pow: add access to pre-digest for algorithm verifiers (paritytech#6900)

* pow: fetch pre-runtime digest to verifier

* Add Other error type

* Fix log target and change docs to refer to pre_runtime

client/consensus/pow/src/lib.rs

@@ -88,10 +88,13 @@ pub enum Error<B: BlockT> {
 	CreateInherents(sp_inherents::Error),
 	#[display(fmt = "Checking inherents failed: {}", _0)]
 	CheckInherents(String),
+	#[display(fmt = "Multiple pre-runtime digests")]
+	MultiplePreRuntimeDigests,
 	Client(sp_blockchain::Error),
 	Codec(codec::Error),
 	Environment(String),
-	Runtime(RuntimeString)
+	Runtime(RuntimeString),
+	Other(String),
 }
 
 impl<B: BlockT> std::convert::From<Error<B>> for String {
@@ -172,6 +175,7 @@ pub trait PowAlgorithm<B: BlockT> {
 		&self,
 		parent: &BlockId<B>,
 		pre_hash: &B::Hash,
+		pre_digest: Option<&[u8]>,
 		seal: &Seal,
 		difficulty: Self::Difficulty,
 	) -> Result<bool, Error<B>>;
@@ -180,6 +184,7 @@ pub trait PowAlgorithm<B: BlockT> {
 		&self,
 		parent: &BlockId<B>,
 		pre_hash: &B::Hash,
+		pre_digest: Option<&[u8]>,
 		difficulty: Self::Difficulty,
 		round: u32,
 	) -> Result<Option<Seal>, Error<B>>;
@@ -368,9 +373,11 @@ impl<B, I, C, S, Algorithm, CAW> BlockImport<B> for PowBlockImport<B, I, C, S, A
 		};
 
 		let pre_hash = block.header.hash();
+		let pre_digest = find_pre_digest::<B>(&block.header)?;
 		if !self.algorithm.verify(
 			&BlockId::hash(parent_hash),
 			&pre_hash,
+			pre_digest.as_ref().map(|v| &v[..]),
 			&inner_seal,
 			difficulty,
 		)? {
@@ -519,7 +526,7 @@ pub fn import_queue<B, Transaction, Algorithm>(
 /// However, it's not recommended to use background threads in the rest of the
 /// codebase.
 ///
-/// `preruntime` is a parameter that allows a custom additional pre-runtime
+/// `pre_runtime` is a parameter that allows a custom additional pre-runtime
 /// digest to be inserted for blocks being built. This can encode authorship
 /// information, or just be a graffiti. `round` is for number of rounds the
 /// CPU miner runs each time. This parameter should be tweaked so that each
@@ -529,7 +536,7 @@ pub fn start_mine<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 	client: Arc<C>,
 	algorithm: Algorithm,
 	mut env: E,
-	preruntime: Option<Vec<u8>>,
+	pre_runtime: Option<Vec<u8>>,
 	round: u32,
 	mut sync_oracle: SO,
 	build_time: std::time::Duration,
@@ -557,7 +564,7 @@ pub fn start_mine<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 				client.as_ref(),
 				&algorithm,
 				&mut env,
-				preruntime.as_ref(),
+				pre_runtime.as_ref(),
 				round,
 				&mut sync_oracle,
 				build_time.clone(),
@@ -581,7 +588,7 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 	client: &C,
 	algorithm: &Algorithm,
 	env: &mut E,
-	preruntime: Option<&Vec<u8>>,
+	pre_runtime: Option<&Vec<u8>>,
 	round: u32,
 	sync_oracle: &mut SO,
 	build_time: std::time::Duration,
@@ -640,8 +647,8 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 		let inherent_data = inherent_data_providers
 			.create_inherent_data().map_err(Error::CreateInherents)?;
 		let mut inherent_digest = Digest::default();
-		if let Some(preruntime) = &preruntime {
-			inherent_digest.push(DigestItem::PreRuntime(POW_ENGINE_ID, preruntime.to_vec()));
+		if let Some(pre_runtime) = &pre_runtime {
+			inherent_digest.push(DigestItem::PreRuntime(POW_ENGINE_ID, pre_runtime.to_vec()));
 		}
 		let proposal = futures::executor::block_on(proposer.propose(
 			inherent_data,
@@ -658,6 +665,7 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 				let seal = algorithm.mine(
 					&BlockId::Hash(best_hash),
 					&header.hash(),
+					pre_runtime.map(|v| &v[..]),
 					difficulty,
 					round,
 				)?;
@@ -702,3 +710,22 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 			.map_err(|e| Error::BlockBuiltError(best_hash, e))?;
 	}
 }
+
+/// Find PoW pre-runtime.
+fn find_pre_digest<B: BlockT>(header: &B::Header) -> Result<Option<Vec<u8>>, Error<B>> {
+	let mut pre_digest: Option<_> = None;
+	for log in header.digest().logs() {
+		trace!(target: "pow", "Checking log {:?}, looking for pre runtime digest", log);
+		match (log, pre_digest.is_some()) {
+			(DigestItem::PreRuntime(POW_ENGINE_ID, _), true) => {
+				return Err(Error::MultiplePreRuntimeDigests)
+			},
+			(DigestItem::PreRuntime(POW_ENGINE_ID, v), false) => {
+				pre_digest = Some(v.clone());
+			},
+			(_, _) => trace!(target: "pow", "Ignoring digest not meant for us"),
+		}
+	}
+
+	Ok(pre_digest)
+}