Get current relay block head without messing with signatures

Turns out we already had a client object available which implemented
the necessary trait; the difficulty was just that I didn't know that
a. the trait existed, or that
b. the client in our possession implemented that trait.

This does make things much neater; it just means propagating the
trait bound backwards as implemented here.

network/src/legacy/router.rs

@@ -32,6 +32,7 @@ use polkadot_primitives::parachain::{
 	CandidateReceipt, ParachainHost, ValidatorIndex, Collation, PoVBlock, ErasureChunk,
 };
 use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
 
 use futures::prelude::*;
 use futures::{task::SpawnExt, future::ready};
@@ -133,6 +134,7 @@ impl<P, T: Clone> Clone for Router<P, T> {
 }
 
 impl<P: ProvideRuntimeApi<Block> + Send + Sync + 'static, T> Router<P, T> where
+	P: HeaderBackend<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 	T: Clone + Executor + Send + 'static,
 {

network/src/legacy/validation.rs

@@ -29,6 +29,7 @@ use polkadot_primitives::parachain::{
 	ValidatorId, PoVBlock,
 };
 use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
 
 use futures::prelude::*;
 use futures::task::SpawnExt;
@@ -167,7 +168,7 @@ impl<P, T> ValidationNetwork<P, T> {
 
 /// A long-lived network which can create parachain statement  routing processes on demand.
 impl<P, T> ParachainNetwork for ValidationNetwork<P, T> where
-	P: ProvideRuntimeApi<Block> + Send + Sync + 'static,
+	P: ProvideRuntimeApi<Block> + HeaderBackend<Block> + Send + Sync + 'static,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 	T: Clone + Executor + Send + Sync + 'static,
 {

network/src/protocol.rs

@@ -40,6 +40,7 @@ use polkadot_validation::{
 };
 use sc_network::{config::Roles, Event, PeerId};
 use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
 
 use std::collections::HashMap;
 use std::pin::Pin;
@@ -110,7 +111,7 @@ pub fn start<C, Api, SP>(
 	executor: SP,
 ) -> Result<Service, futures::task::SpawnError> where
 	C: ChainContext + 'static,
-	Api: ProvideRuntimeApi<Block> + Send + Sync + 'static,
+	Api: ProvideRuntimeApi<Block> + HeaderBackend<Block> + Send + Sync + 'static,
 	Api::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 	SP: Spawn + Clone + Send + 'static,
 {
@@ -566,7 +567,7 @@ async fn worker_loop<Api, Sp>(
 	mut receiver: mpsc::Receiver<ServiceToWorkerMsg>,
 	executor: Sp,
 ) where
-	Api: ProvideRuntimeApi<Block> + Send + Sync + 'static,
+	Api: ProvideRuntimeApi<Block> + HeaderBackend<Block> + Send + Sync + 'static,
 	Api::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 	Sp: Spawn + Clone + Send + 'static,
 {
@@ -690,7 +691,7 @@ async fn statement_import_loop<Api>(
 	mut exit: exit_future::Exit,
 	executor: impl Spawn,
 ) where
-	Api: ProvideRuntimeApi<Block> + Send + Sync + 'static,
+	Api: ProvideRuntimeApi<Block> + HeaderBackend<Block> + Send + Sync + 'static,
 	Api::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
 	let topic = crate::legacy::router::attestation_topic(relay_parent);

validation/src/collation.rs

@@ -22,7 +22,7 @@
 use std::sync::Arc;
 
 use polkadot_primitives::{
-	BlakeTwo256, Block, Hash, HashT, BlockId, Balance, BlockNumber,
+	BlakeTwo256, Block, Hash, HashT, BlockId, Balance,
 	parachain::{
 		CollatorId, CandidateReceipt, CollationInfo,
 		ParachainHost, Id as ParaId, Collation, FeeSchedule, ErasureChunk,
@@ -31,6 +31,7 @@ use polkadot_primitives::{
 };
 use polkadot_erasure_coding as erasure;
 use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
 use parachain::{
 	wasm_executor::{self, ExecutionMode}, UpwardMessage,
 };
@@ -65,20 +66,18 @@ pub trait Collators: Clone {
 }
 
 /// A future which resolves when a collation is available.
-pub async fn collation_fetch<C: Collators, P, GCRB>(
+pub async fn collation_fetch<C: Collators, P>(
 	parachain: ParaId,
 	relay_parent_hash: Hash,
-	get_current_relay_block: GCRB,
 	collators: C,
 	client: Arc<P>,
 	max_block_data_size: Option<u64>,
 ) -> Result<(Collation, HeadData, Balance),C::Error>
 	where
 		P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 		C: Collators + Unpin,
-		P: ProvideRuntimeApi<Block>,
+		P: ProvideRuntimeApi<Block> + HeaderBackend<Block>,
 		<C as Collators>::Collation: Unpin,
-		GCRB: Fn() -> BlockNumber,
 {
 	let relay_parent = BlockId::hash(relay_parent_hash);
 
