From a35fa64a241dcaa179411a500ef6a165d5084e08 Mon Sep 17 00:00:00 2001
From: William Hankins <william@sundae.fi>
Date: Fri, 14 Nov 2025 20:21:04 +0000
Subject: [PATCH] refactor: avoid overwriting blocks when clear-on-start is
 false

Signed-off-by: William Hankins <william@sundae.fi>
---
 modules/chain_store/src/chain_store.rs  | 42 ++++++++++++++++++++++++-
 modules/chain_store/src/stores/fjall.rs | 19 +++++++++++
 modules/chain_store/src/stores/mod.rs   |  1 +
 3 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/modules/chain_store/src/chain_store.rs b/modules/chain_store/src/chain_store.rs
index f280fb4f..d31a646e 100644
--- a/modules/chain_store/src/chain_store.rs
+++ b/modules/chain_store/src/chain_store.rs
@@ -94,6 +94,15 @@ impl ChainStore {
             // Get promise of params message so the params queue is cleared and
             // the message is ready as soon as possible when we need it
             let mut params_message = params_subscription.read();
+
+            // Validate the first stored block matches what is already persisted when clear-on-start is false
+            let Ok((_, first_block_message)) = new_blocks_subscription.read().await else {
+                return;
+            };
+            if let Err(err) = Self::handle_first_block(&store, &first_block_message) {
+                panic!("Corrupted DB: {err}")
+            };
+
             loop {
                 let Ok((_, message)) = new_blocks_subscription.read().await else {
                     return;
@@ -129,7 +138,38 @@ impl ChainStore {
             bail!("Unexpected message type: {message:?}");
         };
 
-        store.insert_block(info, &raw_block.body)
+        if store.should_persist(info.number) {
+            store.insert_block(info, &raw_block.body)?;
+        }
+
+        Ok(())
+    }
+
+    fn handle_first_block(store: &Arc<dyn Store>, message: &Message) -> Result<()> {
+        let Message::Cardano((block_info, CardanoMessage::BlockAvailable(raw_block))) = message
+        else {
+            bail!("Unexpected message type: {message:?}");
+        };
+
+        if !store.should_persist(block_info.number) {
+            if let Some(existing) = store.get_block_by_number(block_info.number)? {
+                if existing.bytes != raw_block.body {
+                    return Err(anyhow::anyhow!(
+                        "Stored block {} does not match. Set clear-store to true",
+                        block_info.number
+                    ));
+                }
+            } else {
+                return Err(anyhow::anyhow!(
+                    "Unable to retrieve block {}. Set clear-store to true",
+                    block_info.number
+                ));
+            }
+        }
+
+        Self::handle_new_block(store, message)?;
+
+        Ok(())
     }
 
     fn handle_blocks_query(
diff --git a/modules/chain_store/src/stores/fjall.rs b/modules/chain_store/src/stores/fjall.rs
index 6dba7d48..32d0365e 100644
--- a/modules/chain_store/src/stores/fjall.rs
+++ b/modules/chain_store/src/stores/fjall.rs
@@ -11,6 +11,7 @@ pub struct FjallStore {
     keyspace: Keyspace,
     blocks: FjallBlockStore,
     txs: FjallTXStore,
+    last_persisted_block: Option<u64>,
 }
 
 const DEFAULT_DATABASE_PATH: &str = "fjall-blocks";
@@ -33,10 +34,20 @@ impl FjallStore {
         let keyspace = fjall_config.open()?;
         let blocks = FjallBlockStore::new(&keyspace)?;
         let txs = FjallTXStore::new(&keyspace)?;
+
+        let last_persisted_block = if !clear {
+            blocks.block_hashes_by_number.iter().next_back().and_then(|res| {
+                res.ok().and_then(|(key, _)| key.as_ref().try_into().ok().map(u64::from_be_bytes))
+            })
+        } else {
+            None
+        };
+
         Ok(Self {
             keyspace,
             blocks,
             txs,
+            last_persisted_block,
         })
     }
 }
@@ -69,6 +80,13 @@ impl super::Store for FjallStore {
         Ok(())
     }
 
+    fn should_persist(&self, block_number: u64) -> bool {
+        match self.last_persisted_block {
+            Some(last) => block_number > last,
+            None => false,
+        }
+    }
+
     fn get_block_by_hash(&self, hash: &[u8]) -> Result<Option<Block>> {
         self.blocks.get_by_hash(hash)
     }
@@ -117,6 +135,7 @@ impl FjallBlockStore {
             BLOCK_HASHES_BY_EPOCH_SLOT_PARTITION,
             fjall::PartitionCreateOptions::default(),
         )?;
+
         Ok(Self {
             blocks,
             block_hashes_by_slot,
diff --git a/modules/chain_store/src/stores/mod.rs b/modules/chain_store/src/stores/mod.rs
index 4be55815..df8a330b 100644
--- a/modules/chain_store/src/stores/mod.rs
+++ b/modules/chain_store/src/stores/mod.rs
@@ -5,6 +5,7 @@ pub mod fjall;
 
 pub trait Store: Send + Sync {
     fn insert_block(&self, info: &BlockInfo, block: &[u8]) -> Result<()>;
+    fn should_persist(&self, block_number: u64) -> bool;
 
     fn get_block_by_hash(&self, hash: &[u8]) -> Result<Option<Block>>;
     fn get_block_by_slot(&self, slot: u64) -> Result<Option<Block>>;