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       1                 :            : // Copyright (c) 2009-2010 Satoshi Nakamoto
       2                 :            : // Copyright (c) 2009-2021 The Bitcoin Core developers
       3                 :            : // Distributed under the MIT software license, see the accompanying
       4                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       5                 :            : 
       6                 :            : #ifndef BITCOIN_COMPRESSOR_H
       7                 :            : #define BITCOIN_COMPRESSOR_H
       8                 :            : 
       9                 :            : #include <prevector.h>
      10                 :            : #include <primitives/transaction.h>
      11                 :            : #include <script/script.h>
      12                 :            : #include <serialize.h>
      13                 :            : #include <span.h>
      14                 :            : 
      15                 :            : /**
      16                 :            :  * This saves us from making many heap allocations when serializing
      17                 :            :  * and deserializing compressed scripts.
      18                 :            :  *
      19                 :            :  * This prevector size is determined by the largest .resize() in the
      20                 :            :  * CompressScript function. The largest compressed script format is a
      21                 :            :  * compressed public key, which is 33 bytes.
      22                 :            :  */
      23                 :            : using CompressedScript = prevector<33, unsigned char>;
      24                 :            : 
      25                 :            : 
      26                 :            : bool CompressScript(const CScript& script, CompressedScript& out);
      27                 :            : unsigned int GetSpecialScriptSize(unsigned int nSize);
      28                 :            : bool DecompressScript(CScript& script, unsigned int nSize, const CompressedScript& in);
      29                 :            : 
      30                 :            : /**
      31                 :            :  * Compress amount.
      32                 :            :  *
      33                 :            :  * nAmount is of type uint64_t and thus cannot be negative. If you're passing in
      34                 :            :  * a CAmount (int64_t), make sure to properly handle the case where the amount
      35                 :            :  * is negative before calling CompressAmount(...).
      36                 :            :  *
      37                 :            :  * @pre Function defined only for 0 <= nAmount <= MAX_MONEY.
      38                 :            :  */
      39                 :            : uint64_t CompressAmount(uint64_t nAmount);
      40                 :            : 
      41                 :            : uint64_t DecompressAmount(uint64_t nAmount);
      42                 :            : 
      43                 :            : /** Compact serializer for scripts.
      44                 :            :  *
      45                 :            :  *  It detects common cases and encodes them much more efficiently.
      46                 :            :  *  3 special cases are defined:
      47                 :            :  *  * Pay to pubkey hash (encoded as 21 bytes)
      48                 :            :  *  * Pay to script hash (encoded as 21 bytes)
      49                 :            :  *  * Pay to pubkey starting with 0x02, 0x03 or 0x04 (encoded as 33 bytes)
      50                 :            :  *
      51                 :            :  *  Other scripts up to 121 bytes require 1 byte + script length. Above
      52                 :            :  *  that, scripts up to 16505 bytes require 2 bytes + script length.
      53                 :            :  */
      54                 :            : struct ScriptCompression
      55                 :            : {
      56                 :            :     /**
      57                 :            :      * make this static for now (there are only 6 special scripts defined)
      58                 :            :      * this can potentially be extended together with a new nVersion for
      59                 :            :      * transactions, in which case this value becomes dependent on nVersion
      60                 :            :      * and nHeight of the enclosing transaction.
      61                 :            :      */
      62                 :            :     static const unsigned int nSpecialScripts = 6;
      63                 :            : 
      64                 :            :     template<typename Stream>
      65                 :          0 :     void Ser(Stream &s, const CScript& script) {
      66                 :          0 :         CompressedScript compr;
      67 [ #  # ][ #  # ]:          0 :         if (CompressScript(script, compr)) {
         [ #  # ][ #  # ]
         [ #  # ][ #  # ]
      68 [ #  # ][ #  # ]:          0 :             s << Span{compr};
         [ #  # ][ #  # ]
         [ #  # ][ #  # ]
      69                 :          0 :             return;
      70                 :            :         }
      71 [ #  # ][ #  # ]:          0 :         unsigned int nSize = script.size() + nSpecialScripts;
                 [ #  # ]
      72 [ #  # ][ #  # ]:          0 :         s << VARINT(nSize);
         [ #  # ][ #  # ]
         [ #  # ][ #  # ]
      73 [ #  # ][ #  # ]:          0 :         s << Span{script};
         [ #  # ][ #  # ]
         [ #  # ][ #  # ]
      74 [ #  # ][ #  # ]:          0 :     }
                 [ #  # ]
      75                 :            : 
      76                 :            :     template<typename Stream>
      77                 :          0 :     void Unser(Stream &s, CScript& script) {
      78                 :          0 :         unsigned int nSize = 0;
      79                 :          0 :         s >> VARINT(nSize);
      80         [ #  # ]:          0 :         if (nSize < nSpecialScripts) {
      81                 :          0 :             CompressedScript vch(GetSpecialScriptSize(nSize), 0x00);
      82 [ #  # ][ #  # ]:          0 :             s >> Span{vch};
      83         [ #  # ]:          0 :             DecompressScript(script, nSize, vch);
      84                 :            :             return;
      85                 :          0 :         }
      86                 :          0 :         nSize -= nSpecialScripts;
      87         [ #  # ]:          0 :         if (nSize > MAX_SCRIPT_SIZE) {
      88                 :            :             // Overly long script, replace with a short invalid one
      89                 :          0 :             script << OP_RETURN;
      90                 :          0 :             s.ignore(nSize);
      91                 :          0 :         } else {
      92                 :          0 :             script.resize(nSize);
      93                 :          0 :             s >> Span{script};
      94                 :            :         }
      95                 :          0 :     }
      96                 :            : };
      97                 :            : 
      98                 :            : struct AmountCompression
      99                 :            : {
     100                 :          0 :     template<typename Stream, typename I> void Ser(Stream& s, I val)
     101                 :            :     {
     102                 :          0 :         s << VARINT(CompressAmount(val));
     103                 :          0 :     }
     104                 :          0 :     template<typename Stream, typename I> void Unser(Stream& s, I& val)
     105                 :            :     {
     106                 :            :         uint64_t v;
     107                 :          0 :         s >> VARINT(v);
     108                 :          0 :         val = DecompressAmount(v);
     109                 :          0 :     }
     110                 :            : };
     111                 :            : 
     112                 :            : /** wrapper for CTxOut that provides a more compact serialization */
     113                 :            : struct TxOutCompression
     114                 :            : {
     115                 :          0 :     FORMATTER_METHODS(CTxOut, obj) { READWRITE(Using<AmountCompression>(obj.nValue), Using<ScriptCompression>(obj.scriptPubKey)); }
     116                 :            : };
     117                 :            : 
     118                 :            : #endif // BITCOIN_COMPRESSOR_H