BCH源码--区块结构和大小

BCH和BTC最大的区别应该就是区块扩容的了，首先来看区块
位于/src/primitives/

CBlockHeader

节点将新交易收集到块中，将它们散列到哈希树中，并扫描nonce值以使块的哈希值满足工作量证明要求。 当他们解决工作证明时，他们将块广播给每个人，并且块被添加到块链中。 块中的第一个事务是一个特殊的事务，它创建一个由块的创建者拥有的新硬币。
注释部分和btc是一样的，结构也是一样的
btc的区块 https://blog.csdn.net/m0_37847176/article/details/81874834

class CBlockHeader {
public:
    // header
    int32_t nVersion;
    uint256 hashPrevBlock;
    uint256 hashMerkleRoot;
    uint32_t nTime;
    uint32_t nBits;
    uint32_t nNonce;

    CBlockHeader() { SetNull(); }

    ADD_SERIALIZE_METHODS;

    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream &s, Operation ser_action) {
        READWRITE(this->nVersion);
        READWRITE(hashPrevBlock);
        READWRITE(hashMerkleRoot);
        READWRITE(nTime);
        READWRITE(nBits);
        READWRITE(nNonce);
    }

    void SetNull() {
        nVersion = 0;
        hashPrevBlock.SetNull();
        hashMerkleRoot.SetNull();
        nTime = 0;
        nBits = 0;
        nNonce = 0;
    }

    bool IsNull() const { return (nBits == 0); }

    uint256 GetHash() const;

    int64_t GetBlockTime() const { return (int64_t)nTime; }
};

下面来CBlock

class CBlock : public CBlockHeader {
public:
    // network and disk
    std::vector<CTransactionRef> vtx;//交易

    // memory only
    mutable bool fChecked;

    CBlock() { SetNull(); }

    CBlock(const CBlockHeader &header) {
        SetNull();
        *((CBlockHeader *)this) = header;
    }

    ADD_SERIALIZE_METHODS;

    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream &s, Operation ser_action) {
        READWRITE(*(CBlockHeader *)this);
        READWRITE(vtx);
    }

    void SetNull() {
        CBlockHeader::SetNull();
        vtx.clear();
        fChecked = false;
    }

    CBlockHeader GetBlockHeader() const {
        CBlockHeader block;
        block.nVersion = nVersion;
        block.hashPrevBlock = hashPrevBlock;
        block.hashMerkleRoot = hashMerkleRoot;
        block.nTime = nTime;
        block.nBits = nBits;
        block.nNonce = nNonce;
        return block;
    }

    std::string ToString() const;
};

---

CBlockLocator

描述区块链中到另一个节点的位置，这样如果另一个节点没有相同的分支，它就可以找到最近的公共中继。 它越靠后，叉子就越远

struct CBlockLocator {
    std::vector<uint256> vHave;

    CBlockLocator() {}

    CBlockLocator(const std::vector<uint256> &vHaveIn) { vHave = vHaveIn; }

    ADD_SERIALIZE_METHODS;

    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream &s, Operation ser_action) {
        int nVersion = s.GetVersion();
        if (!(s.GetType() & SER_GETHASH)) READWRITE(nVersion);
        READWRITE(vHave);
    }

    void SetNull() { vHave.clear(); }

    bool IsNull() const { return vHave.empty(); }
};

---

emmm…没有区块的大小说明，不科学，找找
在src/globals.cpp中声明

uint64_t nMaxBlockSize = DEFAULT_MAX_BLOCK_SIZE;

然后在src/consensus/consensus.h

/** 1MB */
static const uint64_t ONE_MEGABYTE = 1000000;
/** The maximum allowed size for a transaction, in bytes */
static const uint64_t MAX_TX_SIZE = ONE_MEGABYTE;
/** The minimum allowed size for a transaction, in bytes */
static const uint64_t MIN_TX_SIZE = 100;
/** The maximum allowed size for a block, before the UAHF */用户激活硬分叉前最大限制是1M
static const uint64_t LEGACY_MAX_BLOCK_SIZE = ONE_MEGABYTE;
/** Default setting for maximum allowed size for a block, in bytes */
static const uint64_t DEFAULT_MAX_BLOCK_SIZE = 32 * ONE_MEGABYTE;

