code: func GetChaincodeHeaderExtension(hdr *common.Header) (*peer.ChaincodeHeaderExtension, error) {
  	chdr, err := UnmarshalChannelHeader(hdr.ChannelHeader)
  	if err != nil {
  		return nil, err
  	}
  
  	chaincodeHdrExt := &peer.ChaincodeHeaderExtension{}
  	err = proto.Unmarshal(chdr.Extension, chaincodeHdrExt)
  	return chaincodeHdrExt, errors.Wrap(err, "error unmarshaling ChaincodeHeaderExtension")
  }
docs: // GetChaincodeHeaderExtension get chaincode header extension given header