Compute columns in post-PeerDAS checkpoint sync (#6760)

Addresses #6026.

Post-PeerDAS the DB expects to have data columns for the finalized block.


  Instead of forcing the user to submit the columns, this PR computes the columns from the blobs that we can already fetch from the checkpointz server or with the existing CLI options.

Note 1: (EDIT) Pruning concern addressed

Note 2: I have not tested this feature

Note 3: @michaelsproul an alternative I recall is to not require the blobs / columns at this point and expect backfill to populate the finalized block

Author: dapplion

beacon_node/beacon_chain/src/builder.rs

@@ -9,6 +9,7 @@ use crate::fork_choice_signal::ForkChoiceSignalTx;
 use crate::fork_revert::{reset_fork_choice_to_finalization, revert_to_fork_boundary};
 use crate::graffiti_calculator::{GraffitiCalculator, GraffitiOrigin};
 use crate::head_tracker::HeadTracker;
+use crate::kzg_utils::blobs_to_data_column_sidecars;
 use crate::light_client_server_cache::LightClientServerCache;
 use crate::migrate::{BackgroundMigrator, MigratorConfig};
 use crate::observed_data_sidecars::ObservedDataSidecars;
@@ -562,9 +563,30 @@ where
             .put_block(&weak_subj_block_root, weak_subj_block.clone())
             .map_err(|e| format!("Failed to store weak subjectivity block: {e:?}"))?;
         if let Some(blobs) = weak_subj_blobs {
-            store
-                .put_blobs(&weak_subj_block_root, blobs)
-                .map_err(|e| format!("Failed to store weak subjectivity blobs: {e:?}"))?;
+            if self
+                .spec
+                .is_peer_das_enabled_for_epoch(weak_subj_block.epoch())
+            {
+                // After PeerDAS recompute columns from blobs to not force the checkpointz server
+                // into exposing another route.
+                let blobs = blobs
+                    .iter()
+                    .map(|blob_sidecar| &blob_sidecar.blob)
+                    .collect::<Vec<_>>();
+                let data_columns =
+                    blobs_to_data_column_sidecars(&blobs, &weak_subj_block, &self.kzg, &self.spec)
+                        .map_err(|e| {
+                            format!("Failed to compute weak subjectivity data_columns: {e:?}")
+                        })?;
+                // TODO(das): only persist the columns under custody
+                store
+                    .put_data_columns(&weak_subj_block_root, data_columns)
+                    .map_err(|e| format!("Failed to store weak subjectivity data_column: {e:?}"))?;
+            } else {
+                store
+                    .put_blobs(&weak_subj_block_root, blobs)
+                    .map_err(|e| format!("Failed to store weak subjectivity blobs: {e:?}"))?;
+            }
         }
 
         // Stage the database's metadata fields for atomic storage when `build` is called.

beacon_node/store/src/hot_cold_store.rs

@@ -863,6 +863,24 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
         ));
     }
 
+    pub fn put_data_columns(
+        &self,
+        block_root: &Hash256,
+        data_columns: DataColumnSidecarList<E>,
+    ) -> Result<(), Error> {
+        for data_column in data_columns {
+            self.blobs_db.put_bytes(
+                DBColumn::BeaconDataColumn,
+                &get_data_column_key(block_root, &data_column.index),
+                &data_column.as_ssz_bytes(),
+            )?;
+            self.block_cache
+                .lock()
+                .put_data_column(*block_root, data_column);
+        }
+        Ok(())
+    }
+
     pub fn data_columns_as_kv_store_ops(
         &self,
         block_root: &Hash256,