Use GrandpaJustification instead of Vec<u8> in Pallet API (#847)

* Stop passing raw encoded justifications to pallet API

By having the API accept a struct-ified justification we are able to
better utilize the justifications fields for weight calculations.

* Update relayer code to use decoded justifications

* Add justification to `expect()` statement

* Fix some imports

* Make justification wrapper contain decoded justification

* Rename some fields

* Get rid of warnings

* Appease Clippy

* Only decode justification once at init time

* Remove unnecessary method

* Remove justification wrapper

This became kinda unnecessary since we could implement the FinalityProof
trait on GrandpaJustification directly.

bridges/primitives/header-chain/src/justification.rs

@@ -25,7 +25,7 @@ use frame_support::RuntimeDebug;
 use sp_finality_grandpa::{AuthorityId, AuthoritySignature, SetId};
 use sp_runtime::traits::Header as HeaderT;
 use sp_std::collections::{btree_map::BTreeMap, btree_set::BTreeSet};
-use sp_std::prelude::Vec;
+use sp_std::prelude::*;
 
 /// Justification verification error.
 #[derive(RuntimeDebug, PartialEq)]
@@ -58,15 +58,11 @@ pub fn verify_justification<Header: HeaderT>(
 	finalized_target: (Header::Hash, Header::Number),
 	authorities_set_id: SetId,
 	authorities_set: &VoterSet<AuthorityId>,
-	raw_justification: &[u8],
+	justification: &GrandpaJustification<Header>,
 ) -> Result<(), Error>
 where
 	Header::Number: finality_grandpa::BlockNumberOps,
 {
-	// Decode justification first
-	let justification =
-		GrandpaJustification::<Header>::decode(&mut &*raw_justification).map_err(|_| Error::JustificationDecode)?;
-
 	// Ensure that it is justification for the expected header
 	if (justification.commit.target_hash, justification.commit.target_number) != finalized_target {
 		return Err(Error::InvalidJustificationTarget);
@@ -130,7 +126,7 @@ where
 ///
 /// This particular proof is used to prove that headers on a bridged chain
 /// (so not our chain) have been finalized correctly.
-#[derive(Encode, Decode, RuntimeDebug)]
+#[derive(Encode, Decode, RuntimeDebug, Clone, PartialEq, Eq)]
 pub struct GrandpaJustification<Header: HeaderT> {
 	/// The round (voting period) this justification is valid for.
 	pub round: u64,
@@ -140,6 +136,12 @@ pub struct GrandpaJustification<Header: HeaderT> {
 	pub votes_ancestries: Vec<Header>,
 }
 
+impl<H: HeaderT> crate::FinalityProof<H::Number> for GrandpaJustification<H> {
+	fn target_header_number(&self) -> H::Number {
+		self.commit.target_number
+	}
+}
+
 /// A utility trait implementing `finality_grandpa::Chain` using a given set of headers.
 #[derive(RuntimeDebug)]
 struct AncestryChain<Header: HeaderT> {

bridges/primitives/header-chain/src/lib.rs

@@ -94,6 +94,12 @@ impl<H: Default, E> HeaderChain<H, E> for () {
 	}
 }
 
+/// Abstract finality proof that is justifying block finality.
+pub trait FinalityProof<Number>: Clone + Send + Sync + Debug {
+	/// Return number of header that this proof is generated for.
+	fn target_header_number(&self) -> Number;
+}
+
 /// Find header digest that schedules next GRANDPA authorities set.
 pub fn find_grandpa_authorities_scheduled_change<H: HeaderT>(
 	header: &H,

bridges/primitives/header-chain/tests/justification.rs

@@ -18,7 +18,6 @@
 
 use bp_header_chain::justification::{verify_justification, Error};
 use bp_test_utils::*;
-use codec::Encode;
 
 type TestHeader = sp_runtime::testing::Header;
 
@@ -38,7 +37,7 @@ fn valid_justification_accepted() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&make_justification_for_header::<TestHeader>(params).encode()
+			&make_justification_for_header::<TestHeader>(params)
 		),
 		Ok(()),
 	);
@@ -60,7 +59,7 @@ fn valid_justification_accepted_with_single_fork() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&make_justification_for_header::<TestHeader>(params).encode()
+			&make_justification_for_header::<TestHeader>(params)
 		),
 		Ok(()),
 	);
@@ -94,20 +93,12 @@ fn valid_justification_accepted_with_arbitrary_number_of_authorities() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set,
-			&make_justification_for_header::<TestHeader>(params).encode()
+			&make_justification_for_header::<TestHeader>(params)
 		),
 		Ok(()),
 	);
 }
 
-#[test]
-fn justification_with_invalid_encoding_rejected() {
-	assert_eq!(
-		verify_justification::<TestHeader>(header_id::<TestHeader>(1), TEST_GRANDPA_SET_ID, &voter_set(), &[],),
-		Err(Error::JustificationDecode),
-	);
-}
-
 #[test]
 fn justification_with_invalid_target_rejected() {
 	assert_eq!(
@@ -115,7 +106,7 @@ fn justification_with_invalid_target_rejected() {
 			header_id::<TestHeader>(2),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&make_default_justification::<TestHeader>(&test_header(1)).encode(),
+			&make_default_justification::<TestHeader>(&test_header(1)),
 		),
 		Err(Error::InvalidJustificationTarget),
 	);
@@ -131,7 +122,7 @@ fn justification_with_invalid_commit_rejected() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&justification.encode(),
+			&justification,
 		),
 		Err(Error::InvalidJustificationCommit),
 	);
@@ -147,7 +138,7 @@ fn justification_with_invalid_authority_signature_rejected() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&justification.encode(),
+			&justification,
 		),
 		Err(Error::InvalidAuthoritySignature),
 	);
@@ -163,7 +154,7 @@ fn justification_with_invalid_precommit_ancestry() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&justification.encode(),
+			&justification,
 		),
 		Err(Error::InvalidPrecommitAncestries),
 	);
@@ -186,7 +177,7 @@ fn justification_is_invalid_if_we_dont_meet_threshold() {
 			header_id::<TestHeader>(1),
 			TEST_GRANDPA_SET_ID,
 			&voter_set(),
-			&make_justification_for_header::<TestHeader>(params).encode()
+			&make_justification_for_header::<TestHeader>(params)
 		),
 		Err(Error::InvalidJustificationCommit),
 	);