash,
	pov_hash: Hash,
) -> SubsystemResult<()> {
	// We use `awaited` as a proxy for which heads are in the peer's view.
	let peers_to_send: Vec<_> = peers.iter()
		.filter_map(|(peer, state)| if state.awaited.contains_key(&relay_parent) {
			Some(peer.clone())
		} else {
			None
		})
		.collect();

	if peers_to_send.is_empty() { return Ok(()) }

187
	let payload = awaiting_message(relay_parent, vec![pov_hash]);
188

189
	ctx.send_message(AllMessages::NetworkBridge(NetworkBridgeMessage::SendValidationMessage(
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
		peers_to_send,
		payload,
	))).await
}

/// Notify one peer about everything we're awaiting at a given relay-parent.
async fn notify_one_we_are_awaiting_many(
	peer: &PeerId,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	relay_parent_state: &HashMap<Hash, BlockBasedState>,
	relay_parent: Hash,
) -> SubsystemResult<()> {
	let awaiting_hashes = relay_parent_state.get(&relay_parent).into_iter().flat_map(|s| {
		// Send the peer everything we are fetching at this relay-parent
		s.fetching.iter()
			.filter(|(_, senders)| !senders.is_empty()) // that has not been completed already.
			.map(|(pov_hash, _)| *pov_hash)
	}).collect::<Vec<_>>();

	if awaiting_hashes.is_empty() { return Ok(()) }

211
	let payload = awaiting_message(relay_parent, awaiting_hashes);
212

213
	ctx.send_message(AllMessages::NetworkBridge(NetworkBridgeMessage::SendValidationMessage(
214
215
216
217
218
219
220
221
222
		vec![peer.clone()],
		payload,
	))).await
}

/// Distribute a PoV to peers who are awaiting it.
async fn distribute_to_awaiting(
	peers: &mut HashMap<PeerId, PeerState>,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
223
	metrics: &Metrics,
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
	relay_parent: Hash,
	pov_hash: Hash,
	pov: &PoV,
) -> SubsystemResult<()> {
	// Send to all peers who are awaiting the PoV and have that relay-parent in their view.
	//
	// Also removes it from their awaiting set.
	let peers_to_send: Vec<_> = peers.iter_mut()
		.filter_map(|(peer, state)| state.awaited.get_mut(&relay_parent).and_then(|awaited| {
			if awaited.remove(&pov_hash) {
				Some(peer.clone())
			} else {
				None
			}
		}))
		.collect();

	if peers_to_send.is_empty() { return Ok(()) }

243
	let payload = send_pov_message(relay_parent, pov_hash, pov.clone());
244

245
	ctx.send_message(AllMessages::NetworkBridge(NetworkBridgeMessage::SendValidationMessage(
246
247
		peers_to_send,
		payload,
248
249
250
251
252
	))).await?;

	metrics.on_pov_distributed();

	Ok(())
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
}

/// Handles a `FetchPoV` message.
async fn handle_fetch(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	relay_parent: Hash,
	descriptor: CandidateDescriptor,
	response_sender: oneshot::Sender<Arc<PoV>>,
) -> SubsystemResult<()> {
	let relay_parent_state = match state.relay_parent_state.get_mut(&relay_parent) {
		Some(s) => s,
		None => return Ok(()),
	};

	if let Some(pov) = relay_parent_state.known.get(&descriptor.pov_hash) {
		let _  = response_sender.send(pov.clone());
		return Ok(());
	}

	{
		match relay_parent_state.fetching.entry(descriptor.pov_hash) {
			Entry::Occupied(mut e) => {
				// we are already awaiting this PoV if there is an entry.
				e.get_mut().push(response_sender);
				return Ok(());
			}
			Entry::Vacant(e) => {
				e.insert(vec![response_sender]);
			}
		}
	}

	if relay_parent_state.fetching.len() > 2 * relay_parent_state.n_validators {
		log::warn!("Other subsystems have requested PoV distribution to \
			fetch more PoVs than reasonably expected: {}", relay_parent_state.fetching.len());
		return Ok(());
	}

	// Issue an `Awaiting` message to all peers with this in their view.
	notify_all_we_are_awaiting(
		&mut state.peer_state,
		ctx,
		relay_parent,
		descriptor.pov_hash
	).await
}

