block_import: switch to Box<dyn Any> for intermediates representation (#4809)

* block_import: switch to Box<dyn Any> for intermediates representation

* Use Cow and return Error instead of Option

* Remove unused error

* Distinguish NoIntermediate/InvalidIntermediate

substrate/client/consensus/pow/src/lib.rs

@@ -30,6 +30,8 @@
 //! clients.
 
 use std::sync::Arc;
+use std::any::Any;
+use std::borrow::Cow;
 use std::thread;
 use std::collections::HashMap;
 use std::marker::PhantomData;
@@ -63,8 +65,6 @@ pub enum Error<B: BlockT> {
 	InvalidSeal,
 	#[display(fmt = "PoW validation error: invalid difficulty")]
 	InvalidDifficulty,
-	#[display(fmt = "PoW block import expects an intermediate, but not found one")]
-	NoIntermediate,
 	#[display(fmt = "Rejecting block too far in future")]
 	TooFarInFuture,
 	#[display(fmt = "Fetching best header failed using select chain: {:?}", _0)]
@@ -257,6 +257,7 @@ impl<B, I, C, S, Algorithm> BlockImport<B> for PowBlockImport<B, I, C, S, Algori
 	C: ProvideRuntimeApi<B> + Send + Sync + HeaderBackend<B> + AuxStore + ProvideCache<B> + BlockOf,
 	C::Api: BlockBuilderApi<B, Error = sp_blockchain::Error>,
 	Algorithm: PowAlgorithm<B>,
+	Algorithm::Difficulty: 'static,
 {
 	type Error = ConsensusError;
 	type Transaction = sp_api::TransactionFor<C, B>;
@@ -312,10 +313,9 @@ impl<B, I, C, S, Algorithm> BlockImport<B> for PowBlockImport<B, I, C, S, Algori
 			_ => return Err(Error::<B>::HeaderUnsealed(block.header.hash()).into()),
 		};
 
-		let intermediate = PowIntermediate::<B, Algorithm::Difficulty>::decode(
-			&mut &block.intermediates.remove(INTERMEDIATE_KEY)
-				.ok_or(Error::<B>::NoIntermediate)?[..]
-		).map_err(|_| Error::<B>::NoIntermediate)?;
+		let intermediate = block.take_intermediate::<PowIntermediate::<B, Algorithm::Difficulty>>(
+			INTERMEDIATE_KEY
+		)?;
 
 		let difficulty = match intermediate.difficulty {
 			Some(difficulty) => difficulty,
@@ -392,6 +392,7 @@ impl<B: BlockT, Algorithm> PowVerifier<B, Algorithm> {
 
 impl<B: BlockT, Algorithm> Verifier<B> for PowVerifier<B, Algorithm> where
 	Algorithm: PowAlgorithm<B> + Send + Sync,
+	Algorithm::Difficulty: 'static,
 {
 	fn verify(
 		&mut self,
@@ -418,7 +419,7 @@ impl<B: BlockT, Algorithm> Verifier<B> for PowVerifier<B, Algorithm> where
 			justification,
 			intermediates: {
 				let mut ret = HashMap::new();
-				ret.insert(INTERMEDIATE_KEY.to_vec(), intermediate.encode());
+				ret.insert(Cow::from(INTERMEDIATE_KEY), Box::new(intermediate) as Box<dyn Any>);
 				ret
 			},
 			auxiliary: vec![],
@@ -553,6 +554,7 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 ) -> Result<(), Error<B>> where
 	C: HeaderBackend<B> + AuxStore + ProvideRuntimeApi<B>,
 	Algorithm: PowAlgorithm<B>,
+	Algorithm::Difficulty: 'static,
 	E: Environment<B>,
 	E::Proposer: Proposer<B, Transaction = sp_api::TransactionFor<C, B>>,
 	E::Error: std::fmt::Debug,
@@ -659,7 +661,7 @@ fn mine_loop<B: BlockT, C, Algorithm, E, SO, S, CAW>(
 			storage_changes: Some(proposal.storage_changes),
 			intermediates: {
 				let mut ret = HashMap::new();
-				ret.insert(INTERMEDIATE_KEY.to_vec(), intermediate.encode());
+				ret.insert(Cow::from(INTERMEDIATE_KEY), Box::new(intermediate) as Box<dyn Any>);
 				ret
 			},
 			finalized: false,

substrate/primitives/consensus/common/src/block_import.rs

@@ -22,7 +22,9 @@ use serde::{Serialize, Deserialize};
 use std::borrow::Cow;
 use std::collections::HashMap;
 use std::sync::Arc;
+use std::any::Any;
 
+use crate::Error;
 use crate::import_queue::{Verifier, CacheKeyId};
 
 /// Block import result.
@@ -144,7 +146,7 @@ pub struct BlockImportParams<Block: BlockT, Transaction> {
 	/// Intermediate values that are interpreted by block importers. Each block importer,
 	/// upon handling a value, removes it from the intermediate list. The final block importer
 	/// rejects block import if there are still intermediate values that remain unhandled.
-	pub intermediates: HashMap<Vec<u8>, Vec<u8>>,
+	pub intermediates: HashMap<Cow<'static, [u8]>, Box<dyn Any>>,
 	/// Auxiliary consensus data produced by the block.
 	/// Contains a list of key-value pairs. If values are `None`, the keys
 	/// will be deleted.
@@ -223,6 +225,36 @@ impl<Block: BlockT, Transaction> BlockImportParams<Block, Transaction> {
 			import_existing: self.import_existing,
 		}
 	}
+
+	/// Take interemdiate by given key, and remove it from the processing list.
+	pub fn take_intermediate<T: 'static>(&mut self, key: &[u8]) -> Result<Box<T>, Error> {
+		if self.intermediates.contains_key(key) {
+			self.intermediates.remove(key)
+				.ok_or(Error::NoIntermediate)
+				.and_then(|value| {
+					value.downcast::<T>()
+						.map_err(|_| Error::InvalidIntermediate)
+				})
+		} else {
+			Err(Error::NoIntermediate)
+		}
+	}
+
+	/// Get a reference to a given intermediate.
+	pub fn intermediate<T: 'static>(&self, key: &[u8]) -> Result<&T, Error> {
+		self.intermediates.get(key)
+			.ok_or(Error::NoIntermediate)?
+			.downcast_ref::<T>()
+			.ok_or(Error::InvalidIntermediate)
+	}
+
+	/// Get a mutable reference to a given intermediate.
+	pub fn intermediate_mut<T: 'static>(&mut self, key: &[u8]) -> Result<&mut T, Error> {
+		self.intermediates.get_mut(key)
+			.ok_or(Error::NoIntermediate)?
+			.downcast_mut::<T>()
+			.ok_or(Error::InvalidIntermediate)
+	}
 }
 
 /// Block import trait.

substrate/primitives/consensus/common/src/error.rs

@@ -31,6 +31,12 @@ pub enum Error {
 	/// I/O terminated unexpectedly
 	#[display(fmt="I/O terminated unexpectedly.")]
 	IoTerminated,
+	/// Intermediate missing.
+	#[display(fmt="Missing intermediate.")]
+	NoIntermediate,
+	/// Intermediate is of wrong type.
+	#[display(fmt="Invalid intermediate.")]
+	InvalidIntermediate,
 	/// Unable to schedule wakeup.
 	#[display(fmt="Timer error: {}", _0)]
 	FaultyTimer(std::io::Error),