From ab018944a9741c86fbfbf88db8b80b17bc42f48c Mon Sep 17 00:00:00 2001
From: Andronik Ordian <write@reusable.software>
Date: Fri, 4 Jun 2021 19:20:53 +0200
Subject: [PATCH] approval-distribution: send all messages on unify (#3179)

* approval-distribution: send all messages on unify

* update the guide
---
 .../network/approval-distribution/src/lib.rs   | 18 +++++-------------
 .../src/node/approval/approval-distribution.md |  6 ++----
 2 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/polkadot/node/network/approval-distribution/src/lib.rs b/polkadot/node/network/approval-distribution/src/lib.rs
index 7c69ac1363..29c6504c08 100644
--- a/polkadot/node/network/approval-distribution/src/lib.rs
+++ b/polkadot/node/network/approval-distribution/src/lib.rs
@@ -146,8 +146,6 @@ enum LocalSource {
 	No,
 }
 
-type BlockDepth = usize;
-
 /// Information about candidates in the context of a particular block they are included in.
 /// In other words, multiple `CandidateEntry`s may exist for the same candidate,
 /// if it is included by multiple blocks - this is likely the case when there are forks.
@@ -968,7 +966,7 @@ impl State {
 	) {
 		metrics.on_unify_with_peer();
 		let _timer = metrics.time_unify_with_peer();
-		let mut to_send: Vec<(BlockDepth, Hash)> = Vec::new();
+		let mut to_send: Vec<Hash> = Vec::new();
 
 		let view_finalized_number = view.finalized_number;
 		for head in view.into_iter() {
@@ -996,7 +994,7 @@ impl State {
 				block = entry.parent_hash.clone();
 				Some(interesting_block)
 			});
-			to_send.extend(interesting_blocks.enumerate());
+			to_send.extend(interesting_blocks);
 		}
 		// step 6.
 		// send all assignments and approvals for all candidates in those blocks to the peer
@@ -1012,16 +1010,13 @@ impl State {
 		entries: &HashMap<Hash, BlockEntry>,
 		ctx: &mut impl SubsystemContext<Message = ApprovalDistributionMessage>,
 		peer_id: PeerId,
-		blocks: Vec<(BlockDepth, Hash)>,
+		blocks: Vec<Hash>,
 	) {
-		// we will propagate only local assignment/approvals after a certain depth
-		const DEPTH_THRESHOLD: usize = 5;
-
 		let mut assignments = Vec::new();
 		let mut approvals = Vec::new();
 		let num_blocks = blocks.len();
 
-		for (depth, block) in blocks.into_iter() {
+		for block in blocks.into_iter() {
 			let entry = match entries.get(&block) {
 				Some(entry) => entry,
 				None => continue, // should be unreachable
@@ -1036,10 +1031,7 @@ impl State {
 
 			for (candidate_index, candidate_entry) in entry.candidates.iter().enumerate() {
 				let candidate_index = candidate_index as u32;
-				for (validator_index, (approval_state, is_local)) in candidate_entry.approvals.iter() {
-					if depth >= DEPTH_THRESHOLD && !matches!(is_local, LocalSource::Yes) {
-						continue;
-					}
+				for (validator_index, (approval_state, _is_local)) in candidate_entry.approvals.iter() {
 					match approval_state {
 						ApprovalState::Assigned(cert) => {
 							assignments.push((
diff --git a/polkadot/roadmap/implementers-guide/src/node/approval/approval-distribution.md b/polkadot/roadmap/implementers-guide/src/node/approval/approval-distribution.md
index 38fafd791d..68f0ab59b1 100644
--- a/polkadot/roadmap/implementers-guide/src/node/approval/approval-distribution.md
+++ b/polkadot/roadmap/implementers-guide/src/node/approval/approval-distribution.md
@@ -247,8 +247,6 @@ For each block in the view:
   2. Load the `BlockEntry` for the block. If the block is unknown, or the number is less than or equal to the view's finalized number go to step 6.
   3. Inspect the `known_by` set of the `BlockEntry`. If the peer is already present, go to step 6.
   4. Add the peer to `known_by` with a cloned version of `block_entry.knowledge`. and add the hash of the block to `fresh_blocks`.
-  5. Return to step 2 with the ancestor of the block, keeping track of the block depth (+1).
+  5. Return to step 2 with the ancestor of the block.
 
-6. For each block in `fresh_blocks`, send all assignments and approvals for all candidates in those blocks to the peer if the block depth threshold is not reached, otherwise, send only assignments and approvals origination with the local source.
-
-The reason we only send our local assignments and approvals when a certain block depth is reached when unifying with a peer is to avoid DoS attacks. It also helps when a node starts with a large difference between finalized and the highest block.
+6. For each block in `fresh_blocks`, send all assignments and approvals for all candidates in those blocks to the peer.