Expose max_cache_block parameter for parent syncing (#858)

fendermint/app/settings/src/lib.rs

@@ -130,6 +130,8 @@ pub struct TopDownSettings {
     pub proposal_delay: BlockHeight,
     /// The max number of blocks one should make the topdown proposal
     pub max_proposal_range: BlockHeight,
+    /// The max number of blocks to hold in memory for parent syncer
+    pub max_cache_blocks: Option<BlockHeight>,
     /// Parent syncing cron period, in seconds
     #[serde_as(as = "DurationSeconds<u64>")]
     pub polling_interval: Duration,

fendermint/app/src/cmd/run.rs

@@ -219,14 +219,20 @@ async fn run(settings: Settings) -> anyhow::Result<()> {
     let (parent_finality_provider, ipc_tuple) = if topdown_enabled {
         info!("topdown finality enabled");
         let topdown_config = settings.ipc.topdown_config()?;
-        let config = fendermint_vm_topdown::Config::new(
+        let mut config = fendermint_vm_topdown::Config::new(
             topdown_config.chain_head_delay,
             topdown_config.polling_interval,
             topdown_config.exponential_back_off,
             topdown_config.exponential_retry_limit,
         )
         .with_proposal_delay(topdown_config.proposal_delay)
         .with_max_proposal_range(topdown_config.max_proposal_range);
+
+        if let Some(v) = topdown_config.max_cache_blocks {
+            info!(value = v, "setting max cache blocks");
+            config = config.with_max_cache_blocks(v);
+        }
+
         let ipc_provider = Arc::new(make_ipc_provider_proxy(&settings)?);
         let finality_provider =
             CachedFinalityProvider::uninitialized(config.clone(), ipc_provider.clone()).await?;

fendermint/vm/topdown/src/finality/null.rs

@@ -334,13 +334,21 @@ impl FinalityWithNull {
 
         if let Some(latest_height) = self.latest_height_in_cache()? {
             let r = latest_height >= proposal.height;
-            tracing::debug!(is_true = r, "incoming proposal height seen?");
+            tracing::debug!(
+                is_true = r,
+                latest_height,
+                proposal = proposal.height.to_string(),
+                "incoming proposal height seen?"
+            );
             // requires the incoming height cannot be more advanced than our trusted parent node
             Ok(r)
         } else {
             // latest height is not found, meaning we dont have any prefetched cache, we just be
             // strict and vote no simply because we don't know.
-            tracing::debug!("reject proposal, no data in cache");
+            tracing::debug!(
+                proposal = proposal.height.to_string(),
+                "reject proposal, no data in cache"
+            );
             Ok(false)
         }
     }

fendermint/vm/topdown/src/lib.rs

@@ -85,6 +85,11 @@ impl Config {
         self
     }
 
+    pub fn with_max_cache_blocks(mut self, max_cache_blocks: BlockHeight) -> Self {
+        self.max_cache_blocks = Some(max_cache_blocks);
+        self
+    }
+
     pub fn max_proposal_range(&self) -> BlockHeight {
         self.max_proposal_range
             .unwrap_or(DEFAULT_MAX_PROPOSAL_RANGE)