Prune blobs (#5283)

* Prune blobs

* Address review feedback

beacon_chain/beacon_chain_db.nim

@@ -795,6 +795,11 @@ proc putBlobSidecar*(
     value: BlobSidecar) =
   db.blobs.putSZSSZ(blobkey(value.block_root, value.index), value)
 
+proc delBlobSidecar*(
+    db: BeaconChainDB,
+    root: Eth2Digest, index: BlobIndex) : bool =
+  db.blobs.del(blobkey(root, index)).expectDb()
+
 proc updateImmutableValidators*(
     db: BeaconChainDB, validators: openArray[Validator]) =
   # Must be called before storing a state that references the new validators

beacon_chain/nimbus_beacon_node.nim

@@ -1170,6 +1170,25 @@ proc onSlotEnd(node: BeaconNode, slot: Slot) {.async.} =
   # This is the last pruning to do as it clears the "needPruning" condition.
   node.consensusManager[].pruneStateCachesAndForkChoice()
 
+  # prune blobs
+  let blobPruneEpoch = (slot.epoch -
+                        MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS - 1)
+  if slot.is_epoch() and blobPruneEpoch >= node.dag.cfg.DENEB_FORK_EPOCH:
+    var blocks: array[SLOTS_PER_EPOCH.int, BlockId]
+    var count = 0
+    let
+      startIndex = node.dag.getBlockRange(blobPruneEpoch.start_slot, 1,
+                          blocks.toOpenArray(0, SLOTS_PER_EPOCH - 1))
+    for i in startIndex..<SLOTS_PER_EPOCH:
+      let blck = node.dag.getForkedBlock(blocks[int(i)]).valueOr: continue
+      withBlck(blck):
+        when typeof(blck).toFork() < ConsensusFork.Deneb: continue
+        else:
+          for j in 0..len(blck.message.body.blob_kzg_commitments) - 1:
+            if node.db.delBlobSidecar(blocks[int(i)].root, BlobIndex(j)):
+              count = count + 1
+    debug "pruned blobs", count, blobPruneEpoch
+
   if node.config.historyMode == HistoryMode.Prune:
     if not (slot + 1).is_epoch():
       # The epoch slot already is "heavy" due to the epoch processing, leave