1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433
// Copyright (C) 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/>.
//! Overview over request/responses as used in `Polkadot`.
//!
//! `enum Protocol` .... List of all supported protocols.
//!
//! `enum Requests` .... List of all supported requests, each entry matches one in protocols, but
//! has the actual request as payload.
//!
//! `struct IncomingRequest` .... wrapper for incoming requests, containing a sender for sending
//! responses.
//!
//! `struct OutgoingRequest` .... wrapper for outgoing requests, containing a sender used by the
//! networking code for delivering responses/delivery errors.
//!
//! `trait IsRequest` .... A trait describing a particular request. It is used for gathering meta
//! data, like what is the corresponding response type.
//!
//! ## Versioning
//!
//! Versioning for request-response protocols can be done in multiple ways.
//!
//! If you're just changing the protocol name but the binary payloads are the same, just add a new
//! `fallback_name` to the protocol config.
//!
//! One way in which versioning has historically been achieved for req-response protocols is to
//! bundle the new req-resp version with an upgrade of a notifications protocol. The subsystem would
//! then know which request version to use based on stored data about the peer's notifications
//! protocol version.
//!
//! When bumping a notifications protocol version is not needed/desirable, you may add a new
//! req-resp protocol and set the old request as a fallback (see
//! `OutgoingRequest::new_with_fallback`). A request with the new version will be attempted and if
//! the protocol is refused by the peer, the fallback protocol request will be used.
//! Information about the actually used protocol will be returned alongside the raw response, so
//! that you know how to decode it.
use std::{collections::HashMap, time::Duration, u64};
use polkadot_primitives::MAX_CODE_SIZE;
use sc_network::{NetworkBackend, MAX_RESPONSE_SIZE};
use sp_runtime::traits::Block;
use strum::{EnumIter, IntoEnumIterator};
pub use sc_network::{config as network, config::RequestResponseConfig, ProtocolName};
/// Everything related to handling of incoming requests.
pub mod incoming;
/// Everything related to handling of outgoing requests.
pub mod outgoing;
pub use incoming::{IncomingRequest, IncomingRequestReceiver};
pub use outgoing::{OutgoingRequest, OutgoingResult, Recipient, Requests, ResponseSender};
///// Multiplexer for incoming requests.
// pub mod multiplexer;
/// Actual versioned requests and responses that are sent over the wire.
pub mod v1;
/// Actual versioned requests and responses that are sent over the wire.
pub mod v2;
/// A protocol per subsystem seems to make the most sense, this way we don't need any dispatching
/// within protocols.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, EnumIter)]
pub enum Protocol {
/// Protocol for chunk fetching, used by availability distribution and availability recovery.
ChunkFetchingV1,
/// Protocol for fetching collations from collators.
CollationFetchingV1,
/// Protocol for fetching collations from collators when async backing is enabled.
CollationFetchingV2,
/// Protocol for fetching seconded PoVs from validators of the same group.
PoVFetchingV1,
/// Protocol for fetching available data.
AvailableDataFetchingV1,
/// Fetching of statements that are too large for gossip.
StatementFetchingV1,
/// Sending of dispute statements with application level confirmations.
DisputeSendingV1,
/// Protocol for requesting candidates with attestations in statement distribution
/// when async backing is enabled.
AttestedCandidateV2,
/// Protocol for chunk fetching version 2, used by availability distribution and availability
/// recovery.
ChunkFetchingV2,
}
/// Minimum bandwidth we expect for validators - 500Mbit/s is the recommendation, so approximately
/// 50MB per second:
const MIN_BANDWIDTH_BYTES: u64 = 50 * 1024 * 1024;
/// Default request timeout in seconds.
///
/// When decreasing this value, take into account that the very first request might need to open a
/// connection, which can be slow. If this causes problems, we should ensure connectivity via peer
/// sets.
