Proto changes to facilitate backward sync (#271)

* Proto changes to facilitate backward sync

* Update to latest spec types in sync proto

* Use blockpool for more straightforward block headers collection

* Added BlockPool.getRef

* Update beacon_chain/sync_protocol.nim

Co-Authored-By: Jacek Sieka <arnetheduck@gmail.com>

beacon_chain/block_pool.nim

@@ -292,6 +292,10 @@ proc add*(
           (parentSlot.uint64 mod SLOTS_PER_EPOCH.uint64))
   )
 
+proc getRef*(pool: BlockPool, root: Eth2Digest): BlockRef =
+  ## Retrieve a resolved block reference, if available
+  result = pool.blocks.getOrDefault(root)
+
 proc get*(pool: BlockPool, blck: BlockRef): BlockData =
   ## Retrieve the associated block body of a block reference
   doAssert (not blck.isNil), "Trying to get nil BlockRef"
@@ -303,7 +307,7 @@ proc get*(pool: BlockPool, blck: BlockRef): BlockData =
 
 proc get*(pool: BlockPool, root: Eth2Digest): Option[BlockData] =
   ## Retrieve a resolved block reference and its associated body, if available
-  let refs = pool.blocks.getOrDefault(root)
+  let refs = pool.getRef(root)
 
   if not refs.isNil:
     some(pool.get(refs))
@@ -313,7 +317,7 @@ proc get*(pool: BlockPool, root: Eth2Digest): Option[BlockData] =
 proc getOrResolve*(pool: var BlockPool, root: Eth2Digest): BlockRef =
   ## Fetch a block ref, or nil if not found (will be added to list of
   ## blocks-to-resolve)
-  result = pool.blocks.getOrDefault(root)
+  result = pool.getRef(root)
 
   if result.isNil:
     pool.missing[root] = MissingBlock(slots: 1)

beacon_chain/request_manager.nim

@@ -1,8 +1,9 @@
 import
-  options,
+  options, random,
   chronos, chronicles,
   spec/datatypes,
-  eth2_network, beacon_node_types, sync_protocol
+  eth2_network, beacon_node_types, sync_protocol,
+  eth/async_utils
 
 proc init*(T: type RequestManager, network: EthereumNode): T =
   T(network: network)
@@ -10,6 +11,12 @@ proc init*(T: type RequestManager, network: EthereumNode): T =
 type
   FetchAncestorsResponseHandler = proc (b: BeaconBlock) {.gcsafe.}
 
+proc fetchAncestorBlocksFromPeer(peer: Peer, rec: FetchRecord, responseHandler: FetchAncestorsResponseHandler) {.async.} =
+  let blocks = await peer.getBeaconBlocks(rec.root, GENESIS_SLOT, rec.historySlots.int, 0, 1)
+  if blocks.isSome:
+    for b in blocks.get:
+      responseHandler(b)
+
 proc fetchAncestorBlocks*(requestManager: RequestManager,
                           roots: seq[FetchRecord],
                           responseHandler: FetchAncestorsResponseHandler) =
@@ -26,12 +33,4 @@ proc fetchAncestorBlocks*(requestManager: RequestManager,
 
   var fetchComplete = false
   for peer in requestManager.network.randomPeers(ParallelRequests, BeaconSync):
-    closureScope:
+    traceAsyncErrors peer.fetchAncestorBlocksFromPeer(roots.rand(), responseHandler)
-      let response = peer.getAncestorBlocks(roots)
-      response.addCallback do(arg: pointer):
-        if not response.failed and response.read.isSome and not fetchComplete:
-          fetchComplete = true
-          for blk in response.read.get.blocks:
-            responseHandler(blk)
-        else:
-          debug "Failed to obtain ancestor blocks from peer", peer

beacon_chain/spec/datatypes.nim

@@ -235,21 +235,6 @@ type
     block_body_root*: Eth2Digest
     signature*: ValidatorSig
 
-  BeaconBlockHeaderRLP* = object
-    ## Same as BeaconBlock, except `body` is the `hash_tree_root` of the
-    ## associated BeaconBlockBody.
-    # TODO: Dry it up with BeaconBlock
-    # TODO: As a first step, don't change RLP output; only previous user,
-    # but as with others, randao_reveal and eth1_data move to body.
-    # This is from before spec had a version.
-    slot*: uint64
-    parent_root*: Eth2Digest
-    state_root*: Eth2Digest
-    randao_reveal*: ValidatorSig
-    eth1_data*: Eth1Data
-    signature*: ValidatorSig
-    body*: Eth2Digest
-
   # https://github.com/ethereum/eth2.0-specs/blob/v0.6.3/specs/core/0_beacon-chain.md#beaconblockbody
   BeaconBlockBody* = object
     randao_reveal*: ValidatorSig

beacon_chain/sync_protocol.nim

@@ -1,5 +1,5 @@
 import
-  options, tables,
+  options, tables, sequtils, algorithm,
   chronicles, chronos, ranges/bitranges,
   spec/[datatypes, crypto, digest, helpers], eth/rlp,
   beacon_node_types, eth2_network, beacon_chain_db, block_pool, time, ssz
@@ -28,48 +28,46 @@ const
   MaxHeadersToRequest = MaxRootsToRequest
   MaxAncestorBlocksResponse = 256
 
