src/compressor.h

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2016 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 "primitives/transaction.h"
  10 #include "script/script.h"
  11 #include "serialize.h"
  12
  13 class CKeyID;
  14 class CPubKey;
  15 class CScriptID;
  16
  17 /** Compact serializer for scripts.
  18  *
  19  *  It detects common cases and encodes them much more efficiently.
  20  *  3 special cases are defined:
  21  *  * Pay to pubkey hash (encoded as 21 bytes)
  22  *  * Pay to script hash (encoded as 21 bytes)
  23  *  * Pay to pubkey starting with 0x02, 0x03 or 0x04 (encoded as 33 bytes)
  24  *
  25  *  Other scripts up to 121 bytes require 1 byte + script length. Above
  26  *  that, scripts up to 16505 bytes require 2 bytes + script length.
  27  */
  28 class CScriptCompressor
  29 {
  30 private:
  31     /**
  32      * make this static for now (there are only 6 special scripts defined)
  33      * this can potentially be extended together with a new nVersion for
  34      * transactions, in which case this value becomes dependent on nVersion
  35      * and nHeight of the enclosing transaction.
  36      */
  37     static const unsigned int nSpecialScripts = 6;
  38
  39     CScript &script;
  40 protected:
  41     /**
  42      * These check for scripts for which a special case with a shorter encoding is defined.
  43      * They are implemented separately from the CScript test, as these test for exact byte
  44      * sequence correspondences, and are more strict. For example, IsToPubKey also verifies
  45      * whether the public key is valid (as invalid ones cannot be represented in compressed
  46      * form).
  47      */
  48     bool IsToKeyID(CKeyID &hash) const;
  49     bool IsToScriptID(CScriptID &hash) const;
  50     bool IsToPubKey(CPubKey &pubkey) const;
  51
  52     bool Compress(std::vector<unsigned char> &out) const;
  53     unsigned int GetSpecialSize(unsigned int nSize) const;
  54     bool Decompress(unsigned int nSize, const std::vector<unsigned char> &out);
  55 public:
  56     CScriptCompressor(CScript &scriptIn) : script(scriptIn) { }
  57
  58     template<typename Stream>
  59     void Serialize(Stream &s) const {
  60         std::vector<unsigned char> compr;
  61         if (Compress(compr)) {
  62             s << CFlatData(compr);
  63             return;
  64         }
  65         unsigned int nSize = script.size() + nSpecialScripts;
  66         s << VARINT(nSize);
  67         s << CFlatData(script);
  68     }
  69
  70     template<typename Stream>
  71     void Unserialize(Stream &s) {
  72         unsigned int nSize = 0;
  73         s >> VARINT(nSize);
  74         if (nSize < nSpecialScripts) {
  75             std::vector<unsigned char> vch(GetSpecialSize(nSize), 0x00);
  76             s >> REF(CFlatData(vch));
  77             Decompress(nSize, vch);
  78             return;
  79         }
  80         nSize -= nSpecialScripts;
  81         if (nSize > MAX_SCRIPT_SIZE) {
  82             // Overly long script, replace with a short invalid one
  83             script << OP_RETURN;
  84             s.ignore(nSize);
  85         } else {
  86             script.resize(nSize);
  87             s >> REF(CFlatData(script));
  88         }
  89     }
  90 };
  91
  92 /** wrapper for CTxOut that provides a more compact serialization */
  93 class CTxOutCompressor
  94 {
  95 private:
  96     CTxOut &txout;
  97
  98 public:
  99     static uint64_t CompressAmount(uint64_t nAmount);
 100     static uint64_t DecompressAmount(uint64_t nAmount);
 101
 102     CTxOutCompressor(CTxOut &txoutIn) : txout(txoutIn) { }
 103
 104     ADD_SERIALIZE_METHODS;
 105
 106     template <typename Stream, typename Operation>
 107     inline void SerializationOp(Stream& s, Operation ser_action) {
 108         if (!ser_action.ForRead()) {
 109             uint64_t nVal = CompressAmount(txout.nValue);
 110             READWRITE(VARINT(nVal));
 111         } else {
 112             uint64_t nVal = 0;
 113             READWRITE(VARINT(nVal));
 114             txout.nValue = DecompressAmount(nVal);
 115         }
 116         CScriptCompressor cscript(REF(txout.scriptPubKey));
 117         READWRITE(cscript);
 118     }
 119 };
 120
 121 #endif // BITCOIN_COMPRESSOR_H