blockencodings.h

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// Copyright (c) 2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_BLOCKENCODINGS_H
#define BITCOIN_BLOCKENCODINGS_H
 
#include <primitives/block.h>
#include <serialize.h>
#include <shortidprocessor.h>
 
#include <cstdint>
#include <memory>
#include <vector>
 
class Config;
class CTxMemPool;
 
// Transaction compression schemes for compact block relay can be introduced by
// writing an actual formatter here.
using TransactionCompression = DefaultFormatter;
 
class BlockTransactionsRequest {
public:
    // A BlockTransactionsRequest message
    BlockHash blockhash;
    std::vector<uint32_t> indices;
 
    SERIALIZE_METHODS(BlockTransactionsRequest, obj) {
        READWRITE(obj.blockhash,
                  Using<VectorFormatter<DifferenceFormatter>>(obj.indices));
    }
};
 
class BlockTransactions {
public:
    // A BlockTransactions message
    BlockHash blockhash;
    std::vector<CTransactionRef> txn;
 
    BlockTransactions() = default;
    explicit BlockTransactions(const BlockTransactionsRequest &req)
        : blockhash(req.blockhash), txn(req.indices.size()) {}
 
    SERIALIZE_METHODS(BlockTransactions, obj) {
        READWRITE(obj.blockhash,
                  Using<VectorFormatter<TransactionCompression>>(obj.txn));
    }
};
 
// Dumb serialization/storage-helper for CBlockHeaderAndShortTxIDs and
// PartiallyDownloadedBlock
struct PrefilledTransaction {
    // Used as an offset since last prefilled tx in CBlockHeaderAndShortTxIDs
    uint32_t index;
    CTransactionRef tx;
 
    template <typename Stream> void SerData(Stream &s) { s << tx; }
    template <typename Stream> void UnserData(Stream &s) { s >> tx; }
};
 
struct ShortIdProcessorPrefilledTransactionAdapter {
    uint32_t getIndex(const PrefilledTransaction &pt) const { return pt.index; }
    CTransactionRef getItem(const PrefilledTransaction &pt) const {
        return pt.tx;
    }
};
 
typedef enum ReadStatus_t {
    READ_STATUS_OK,
    // Invalid object, peer is sending bogus crap.
    // FIXME: differenciate bogus crap from crap that do not fit our policy.
    READ_STATUS_INVALID,
    // Failed to process object.
    READ_STATUS_FAILED,
    // Used only by FillBlock to indicate a failure in CheckBlock.
    READ_STATUS_CHECKBLOCK_FAILED,
} ReadStatus;
 
class CBlockHeaderAndShortTxIDs {
private:
    mutable uint64_t shorttxidk0{0}, shorttxidk1{0};
    uint64_t nonce;
 
    void FillShortTxIDSelector() const;
 
    friend class PartiallyDownloadedBlock;
 
protected:
    std::vector<uint64_t> shorttxids;
    std::vector<PrefilledTransaction> prefilledtxn;
 
public:
    static constexpr int SHORTTXIDS_LENGTH = 6;
 
    CBlockHeader header;
 
    CBlockHeaderAndShortTxIDs() = default;
 
    explicit CBlockHeaderAndShortTxIDs(const CBlock &block,
                                       const uint64_t nonce);
 
    uint64_t GetShortID(const TxHash &txhash) const;
 
    size_t BlockTxCount() const {
        return shorttxids.size() + prefilledtxn.size();
    }
 
    SERIALIZE_METHODS(CBlockHeaderAndShortTxIDs, obj) {
        READWRITE(
            obj.header, obj.nonce,
            Using<VectorFormatter<CustomUintFormatter<SHORTTXIDS_LENGTH>>>(
                obj.shorttxids),
            Using<VectorFormatter<DifferentialIndexedItemFormatter>>(
                obj.prefilledtxn));
 
        if (ser_action.ForRead()) {
            if (obj.prefilledtxn.size() > 0) {
                // Thanks to the DifferenceFormatter, the index values in the
                // deserialized prefilled txs are absolute and sorted, so the
                // last vector item has the highest index value.
                uint64_t highestPrefilledIndex = obj.prefilledtxn.back().index;
 
                // Make sure the indexes do not overflow 32 bits.
                if (highestPrefilledIndex + obj.shorttxids.size() >
                    std::numeric_limits<uint32_t>::max()) {
                    throw std::ios_base::failure("indexes overflowed 32 bits");
                }
 
                // Make sure the indexes are contiguous. E.g. if there is no
                // shortid but 2 prefilled txs with absolute indexes 0 and 2,
                // then the tx at index 1 cannot be recovered.
                if (highestPrefilledIndex >= obj.BlockTxCount()) {
                    throw std::ios_base::failure("non contiguous indexes");
                }
            }
 
            // Always derive SipHash keys on the read path, including when
            // prefilledtxn is empty (shorttxids-only compact blocks).
            obj.FillShortTxIDSelector();
        }
    }
};
 
class PartiallyDownloadedBlock {
    struct CTransactionRefCompare {
        bool operator()(const CTransactionRef &lhs,
                        const CTransactionRef &rhs) const {
            return lhs->GetHash() == rhs->GetHash();
        }
    };
 
    using TransactionShortIdProcessor =
        ShortIdProcessor<PrefilledTransaction,
                         ShortIdProcessorPrefilledTransactionAdapter,
                         CTransactionRefCompare>;
 
    // FIXME This better fits a unique_ptr, but the unit tests needs a copy
    // operator for this class. It can be trivially changed when the unit tests
    // are refactored.
    std::shared_ptr<TransactionShortIdProcessor> shortidProcessor;
 
protected:
    size_t prefilled_count = 0, mempool_count = 0, extra_count = 0;
    const CTxMemPool *pool;
    const Config *config;
 
public:
    CBlockHeader header;
    PartiallyDownloadedBlock(const Config &configIn, CTxMemPool *poolIn)
        : pool(poolIn), config(&configIn) {}
 
    // extra_txn is a list of extra orphan/conflicted/etc transactions to look
    // at
    ReadStatus InitData(const CBlockHeaderAndShortTxIDs &cmpctblock,
                        const std::vector<CTransactionRef> &extra_txn);
    bool IsTxAvailable(size_t index) const;
    ReadStatus FillBlock(CBlock &block,
                         const std::vector<CTransactionRef> &vtx_missing);
};
 
#endif // BITCOIN_BLOCKENCODINGS_H