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// Copyright 2017-2020 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
// 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 <>.

//! Collation node logic.
//! A collator node lives on a distinct parachain and submits a proposal for
//! a state transition, along with a proof for its validity
//! (what we might call a witness or block data).
//! One of collators' other roles is to route messages between chains.
//! Each parachain produces a list of "egress" posts of messages for each other
//! parachain on each block, for a total of N^2 lists all together.
//! We will refer to the egress list at relay chain block X of parachain A with
//! destination B as egress(X)[A -> B]
//! On every block, each parachain will be intended to route messages from some
//! subset of all the other parachains. (NOTE: in practice this is not done until PoC-3)
//! Since the egress information is unique to every block, when routing from a
//! parachain a collator must gather all egress posts from that parachain
//! up to the last point in history that messages were successfully routed
//! from that parachain, accounting for relay chain blocks where no candidate
//! from the collator's parachain was produced.
//! In the case that all parachains route to each other and a candidate for the
//! collator's parachain was included in the last relay chain block, the collator
//! only has to gather egress posts from other parachains one block back in relay
//! chain history.
//! This crate defines traits which provide context necessary for collation logic
//! to be performed, as the collation logic itself.

use std::collections::HashSet;
use std::sync::Arc;
use std::time::Duration;
use std::pin::Pin;
use futures::{future, Future, Stream, FutureExt, TryFutureExt, StreamExt, task::Spawn};
use sc_client::BlockchainEvents;
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use sp_core::Pair;
use sp_runtime::traits::BlakeTwo256;
use polkadot_primitives::{
	BlockId, Hash, Block,
		self, BlockData, DutyRoster, HeadData, Id as ParaId,
		PoVBlock, ValidatorId, CollatorPair, LocalValidationData
	ProvideRuntimeApi, AbstractService, ParachainHost, IsKusama,
	service::{self, Roles}
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pub use polkadot_cli::service::Configuration;
pub use polkadot_validation::SignedStatement;
pub use polkadot_primitives::parachain::CollatorId;
pub use sc_network::PeerId;
pub use service::RuntimeApiCollection;
const COLLATION_TIMEOUT: Duration = Duration::from_secs(30);
/// An abstraction over the `Network` with useful functions for a `Collator`.
	/// Create a `Stream` of checked statements for the given `relay_parent`.
	/// The returned stream will not terminate, so it is required to make sure that the stream is
	/// dropped when it is not required anymore. Otherwise, it will stick around in memory
	/// infinitely.
	fn checked_statements(&self, relay_parent: Hash) -> Pin<Box<dyn Stream<Item=SignedStatement>>>;
impl Network for polkadot_network::protocol::Service {
	fn checked_statements(&self, relay_parent: Hash) -> Pin<Box<dyn Stream<Item=SignedStatement>>> {
		polkadot_network::protocol::Service::checked_statements(self, relay_parent)
/// Error to return when the head data was invalid.
#[derive(Clone, Copy, Debug)]
pub struct InvalidHead;

/// Collation errors.
pub enum Error {
	/// Error on the collator side of things.

impl fmt::Display for Error {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match *self {
			Error::Polkadot(ref err) => write!(f, "Polkadot node error: {}", err),
			Error::Collator(_) => write!(f, "Collator node error: Invalid head data"),

pub type PolkadotClient<B, E, R> = sc_client::Client<B, E, Block, R>;
/// Something that can build a `ParachainContext`.
pub trait BuildParachainContext {
	/// The parachain context produced by the `build` function.
	type ParachainContext: self::ParachainContext;

	/// Build the `ParachainContext`.
	fn build<B, E, R, SP, Extrinsic>(
		client: Arc<PolkadotClient<B, E, R>>,
		network: impl Network + Clone + 'static,
	) -> Result<Self::ParachainContext, ()>
			PolkadotClient<B, E, R>: ProvideRuntimeApi<Block>,
			<PolkadotClient<B, E, R> as ProvideRuntimeApi<Block>>::Api: RuntimeApiCollection<Extrinsic>,
			// Rust bug:
			<<PolkadotClient<B, E, R> as ProvideRuntimeApi<Block>>::Api as sp_api::ApiExt<Block>>::StateBackend:
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			Extrinsic: codec::Codec + Send + Sync + 'static,
			E: sc_client::CallExecutor<Block> + Clone + Send + Sync + 'static,
			SP: Spawn + Clone + Send + Sync + 'static,
			R: Send + Sync + 'static,
			B: sc_client_api::Backend<Block> + 'static,
			// Rust bug:
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			B::State: sp_api::StateBackend<BlakeTwo256>;
/// Parachain context needed for collation.
/// This can be implemented through an externally attached service or a stub.
/// This is expected to be a lightweight, shared type like an Arc.
pub trait ParachainContext: Clone {
	type ProduceCandidate: Future<Output = Result<(BlockData, HeadData), InvalidHead>>;
	/// Produce a candidate, given the relay parent hash, the latest ingress queue information
	/// and the last parachain head.
	fn produce_candidate(
	) -> Self::ProduceCandidate;
/// Produce a candidate for the parachain, with given contexts, parent head, and signing key.
pub async fn collate<P>(
	local_id: ParaId,
	local_validation_data: LocalValidationData,
	key: Arc<CollatorPair>,
	-> Result<parachain::Collation, Error>
		P: ParachainContext,
		P::ProduceCandidate: Send,
	let (block_data, head_data) = para_context.produce_candidate(