-func toHeader(b: BeaconBlock): BeaconBlockHeaderRLP =
+func toHeader(b: BeaconBlock): BeaconBlockHeader =
-  BeaconBlockHeaderRLP(
+  BeaconBlockHeader(
-    slot: b.slot.uint64,
+    slot: b.slot,
-    parent_root: b.previous_block_root,
+    previous_block_root: b.previous_block_root,
     state_root: b.state_root,
-    randao_reveal: b.body.randao_reveal,
+    block_body_root: hash_tree_root(b.body),
-    eth1_data : b.body.eth1_data,
+    signature: b.signature
-    signature: b.signature,
-    body: hash_tree_root(b.body)
   )
 
-proc fromHeaderAndBody(b: var BeaconBlock, h: BeaconBlockHeaderRLP, body: BeaconBlockBody) =
+proc fromHeaderAndBody(b: var BeaconBlock, h: BeaconBlockHeader, body: BeaconBlockBody) =
-  doAssert(hash_tree_root(body) == h.body)
+  doAssert(hash_tree_root(body) == h.block_body_root)
-  b.slot = h.slot.Slot
+  b.slot = h.slot
-  b.previous_block_root = h.parent_root
+  b.previous_block_root = h.previous_block_root
   b.state_root = h.state_root
-  b.body.randao_reveal = h.randao_reveal
-  b.body.eth1_data = h.eth1_data
-  b.signature = h.signature
   b.body = body
+  b.signature = h.signature
 
 proc importBlocks(node: BeaconNode,
-                  roots: openarray[(Eth2Digest, Slot)],
+                  blocks: openarray[BeaconBlock]) =
-                  headers: openarray[BeaconBlockHeaderRLP],
+  for blk in blocks:
-                  bodies: openarray[BeaconBlockBody]) =
-  var bodyMap = initTable[Eth2Digest, int]()
-
-  for i, b in bodies:
-    bodyMap[hash_tree_root(b)] = i
-
-  var goodBlocks, badBlocks = 0
-  for h in headers:
-    let iBody = bodyMap.getOrDefault(h.body, -1)
-    if iBody >= 0:
-      var blk: BeaconBlock
-      blk.fromHeaderAndBody(h, bodies[iBody])
     node.onBeaconBlock(blk)
-      inc goodBlocks
+  info "Forward sync imported blocks", len = blocks.len
-    else:
+
-      inc badBlocks
+proc mergeBlockHeadersAndBodies(headers: openarray[BeaconBlockHeader], bodies: openarray[BeaconBlockBody]): Option[seq[BeaconBlock]] =
+  if bodies.len != headers.len:
+    info "Cannot merge bodies and headers. Length mismatch.", bodies = bodies.len, headers = headers.len
+    return
+
+  var res: seq[BeaconBlock]
+  for i in 0 ..< headers.len:
+    if hash_tree_root(bodies[i]) != headers[i].block_body_root:
+      info "Block body is wrong for header"
+      return
+
+    res.setLen(res.len + 1)
+    res[^1].fromHeaderAndBody(headers[i], bodies[i])
+  some(res)
+
+proc getBeaconBlocks*(peer: Peer, blockRoot: Eth2Digest, slot: Slot, maxBlocks, skipSlots: int, backward: uint8): Future[Option[seq[BeaconBlock]]] {.gcsafe, async.}
 
-  info "Forward sync imported blocks", goodBlocks, badBlocks, headers = headers.len, bodies = bodies.len, roots = roots.len
 
 p2pProtocol BeaconSync(version = 1,
                        shortName = "bcs",
@@ -112,39 +110,19 @@ p2pProtocol BeaconSync(version = 1,
 
         var s = bestSlot + 1
         while s <= m.bestSlot:
-          debug "Waiting for block roots", fromPeer = peer, remoteBestSlot = m.bestSlot, peer
+          debug "Waiting for block headers", fromPeer = peer, remoteBestSlot = m.bestSlot, peer
-          let r = await peer.getBeaconBlockRoots(s, MaxRootsToRequest)
+          let headersLeft = int(m.bestSlot - s)
-          if not r.isSome:
+          let blocks = await peer.getBeaconBlocks(bestRoot, s, min(headersLeft, MaxHeadersToRequest), 0, 0)
-            debug "Block roots not received", peer
+          if blocks.isSome:
+            if blocks.get.len == 0:
+              info "Got 0 blocks while syncing", peer
               break
-          let roots = r.get.roots
+            node.importBlocks(blocks.get)
-          debug "Received block roots", len = roots.len, peer
+            let lastSlot = blocks.get[^1].slot
-          if roots.len != 0:
+            if lastSlot <= s:
-            if roots.len > MaxRootsToRequest:
+              info "Slot did not advance during sync", peer
-              # Attack?
-              await peer.disconnect(BreachOfProtocol, true)
               break
   
