fetch multiple blocks at a time

* avoid crash on invalid block production (fixes #209)
* fetch blocks every second, roughly
* fix start.sh param order
* run beacon node sim at slower pace

beacon_chain/beacon_node.nim

@@ -11,8 +11,10 @@ import
 
 const
   topicBeaconBlocks = "ethereum/2.1/beacon_chain/blocks"
+  topicBeaconBlocks2 = "ethereum/2.1/beacon_chain/blocks2"
   topicAttestations = "ethereum/2.1/beacon_chain/attestations"
-  topicfetchBlocks = "ethereum/2.1/beacon_chain/fetch"
+  topicFetchBlocks = "ethereum/2.1/beacon_chain/fetch"
+  topicFetchBlocks2 = "ethereum/2.1/beacon_chain/fetch2"
 
   dataDirValidators = "validators"
   networkMetadataFile = "network.json"
@@ -364,8 +366,12 @@ proc proposeBlock(node: BeaconNode,
 
   let blockRoot = signed_root(newBlock)
 
-  # TODO return new BlockRef from add?
   let newBlockRef = node.blockPool.add(node.state, blockRoot, newBlock)
+  if newBlockRef == nil:
+    warn "Unable to add proposed block to block pool",
+      newBlock = shortLog(newBlock),
+      blockRoot = shortLog(blockRoot)
+    return head
 
   info "Block proposed",
     blck = shortLog(newBlock),
@@ -379,21 +385,36 @@ proc proposeBlock(node: BeaconNode,
 
   return newBlockRef
 
-proc fetchBlocks(node: BeaconNode, roots: seq[Eth2Digest]) =
+proc fetchBlocks(node: BeaconNode, roots: seq[FetchRecord]) =
   if roots.len == 0: return
 
+  debug "Fetching blocks", roots
+
   # TODO shouldn't send to all!
   # TODO should never fail - asyncCheck is wrong here..
-  asyncCheck node.network.broadcast(topicfetchBlocks, roots)
+  asyncCheck node.network.broadcast(topicfetchBlocks2, roots)
 
-proc onFetchBlocks(node: BeaconNode, roots: seq[Eth2Digest]) =
+proc onFetchBlocks(node: BeaconNode, roots: seq[FetchRecord]) =
   # TODO placeholder logic for block recovery
-  debug "fetchBlocks received", roots = roots.len
-  for root in roots:
-    if (let blck = node.db.getBlock(root); blck.isSome()):
-      # TODO should never fail - asyncCheck is wrong here..
+  var resp: seq[BeaconBlock]
+  for rec in roots:
+    if (var blck = node.db.getBlock(rec.root); blck.isSome()):
+      # TODO validate historySlots
+      let firstSlot = blck.get().slot - rec.historySlots
+
+      for i in 0..<rec.historySlots.int:
+        resp.add(blck.get())
+
         # TODO should obviously not spam, but rather send it back to the requester
-      asyncCheck node.network.broadcast(topicBeaconBlocks, blck.get())
+        if (blck = node.db.getBlock(blck.get().previous_block_root);
+            blck.isNone() or blck.get().slot < firstSlot):
+          break
+
+  debug "fetchBlocks received", roots = roots.len, resp = resp.len
+
+  # TODO should never fail - asyncCheck is wrong here..
+  if resp.len > 0:
+    asyncCheck node.network.broadcast(topicBeaconBlocks2, resp)
 
 proc onAttestation(node: BeaconNode, attestation: Attestation) =
   # We received an attestation from the network but don't know much about it
@@ -414,10 +435,6 @@ proc onBeaconBlock(node: BeaconNode, blck: BeaconBlock) =
     blockRoot = shortLog(blockRoot)
 
   if node.blockPool.add(node.state, blockRoot, blck).isNil:
-    # TODO this will cause us to fetch parent, even for invalid blocks.. fix
-    #debug "Missing block detected. Fetching from network",
-    #  `block` = blck.previous_block_root
-    node.fetchBlocks(@[blck.previous_block_root])
     return
 
