ethstats: prevent panic if head block is not available (#29020)

This pull request fixes a flaw in ethstats which can lead to node crash

A panic could happens when the local blockchain is reorging which causes the original head block not to be  reachable (since number->hash canonical mapping is deleted). In order to prevent the panic, the block nilness is now checked in ethstats.

ethstats/ethstats.go

@@ -611,6 +611,10 @@ func (s *Service) reportBlock(conn *connWrapper, block *types.Block) error {
  // Gather the block details from the header or block chain
  details := s.assembleBlockStats(block)
 
+ // Short circuit if the block detail is not available.
+ if details == nil {
+ return nil
+ }
  // Assemble the block report and send it to the server
  log.Trace("Sending new block to ethstats", "number", details.Number, "hash", details.Hash)
 
@@ -638,10 +642,16 @@ func (s *Service) assembleBlockStats(block *types.Block) *blockStats {
  // check if backend is a full node
  fullBackend, ok := s.backend.(fullNodeBackend)
  if ok {
+ // Retrieve current chain head if no block is given.
  if block == nil {
  head := fullBackend.CurrentBlock()
  block, _ = fullBackend.BlockByNumber(context.Background(), rpc.BlockNumber(head.Number.Uint64()))
  }
+ // Short circuit if no block is available. It might happen when
+ // the blockchain is reorging.
+ if block == nil {
+ return nil
+ }
  header = block.Header()
  td = fullBackend.GetTd(context.Background(), header.Hash())