pause relays(s) when node is syncing (#605)

bridges/relays/ethereum/src/ethereum_exchange.rs

@@ -248,6 +248,10 @@ impl TargetClient<EthereumToSubstrateExchange> for SubstrateTransactionsTarget {
 	}
 
 	async fn best_finalized_header_id(&self) -> Result<EthereumHeaderId, RpcError> {
+		// we can't continue to relay exchange proofs if Substrate node is out of sync, because
+		// it may have already received (some of) proofs that we're going to relay
+		self.client.ensure_synced().await?;
+
 		self.client.best_ethereum_finalized_block().await
 	}
 

bridges/relays/ethereum/src/ethereum_sync_loop.rs

@@ -130,6 +130,9 @@ impl RelayClient for EthereumHeadersSource {
 #[async_trait]
 impl SourceClient<EthereumHeadersSyncPipeline> for EthereumHeadersSource {
 	async fn best_block_number(&self) -> Result<u64, RpcError> {
+		// we **CAN** continue to relay headers if Ethereum node is out of sync, because
+		// Substrate node may be missing headers that are already available at the Ethereum
+
 		self.client.best_block_number().await.map_err(Into::into)
 	}
 
@@ -204,6 +207,10 @@ impl RelayClient for SubstrateHeadersTarget {
 #[async_trait]
 impl TargetClient<EthereumHeadersSyncPipeline> for SubstrateHeadersTarget {
 	async fn best_header_id(&self) -> Result<EthereumHeaderId, RpcError> {
+		// we can't continue to relay headers if Substrate node is out of sync, because
+		// it may have already received (some of) headers that we're going to relay
+		self.client.ensure_synced().await?;
+
 		self.client.best_ethereum_block().await
 	}
 

bridges/relays/ethereum/src/substrate_sync_loop.rs

@@ -131,6 +131,10 @@ impl RelayClient for EthereumHeadersTarget {
 #[async_trait]
 impl TargetClient<SubstrateHeadersSyncPipeline> for EthereumHeadersTarget {
 	async fn best_header_id(&self) -> Result<RialtoHeaderId, RpcError> {
+		// we can't continue to relay headers if Ethereum node is out of sync, because
+		// it may have already received (some of) headers that we're going to relay
+		self.client.ensure_synced().await?;
+
 		self.client.best_substrate_block(self.contract).await
 	}