Blobs sidecars by range (#4464)

* Add blobs_sidecars_by_range RPC

* Update beacon_chain/spec/datatypes/eip4844.nim

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

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

beacon_chain/beacon_chain_db.nim

@@ -1050,6 +1050,13 @@ proc getBlockSSZ*(
     getBlockSSZ(db, key, data, eip4844.TrustedSignedBeaconBlock)
 
 
+proc getBlobsSidecarSZ*(db: BeaconChainDB, key: Eth2Digest, data: var seq[byte]):
+    bool =
+  let dataPtr = addr data # Short-lived
+  func decode(data: openArray[byte]) =
+    assign(dataPtr[], data)
+  db.blobs.get(key.data, decode).expectDb()
+
 proc getBlockSZ*(
     db: BeaconChainDB, key: Eth2Digest, data: var seq[byte],
     T: type phase0.TrustedSignedBeaconBlock): bool =

beacon_chain/rpc/rest_constants.nim

@@ -219,3 +219,5 @@ const
     "Block has incorrect fork"
   ValidatorNotActive* =
     "Validator inactive"
+  BlobsOutOfRange* =
+    "Requested slot is outside of blobs window"

beacon_chain/spec/datatypes/eip4844.nim

@@ -35,6 +35,8 @@ const
 
   # https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.2/specs/eip4844/polynomial-commitments.md#constants
   BLS_MODULUS* = "52435875175126190479447740508185965837690552500527637822603658699938581184513".u256
+  # https://github.com/ethereum/consensus-specs/blob/v1.3.0-rc.0/specs/eip4844/p2p-interface.md#configuration
+  MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS* = 4096'u64
 
 type
   # this block belongs elsewhere - will figure out after implementing c-kzg bindings

beacon_chain/sync/sync_protocol.nim

@@ -14,7 +14,7 @@ import
   std/[options, tables, sets, macros],
   chronicles, chronos, snappy/codec,
   libp2p/switch,
-  ../spec/datatypes/[phase0, altair, bellatrix, capella],
+  ../spec/datatypes/[phase0, altair, bellatrix, capella, eip4844],
   ../spec/[helpers, forks, network],
   ".."/[beacon_clock],
   ../networking/eth2_network,
@@ -26,6 +26,7 @@ logScope:
 
 const
   MAX_REQUEST_BLOCKS* = 1024
+  MAX_REQUEST_BLOBS_SIDECARS = 128
 
   blockResponseCost = allowedOpsPerSecondCost(64) # Allow syncing ~64 blocks/sec (minus request costs)
 
@@ -400,6 +401,77 @@ p2pProtocol BeaconSync(version = 1,
     debug "Block root request done",
       peer, roots = blockRoots.len, count, found
 
+  # https://github.com/ethereum/consensus-specs/blob/v1.3.0-rc.0/specs/eip4844/p2p-interface.md#blobssidecarsbyrange-v1
+  proc blobsSidecarsByRange(
+      peer: Peer,
+      startSlot: Slot,
+      reqCount: uint64,
+      response: MultipleChunksResponse[
+        BlobsSidecar, MAX_REQUEST_BLOBS_SIDECARS])
+      {.async, libp2pProtocol("blobs_sidecars_by_range", 1).} =
+    # TODO This code is more complicated than it needs to be, since the type
+    #      of the multiple chunks response is not actually used in this server
+    #      implementation (it's used to derive the signature of the client
+    #      function, not in the code below!)
+    # TODO although you can't tell from this function definition, a magic
+    #      client call that returns `seq[ref BlobsSidecar]` will
+    #      will be generated by the libp2p macro - we guarantee that seq items
+    #      are `not-nil` in the implementation
+
+    trace "got blobs range request", peer, startSlot, count = reqCount
+    if reqCount == 0:
+      raise newException(InvalidInputsError, "Empty range requested")
+
+    let
+      dag = peer.networkState.dag
+      epochBoundary =
+        if MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS >= dag.head.slot.epoch:
+          GENESIS_EPOCH
+        else:
+          dag.head.slot.epoch - MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS
+
+    if startSlot.epoch < epochBoundary:
+      raise newException(ResourceUnavailableError, BlobsOutOfRange)
+
+    var blockIds: array[MAX_REQUEST_BLOBS_SIDECARS, BlockId]
+    let
+      # Limit number of blocks in response
+      count = int min(reqCount, blockIds.lenu64)
+      endIndex = count - 1
+      startIndex =
+        dag.getBlockRange(startSlot, 1, blockIds.toOpenArray(0, endIndex))
+
+    var
+      found = 0
+      bytes: seq[byte]
+
+    for i in startIndex..endIndex:
+      if dag.db.getBlobsSidecarSZ(blockIds[i].root, bytes):
+        # In general, there is not much intermediate time between post-merge
+        # blocks all being optimistic and none of them being optimistic. The
+        # EL catches up, tells the CL the head is verified, and that's it.
+        if  blockIds[i].slot.epoch >= dag.cfg.BELLATRIX_FORK_EPOCH and
+            dag.is_optimistic(dag.head.root):
+          continue
+
+        let uncompressedLen = uncompressedLenFramed(bytes).valueOr:
+          warn "Cannot read blobs sidecar size, database corrupt?",
+            bytes = bytes.len(), blck = shortLog(blockIds[i])
+          continue
+
+        # TODO extract from libp2pProtocol
+        peer.awaitQuota(blockResponseCost, "blobs_sidecars_by_range/1")
+        peer.network.awaitQuota(blockResponseCost, "blobs_sidecars_by_range/1")
+
+        await response.writeBytesSZ(
+          uncompressedLen, bytes,
+          peer.networkState.forkDigestAtEpoch(blockIds[i].slot.epoch).data)
+
+        inc found
+
+    debug "BlobsSidecar range request done",
+      peer, startSlot, count
+
   # https://github.com/ethereum/consensus-specs/blob/v1.3.0-rc.0/specs/altair/light-client/p2p-interface.md#getlightclientbootstrap
   proc lightClientBootstrap(
       peer: Peer,