src/script/script.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_SCRIPT_SCRIPT_H
   7 #define BITCOIN_SCRIPT_SCRIPT_H
   8
   9 #include "crypto/common.h"
  10 #include "prevector.h"
  11 #include "serialize.h"
  12
  13 #include <assert.h>
  14 #include <climits>
  15 #include <limits>
  16 #include <stdexcept>
  17 #include <stdint.h>
  18 #include <string.h>
  19 #include <string>
  20 #include <vector>
  21
  22 // Maximum number of bytes pushable to the stack
  23 static const unsigned int MAX_SCRIPT_ELEMENT_SIZE = 520;
  24
  25 // Maximum number of non-push operations per script
  26 static const int MAX_OPS_PER_SCRIPT = 201;
  27
  28 // Maximum number of public keys per multisig
  29 static const int MAX_PUBKEYS_PER_MULTISIG = 20;
  30
  31 // Maximum script length in bytes
  32 static const int MAX_SCRIPT_SIZE = 10000;
  33
  34 // Maximum number of values on script interpreter stack
  35 static const int MAX_STACK_SIZE = 1000;
  36
  37 // Threshold for nLockTime: below this value it is interpreted as block number,
  38 // otherwise as UNIX timestamp.
  39 static const unsigned int LOCKTIME_THRESHOLD = 500000000; // Tue Nov  5 00:53:20 1985 UTC
  40
  41 template <typename T>
  42 std::vector<unsigned char> ToByteVector(const T& in)
  43 {
  44     return std::vector<unsigned char>(in.begin(), in.end());
  45 }
  46
  47 /** Script opcodes */
  48 enum opcodetype
  49 {
  50     // push value
  51     OP_0 = 0x00,
  52     OP_FALSE = OP_0,
  53     OP_PUSHDATA1 = 0x4c,
  54     OP_PUSHDATA2 = 0x4d,
  55     OP_PUSHDATA4 = 0x4e,
  56     OP_1NEGATE = 0x4f,
  57     OP_RESERVED = 0x50,
  58     OP_1 = 0x51,
  59     OP_TRUE=OP_1,
  60     OP_2 = 0x52,
  61     OP_3 = 0x53,
  62     OP_4 = 0x54,
  63     OP_5 = 0x55,
  64     OP_6 = 0x56,
  65     OP_7 = 0x57,
  66     OP_8 = 0x58,
  67     OP_9 = 0x59,
  68     OP_10 = 0x5a,
  69     OP_11 = 0x5b,
  70     OP_12 = 0x5c,
  71     OP_13 = 0x5d,
  72     OP_14 = 0x5e,
  73     OP_15 = 0x5f,
  74     OP_16 = 0x60,
  75
  76     // control
  77     OP_NOP = 0x61,
  78     OP_VER = 0x62,
  79     OP_IF = 0x63,
  80     OP_NOTIF = 0x64,
  81     OP_VERIF = 0x65,
  82     OP_VERNOTIF = 0x66,
  83     OP_ELSE = 0x67,
  84     OP_ENDIF = 0x68,
  85     OP_VERIFY = 0x69,
  86     OP_RETURN = 0x6a,
  87
  88     // stack ops
  89     OP_TOALTSTACK = 0x6b,
  90     OP_FROMALTSTACK = 0x6c,
  91     OP_2DROP = 0x6d,
  92     OP_2DUP = 0x6e,
  93     OP_3DUP = 0x6f,
  94     OP_2OVER = 0x70,
  95     OP_2ROT = 0x71,
  96     OP_2SWAP = 0x72,
  97     OP_IFDUP = 0x73,
  98     OP_DEPTH = 0x74,
  99     OP_DROP = 0x75,
 100     OP_DUP = 0x76,
 101     OP_NIP = 0x77,
 102     OP_OVER = 0x78,