	let pov_block = PoVBlock {

	let pov_block_hash = pov_block.hash();
	let signature = key.sign(&parachain::collator_signature_payload(

	let info = parachain::CollationInfo {
		parachain_index: local_id,
		collator: key.public(),

	let collation = parachain::Collation {
fn build_collator_service<S, P, Extrinsic>(
	service: (S, polkadot_service::FullNodeHandles),
	para_id: ParaId,
	key: Arc<CollatorPair>,
	build_parachain_context: P,
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) -> Result<S, polkadot_service::Error>
		S: AbstractService<Block = service::Block>,
		sc_client::Client<S::Backend, S::CallExecutor, service::Block, S::RuntimeApi>: ProvideRuntimeApi<Block>,
		<sc_client::Client<S::Backend, S::CallExecutor, service::Block, S::RuntimeApi> as ProvideRuntimeApi<Block>>::Api:
				Error = sp_blockchain::Error,
				StateBackend = sc_client_api::StateBackendFor<S::Backend, Block>
		// Rust bug:
		S::Backend: service::Backend<service::Block>,
		// Rust bug:
		<S::Backend as service::Backend<service::Block>>::State:
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		// Rust bug:
		S::CallExecutor: service::CallExecutor<service::Block>,
		// Rust bug:
		S::SelectChain: service::SelectChain<service::Block>,
		P: BuildParachainContext,
		P::ParachainContext: Send + 'static,
		<P::ParachainContext as ParachainContext>::ProduceCandidate: Send,
		Extrinsic: service::Codec + Send + Sync + 'static,
	let (service, handles) = service;
	let spawner = service.spawn_task_handle();
	let polkadot_network = match handles.polkadot_network {
		None => return Err(
			"Collator cannot run when Polkadot-specific networking has not been started".into()
		Some(n) => n,
	let client = service.client();

	let parachain_context = match
	) {
		Ok(ctx) => ctx,
		Err(()) => {
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			return Err("Could not build the parachain context!".into())
	let work = async move {
		let mut notification_stream = client.import_notification_stream();

		while let Some(notification) = {
			macro_rules! try_fr {
				($e:expr) => {
					match $e {
						Ok(x) => x,
						Err(e) => return future::Either::Left(future::err(Error::Polkadot(
			let relay_parent = notification.hash;
			let id = BlockId::hash(relay_parent);

			let network = polkadot_network.clone();
			let client = client.clone();
			let key = key.clone();
			let parachain_context = parachain_context.clone();

			let work = future::lazy(move |_| {
				let api = client.runtime_api();
				let local_validation = match try_fr!(api.local_validation_data(&id, para_id)) {
					Some(local_validation) => local_validation,
					None => return future::Either::Left(future::ok(())),

				let validators = try_fr!(api.validators(&id));

				let targets = compute_targets(

				let collation_work = collate(
				).map_ok(move |collation| {
					network.distribute_collation(targets, collation)

			let deadlined = future::select(
				work.then(|f| f).boxed(),

			let silenced = deadlined
				.map(|either| {
					if let future::Either::Right(_) = either {
						warn!("Collation failure: timeout");
			let future =;
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	service.spawn_essential_task("collation", work);
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/// Async function that will run the collator node with the given `RelayChainContext` and `ParachainContext`
/// built by the given `BuildParachainContext` and arguments to the underlying polkadot node.
pub async fn start_collator<P>(
	build_parachain_context: P,
	para_id: ParaId,
	key: Arc<CollatorPair>,
	config: Configuration,
) -> Result<(), polkadot_service::Error>
	P: BuildParachainContext,
	P::ParachainContext: Send + 'static,
	<P::ParachainContext as ParachainContext>::ProduceCandidate: Send,
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	let is_kusama = config.chain_spec.is_kusama();
	match (is_kusama, config.roles) {
		(_, Roles::LIGHT) => return Err(
			polkadot_service::Error::Other("light nodes are unsupported as collator".into())
		(true, _) =>
				service::kusama_new_full(config, Some((key.public(), para_id)), None, false, 6000, None)?,
		(false, _) =>
				service::polkadot_new_full(config, Some((key.public(), para_id)), None, false, 6000, None)?,

fn compute_targets(para_id: ParaId, session_keys: &[ValidatorId], roster: DutyRoster) -> HashSet<ValidatorId> {
	use polkadot_primitives::parachain::Chain;

		.filter(|&(_, c)| c == &Chain::Parachain(para_id))
		.filter_map(|(i, _)| session_keys.get(i))

mod tests {
	use super::*;

	struct DummyParachainContext;

	impl ParachainContext for DummyParachainContext {
		type ProduceCandidate = future::Ready<Result<(BlockData, HeadData), InvalidHead>>;
		fn produce_candidate(
			_local_validation: LocalValidationData,
		) -> Self::ProduceCandidate {
			// send messages right back.
				BlockData(vec![1, 2, 3, 4, 5,]),
				HeadData(vec![9, 9, 9]),

	struct BuildDummyParachainContext;

	impl BuildParachainContext for BuildDummyParachainContext {
		type ParachainContext = DummyParachainContext;

		fn build<B, E, R, SP, Extrinsic>(
			_: Arc<PolkadotClient<B, E, R>>,
			_: SP,
			_: impl Network + Clone + 'static,
		) -> Result<Self::ParachainContext, ()> {

	// Make sure that the future returned by `start_collator` implementes `Send`.
	fn start_collator_is_send() {
		fn check_send<T: Send>(_: T) {}