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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 version for
      59                 :             :      * transactions, in which case this value becomes dependent on version
      60                 :             :      * and nHeight of the enclosing transaction.
      61                 :             :      */
      62                 :             :     static const unsigned int nSpecialScripts = 6;
      63                 :             : 
      64                 :             :     template<typename Stream>
      65                 :       26231 :     void Ser(Stream &s, const CScript& script) {
      66                 :       26231 :         CompressedScript compr;
      67   [ +  -  +  + ]:       26231 :         if (CompressScript(script, compr)) {
      68         [ +  - ]:        5967 :             s << Span{compr};
      69                 :             :             return;
      70                 :             :         }
      71   [ +  +  +  - ]:       31514 :         unsigned int nSize = script.size() + nSpecialScripts;
      72   [ +  -  +  + ]:       40528 :         s << VARINT(nSize);
      73         [ +  - ]:       20264 :         s << Span{script};
      74                 :       26231 :     }
      75                 :             : 
      76                 :             :     template<typename Stream>
      77                 :       93814 :     void Unser(Stream &s, CScript& script) {
      78                 :       93814 :         unsigned int nSize = 0;
      79                 :       93814 :         s >> VARINT(nSize);
      80         [ +  + ]:       93814 :         if (nSize < nSpecialScripts) {
      81         [ -  + ]:       12178 :             CompressedScript vch(GetSpecialScriptSize(nSize), 0x00);
      82         [ +  - ]:       12178 :             s >> Span{vch};
      83         [ +  - ]:       12178 :             DecompressScript(script, nSize, vch);
      84                 :             :             return;
      85                 :       12178 :         }
      86                 :       81636 :         nSize -= nSpecialScripts;
      87         [ +  + ]:       81636 :         if (nSize > MAX_SCRIPT_SIZE) {
      88                 :             :             // Overly long script, replace with a short invalid one
      89                 :           1 :             script << OP_RETURN;
      90                 :           1 :             s.ignore(nSize);
      91                 :             :         } else {
      92         [ +  + ]:       81635 :             script.resize(nSize);
      93                 :       81635 :             s >> Span{script};
      94                 :             :         }
      95                 :             :     }
      96                 :             : };
      97                 :             : 
      98                 :             : struct AmountCompression
      99                 :             : {
     100                 :       26231 :     template<typename Stream, typename I> void Ser(Stream& s, I val)
     101                 :             :     {
     102                 :       26231 :         s << VARINT(CompressAmount(val));
     103                 :       26231 :     }
     104                 :       93814 :     template<typename Stream, typename I> void Unser(Stream& s, I& val)
     105                 :             :     {
     106                 :             :         uint64_t v;
     107                 :       93814 :         s >> VARINT(v);
     108                 :       93814 :         val = DecompressAmount(v);
     109                 :       93814 :     }
     110                 :             : };
     111                 :             : 
     112                 :             : /** wrapper for CTxOut that provides a more compact serialization */
     113                 :             : struct TxOutCompression
     114                 :             : {
     115                 :      240090 :     FORMATTER_METHODS(CTxOut, obj) { READWRITE(Using<AmountCompression>(obj.nValue), Using<ScriptCompression>(obj.scriptPubKey)); }
     116                 :             : };
     117                 :             : 
     118                 :             : #endif // BITCOIN_COMPRESSOR_H