#[allow(dead_code)]
const DEFAULT_REQUEST_TIMEOUT: Duration = Duration::from_secs(3);
/// Request timeout where we can assume the connection is already open (e.g. we have peers in a
/// peer set as well).
const DEFAULT_REQUEST_TIMEOUT_CONNECTED: Duration = Duration::from_secs(1);
/// Timeout for requesting availability chunks.
pub const CHUNK_REQUEST_TIMEOUT: Duration = DEFAULT_REQUEST_TIMEOUT_CONNECTED;
/// This timeout is based on what seems sensible from a time budget perspective, considering 6
/// second block time. This is going to be tough, if we have multiple forks and large PoVs, but we
/// only have so much time.
const POV_REQUEST_TIMEOUT_CONNECTED: Duration = Duration::from_millis(1200);
/// We want timeout statement requests fast, so we don't waste time on slow nodes. Responders will
/// try their best to either serve within that timeout or return an error immediately. (We need to
/// fit statement distribution within a block of 6 seconds.)
const STATEMENTS_TIMEOUT: Duration = Duration::from_secs(1);
/// We want attested candidate requests to time out relatively fast,
/// because slow requests will bottleneck the backing system. Ideally, we'd have
/// an adaptive timeout based on the candidate size, because there will be a lot of variance
/// in candidate sizes: candidates with no code and no messages vs candidates with code
/// and messages.
///
/// We supply leniency because there are often large candidates and asynchronous
/// backing allows them to be included over a longer window of time. Exponential back-off
/// up to a maximum of 10 seconds would be ideal, but isn't supported by the
/// infrastructure here yet: see https://github.com/paritytech/polkadot/issues/6009
const ATTESTED_CANDIDATE_TIMEOUT: Duration = Duration::from_millis(2500);
/// We don't want a slow peer to slow down all the others, at the same time we want to get out the
/// data quickly in full to at least some peers (as this will reduce load on us as they then can
/// start serving the data). So this value is a trade-off. 3 seems to be sensible. So we would need
/// to have 3 slow nodes connected, to delay transfer for others by `STATEMENTS_TIMEOUT`.
pub const MAX_PARALLEL_STATEMENT_REQUESTS: u32 = 3;
/// We don't want a slow peer to slow down all the others, at the same time we want to get out the
/// data quickly in full to at least some peers (as this will reduce load on us as they then can
/// start serving the data). So this value is a tradeoff. 5 seems to be sensible. So we would need
/// to have 5 slow nodes connected, to delay transfer for others by `ATTESTED_CANDIDATE_TIMEOUT`.
pub const MAX_PARALLEL_ATTESTED_CANDIDATE_REQUESTS: u32 = 5;
/// Response size limit for responses of POV like data.
///
/// Same as what we use in substrate networking.
const POV_RESPONSE_SIZE: u64 = MAX_RESPONSE_SIZE;
/// Maximum response sizes for `StatementFetchingV1`.
///
/// This is `MAX_CODE_SIZE` plus some additional space for protocol overhead.
const STATEMENT_RESPONSE_SIZE: u64 = MAX_CODE_SIZE as u64 + 10_000;
/// Maximum response sizes for `AttestedCandidateV2`.
///
/// This is `MAX_CODE_SIZE` plus some additional space for protocol overhead and
/// additional backing statements.
const ATTESTED_CANDIDATE_RESPONSE_SIZE: u64 = MAX_CODE_SIZE as u64 + 100_000;
/// We can have relative large timeouts here, there is no value of hitting a
/// timeout as we want to get statements through to each node in any case.
pub const DISPUTE_REQUEST_TIMEOUT: Duration = Duration::from_secs(12);
impl Protocol {
/// Get a configuration for a given Request response protocol.
///
/// Returns a `ProtocolConfig` for this protocol.
/// Use this if you plan only to send requests for this protocol.
pub fn get_outbound_only_config<B: Block, N: NetworkBackend<B, <B as Block>::Hash>>(
self,
req_protocol_names: &ReqProtocolNames,
) -> N::RequestResponseProtocolConfig {
self.create_config::<B, N>(req_protocol_names, None)
}
/// Get a configuration for a given Request response protocol.
///
/// Returns a receiver for messages received on this protocol and the requested
/// `ProtocolConfig`.