 103     OP_PICK = 0x79,
 104     OP_ROLL = 0x7a,
 105     OP_ROT = 0x7b,
 106     OP_SWAP = 0x7c,
 107     OP_TUCK = 0x7d,
 108
 109     // splice ops
 110     OP_CAT = 0x7e,
 111     OP_SUBSTR = 0x7f,
 112     OP_LEFT = 0x80,
 113     OP_RIGHT = 0x81,
 114     OP_SIZE = 0x82,
 115
 116     // bit logic
 117     OP_INVERT = 0x83,
 118     OP_AND = 0x84,
 119     OP_OR = 0x85,
 120     OP_XOR = 0x86,
 121     OP_EQUAL = 0x87,
 122     OP_EQUALVERIFY = 0x88,
 123     OP_RESERVED1 = 0x89,
 124     OP_RESERVED2 = 0x8a,
 125
 126     // numeric
 127     OP_1ADD = 0x8b,
 128     OP_1SUB = 0x8c,
 129     OP_2MUL = 0x8d,
 130     OP_2DIV = 0x8e,
 131     OP_NEGATE = 0x8f,
 132     OP_ABS = 0x90,
 133     OP_NOT = 0x91,
 134     OP_0NOTEQUAL = 0x92,
 135
 136     OP_ADD = 0x93,
 137     OP_SUB = 0x94,
 138     OP_MUL = 0x95,
 139     OP_DIV = 0x96,
 140     OP_MOD = 0x97,
 141     OP_LSHIFT = 0x98,
 142     OP_RSHIFT = 0x99,
 143
 144     OP_BOOLAND = 0x9a,
 145     OP_BOOLOR = 0x9b,
 146     OP_NUMEQUAL = 0x9c,
 147     OP_NUMEQUALVERIFY = 0x9d,
 148     OP_NUMNOTEQUAL = 0x9e,
 149     OP_LESSTHAN = 0x9f,
 150     OP_GREATERTHAN = 0xa0,
 151     OP_LESSTHANOREQUAL = 0xa1,
 152     OP_GREATERTHANOREQUAL = 0xa2,
 153     OP_MIN = 0xa3,
 154     OP_MAX = 0xa4,
 155
 156     OP_WITHIN = 0xa5,
 157
 158     // crypto
 159     OP_RIPEMD160 = 0xa6,
 160     OP_SHA1 = 0xa7,
 161     OP_SHA256 = 0xa8,
 162     OP_HASH160 = 0xa9,
 163     OP_HASH256 = 0xaa,
 164     OP_CODESEPARATOR = 0xab,
 165     OP_CHECKSIG = 0xac,
 166     OP_CHECKSIGVERIFY = 0xad,
 167     OP_CHECKMULTISIG = 0xae,
 168     OP_CHECKMULTISIGVERIFY = 0xaf,
 169
 170     // expansion
 171     OP_NOP1 = 0xb0,
 172     OP_CHECKLOCKTIMEVERIFY = 0xb1,
 173     OP_NOP2 = OP_CHECKLOCKTIMEVERIFY,
 174     OP_CHECKSEQUENCEVERIFY = 0xb2,
 175     OP_NOP3 = OP_CHECKSEQUENCEVERIFY,
 176     OP_NOP4 = 0xb3,
 177     OP_NOP5 = 0xb4,
 178     OP_NOP6 = 0xb5,
 179     OP_NOP7 = 0xb6,
 180     OP_NOP8 = 0xb7,
 181     OP_NOP9 = 0xb8,
 182     OP_NOP10 = 0xb9,
 183
 184
 185     // template matching params
 186     OP_SMALLINTEGER = 0xfa,
 187     OP_PUBKEYS = 0xfb,
 188     OP_PUBKEYHASH = 0xfd,
 189     OP_PUBKEY = 0xfe,
 190
 191     OP_INVALIDOPCODE = 0xff,
 192 };
 193
 194 // Maximum value that an opcode can be
 195 static const unsigned int MAX_OPCODE = OP_NOP10;
 196
 197 const char* GetOpName(opcodetype opcode);
 198
 199 class scriptnum_error : public std::runtime_error
 200 {
 201 public:
 202     explicit scriptnum_error(const std::string& str) : std::runtime_error(str) {}
 203 };
 204
 205 class CScriptNum
 206 {
 207 /**
 208  * Numeric opcodes (OP_1ADD, etc) are restricted to operating on 4-byte integers.