-            let headers = await peer.getBeaconBlockHeaders(bestRoot, s, roots.len, 0)
-            var bodiesRequest = newSeqOfCap[Eth2Digest](roots.len)
-            for r in roots:
-              bodiesRequest.add(r[0])
-
-            debug "Block headers received. Requesting block bodies", peer
-            let bodies = await peer.getBeaconBlockBodies(bodiesRequest)
-            node.importBlocks(roots, headers.get.blockHeaders, bodies.get.blockBodies)
-
-            let lastSlot = roots[^1][1]
-            if roots.len == MaxRootsToRequest:
-              # Next batch of roots starts with the last slot of the current one
-              # to make sure we did not miss any roots with this slot that did
-              # not fit into the response.
-
-              if s == lastSlot:
-                info "Too many roots for a single slot while syncing"
-                break
-              s = lastSlot
-            else:
             s = lastSlot + 1
           else:
             break
@@ -182,12 +160,40 @@ p2pProtocol BeaconSync(version = 1,
             blockRoot: Eth2Digest,
             slot: Slot,
             maxHeaders: int,
-            skipSlots: int) {.libp2pProtocol("rpc/beacon_block_headers", "1.0.0").} =
+            skipSlots: int,
-      # TODO: validate implement slipSlots
+            backward: uint8) {.libp2pProtocol("rpc/beacon_block_headers", "1.0.0").} =
       let maxHeaders = min(MaxHeadersToRequest, maxHeaders)
-      var s = slot
+      var headers: seq[BeaconBlockHeader]
-      var headers = newSeqOfCap[BeaconBlockHeaderRLP](maxHeaders)
       let db = peer.networkState.db
+
+      if backward != 0:
+        # TODO: implement skipSlots
+
+        var blockRoot = blockRoot
+        if slot != GENESIS_SLOT:
+          # TODO: Get block from the best chain by slot
+          # blockRoot = ...
+          discard
+
+        let blockPool = peer.networkState.node.blockPool
+        var br = blockPool.getRef(blockRoot)
+        var blockRefs = newSeqOfCap[BlockRef](maxHeaders)
+
+        while not br.isNil:
+          blockRefs.add(br)
+          if blockRefs.len == maxHeaders:
+            break
+          br = br.parent
+
+        headers = newSeqOfCap[BeaconBlockHeader](blockRefs.len)
+        for i in blockRefs.high .. 0:
+          headers.add(blockPool.get(blockRefs[i]).data.toHeader)
+      else:
+        # TODO: This branch has to be revisited and possibly somehow merged with the
+        # branch above once we can traverse the best chain forward
+        # TODO: implement skipSlots
+        headers = newSeqOfCap[BeaconBlockHeader](maxHeaders)
+        var s = slot
         let blockPool = peer.networkState.node.blockPool
         let maxSlot = blockPool.head.blck.slot
         while s <= maxSlot:
@@ -195,9 +201,10 @@ p2pProtocol BeaconSync(version = 1,
             headers.add(db.getBlock(r).get().toHeader)
             if headers.len == maxHeaders: break
           s += 1
+
       await response.send(headers)
 
-    proc beaconBlockHeaders(peer: Peer, blockHeaders: openarray[BeaconBlockHeaderRLP])
+    proc beaconBlockHeaders(peer: Peer, blockHeaders: openarray[BeaconBlockHeader])
 
   requestResponse:
     proc getAncestorBlocks(
@@ -244,9 +251,33 @@ p2pProtocol BeaconSync(version = 1,
       for r in blockRoots:
         if (let blk = db.getBlock(r); blk.isSome):
           bodies.add(blk.get().body)
+        else:
+          bodies.setLen(bodies.len + 1) # According to wire spec. Pad with zero body.
       await response.send(bodies)
 
     proc beaconBlockBodies(
             peer: Peer,
             blockBodies: openarray[BeaconBlockBody])
 
+proc getBeaconBlocks*(peer: Peer, blockRoot: Eth2Digest, slot: Slot, maxBlocks, skipSlots: int, backward: uint8): Future[Option[seq[BeaconBlock]]] {.async.} =
+  ## Retrieve block headers and block bodies from the remote peer, merge them into blocks.
+  assert(maxBlocks <= MaxHeadersToRequest)
+  let headersResp = await peer.getBeaconBlockHeaders(blockRoot, slot, maxBlocks, skipSlots, backward)
+  if headersResp.isNone: return
+
+  let headers = headersResp.get.blockHeaders
+  if headers.len == 0:
+    info "Peer has no headers", peer
+    var res: seq[BeaconBlock]
+    return some(res)
+
+  let bodiesRequest = headers.mapIt(signing_root(it))
+
+  debug "Block headers received. Requesting block bodies", peer
+  let bodiesResp = await peer.getBeaconBlockBodies(bodiesRequest)
+  if bodiesResp.isNone:
+    info "Did not receive bodies", peer
+    return
+
+  result = mergeBlockHeadersAndBodies(headers, bodiesResp.get.blockBodies)
+  # If result.isNone: disconnect with BreachOfProtocol?