@@ -89,7 +88,6 @@ pub async fn collation_fetch<C: Collators, P, GCRB>(
 		let res = validate_collation(
 			&*client,
 			&relay_parent,
-			get_current_relay_block(),
 			&collation,
 			max_block_data_size,
 		);
@@ -284,15 +282,14 @@ pub fn validate_chunk(
 fn do_validation<P>(
 	client: &P,
 	relay_parent: &BlockId,
-	current_relay_block: BlockNumber,
 	pov_block: &PoVBlock,
 	para_id: ParaId,
 	max_block_data_size: Option<u64>,
 	fees_charged: Option<Balance>,
 	head_data: &HeadData,
 	upward_messages: &Vec<UpwardMessage>,
 ) -> Result<(HeadData, Balance), Error> where
-	P: ProvideRuntimeApi<Block>,
+	P: ProvideRuntimeApi<Block> + HeaderBackend<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
 	use parachain::ValidationParams;
@@ -315,7 +312,7 @@ fn do_validation<P>(
 	let params = ValidationParams {
 		parent_head: chain_status.head_data.0.clone(),
 		block_data: pov_block.block_data.0.clone(),
-		current_relay_block,
+		current_relay_block: client.info().best_number,
 	};
 
 	let ext = Externalities::new(chain_status.balance, chain_status.fee_schedule);
@@ -405,13 +402,12 @@ pub fn validate_receipt<P>(
 	receipt: &CandidateReceipt,
 	max_block_data_size: Option<u64>,
 ) -> Result<Vec<ErasureChunk>, Error> where
-	P: ProvideRuntimeApi<Block>,
+	P: ProvideRuntimeApi<Block> + HeaderBackend<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
 	let (parent_head, _fees) = do_validation(
 		client,
 		relay_parent,
-		receipt.current_relay_block,
 		pov_block,
 		receipt.parachain_index,
 		max_block_data_size,
@@ -457,11 +453,10 @@ pub fn validate_receipt<P>(
 pub fn validate_collation<P>(
 	client: &P,
 	relay_parent: &BlockId,
-	current_relay_block: BlockNumber,
 	collation: &Collation,
 	max_block_data_size: Option<u64>,
 ) -> Result<(HeadData, Balance), Error> where
-	P: ProvideRuntimeApi<Block>,
+	P: ProvideRuntimeApi<Block> + HeaderBackend<Block>,
 	P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 {
 	let para_id = collation.info.parachain_index;

validation/src/shared_table/mod.rs

@@ -38,6 +38,7 @@ use super::{GroupInfo, TableRouter};
 use self::includable::IncludabilitySender;
 use primitives::Pair;
 use sp_api::ProvideRuntimeApi;
+use sp_blockchain::HeaderBackend;
 
 mod includable;
 
@@ -267,7 +268,7 @@ impl<Fetch: Future + Unpin> ParachainWork<Fetch> {
 			impl Send + FnMut(&BlockId, &PoVBlock, &CandidateReceipt) -> Result<ErasureChunk, ()> + Unpin,
 		>
 		where
-			P: Send + Sync + 'static,
+			P: HeaderBackend<Block> + Send + Sync + 'static,
 			P::Api: ParachainHost<Block, Error = sp_blockchain::Error>,
 	{
 		let max_block_data_size = self.max_block_data_size;

validation/src/validation_service/mod.rs

@@ -34,7 +34,7 @@ use sp_blockchain::HeaderBackend;
 use block_builder::BlockBuilderApi;
 use consensus::SelectChain;
 use futures::{future::ready, prelude::*, task::{Spawn, SpawnExt}};
-use polkadot_primitives::{Block, Hash, BlockId, BlockNumber};
+use polkadot_primitives::{Block, Hash, BlockId};
 use polkadot_primitives::parachain::{
 	Chain, ParachainHost, Id as ParaId, ValidatorIndex, ValidatorId, ValidatorPair,
 };
@@ -368,19 +368,16 @@ impl<C, N, P, SP> ParachainValidationInstances<C, N, P, SP> where
 	}
 
 	// launch parachain work asynchronously.
-	fn launch_work<GCRB>(
+	fn launch_work(
 		&self,
 		relay_parent: Hash,
 		validation_para: ParaId,
 		build_router: N::BuildTableRouter,
 		max_block_data_size: Option<u64>,
 		authorities_num: usize,
 		local_id: ValidatorIndex,
-		get_current_relay_block: GCRB,
 	)
-	where
-		GCRB: Fn() -> BlockNumber + Send,
-	{
+	where {
 		let (collators, client) = (self.collators.clone(), self.client.clone());
 		let availability_store = self.availability_store.clone();
 
@@ -389,7 +386,6 @@ impl<C, N, P, SP> ParachainValidationInstances<C, N, P, SP> where
 			let collation_work = crate::collation::collation_fetch(
 				validation_para,
 				relay_parent,
-				get_current_relay_block,
 				collators,
 				client.clone(),
 				max_block_data_size,