 209  * The semantics are subtle, though: operands must be in the range [-2^31 +1...2^31 -1],
 210  * but results may overflow (and are valid as long as they are not used in a subsequent
 211  * numeric operation). CScriptNum enforces those semantics by storing results as
 212  * an int64 and allowing out-of-range values to be returned as a vector of bytes but
 213  * throwing an exception if arithmetic is done or the result is interpreted as an integer.
 214  */
 215 public:
 216
 217     explicit CScriptNum(const int64_t& n)
 218     {
 219         m_value = n;
 220     }
 221
 222     static const size_t nDefaultMaxNumSize = 4;
 223
 224     explicit CScriptNum(const std::vector<unsigned char>& vch, bool fRequireMinimal,
 225                         const size_t nMaxNumSize = nDefaultMaxNumSize)
 226     {
 227         if (vch.size() > nMaxNumSize) {
 228             throw scriptnum_error("script number overflow");
 229         }
 230         if (fRequireMinimal && vch.size() > 0) {
 231             // Check that the number is encoded with the minimum possible
 232             // number of bytes.
 233             //
 234             // If the most-significant-byte - excluding the sign bit - is zero
 235             // then we're not minimal. Note how this test also rejects the
 236             // negative-zero encoding, 0x80.
 237             if ((vch.back() & 0x7f) == 0) {
 238                 // One exception: if there's more than one byte and the most
 239                 // significant bit of the second-most-significant-byte is set
 240                 // it would conflict with the sign bit. An example of this case
 241                 // is +-255, which encode to 0xff00 and 0xff80 respectively.
 242                 // (big-endian).
 243                 if (vch.size() <= 1 || (vch[vch.size() - 2] & 0x80) == 0) {
 244                     throw scriptnum_error("non-minimally encoded script number");
 245                 }
 246             }
 247         }
 248         m_value = set_vch(vch);
 249     }
 250
 251     inline bool operator==(const int64_t& rhs) const    { return m_value == rhs; }
 252     inline bool operator!=(const int64_t& rhs) const    { return m_value != rhs; }
 253     inline bool operator<=(const int64_t& rhs) const    { return m_value <= rhs; }
 254     inline bool operator< (const int64_t& rhs) const    { return m_value <  rhs; }
 255     inline bool operator>=(const int64_t& rhs) const    { return m_value >= rhs; }
 256     inline bool operator> (const int64_t& rhs) const    { return m_value >  rhs; }
 257
 258     inline bool operator==(const CScriptNum& rhs) const { return operator==(rhs.m_value); }
 259     inline bool operator!=(const CScriptNum& rhs) const { return operator!=(rhs.m_value); }
 260     inline bool operator<=(const CScriptNum& rhs) const { return operator<=(rhs.m_value); }
 261     inline bool operator< (const CScriptNum& rhs) const { return operator< (rhs.m_value); }
 262     inline bool operator>=(const CScriptNum& rhs) const { return operator>=(rhs.m_value); }
 263     inline bool operator> (const CScriptNum& rhs) const { return operator> (rhs.m_value); }
 264
 265     inline CScriptNum operator+(   const int64_t& rhs)    const { return CScriptNum(m_value + rhs);}
 266     inline CScriptNum operator-(   const int64_t& rhs)    const { return CScriptNum(m_value - rhs);}
 267     inline CScriptNum operator+(   const CScriptNum& rhs) const { return operator+(rhs.m_value);   }
 268     inline CScriptNum operator-(   const CScriptNum& rhs) const { return operator-(rhs.m_value);   }
 269
 270     inline CScriptNum& operator+=( const CScriptNum& rhs)       { return operator+=(rhs.m_value);  }
 271     inline CScriptNum& operator-=( const CScriptNum& rhs)       { return operator-=(rhs.m_value);  }
 272
 273     inline CScriptNum operator&(   const int64_t& rhs)    const { return CScriptNum(m_value & rhs);}
 274     inline CScriptNum operator&(   const CScriptNum& rhs) const { return operator&(rhs.m_value);   }
 275