   # The block we received contains attestations, and we might not yet know about
@@ -517,12 +534,6 @@ proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, asyn
     scheduledSlot = humaneSlotNum(scheduledSlot),
     slot = humaneSlotNum(slot)
 
-  # TODO in this setup, we retry fetching blocks at the beginning of every slot,
-  #      hoping that we'll get some before it's time to attest or propose - is
-  #      there a better time to do this?
-  let missingBlocks = node.blockPool.checkUnresolved()
-  node.fetchBlocks(missingBlocks)
-
   if slot < lastSlot:
     # This can happen if the system clock changes time for example, and it's
     # pretty bad
@@ -646,6 +657,14 @@ proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, asyn
   addTimer(nextSlotStart) do (p: pointer):
     asyncCheck node.onSlotStart(slot, nextSlot)
 
+proc onSecond(node: BeaconNode, moment: Moment) {.async.} =
+  let missingBlocks = node.blockPool.checkUnresolved()
+  node.fetchBlocks(missingBlocks)
+
+  let nextSecond = max(Moment.now(), moment + chronos.seconds(1))
+  addTimer(nextSecond) do (p: pointer):
+    asyncCheck node.onSecond(nextSecond)
+
 proc run*(node: BeaconNode) =
   waitFor node.network.subscribe(topicBeaconBlocks) do (blck: BeaconBlock):
     node.onBeaconBlock(blck)
@@ -654,8 +673,19 @@ proc run*(node: BeaconNode) =
     node.onAttestation(attestation)
 
   waitFor node.network.subscribe(topicfetchBlocks) do (roots: seq[Eth2Digest]):
+    # Backwards compat, remove eventually
+    # TODO proof of concept block fetcher - need serious anti-spam rework
+    node.onFetchBlocks(roots.mapIt(FetchRecord(root: it, historySlots: 1)))
+
+  waitFor node.network.subscribe(topicfetchBlocks2) do (roots: seq[FetchRecord]):
+    # TODO proof of concept block fetcher - need serious anti-spam rework
     node.onFetchBlocks(roots)
 
+  waitFor node.network.subscribe(topicBeaconBlocks2) do (blcks: seq[BeaconBlock]):
+    # TODO proof of concept block transfer - need serious anti-spam rework
+    for blck in blcks:
+      node.onBeaconBlock(blck)
+
   let
     slot = node.beaconClock.now().toSlot()
     startSlot =
@@ -670,6 +700,10 @@ proc run*(node: BeaconNode) =
   addTimer(fromNow) do (p: pointer):
     asyncCheck node.onSlotStart(startSlot - 1, startSlot)
 
+  let second = Moment.now() + chronos.seconds(1)
+  addTimer(second) do (p: pointer):
+    asyncCheck node.onSecond(second)
+
   runForever()
 
 var gPidFile: string

beacon_chain/beacon_node_types.nim

@@ -180,6 +180,7 @@ type
     db*: BeaconChainDB
 
   UnresolvedBlock* = object
+    slots*: uint64 # number of slots that are suspected missing
     tries*: int
 
   BlockRef* = ref object {.acyclic.}
@@ -259,5 +260,9 @@ type
     totalValidators*: uint64
     lastUserValidator*: uint64
 
+  FetchRecord* = object
+    root*: Eth2Digest
+    historySlots*: uint64
+
 proc userValidatorsRange*(d: NetworkMetadata): HSlice[int, int] =
   0 .. d.lastUserValidator.int

beacon_chain/block_pool.nim

@@ -249,11 +249,25 @@ proc add*(
   #      them out without penalty - but signing invalid attestations carries
   #      a risk of being slashed, making attestations a more valuable spam
   #      filter.
+  # TODO when we receive the block, we don't know how many others we're missing
+  #      from that branch, so right now, we'll just do a blind guess
   debug "Unresolved block",
     blck = shortLog(blck),
     blockRoot = shortLog(blockRoot)
 