/// Handles a `DistributePoV` message.
async fn handle_distribute(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	relay_parent: Hash,
	descriptor: CandidateDescriptor,
	pov: Arc<PoV>,
) -> SubsystemResult<()> {
	let relay_parent_state = match state.relay_parent_state.get_mut(&relay_parent) {
		None => return Ok(()),
		Some(s) => s,
	};

	if let Some(our_awaited) = relay_parent_state.fetching.get_mut(&descriptor.pov_hash) {
		// Drain all the senders, but keep the entry in the map around intentionally.
		//
		// It signals that we were at one point awaiting this, so we will be able to tell
		// why peers are sending it to us.
		for response_sender in our_awaited.drain(..) {
			let _ = response_sender.send(pov.clone());
		}
	}

	relay_parent_state.known.insert(descriptor.pov_hash, pov.clone());

	distribute_to_awaiting(
		&mut state.peer_state,
		ctx,
329
		&state.metrics,
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
		relay_parent,
		descriptor.pov_hash,
		&*pov,
	).await
}

/// Report a reputation change for a peer.
async fn report_peer(
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	peer: PeerId,
	rep: Rep,
) -> SubsystemResult<()> {
	ctx.send_message(AllMessages::NetworkBridge(NetworkBridgeMessage::ReportPeer(peer, rep))).await
}

/// Handle a notification from a peer that they are awaiting some PoVs.
async fn handle_awaiting(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	peer: PeerId,
	relay_parent: Hash,
	pov_hashes: Vec<Hash>,
) -> SubsystemResult<()> {
	if !state.our_view.0.contains(&relay_parent) {
		report_peer(ctx, peer, COST_AWAITED_NOT_IN_VIEW).await?;
		return Ok(());
	}

	let relay_parent_state = match state.relay_parent_state.get_mut(&relay_parent) {
		None => {
			log::warn!("PoV Distribution relay parent state out-of-sync with our view");
			return Ok(());
		}
		Some(s) => s,
	};

	let peer_awaiting = match
		state.peer_state.get_mut(&peer).and_then(|s| s.awaited.get_mut(&relay_parent))
	{
		None => {
			report_peer(ctx, peer, COST_AWAITED_NOT_IN_VIEW).await?;
			return Ok(());
		}
		Some(a) => a,
	};

	let will_be_awaited = peer_awaiting.len() + pov_hashes.len();
	if will_be_awaited <= 2 * relay_parent_state.n_validators {
		for pov_hash in pov_hashes {
			// For all requested PoV hashes, if we have it, we complete the request immediately.
			// Otherwise, we note that the peer is awaiting the PoV.
			if let Some(pov) = relay_parent_state.known.get(&pov_hash) {
382
383
384
385
				let payload = send_pov_message(relay_parent, pov_hash, (&**pov).clone());
				ctx.send_message(AllMessages::NetworkBridge(
					NetworkBridgeMessage::SendValidationMessage(vec![peer.clone()], payload)
				)).await?;
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
			} else {
				peer_awaiting.insert(pov_hash);
			}
		}
	} else {
		report_peer(ctx, peer, COST_APPARENT_FLOOD).await?;
	}

	Ok(())
}

/// Handle an incoming PoV from our peer. Reports them if unexpected, rewards them if not.
///
/// Completes any requests awaiting that PoV.
async fn handle_incoming_pov(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
	peer: PeerId,
	relay_parent: Hash,
	pov_hash: Hash,
	pov: PoV,
) -> SubsystemResult<()> {
	let relay_parent_state = match state.relay_parent_state.get_mut(&relay_parent) {
		None =>	{
			report_peer(ctx, peer, COST_UNEXPECTED_POV).await?;
			return Ok(());
		},
		Some(r) => r,
	};

	let pov = {
		// Do validity checks and complete all senders awaiting this PoV.
		let fetching = match relay_parent_state.fetching.get_mut(&pov_hash) {
			None => {
				report_peer(ctx, peer, COST_UNEXPECTED_POV).await?;
				return Ok(());
			}
			Some(f) => f,
		};

		let hash = pov.hash();
		if hash != pov_hash {
			report_peer(ctx, peer, COST_UNEXPECTED_POV).await?;
			return Ok(());
		}

		let pov = Arc::new(pov);

		if fetching.is_empty() {
			// fetching is empty whenever we were awaiting something and
			// it was completed afterwards.
			report_peer(ctx, peer.clone(), BENEFIT_LATE_POV).await?;
		} else {
			// fetching is non-empty when the peer just provided us with data we needed.
			report_peer(ctx, peer.clone(), BENEFIT_FRESH_POV).await?;
		}

		for response_sender in fetching.drain(..) {
			let _ = response_sender.send(pov.clone());
		}

		pov
	};

	// make sure we don't consider this peer as awaiting that PoV anymore.
	if let Some(peer_state) = state.peer_state.get_mut(&peer) {
		peer_state.awaited.remove(&pov_hash);
	}

