Revert "Revert "Check for parent of first ready block being on chain (p…

…aritytech#1812)""

This reverts commit 892bf8e.

substrate/client/network/sync/src/blocks.rs

@@ -212,6 +212,31 @@ impl<B: BlockT> BlockCollection<B> {
  ready
  }
 
+ /// Returns the block header of the first block that is ready for importing.
+ /// `from` is the maximum block number for the start of the range that we are interested in.
+ /// The function will return None if the first block ready is higher than `from`.
+ /// The logic is structured to be consistent with ready_blocks().
+ pub fn first_ready_block_header(&self, from: NumberFor<B>) -> Option<B::Header> {
+ let mut prev = from;
+ for (&start, range_data) in &self.blocks {
+ if start > prev {
+ break
+ }
+
+ match range_data {
+ BlockRangeState::Complete(blocks) => {
+ let len = (blocks.len() as u32).into();
+ prev = start + len;
+ if let Some(BlockData { block, .. }) = blocks.first() {
+ return block.header.clone()
+ }
+ },
+ _ => continue,
+ }
+ }
+ None
+ }
+
  pub fn clear_queued(&mut self, hash: &B::Hash) {
  if let Some((from, to)) = self.queued_blocks.remove(hash) {
  let mut block_num = from;