Ease parachain candidate code fetching (#2593)

* code stored in para + modify CandidateDescriptor.

* WIP: digest + some more impl

* validation_code_hash in payload + check in inclusion

* check in client + refator

* tests

* fix encoding indices

* remove old todos

* fix test

* fix test

* add test

* fetch validation code inside collation-generation from the relay-chain

* HashMismatch -> PoVHashMismatch + miscompilation

* refactor, store hash when needed

* storage rename: more specific but slightly too verbose

* do not hash on candidate validation, fetch hash instead

* better test

* fix test

* guide updates

* don't panic in runtime

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

polkadot/node/collation-generation/src/lib.rs

@@ -33,7 +33,7 @@ use polkadot_node_subsystem::{
 };
 use polkadot_node_subsystem_util::{
 	request_availability_cores_ctx, request_persisted_validation_data_ctx,
-	request_validators_ctx,
+	request_validators_ctx, request_validation_code_ctx,
 	metrics::{self, prometheus},
 };
 use polkadot_primitives::v1::{
@@ -244,9 +244,10 @@ async fn handle_new_activations<Context: SubsystemContext>(
 				continue;
 			}
 
-			// we get validation data synchronously for each core instead of
+			// we get validation data and validation code synchronously for each core instead of
 			// within the subtask loop, because we have only a single mutable handle to the
 			// context, so the work can't really be distributed
+
 			let validation_data = match request_persisted_validation_data_ctx(
 				relay_parent,
 				scheduled_core.para_id,
@@ -270,6 +271,30 @@ async fn handle_new_activations<Context: SubsystemContext>(
 				}
 			};
 
+			let validation_code = match request_validation_code_ctx(
+				relay_parent,
+				scheduled_core.para_id,
+				assumption,
+				ctx,
+			)
+			.await?
+			.await??
+			{
+				Some(v) => v,
+				None => {
+					tracing::trace!(
+						target: LOG_TARGET,
+						core_idx = %core_idx,
+						relay_parent = ?relay_parent,
+						our_para = %config.para_id,
+						their_para = %scheduled_core.para_id,
+						"validation code is not available",
+					);
+					continue
+				}
+			};
+			let validation_code_hash = validation_code.hash();
+
 			let task_config = config.clone();
 			let mut task_sender = sender.clone();
 			let metrics = metrics.clone();
@@ -295,6 +320,7 @@ async fn handle_new_activations<Context: SubsystemContext>(
 					&scheduled_core.para_id,
 					&persisted_validation_data_hash,
 					&pov_hash,
+					&validation_code_hash,
 				);
 
 				let erasure_root = match erasure_root(
@@ -334,6 +360,7 @@ async fn handle_new_activations<Context: SubsystemContext>(
 						pov_hash,
 						erasure_root,
 						para_head: commitments.head_data.hash(),
+						validation_code_hash: validation_code_hash,
 					},
 				};
 
@@ -474,7 +501,7 @@ mod tests {
 		};
 		use polkadot_primitives::v1::{
 			BlockNumber, CollatorPair, Id as ParaId,
-			PersistedValidationData, ScheduledCore,
+			PersistedValidationData, ScheduledCore, ValidationCode,
 		};
 		use std::pin::Pin;
 
@@ -696,6 +723,16 @@ mod tests {
 						))) => {
 							tx.send(Ok(vec![Default::default(); 3])).unwrap();
 						}
+						Some(AllMessages::RuntimeApi(RuntimeApiMessage::Request(
+							_hash,
+							RuntimeApiRequest::ValidationCode(
+								_para_id,
+								OccupiedCoreAssumption::Free,
+								tx,
+							),
+						))) => {
+							tx.send(Ok(Some(ValidationCode(vec![1, 2, 3])))).unwrap();
+						}
 						Some(msg) => {
 							panic!("didn't expect any other overseer requests; got {:?}", msg)
 						}
@@ -733,11 +770,13 @@ mod tests {
 			let expect_validation_data_hash
 				= PersistedValidationData::<Hash, BlockNumber>::default().hash();
 			let expect_relay_parent = Hash::repeat_byte(4);
+			let expect_validation_code_hash = ValidationCode(vec![1, 2, 3]).hash();
 			let expect_payload = collator_signature_payload(
 				&expect_relay_parent,
 				&config.para_id,
 				&expect_validation_data_hash,
 				&expect_pov_hash,
+				&expect_validation_code_hash,
 			);
 			let expect_descriptor = CandidateDescriptor {
 				signature: config.key.sign(&expect_payload),
@@ -748,6 +787,7 @@ mod tests {
 				pov_hash: expect_pov_hash,
 				erasure_root: Default::default(), // this isn't something we're checking right now
 				para_head: test_collation().head_data.hash(),
+				validation_code_hash: expect_validation_code_hash,
 			};
 
 			assert_eq!(sent_messages.len(), 1);
@@ -768,6 +808,7 @@ mod tests {
 							&descriptor.para_id,
 							&descriptor.persisted_validation_data_hash,
 							&descriptor.pov_hash,
+							&descriptor.validation_code_hash,
 						)
 						.as_ref(),
 						&descriptor.collator,