code: func NewBlockHeader(version int32, prevHash, merkleRootHash *chainhash.Hash,
  	bits uint32, nonce uint32) *BlockHeader {
  
  	// Limit the timestamp to one second precision since the protocol
  	// doesn't support better.
  	return &BlockHeader{
  		Version:    version,
  		PrevBlock:  *prevHash,
  		MerkleRoot: *merkleRootHash,
  		Timestamp:  time.Unix(time.Now().Unix(), 0),
  		Bits:       bits,
  		Nonce:      nonce,
  	}
  }
docs: // NewBlockHeader returns a new BlockHeader using the provided version, previous
  // block hash, merkle root hash, difficulty bits, and nonce used to generate the
  // block with defaults for the remaining fields.