比特币源码阅读(leveldb-CBlockIndex)

源码里面的CBlockIndex结构体，对应着leveldb的数据，具体的key和value见下图

https://en.bitcoin.it/wiki/Bitcoin_Core_0.11_(ch_2):_Data_Storage

2018-08-07 15-27-34 的屏幕截图.png
src/chain.h

/** The block chain is a tree shaped structure starting with the
 * genesis block at the root, with each block potentially having multiple
 * candidates to be the next block. A blockindex may have multiple pprev pointing
 * to it, but at most one of them can be part of the currently active branch.
 */
class CBlockIndex
{
public:
    //! pointer to the hash of the block, if any. Memory is owned by this CBlockIndex
    const uint256* phashBlock; //区块hash

    //! pointer to the index of the predecessor(前任) of this block
    CBlockIndex* pprev; //前一个CBlockIndex

    //! pointer to the index of some further predecessor of this block
    CBlockIndex* pskip;

    //! height of the entry in the chain. The genesis block has height 0
    int nHeight;

    //! Which # file this block is stored in (blk?????.dat)
    int nFile;

    //! Byte offset within blk?????.dat where this block's data is stored
    unsigned int nDataPos;

    //! Byte offset within rev?????.dat where this block's undo data is stored
    unsigned int nUndoPos;

    //! (memory only) Total amount of work (expected number of hashes) in the chain up to and including this block
    arith_uint256 nChainWork;

    //! Number of transactions in this block.
    //! Note: in a potential headers-first mode, this number cannot be relied upon
    unsigned int nTx;

    //! (memory only) Number of transactions in the chain up to and including this block.
    //! This value will be non-zero only if and only if transactions for this block and all its parents are available.
    //! Change to 64-bit type when necessary; won't happen before 2030
    unsigned int nChainTx;

    //! Verification status of this block. See enum BlockStatus
    uint32_t nStatus;

    //! block header
    int32_t nVersion;
    uint256 hashMerkleRoot;
    uint32_t nTime; //A timestamp recording when this block was created 
    uint32_t nBits;
    uint32_t nNonce;

    //! (memory only) Sequential id assigned to distinguish order in which blocks are received.
    int32_t nSequenceId;

    //! (memory only) Maximum nTime in the chain up to and including this block.
    unsigned int nTimeMax;

    void SetNull()
    {
        phashBlock = nullptr;
        pprev = nullptr;
        pskip = nullptr;
        nHeight = 0;
        nFile = 0;
        nDataPos = 0;
        nUndoPos = 0;
        nChainWork = arith_uint256();
        nTx = 0;
        nChainTx = 0;
        nStatus = 0;
        nSequenceId = 0;
        nTimeMax = 0;

        nVersion       = 0;
        hashMerkleRoot = uint256();
        nTime          = 0;
        nBits          = 0;
        nNonce         = 0;
    }

    CBlockIndex()
    {
        SetNull();
    }

    explicit CBlockIndex(const CBlockHeader& block)
    {
        SetNull();

        nVersion       = block.nVersion;
        hashMerkleRoot = block.hashMerkleRoot;
        nTime          = block.nTime;
        nBits          = block.nBits;
        nNonce         = block.nNonce;
    }

    CDiskBlockPos GetBlockPos() const {
        CDiskBlockPos ret;
        if (nStatus & BLOCK_HAVE_DATA) { //BLOCK_HAVE_DATA：full block available in blk*.dat
            ret.nFile = nFile;
            ret.nPos  = nDataPos;
        }
        return ret;
    }

    CDiskBlockPos GetUndoPos() const {
        CDiskBlockPos ret;
        if (nStatus & BLOCK_HAVE_UNDO) { //BLOCK_HAVE_UNDO：undo data available in rev*.dat
            ret.nFile = nFile;
            ret.nPos  = nUndoPos;
        }
        return ret;
    }

    CBlockHeader GetBlockHeader() const
    {
        CBlockHeader block;
        block.nVersion       = nVersion;
        if (pprev)
            block.hashPrevBlock = pprev->GetBlockHash();
        block.hashMerkleRoot = hashMerkleRoot;
        block.nTime          = nTime;
        block.nBits          = nBits;
        block.nNonce         = nNonce;
        return block;
    }

    uint256 GetBlockHash() const
    {
        return *phashBlock;
    }

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

    int64_t GetBlockTimeMax() const
    {
        return (int64_t)nTimeMax;
    }

    static constexpr int nMedianTimeSpan = 11;

    int64_t GetMedianTimePast() const //Median：中间的
    {
        int64_t pmedian[nMedianTimeSpan];
        int64_t* pbegin = &pmedian[nMedianTimeSpan];
        int64_t* pend = &pmedian[nMedianTimeSpan];

        const CBlockIndex* pindex = this;
        for (int i = 0; i < nMedianTimeSpan && pindex; i++, pindex = pindex->pprev)
            *(--pbegin) = pindex->GetBlockTime();

        std::sort(pbegin, pend);
        return pbegin[(pend - pbegin)/2];
    }

    std::string ToString() const
    {
        return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
            pprev, nHeight,
            hashMerkleRoot.ToString(),
            GetBlockHash().ToString());
    }

    //根据nStatus判断
    //! Check whether this block index entry is valid up to the passed validity(有效性) level.
    bool IsValid(enum BlockStatus nUpTo = BLOCK_VALID_TRANSACTIONS) const
    {
        assert(!(nUpTo & ~BLOCK_VALID_MASK)); // Only validity flags allowed.
        if (nStatus & BLOCK_FAILED_MASK)
            return false;
        return ((nStatus & BLOCK_VALID_MASK) >= nUpTo);
    }

    //根据nUpTo修改nStatus 
    //! Raise the validity level of this block index entry.
    //! Returns true if the validity was changed.
    bool RaiseValidity(enum BlockStatus nUpTo)
    {
        assert(!(nUpTo & ~BLOCK_VALID_MASK)); // Only validity flags allowed.
        if (nStatus & BLOCK_FAILED_MASK)
            return false;
        if ((nStatus & BLOCK_VALID_MASK) < nUpTo) {
            nStatus = (nStatus & ~BLOCK_VALID_MASK) | nUpTo;
            return true;
        }
        return false;
    }

    //! Build the skiplist pointer for this entry.
    void BuildSkip();

    //! Efficiently find an ancestor(祖先) of this block.
    CBlockIndex* GetAncestor(int height);
    const CBlockIndex* GetAncestor(int height) const;
};