Custom RPC for Merkle Mountain Range pallet (#8137)

* Add MMR custom RPC.

* Change RuntimeApi to avoid hardcoding leaf type.

* Properly implement the new RuntimeAPI and wire up RPC.

* Extract Offchain DB as separate execution extension.

* Enable offchain DB access for offchain calls.

* Fix offchain_election tests.

* Skip block initialisation for proof generation.

* Fix integration test setup.

* Fix offchain tests. Not sure how I missed them earlier 🤷.

* Fix long line.

* One more test missing.

* Update mock for multi-phase.

* Address review grumbbles.

* Address review grumbles.

* Fix line width of a comment

substrate/bin/node/runtime/src/lib.rs

@@ -1377,23 +1377,31 @@ impl_runtime_apis! {
 
 	impl pallet_mmr::primitives::MmrApi<
 		Block,
-		mmr::Leaf,
 		mmr::Hash,
 	> for Runtime {
-		fn generate_proof(leaf_index: u64) -> Result<(mmr::Leaf, mmr::Proof<mmr::Hash>), mmr::Error> {
+		fn generate_proof(leaf_index: u64)
+			-> Result<(mmr::EncodableOpaqueLeaf, mmr::Proof<mmr::Hash>), mmr::Error>
+		{
 			Mmr::generate_proof(leaf_index)
+				.map(|(leaf, proof)| (mmr::EncodableOpaqueLeaf::from_leaf(&leaf), proof))
 		}
 
-		fn verify_proof(leaf: mmr::Leaf, proof: mmr::Proof<mmr::Hash>) -> Result<(), mmr::Error> {
+		fn verify_proof(leaf: mmr::EncodableOpaqueLeaf, proof: mmr::Proof<mmr::Hash>)
+			-> Result<(), mmr::Error>
+		{
+			let leaf: mmr::Leaf = leaf
+				.into_opaque_leaf()
+				.try_decode()
+				.ok_or(mmr::Error::Verify)?;
 			Mmr::verify_leaf(leaf, proof)
 		}
 
 		fn verify_proof_stateless(
 			root: mmr::Hash,
-			leaf: Vec<u8>,
+			leaf: mmr::EncodableOpaqueLeaf,
 			proof: mmr::Proof<mmr::Hash>
 		) -> Result<(), mmr::Error> {
-			let node = mmr::DataOrHash::Data(mmr::OpaqueLeaf(leaf));
+			let node = mmr::DataOrHash::Data(leaf.into_opaque_leaf());
 			pallet_mmr::verify_leaf_proof::<mmr::Hashing, _>(root, node, proof)
 		}
 	}