pub fn get_config<B: Block, N: NetworkBackend<B, <B as Block>::Hash>>(
self,
req_protocol_names: &ReqProtocolNames,
) -> (async_channel::Receiver<network::IncomingRequest>, N::RequestResponseProtocolConfig) {
let (tx, rx) = async_channel::bounded(self.get_channel_size());
let cfg = self.create_config::<B, N>(req_protocol_names, Some(tx));
(rx, cfg)
}
fn create_config<B: Block, N: NetworkBackend<B, <B as Block>::Hash>>(
self,
req_protocol_names: &ReqProtocolNames,
tx: Option<async_channel::Sender<network::IncomingRequest>>,
) -> N::RequestResponseProtocolConfig {
let name = req_protocol_names.get_name(self);
let legacy_names = self.get_legacy_name().into_iter().map(Into::into).collect();
match self {
Protocol::ChunkFetchingV1 | Protocol::ChunkFetchingV2 => N::request_response_config(
name,
legacy_names,
1_000,
POV_RESPONSE_SIZE,
// We are connected to all validators:
CHUNK_REQUEST_TIMEOUT,
tx,
),
Protocol::CollationFetchingV1 | Protocol::CollationFetchingV2 =>
N::request_response_config(
name,
legacy_names,
1_000,
POV_RESPONSE_SIZE,
// Taken from initial implementation in collator protocol:
POV_REQUEST_TIMEOUT_CONNECTED,
tx,
),
Protocol::PoVFetchingV1 => N::request_response_config(
name,
legacy_names,
1_000,
POV_RESPONSE_SIZE,
POV_REQUEST_TIMEOUT_CONNECTED,
tx,
),
Protocol::AvailableDataFetchingV1 => N::request_response_config(
name,
legacy_names,
1_000,
// Available data size is dominated by the PoV size.
POV_RESPONSE_SIZE,
POV_REQUEST_TIMEOUT_CONNECTED,
tx,
),
Protocol::StatementFetchingV1 => N::request_response_config(
name,
legacy_names,
1_000,
// Available data size is dominated code size.
STATEMENT_RESPONSE_SIZE,
// We need statement fetching to be fast and will try our best at the responding
// side to answer requests within that timeout, assuming a bandwidth of 500Mbit/s
// - which is the recommended minimum bandwidth for nodes on Kusama as of April
// 2021.
// Responders will reject requests, if it is unlikely they can serve them within
// the timeout, so the requester can immediately try another node, instead of
// waiting for timeout on an overloaded node. Fetches from slow nodes will likely
// fail, but this is desired, so we can quickly move on to a faster one - we should
// also decrease its reputation.
Duration::from_secs(1),
tx,
),
Protocol::DisputeSendingV1 => N::request_response_config(
name,
legacy_names,
1_000,
// Responses are just confirmation, in essence not even a bit. So 100 seems
// plenty.
100,
DISPUTE_REQUEST_TIMEOUT,
tx,
),
Protocol::AttestedCandidateV2 => N::request_response_config(
name,
legacy_names,
1_000,
ATTESTED_CANDIDATE_RESPONSE_SIZE,
ATTESTED_CANDIDATE_TIMEOUT,
tx,
),
}
}
// Channel sizes for the supported protocols.
fn get_channel_size(self) -> usize {
match self {
// Hundreds of validators will start requesting their chunks once they see a candidate
// awaiting availability on chain. Given that they will see that block at different
// times (due to network delays), 100 seems big enough to accommodate for "bursts",
// assuming we can service requests relatively quickly, which would need to be measured
// as well.
Protocol::ChunkFetchingV1 | Protocol::ChunkFetchingV2 => 100,
// 10 seems reasonable, considering group sizes of max 10 validators.
Protocol::CollationFetchingV1 | Protocol::CollationFetchingV2 => 10,
// 10 seems reasonable, considering group sizes of max 10 validators.
Protocol::PoVFetchingV1 => 10,
// Validators are constantly self-selecting to request available data which may lead
// to constant load and occasional burstiness.
Protocol::AvailableDataFetchingV1 => 100,
// Our queue size approximation is how many blocks of the size of
// a runtime we can transfer within a statements timeout, minus the requests we handle
// in parallel.
Protocol::StatementFetchingV1 => {
// We assume we can utilize up to 70% of the available bandwidth for statements.
// This is just a guess/estimate, with the following considerations: If we are
// faster than that, queue size will stay low anyway, even if not - requesters will
// get an immediate error, but if we are slower, requesters will run in a timeout -
// wasting precious time.
let available_bandwidth = 7 * MIN_BANDWIDTH_BYTES / 10;
let size = u64::saturating_sub(
STATEMENTS_TIMEOUT.as_millis() as u64 * available_bandwidth /
(1000 * MAX_CODE_SIZE as u64),
MAX_PARALLEL_STATEMENT_REQUESTS as u64,
);
debug_assert!(
size > 0,
"We should have a channel size greater zero, otherwise we won't accept any requests."
