From 127ea7dff3f34cfc2fdc81c95038abe04cd46554 Mon Sep 17 00:00:00 2001
From: Pierre Krieger <pierre.krieger1708@gmail.com>
Date: Thu, 2 May 2024 11:44:30 +0200
Subject: [PATCH] Assume that all parachain peers know all paraheads (#1812)

* Assume that all parachain peers know all paraheads

* PR link
---
 light-base/src/sync_service/parachain.rs | 43 ++++++++++++++++++------
 wasm-node/CHANGELOG.md                   |  4 +++
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/light-base/src/sync_service/parachain.rs b/light-base/src/sync_service/parachain.rs
index d27bb9bb2b..508364cb91 100644
--- a/light-base/src/sync_service/parachain.rs
+++ b/light-base/src/sync_service/parachain.rs
@@ -1225,18 +1225,34 @@ impl<TPlat: PlatformRef> ParachainBackgroundTask<TPlat> {
                         block_number,
                         block_hash,
                     }),
-                    _,
+                    runtime_subscription,
                 ) => {
-                    // If `block_number` is over the finalized block, then which source knows which
-                    // block is precisely tracked. Otherwise, it is assumed that all sources are on
-                    // the finalized chain and thus that all sources whose best block is superior
-                    // to `block_number` have it.
-                    let list = if block_number > self.sync_sources.finalized_block_height() {
-                        self.sync_sources
-                            .knows_non_finalized_block(block_number, &block_hash)
-                            .map(|local_id| self.sync_sources[local_id].0.clone())
-                            .collect()
-                    } else {
+                    // If `block_number` is inferior or equal to the finalized block, or that
+                    // it is a parahead of the relay chain, then we assume that all parachain
+                    // nodes know this block.
+                    // Otherwise, which source knows which block is precisely tracked.
+                    let any_source_goes =
+                        if block_number > self.sync_sources.finalized_block_height() {
+                            if let ParachainBackgroundState::Subscribed(runtime_subscription) =
+                                runtime_subscription
+                            {
+                                runtime_subscription
+                                    .async_tree
+                                    .input_output_iter_unordered()
+                                    .filter_map(|item| item.async_op_user_data)
+                                    .filter_map(|block| block.as_ref())
+                                    .any(|item| {
+                                        // TODO: CPU-expensive
+                                        header::hash_from_scale_encoded_header(item) == block_hash
+                                    })
+                            } else {
+                                false
+                            }
+                        } else {
+                            true
+                        };
+
+                    let list = if any_source_goes {
                         self.sync_sources
                             .keys()
                             .filter(|local_id| {
@@ -1244,6 +1260,11 @@ impl<TPlat: PlatformRef> ParachainBackgroundTask<TPlat> {
                             })
                             .map(|local_id| self.sync_sources[local_id].0.clone())
                             .collect()
+                    } else {
+                        self.sync_sources
+                            .knows_non_finalized_block(block_number, &block_hash)
+                            .map(|local_id| self.sync_sources[local_id].0.clone())
+                            .collect()
                     };
 
                     let _ = send_back.send(list);
diff --git a/wasm-node/CHANGELOG.md b/wasm-node/CHANGELOG.md
index 6bf30f1e4b..a589552ffe 100644
--- a/wasm-node/CHANGELOG.md
+++ b/wasm-node/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Changed
+
+- When it comes to determining which peers know which block, smoldot now assumes that all parachain nodes know all paraheads found in the relay chain. This solves some issues when. ([#1812](https://github.com/smol-dot/smoldot/pull/1812))
+
 ## 2.0.25 - 2024-04-29
 
 ### Changed