Add block announce validator. (#3346)

* Add `BlockAnnounceValidator` trait.

* Add associated data to block announcement.

* Make tests compile.

* Move validator into `sync.rs`.

* Smaller changes.

* Update core/network/src/protocol.rs

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update core/network/src/protocol.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/network/src/test/sync.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Formatting.

* Remove assoc. data from `BlockImportNotification`.

* Use `Option<Vec<u8>>` for associated data.

* Update core/network/src/protocol/sync.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Fix type error.

substrate/core/network/src/protocol/message.rs

@@ -273,6 +273,8 @@ pub mod generic {
 		pub header: H,
 		/// Block state. TODO: Remove `Option` and custom encoding when v4 becomes common.
 		pub state: Option<BlockState>,
+		/// Data associated with this block announcement, e.g. a candidate message.
+		pub data: Option<Vec<u8>>,
 	}
 
 	// Custom Encode/Decode impl to maintain backwards compatibility with v3.
@@ -284,6 +286,9 @@ pub mod generic {
 			if let Some(state) = &self.state {
 				state.encode_to(dest);
 			}
+			if let Some(data) = &self.data {
+				data.encode_to(dest)
+			}
 		}
 	}
 
@@ -291,9 +296,11 @@ pub mod generic {
 		fn decode<I: Input>(input: &mut I) -> Result<Self, codec::Error> {
 			let header = H::decode(input)?;
 			let state = BlockState::decode(input).ok();
+			let data = Vec::decode(input).ok();
 			Ok(BlockAnnounce {
 				header,
 				state,
+				data,
 			})
 		}
 	}

substrate/core/network/src/protocol/sync.rs

@@ -28,11 +28,15 @@
 //!
 
 use blocks::BlockCollection;
-use client::{BlockStatus, ClientInfo, error::Error as ClientError};
-use consensus::{BlockOrigin, import_queue::{IncomingBlock, BlockImportResult, BlockImportError}};
+use client::{ClientInfo, error::Error as ClientError};
+use consensus::{BlockOrigin, BlockStatus,
+	block_validation::{BlockAnnounceValidator, Validation},
+	import_queue::{IncomingBlock, BlockImportResult, BlockImportError}
+};
 use crate::{
 	config::{Roles, BoxFinalityProofRequestBuilder},
-	message::{self, generic::FinalityProofRequest, BlockAttributes, BlockRequest, BlockResponse, FinalityProofResponse},
+	message::{self, generic::FinalityProofRequest, BlockAnnounce, BlockAttributes, BlockRequest, BlockResponse,
+	FinalityProofResponse},
 	protocol
 };
 use either::Either;
@@ -122,6 +126,8 @@ pub struct ChainSync<B: BlockT> {
 	request_builder: Option<BoxFinalityProofRequestBuilder<B>>,
 	/// A flag that caches idle state with no pending requests.
 	is_idle: bool,
+	/// A type to check incoming block announcements.
+	block_announce_validator: Box<dyn BlockAnnounceValidator<B> + Send>
 }
 
 /// All the data we have about a Peer that we are trying to sync with
@@ -271,7 +277,8 @@ impl<B: BlockT> ChainSync<B> {
 		role: Roles,
 		client: Arc<dyn crate::chain::Client<B>>,
 		info: &ClientInfo<B>,
-		request_builder: Option<BoxFinalityProofRequestBuilder<B>>
+		request_builder: Option<BoxFinalityProofRequestBuilder<B>>,
+		block_announce_validator: Box<dyn BlockAnnounceValidator<B> + Send>
 	) -> Self {
 		let mut required_block_attributes = BlockAttributes::HEADER | BlockAttributes::JUSTIFICATION;
 
@@ -293,6 +300,7 @@ impl<B: BlockT> ChainSync<B> {
 			best_importing_number: Zero::zero(),
 			request_builder,
 			is_idle: false,
+			block_announce_validator,
 		}
 	}
 
@@ -885,9 +893,10 @@ impl<B: BlockT> ChainSync<B> {
 	/// header (call `on_block_data`). The network request isn't sent
 	/// in this case. Both hash and header is passed as an optimization
 	/// to avoid rehashing the header.
-	pub fn on_block_announce(&mut self, who: PeerId, hash: B::Hash, header: &B::Header, is_best: bool)
+	pub fn on_block_announce(&mut self, who: PeerId, hash: B::Hash, announce: &BlockAnnounce<B::Header>, is_best: bool)
 		-> OnBlockAnnounce<B>
 	{
+		let header = &announce.header;
 		let number = *header.number();
 		debug!(target: "sync", "Received block announcement with number {:?}", number);
 		if number.is_zero() {
@@ -932,6 +941,20 @@ impl<B: BlockT> ChainSync<B> {
 			return OnBlockAnnounce::Nothing
 		}
 
+		// Let external validator check the block announcement.
+		let assoc_data = announce.data.as_ref().map_or(&[][..], |v| v.as_slice());
+		match self.block_announce_validator.validate(&header, assoc_data) {
+			Ok(Validation::Success) => (),
+			Ok(Validation::Failure) => {
+				debug!(target: "sync", "block announcement validation of block {} from {} failed", hash, who);
+				return OnBlockAnnounce::Nothing
+			}
+			Err(e) => {
+				error!(target: "sync", "block announcement validation errored: {}", e);
+				return OnBlockAnnounce::Nothing
+			}
+		}
+
 		// stale block case
 		let requires_additional_data = !self.role.is_light();
 		if number <= self.best_queued_number {