Sync-related fixes:

* off-by-one error in the returned range of blocks
* larger request time-outs to deal with non-responsive servers
* fix an unhandled exception when we fail to deliver a response chunk

beacon_chain/beacon_node.nim

@@ -491,9 +491,13 @@ proc onBeaconBlock(node: BeaconNode, blck: BeaconBlock) =
   # The block we received contains attestations, and we might not yet know about
   # all of them. Let's add them to the attestation pool - in case they block
   # is not yet resolved, neither will the attestations be!
+  # But please note that we only care about recent attestations.
   # TODO shouldn't add attestations if the block turns out to be invalid..
-  for attestation in blck.body.attestations:
-    node.onAttestation(attestation)
+  let currentSlot = node.beaconClock.now.toSlot
+  if currentSlot.afterGenesis and
+     blck.slot.epoch + 1 >= currentSlot.slot.epoch:
+    for attestation in blck.body.attestations:
+      node.onAttestation(attestation)
 
 proc handleAttestations(node: BeaconNode, head: BlockRef, slot: Slot) =
   ## Perform all attestations that the validators attached to this node should

beacon_chain/block_pool.nim

@@ -354,7 +354,7 @@ proc getBlockRange*(pool: BlockPool, headBlock: Eth2Digest,
 
   # Then we see if this aligned position is within our wanted
   # range. If it's outside it, we must skip more blocks:
-  let lastWantedSlot = startSlot.int + output.len * skipStep
+  let lastWantedSlot = startSlot.int + (output.len - 1) * skipStep
   if alignedHeadSlot > lastWantedSlot:
     blocksToSkip += (alignedHeadSlot - lastWantedSlot)
 

beacon_chain/libp2p_daemon_backend.nim

@@ -614,7 +614,10 @@ proc p2pProtocolBackendImpl*(p: P2PProtocol): Backend =
           # the `response` API in the high-level protocols more complicated for now).
           chronicles.debug "response size limit reached", peer, reqName = `msgNameLit`
         except CatchableError as `errVar`:
-          `await` sendErrorResponse(`peerVar`, `streamVar`, ServerError, `errVar`.msg)
+          try:
+            `await` sendErrorResponse(`peerVar`, `streamVar`, ServerError, `errVar`.msg)
+          except CatchableError as err:
+            debug "Failed to deliver error response", peer = `peerVar`
 
     ##
     ## Implement Senders and Handshake

beacon_chain/sync_protocol.nim

@@ -104,7 +104,9 @@ p2pProtocol BeaconSync(version = 1,
       let
         node = peer.networkState.node
         ourStatus = node.getCurrentStatus
-        theirStatus = await peer.status(ourStatus)
+        # TODO: The timeout here is so high only because we fail to
+        # respond in time due to high CPU load in our single thread.
+        theirStatus = await peer.status(ourStatus, timeout = 60.seconds)
 
       if theirStatus.isSome:
         await peer.handleInitialStatus(node, ourStatus, theirStatus.get)
@@ -186,8 +188,9 @@ proc handleInitialStatus(peer: Peer,
     libp2p_peers.set peer.network.peers.len.int64
 
     debug "Peer connected. Initiating sync", peer,
-          headSlot = ourStatus.headSlot,
-          remoteHeadSlot = theirStatus.headSlot
+          localHeadSlot = ourStatus.headSlot,
+          remoteHeadSlot = theirStatus.headSlot,
+          remoteHeadRoot = theirStatus.headRoot
 
     let bestDiff = cmp((ourStatus.finalizedEpoch, ourStatus.headSlot),
                        (theirStatus.finalizedEpoch, theirStatus.headSlot))
@@ -207,8 +210,11 @@ proc handleInitialStatus(peer: Peer,
                                          ourHeadSlot = s,
                                          numBlocksToRequest
 
+        # TODO: The timeout here is so high only because we fail to
+        # respond in time due to high CPU load in our single thread.
         let blocks = await peer.beaconBlocksByRange(theirStatus.headRoot, s,
-                                                    numBlocksToRequest, 1'u64)
+                                                    numBlocksToRequest, 1'u64,
+                                                    timeout = 60.seconds)
         if blocks.isSome:
           info "got blocks", total = blocks.get.len
           if blocks.get.len == 0: