code: func (node *blockNode) Header() wire.BlockHeader {
  	// No lock is needed because all accessed fields are immutable.
  	prevHash := &zeroHash
  	if node.parent != nil {
  		prevHash = &node.parent.hash
  	}
  	return wire.BlockHeader{
  		Version:    node.version,
  		PrevBlock:  *prevHash,
  		MerkleRoot: node.merkleRoot,
  		Timestamp:  time.Unix(node.timestamp, 0),
  		Bits:       node.bits,
  		Nonce:      node.nonce,
  	}
  }
docs: // Header constructs a block header from the node and returns it.
  //
  // This function is safe for concurrent access.