在上一篇以太坊rlp编解码规则及实现中，我们看到了字符数组编解码的实现，下面在计算以太坊区块hash时，我们会看到rlp列表编码的使用
以太坊区块头
首先请看go-ethereum中以太坊区块头的定义
type Header struct {
ParentHash common.Hash `json:"parentHash" gencodec:"required"`
UncleHash common.Hash `json:"sha3Uncles" gencodec:"required"`
Coinbase common.Address `json:"miner" gencodec:"required"`
Root common.Hash `json:"stateRoot" gencodec:"required"`
TxHash common.Hash `json:"transactionsRoot" gencodec:"required"`
ReceiptHash common.Hash `json:"receiptsRoot" gencodec:"required"`
Bloom Bloom `json:"logsBloom" gencodec:"required"`
Difficulty *big.Int `json:"difficulty" gencodec:"required"`
Number *big.Int `json:"number" gencodec:"required"`
GasLimit *big.Int `json:"gasLimit" gencodec:"required"`
GasUsed *big.Int `json:"gasUsed" gencodec:"required"`
Time *big.Int `json:"timestamp" gencodec:"required"`
Extra []byte `json:"extraData" gencodec:"required"`
MixDigest common.Hash `json:"mixHash" gencodec:"required"`
Nonce BlockNonce `json:"nonce" gencodec:"required"`
}
存在两种区块hash值
(1)header_hash_nononce，eth.getWork获取的第一个字段就是这个，这个hash是对header除 MixDigest，Nonce外进行rlp编码后进行hash得到的
(2)header_hash, eth.getBlock得到的数据中的hash就是这个，这个hash是对整个header进行rlp编码后进行hash得到的
注意：
上面所说的rlp编码是指将header的各个字段看作一个列表进行编码
上面所说的hash是指keccakf 256算法，keccakf是sha3所采用的hash算法,算法可参见ethash算法库
区块头rlp编码及hash的计算
int start_index = 0;
int data_index = 1 + 8;
char buf[4096] = {0};
void *p = buf + data_index;
size_t left = sizeof(buf) - data_index;
rlp_pack_buf(&p, &left, parent_hash_bin, sdslen(parent_hash_bin));
rlp_pack_buf(&p, &left, uncles_hash_bin, sdslen(uncles_hash_bin));
rlp_pack_buf(&p, &left, miner_bin, sdslen(miner_bin));
rlp_pack_buf(&p, &left, state_root_bin, sdslen(state_root_bin));
rlp_pack_buf(&p, &left, tx_hash_bin, sdslen(tx_hash_bin));
rlp_pack_buf(&p, &left, receipt_hash_bin, sdslen(receipt_hash_bin));
rlp_pack_buf(&p, &left, bloom_bin, sdslen(bloom_bin));
rlp_pack_buf(&p, &left, diff_bin, sdslen(diff_bin));
rlp_pack_buf(&p, &left, number_bin, sdslen(number_bin));
rlp_pack_buf(&p, &left, gas_limit_bin, sdslen(gas_limit_bin));
rlp_pack_buf(&p, &left, gas_used_bin, sdslen(gas_used_bin));
rlp_pack_buf(&p, &left, time_bin, sdslen(time_bin));
rlp_pack_buf(&p, &left, extra_data_bin, sdslen(extra_data_bin));
//不包含这两个就是header_hash_nononce
rlp_pack_buf(&p, &left, mixdigest_bin, sdslen(mixdigest_bin));
rlp_pack_buf(&p, &left, nonce_bin, sdslen(nonce_bin));
//列表前缀的处理
size_t alllen = sizeof(buf) - data_index - left;
if (alllen <= 55) {
start_index = data_index - 1;
buf[start_index] = 192 + alllen;
} else {
char len_buf[8] = {0};
void *len_buf_p = len_buf;
size_t len_buf_left = sizeof(len_buf);
int space = rlp_pack_varint_be(&len_buf_p, &len_buf_left, alllen);
start_index = data_index - 1 - space;
buf[start_index] = 247 + space;
memcpy(buf + start_index + 1, len_buf, space);
}
size_t buf_alllen = sizeof(buf) - left - start_index;
sds hash = sdsnewlen(NULL, 32);
sha3_256((uint8_t *)hash, 32, (uint8_t*)(buf + start_index), buf_alllen);
return hash;