-  pool.unresolved[blck.previous_block_root] = UnresolvedBlock()
+  let parentSlot = blck.slot - 1
+
+  pool.unresolved[blck.previous_block_root] = UnresolvedBlock(
+    slots:
+      # The block is at least two slots ahead - try to grab whole history
+      if parentSlot > pool.head.slot:
+        parentSlot - pool.head.slot
+      else:
+        # It's a sibling block from a branch that we're missing - fetch one
+        # epoch at a time
+        max(1.uint64, SLOTS_PER_EPOCH.uint64 -
+          (parentSlot.uint64 mod SLOTS_PER_EPOCH.uint64))
+  )
   pool.pending[blockRoot] = blck
 
 proc get*(pool: BlockPool, blck: BlockRef): BlockData =
@@ -280,13 +294,13 @@ proc getOrResolve*(pool: var BlockPool, root: Eth2Digest): BlockRef =
   result = pool.blocks.getOrDefault(root)
 
   if result.isNil:
-    pool.unresolved[root] = UnresolvedBlock()
+    pool.unresolved[root] = UnresolvedBlock(slots: 1)
 
 iterator blockRootsForSlot*(pool: BlockPool, slot: uint64|Slot): Eth2Digest =
   for br in pool.blocksBySlot.getOrDefault(slot.uint64, @[]):
     yield br.root
 
-proc checkUnresolved*(pool: var BlockPool): seq[Eth2Digest] =
+proc checkUnresolved*(pool: var BlockPool): seq[FetchRecord] =
   ## Return a list of blocks that we should try to resolve from other client -
   ## to be called periodically but not too often (once per slot?)
   var done: seq[Eth2Digest]
@@ -305,7 +319,7 @@ proc checkUnresolved*(pool: var BlockPool): seq[Eth2Digest] =
   # simple (simplistic?) exponential backoff for retries..
   for k, v in pool.unresolved.pairs():
     if v.tries.popcount() == 1:
-      result.add(k)
+      result.add(FetchRecord(root: k, historySlots: v.slots))
 
 proc skipAndUpdateState(
     state: var BeaconState, blck: BeaconBlock, flags: UpdateFlags,

tests/simulation/start.sh

@@ -23,7 +23,7 @@ mkdir -p $BUILD_OUTPUTS_DIR
 # Run with "SHARD_COUNT=4 ./start.sh" to change these
 DEFS="-d:SHARD_COUNT=${SHARD_COUNT:-4} "      # Spec default: 1024
 DEFS+="-d:SLOTS_PER_EPOCH=${SLOTS_PER_EPOCH:-8} "   # Spec default: 64
-DEFS+="-d:SECONDS_PER_SLOT=${SECONDS_PER_SLOT:-6} " # Spec default: 6
+DEFS+="-d:SECONDS_PER_SLOT=${SECONDS_PER_SLOT:-12} " # Spec default: 6
 
 LAST_VALIDATOR_NUM=$(( $NUM_VALIDATORS - 1 ))
 LAST_VALIDATOR="$VALIDATORS_DIR/v$(printf '%07d' $LAST_VALIDATOR_NUM).deposit.json"
@@ -44,8 +44,9 @@ if [[ -z "$SKIP_BUILDS" ]]; then
 fi
 
 if [ ! -f $SNAPSHOT_FILE ]; then
-  $BEACON_NODE_BIN createTestnet \
+  $BEACON_NODE_BIN \
     --dataDir=$SIMULATION_DIR/node-0 \
+    createTestnet \
     --networkId=1000 \
     --validatorsDir=$VALIDATORS_DIR \
     --totalValidators=$NUM_VALIDATORS \

tests/test_block_pool.nim

@@ -63,7 +63,7 @@ suite "Block pool processing":
 
     check:
       pool.get(b2Root).isNone() # Unresolved, shouldn't show up
-      b1Root in pool.checkUnresolved()
+      FetchRecord(root: b1Root, historySlots: 1) in pool.checkUnresolved()
 
     discard pool.add(state, b1Root, b1)