Bugfix: the client can miss the genesis event in the absence of new deposits

beacon_chain/eth1_monitor.nim

@@ -463,6 +463,13 @@ proc signalGenesis(m: Eth1Monitor, genesisState: BeaconStateRef) =
 template hasEnoughValidators(m: Eth1Monitor, blk: Eth1Block): bool =
   blk.activeValidatorsCount >= m.preset.MIN_GENESIS_ACTIVE_VALIDATOR_COUNT
 
+func chainHasEnoughValidators(m: Eth1Monitor): bool =
+  if m.eth1Chain.blocks.len > 0:
+    m.hasEnoughValidators(m.eth1Chain.blocks[^1])
+  else:
+    m.eth1Chain.knownStart.deposit_count >=
+      m.preset.MIN_GENESIS_ACTIVE_VALIDATOR_COUNT
+
 func isAfterMinGenesisTime(m: Eth1Monitor, blk: Eth1Block): bool =
   doAssert blk.timestamp != 0
   let t = genesis_time_from_eth1_timestamp(m.preset, uint64 blk.timestamp)
@@ -527,21 +534,23 @@ proc stop*(m: Eth1Monitor) =
 proc syncBlockRange(m: Eth1Monitor, fromBlock, toBlock: Eth1BlockNumber) {.async.} =
   var currentBlock = fromBlock
   while currentBlock <= toBlock:
-    var depositLogs: JsonNode = nil
+    var
+      depositLogs: JsonNode = nil
+      blocksPerRequest = 5000'u64 # This is roughly a day of Eth1 blocks
+      maxBlockNumberRequested: Eth1BlockNumber
 
-    var blocksPerRequest = 5000'u64 # This is roughly a day of Eth1 blocks
     while true:
-      let requestToBlock = min(toBlock, currentBlock + blocksPerRequest - 1)
+      maxBlockNumberRequested = min(toBlock, currentBlock + blocksPerRequest - 1)
 
       debug "Obtaining deposit log events",
             fromBlock = currentBlock,
-            toBlock = requestToBlock
+            toBlock = maxBlockNumberRequested
       try:
         depositLogs = await m.dataProvider.ns.getJsonLogs(
           DepositEvent,
           fromBlock = some blockId(currentBlock),
-          toBlock = some blockId(requestToBlock))
-        currentBlock = requestToBlock + 1
+          toBlock = some blockId(maxBlockNumberRequested))
+        currentBlock = maxBlockNumberRequested + 1
         break
       except CatchableError as err:
         blocksPerRequest = blocksPerRequest div 2
@@ -568,7 +577,8 @@ proc syncBlockRange(m: Eth1Monitor, fromBlock, toBlock: Eth1BlockNumber) {.async
       m.eth1Chain.addBlock blk
 
     if eth1Blocks.len > 0:
-      let lastBlock = eth1Blocks[^1]
+      let lastIdx = eth1Blocks.len - 1
+      template lastBlock: auto = eth1Blocks[lastIdx]
 
       when hasDepositRootChecks:
         let status = await m.dataProvider.fetchDepositContractData(lastBlock)
@@ -582,10 +592,31 @@ proc syncBlockRange(m: Eth1Monitor, fromBlock, toBlock: Eth1BlockNumber) {.async
              blockNumber = lastBlock.number,
              depositsProcessed = lastBlock.voteData.deposit_count
  
-      if m.genesisStateFut != nil and m.hasEnoughValidators(lastBlock):
+    if m.genesisStateFut != nil and m.chainHasEnoughValidators:
+      let lastIdx = m.eth1Chain.blocks.len - 1
+      template lastBlock: auto = m.eth1Chain.blocks[lastIdx]
+      
+      if maxBlockNumberRequested == toBlock and
+         (m.eth1Chain.blocks.len == 0 or lastBlock.number != toBlock):
+        let web3Block = await m.dataProvider.getBlockByNumber(toBlock)
+
+        debug "Latest block doesn't hold deposits. Obtaining it",
+               ts = web3Block.timestamp.uint64,
+               number = web3Block.number.uint64
+
+        m.eth1Chain.addBlock Eth1Block(
+          number: Eth1BlockNumber web3Block.number,
+          timestamp: Eth1BlockTimestamp web3Block.timestamp,
+          voteData: Eth1Data(
+            block_hash: web3Block.hash.asEth2Digest,
+            deposit_count: lastBlock.voteData.deposit_count,
+            deposit_root: lastBlock.voteData.deposit_root),
+          activeValidatorsCount: lastBlock.activeValidatorsCount)
+      else:
         await m.dataProvider.fetchTimestamp(lastBlock)
-        if m.isAfterMinGenesisTime(lastBlock):
+
       var genesisBlockIdx = m.eth1Chain.blocks.len - 1
+      if m.isAfterMinGenesisTime(m.eth1Chain.blocks[genesisBlockIdx]):
         for i in 1 ..< eth1Blocks.len:
           let idx = (m.eth1Chain.blocks.len - 1) - i
           let blk = m.eth1Chain.blocks[idx]
@@ -650,7 +681,7 @@ proc handleEth1Progress(m: Eth1Monitor) {.async.} =
     await m.syncBlockRange(eth1SyncedTo + 1, targetBlock)
     eth1SyncedTo = targetBlock
 
-    while m.eth1Chain.blocks.len > 0:
+    while m.eth1Chain.blocks.len > 1:
       # We'll clean old blocks that can no longer be voting candidates.
       # Technically, we should check that the block is outside of the current
       # voting period as determined by its timestamp, but we'll approximate