);
size as usize
},
// Incoming requests can get bursty, we should also be able to handle them fast on
// average, so something in the ballpark of 100 should be fine. Nodes will retry on
// failure, so having a good value here is mostly about performance tuning.
Protocol::DisputeSendingV1 => 100,
Protocol::AttestedCandidateV2 => {
// We assume we can utilize up to 70% of the available bandwidth for statements.
// This is just a guess/estimate, with the following considerations: If we are
// faster than that, queue size will stay low anyway, even if not - requesters will
// get an immediate error, but if we are slower, requesters will run in a timeout -
// wasting precious time.
let available_bandwidth = 7 * MIN_BANDWIDTH_BYTES / 10;
let size = u64::saturating_sub(
ATTESTED_CANDIDATE_TIMEOUT.as_millis() as u64 * available_bandwidth /
(1000 * MAX_CODE_SIZE as u64),
MAX_PARALLEL_ATTESTED_CANDIDATE_REQUESTS as u64,
);
debug_assert!(
size > 0,
"We should have a channel size greater zero, otherwise we won't accept any requests."
);
size as usize
},
}
}
/// Legacy protocol name associated with each peer set, if any.
/// The request will be tried on this legacy protocol name if the remote refuses to speak the
/// protocol.
const fn get_legacy_name(self) -> Option<&'static str> {
match self {
Protocol::ChunkFetchingV1 => Some("/polkadot/req_chunk/1"),
Protocol::CollationFetchingV1 => Some("/polkadot/req_collation/1"),
Protocol::PoVFetchingV1 => Some("/polkadot/req_pov/1"),
Protocol::AvailableDataFetchingV1 => Some("/polkadot/req_available_data/1"),
Protocol::StatementFetchingV1 => Some("/polkadot/req_statement/1"),
Protocol::DisputeSendingV1 => Some("/polkadot/send_dispute/1"),
// Introduced after legacy names became legacy.
Protocol::AttestedCandidateV2 => None,
Protocol::CollationFetchingV2 => None,
Protocol::ChunkFetchingV2 => None,
}
}
}
/// Common properties of any `Request`.
pub trait IsRequest {
/// Each request has a corresponding `Response`.
type Response;
/// What protocol this `Request` implements.
const PROTOCOL: Protocol;
}
/// Type for getting on the wire [`Protocol`] names using genesis hash & fork id.
#[derive(Clone)]
pub struct ReqProtocolNames {
names: HashMap<Protocol, ProtocolName>,
}
impl ReqProtocolNames {
/// Construct [`ReqProtocolNames`] from `genesis_hash` and `fork_id`.
pub fn new<Hash: AsRef<[u8]>>(genesis_hash: Hash, fork_id: Option<&str>) -> Self {
let mut names = HashMap::new();
for protocol in Protocol::iter() {
names.insert(protocol, Self::generate_name(protocol, &genesis_hash, fork_id));
}
Self { names }
}
/// Get on the wire [`Protocol`] name.
pub fn get_name(&self, protocol: Protocol) -> ProtocolName {
self.names
.get(&protocol)
.expect("All `Protocol` enum variants are added above via `strum`; qed")
.clone()
}
/// Protocol name of this protocol based on `genesis_hash` and `fork_id`.
fn generate_name<Hash: AsRef<[u8]>>(
protocol: Protocol,
genesis_hash: &Hash,
fork_id: Option<&str>,
) -> ProtocolName {
let prefix = if let Some(fork_id) = fork_id {
format!("/{}/{}", hex::encode(genesis_hash), fork_id)
} else {
format!("/{}", hex::encode(genesis_hash))
};
let short_name = match protocol {
// V1:
Protocol::ChunkFetchingV1 => "/req_chunk/1",
Protocol::CollationFetchingV1 => "/req_collation/1",
Protocol::PoVFetchingV1 => "/req_pov/1",
Protocol::AvailableDataFetchingV1 => "/req_available_data/1",
Protocol::StatementFetchingV1 => "/req_statement/1",
Protocol::DisputeSendingV1 => "/send_dispute/1",
// V2:
Protocol::CollationFetchingV2 => "/req_collation/2",
Protocol::AttestedCandidateV2 => "/req_attested_candidate/2",
Protocol::ChunkFetchingV2 => "/req_chunk/2",
};
format!("{}{}", prefix, short_name).into()
}
}