一笔交易最大是1M,最小是100b
可以查询一下看看

parallels@parallels-vm:~$ bitcoin-cli getexcessiveblock
{
  "excessiveBlockSize": 32000000
}

所以最大区块大小是32M

---

然后来看BTC的区块限制,应该是这个，在miner.cpp

/** Default for -blockmaxweight, which controls the range of block weights the mining code will create **/
static const unsigned int DEFAULT_BLOCK_MAX_WEIGHT = 3,000,000;
/** Default for -blockmaxsize, which controls the maximum size of block the mining code will create **/
static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 750,000;
/** The maximum allowed size for a serialized block, in bytes (only for buffer size limits) */
static const unsigned int MAX_BLOCK_SERIALIZED_SIZE = 4,000,000;

BlockAssembler::BlockAssembler(const CChainParams& _chainparams)
    : chainparams(_chainparams)
{
    // Block resource limits区块资源限制
    // If neither -blockmaxsize or -blockmaxweight is given, limit to DEFAULT_BLOCK_MAX_*
    // If only one is given, only restrict the specified resource.
    // If both are given, restrict both.
    nBlockMaxWeight = DEFAULT_BLOCK_MAX_WEIGHT;//3M
    nBlockMaxSize = DEFAULT_BLOCK_MAX_SIZE;//750k
    bool fWeightSet = false;
    if (mapArgs.count("-blockmaxweight")) {
        nBlockMaxWeight = GetArg("-blockmaxweight", DEFAULT_BLOCK_MAX_WEIGHT);
        nBlockMaxSize = MAX_BLOCK_SERIALIZED_SIZE;
        fWeightSet = true;
    }
    if (mapArgs.count("-blockmaxsize")) {
        nBlockMaxSize = GetArg("-blockmaxsize", DEFAULT_BLOCK_MAX_SIZE);
        if (!fWeightSet) {
            nBlockMaxWeight = nBlockMaxSize * WITNESS_SCALE_FACTOR;
        }
    }
    // Limit weight to between 4K and MAX_BLOCK_WEIGHT-4K for sanity:
    nBlockMaxWeight = std::max((unsigned int)4000, std::min((unsigned int)(MAX_BLOCK_WEIGHT-4000), nBlockMaxWeight));
    // Limit size to between 1K and MAX_BLOCK_SERIALIZED_SIZE-1K for sanity:
    nBlockMaxSize = std::max((unsigned int)1000, std::min((unsigned int)(MAX_BLOCK_SERIALIZED_SIZE-1000), nBlockMaxSize));

    // Whether we need to account for byte usage (in addition to weight usage)
    fNeedSizeAccounting = (nBlockMaxSize < MAX_BLOCK_SERIALIZED_SIZE-1000);
}

为什么是4k和1k呢，这是给coinbase预留的内存大小，因为一个区块肯定会有coinbase交易。
从上面的代码来看，nBlockMaxSize可以是1k到4M-1K大小的，不是我们所熟知的1M大小的限制
所以1M的限制在那里呢，我看下挖矿的代码, 貌似发现了

/** The maximum allowed size for a block excluding witness data, in bytes (network rule) */
static const unsigned int MAX_BLOCK_BASE_SIZE = 1000000;

从注释看是，除见证数据之外的块的最大允许大小，在源码中查找可以在main.cpp的CheckBlock中找到这个常量的使用

// Size limits
    if (block.vtx.empty() || block.vtx.size() > MAX_BLOCK_BASE_SIZE || ::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) > MAX_BLOCK_BASE_SIZE)
        return state.DoS(100, false, REJECT_INVALID, "bad-blk-length", false, "size limits failed");

所谓的区块大小限制应该是针对区块中的交易的
所以算起来是带上隔离见证数据的话，区块大小能达到4M