introduce light supernodes (#7752)

* introduce light supernodes

* some more changes

* add options in docs

* synchronize docs with --help

* completely disable reconstruction temporarily

* put docs entry in right order

* add -Wno-stringop-overflow to test-libnimbus-lc target

---------

Co-authored-by: tersec <tersec@users.noreply.github.com>

Author: agnxsh

Makefile

@@ -720,6 +720,7 @@ test_libnimbus_lc: libnimbus_lc.a
 				--std=c17 -flto \
 				-pedantic -pedantic-errors \
 				-Wall -Wextra -Werror -Wno-maybe-uninitialized \
+				-Wno-stringop-overflow \
 				-Wno-unsafe-buffer-usage -Wno-unknown-warning-option \
 				-o build/test_libnimbus_lc \
 				beacon_chain/libnimbus_lc/test_libnimbus_lc.c \

beacon_chain/conf.nim

@@ -251,6 +251,11 @@ type
       desc: "Subscribe to all column subnets, thereby becoming a PeerDAS supernode"
       name: "peerdas-supernode" .}: bool
 
+    lightSupernode* {.
+      defaultValue: false,
+      desc: "Subscribe to the first half of column subnets"
+      name: "light-supernode" .}: bool
+
     slashingDbKind* {.
       hidden
       defaultValue: SlashingDbKind.v2

beacon_chain/nimbus_beacon_node.nim

@@ -417,14 +417,24 @@ proc initFullNode(
     blobQuarantine = newClone(BlobQuarantine.init(
       dag.cfg, dag.db.getQuarantineDB(), 10, onBlobSidecarAdded))
     supernode = node.config.peerdasSupernode or node.config.debugPeerdasSupernode
+    lightSupernode = node.config.lightSupernode
     localCustodyGroups =
       if supernode:
         dag.cfg.NUMBER_OF_CUSTODY_GROUPS
+      elif lightSupernode:
+        dag.cfg.NUMBER_OF_CUSTODY_GROUPS div 2
       else:
         dag.cfg.CUSTODY_REQUIREMENT
     custodyColumns =
-      dag.cfg.resolve_columns_from_custody_groups(
-        node.network.nodeId, localCustodyGroups)
+      if node.config.lightSupernode:
+        # Just the first half of custody columns
+        var res: HashSet[ColumnIndex]
+        for i in 0..<dag.cfg.NUMBER_OF_CUSTODY_GROUPS div 2:
+          res.incl ColumnIndex(i)
+        res
+      else:
+        dag.cfg.resolve_columns_from_custody_groups(
+          node.network.nodeId, localCustodyGroups)
 
   var sortedColumns = custodyColumns.toSeq()
   sort(sortedColumns)
@@ -1294,20 +1304,33 @@ func getSyncCommitteeSubnets(node: BeaconNode, epoch: Epoch): SyncnetBits =
   subnets + node.getNextSyncCommitteeSubnets(epoch)
 
 func readCustodyGroupSubnets(node: BeaconNode): uint64 =
-  let vcus_count = node.dataColumnQuarantine.custodyColumns.lenu64
+  let
+    custodyGroups = node.dag.cfg.NUMBER_OF_CUSTODY_GROUPS
+    vcus_count = node.dataColumnQuarantine.custodyColumns.lenu64
   if node.config.peerdasSupernode or node.config.debugPeerdasSupernode:
-    node.dag.cfg.NUMBER_OF_CUSTODY_GROUPS
+    custodyGroups
+  elif node.config.lightSupernode:
+    custodyGroups div 2
   elif vcus_count > node.dag.cfg.CUSTODY_REQUIREMENT:
     vcus_count
   else:
     node.dag.cfg.CUSTODY_REQUIREMENT
 
 proc updateDataColumnSidecarHandlers(node: BeaconNode, gossipEpoch: Epoch) =
   let
+    custody_groups = node.dag.cfg.NUMBER_OF_CUSTODY_GROUPS
     forkDigest = node.dag.forkDigests[].atEpoch(gossipEpoch, node.dag.cfg)
     targetSubnets = node.readCustodyGroupSubnets()
-    custody = node.dag.cfg.get_custody_groups(
-      node.network.nodeId, targetSubnets.uint64)
+    custody =
+      if node.config.lightSupernode:
+        # Light supernode serves only half of the custody groups
+        var res = newSeqOfCap[CustodyIndex](custody_groups div 2)
+        for i in 0..<custody_groups div 2:
+          res.add CustodyIndex(i)
+        res
+      else:
+        node.dag.cfg.get_custody_groups(
+        node.network.nodeId, targetSubnets.uint64)
 
   for i in custody:
     let topic = getDataColumnSidecarTopic(forkDigest, i)
@@ -1736,10 +1759,17 @@ proc reconstructDataColumns(node: BeaconNode, slot: Slot) =
   # https://github.com/ethereum/consensus-specs/blob/v1.6.0-beta.0/specs/fulu/das-core.md#reconstruction-and-cross-seeding
   # "If the node obtains 50%+ of all the columns, it SHOULD reconstruct the
   # full data matrix via the recover_matrix helper."
+  if node.config.lightSupernode:
+    return
+
   if node.dataColumnQuarantine.custodyColumns.lenu64 <
       node.dag.cfg.NUMBER_OF_CUSTODY_GROUPS div 2:
     return
 
+  # Currently, this logic is broken
+  if true:
+    return
+
   logScope:
     slot = slot
 
@@ -2014,6 +2044,7 @@ proc onSlotEnd(node: BeaconNode, slot: Slot) {.async.} =
 
   if (not node.config.peerdasSupernode) and
      (not node.config.debugPeerdasSupernode) and
+     (not node.config.lightSupernode) and
      node.dataColumnQuarantine[].len == 0 and
      node.attachedValidatorBalanceTotal > 0.Gwei:
     # Detect new validator custody at the last slot of every epoch

docs/the_nimbus_book/src/options.md

@@ -50,6 +50,7 @@ The following options are available:
      --agent-string            Node agent string which is used as identifier in network [=nimbus].
      --subscribe-all-subnets   Subscribe to all subnet topics when gossiping [=false].
      --peerdas-supernode       Subscribe to all column subnets, thereby becoming a PeerDAS supernode [=false].
+     --light-supernode         Subscribe to the first half of column subnets [=false].
      --num-threads             Number of worker threads ("0" = use as many threads as there are CPU cores
                                available) [=0].
      --jwt-secret              A file containing the hex-encoded 256 bit secret key to be used for