	// distribute the PoV to all other peers who are awaiting it.
	distribute_to_awaiting(
		&mut state.peer_state,
		ctx,
459
		&state.metrics,
460
461
462
463
464
465
466
467
468
469
		relay_parent,
		pov_hash,
		&*pov,
	).await
}

/// Handles a network bridge update.
async fn handle_network_update(
	state: &mut State,
	ctx: &mut impl SubsystemContext<Message = PoVDistributionMessage>,
470
	update: NetworkBridgeEvent<protocol_v1::PoVDistributionMessage>,
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
) -> SubsystemResult<()> {
	match update {
		NetworkBridgeEvent::PeerConnected(peer, _observed_role) => {
			state.peer_state.insert(peer, PeerState { awaited: HashMap::new() });
			Ok(())
		}
		NetworkBridgeEvent::PeerDisconnected(peer) => {
			state.peer_state.remove(&peer);
			Ok(())
		}
		NetworkBridgeEvent::PeerViewChange(peer_id, view) => {
			if let Some(peer_state) = state.peer_state.get_mut(&peer_id) {
				// prune anything not in the new view.
				peer_state.awaited.retain(|relay_parent, _| view.0.contains(&relay_parent));

				// introduce things from the new view.
				for relay_parent in view.0.iter() {
					if let Entry::Vacant(entry) = peer_state.awaited.entry(*relay_parent) {
						entry.insert(HashSet::new());

						// Notify the peer about everything we're awaiting at the new relay-parent.
						notify_one_we_are_awaiting_many(
							&peer_id,
							ctx,
							&state.relay_parent_state,
							*relay_parent,
						).await?;
					}
				}
			}

			Ok(())
		}
504
505
506
507
		NetworkBridgeEvent::PeerMessage(peer, message) => {
			match message {
				protocol_v1::PoVDistributionMessage::Awaiting(relay_parent, pov_hashes)
					=> handle_awaiting(
508
509
510
511
512
513
						state,
						ctx,
						peer,
						relay_parent,
						pov_hashes,
					).await,
514
515
				protocol_v1::PoVDistributionMessage::SendPoV(relay_parent, pov_hash, pov)
					=> handle_incoming_pov(
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
						state,
						ctx,
						peer,
						relay_parent,
						pov_hash,
						pov,
					).await,
			}
		}
		NetworkBridgeEvent::OurViewChange(view) => {
			state.our_view = view;
			Ok(())
		}
	}
}

532
533
534
535
536
impl PoVDistribution {
	/// Create a new instance of `PovDistribution`.
	pub fn new(metrics: Metrics) -> Self {
		Self { metrics }
	}
537

538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
	async fn run(
		self,
		mut ctx: impl SubsystemContext<Message = PoVDistributionMessage>,
	) -> SubsystemResult<()> {
		let mut state = State {
			relay_parent_state: HashMap::new(),
			peer_state: HashMap::new(),
			our_view: View(Vec::new()),
			metrics: self.metrics,
		};

		loop {
			match ctx.recv().await? {
				FromOverseer::Signal(signal) => if handle_signal(&mut state, &mut ctx, signal).await? {
					return Ok(());
				},
				FromOverseer::Communication { msg } => match msg {
					PoVDistributionMessage::FetchPoV(relay_parent, descriptor, response_sender) =>
						handle_fetch(
							&mut state,
							&mut ctx,
							relay_parent,
							descriptor,
							response_sender,
						).await?,
					PoVDistributionMessage::DistributePoV(relay_parent, descriptor, pov) =>
						handle_distribute(
							&mut state,
							&mut ctx,
							relay_parent,
							descriptor,
							pov,
						).await?,
					PoVDistributionMessage::NetworkBridgeUpdateV1(event) =>
						handle_network_update(
							&mut state,
							&mut ctx,
							event,
						).await?,
				},
			}
579
580
581
582
		}
	}
}

583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616


#[derive(Clone)]
struct MetricsInner {
	povs_distributed: prometheus::Counter<prometheus::U64>,
}

/// Availability Distribution metrics.
#[derive(Default, Clone)]
pub struct Metrics(Option<MetricsInner>);

impl Metrics {
	fn on_pov_distributed(&self) {
		if let Some(metrics) = &self.0 {
			metrics.povs_distributed.inc();
		}
	}
}

impl metrics::Metrics for Metrics {
	fn try_register(registry: &prometheus::Registry) -> std::result::Result<Self, prometheus::PrometheusError> {
		let metrics = MetricsInner {
			povs_distributed: prometheus::register(
				prometheus::Counter::new(
					"parachain_povs_distributed_total",
					"Number of PoVs distributed to other peers."
				)?,
				registry,
			)?,
		};
		Ok(Metrics(Some(metrics)))
	}
}

617
#[cfg(test)]
618
mod tests;