一开始看到header.extra这个可变长度字段很是惊喜和诧异，因为它是变长的，那矿工不是可以随意写数据到这个字段，万一矿工作恶加入一个很大的数据，那其他节点不得累死？解决这一疑惑的唯一方式------看代码
type Header struct {
...
Extra []byte `json:"extraData" gencodec:"required"`
...
}
Header.extra字段有长度限制
MaximumExtraDataSize uint64 = 32
func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
// Ensure that the header's extra-data section is of a reasonable size
if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
}
}
DAO分叉后extra被占用了，没法用作其他用途
func (self *worker) commitNewWork() {
// If we are care about TheDAO hard-fork check whether to override the extra-data or not
if daoBlock := self.config.DAOForkBlock; daoBlock != nil {
// Check whether the block is among the fork extra-override range
limit := new(big.Int).Add(daoBlock, params.DAOForkExtraRange)
if header.Number.Cmp(daoBlock) >= 0 && header.Number.Cmp(limit) < 0 {
// Depending whether we support or oppose the fork, override differently
if self.config.DAOForkSupport {
header.Extra = common.CopyBytes(params.DAOForkBlockExtra)
} else if bytes.Equal(header.Extra, params.DAOForkBlockExtra) {
header.Extra = []byte{} // If miner opposes, don't let it use the reserved extra-data
}
}
}
}
unc VerifyDAOHeaderExtraData(config *params.ChainConfig, header *types.Header) error {
// Short circuit validation if the node doesn't care about the DAO fork
if config.DAOForkBlock == nil {
return nil
}
// Make sure the block is within the fork's modified extra-data range
if header.Number.Cmp(config.DAOForkBlock) < 0 || header.Number.Cmp(limit) >= 0 {
return nil
}
// Depending on whether we support or oppose the fork, validate the extra-data contents
if config.DAOForkSupport {
if !bytes.Equal(header.Extra, params.DAOForkBlockExtra) {
return ErrBadProDAOExtra
}
} else {
if bytes.Equal(header.Extra, params.DAOForkBlockExtra) {
return ErrBadNoDAOExtra
}
}
// All ok, header has the same extra-data we expect
return nil
}
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