 276     inline CScriptNum& operator&=( const CScriptNum& rhs)       { return operator&=(rhs.m_value);  }
 277
 278     inline CScriptNum operator-()                         const
 279     {
 280         assert(m_value != std::numeric_limits<int64_t>::min());
 281         return CScriptNum(-m_value);
 282     }
 283
 284     inline CScriptNum& operator=( const int64_t& rhs)
 285     {
 286         m_value = rhs;
 287         return *this;
 288     }
 289
 290     inline CScriptNum& operator+=( const int64_t& rhs)
 291     {
 292         assert(rhs == 0 || (rhs > 0 && m_value <= std::numeric_limits<int64_t>::max() - rhs) ||
 293                            (rhs < 0 && m_value >= std::numeric_limits<int64_t>::min() - rhs));
 294         m_value += rhs;
 295         return *this;
 296     }
 297
 298     inline CScriptNum& operator-=( const int64_t& rhs)
 299     {
 300         assert(rhs == 0 || (rhs > 0 && m_value >= std::numeric_limits<int64_t>::min() + rhs) ||
 301                            (rhs < 0 && m_value <= std::numeric_limits<int64_t>::max() + rhs));
 302         m_value -= rhs;
 303         return *this;
 304     }
 305
 306     inline CScriptNum& operator&=( const int64_t& rhs)
 307     {
 308         m_value &= rhs;
 309         return *this;
 310     }
 311
 312     int getint() const
 313     {
 314         if (m_value > std::numeric_limits<int>::max())
 315             return std::numeric_limits<int>::max();
 316         else if (m_value < std::numeric_limits<int>::min())
 317             return std::numeric_limits<int>::min();
 318         return m_value;
 319     }
 320
 321     std::vector<unsigned char> getvch() const
 322     {
 323         return serialize(m_value);
 324     }
 325
 326     static std::vector<unsigned char> serialize(const int64_t& value)
 327     {
 328         if(value == 0)
 329             return std::vector<unsigned char>();
 330
 331         std::vector<unsigned char> result;
 332         const bool neg = value < 0;
 333         uint64_t absvalue = neg ? -value : value;
 334
 335         while(absvalue)
 336         {
 337             result.push_back(absvalue & 0xff);
 338             absvalue >>= 8;
 339         }
 340
 341 //    - If the most significant byte is >= 0x80 and the value is positive, push a
 342 //    new zero-byte to make the significant byte < 0x80 again.
 343
 344 //    - If the most significant byte is >= 0x80 and the value is negative, push a
 345 //    new 0x80 byte that will be popped off when converting to an integral.
 346
 347 //    - If the most significant byte is < 0x80 and the value is negative, add
 348 //    0x80 to it, since it will be subtracted and interpreted as a negative when
 349 //    converting to an integral.
 350
 351         if (result.back() & 0x80)
 352             result.push_back(neg ? 0x80 : 0);
 353         else if (neg)
 354             result.back() |= 0x80;
 355
 356         return result;
 357     }
 358
 359 private:
 360     static int64_t set_vch(const std::vector<unsigned char>& vch)
 361     {
 362       if (vch.empty())
 363           return 0;
 364
 365       int64_t result = 0;
 366       for (size_t i = 0; i != vch.size(); ++i)
 367           result |= static_cast<int64_t>(vch[i]) << 8*i;
 368
 369       // If the input vector's most significant byte is 0x80, remove it from
 370       // the result's msb and return a negative.
 371       if (vch.back() & 0x80)
 372           return -((int64_t)(result & ~(0x80ULL << (8 * (vch.size() - 1)))));
 373
 374       return result;
 375     }
 376
 377     int64_t m_value;
 378 };
 379
 380 typedef prevector<28, unsigned char> CScriptBase;
 381
 382 /** Serialized script, used inside transaction inputs and outputs */
 383 class CScript : public CScriptBase
 384 {
 385 protected:
 386     CScript& push_int64(int64_t n)
 387     {
 388         if (n == -1 || (n >= 1 && n <= 16))
 389         {
 390             push_back(n + (OP_1 - 1));
 391         }
 392         else if (n == 0)
 393         {
 394             push_back(OP_0);
 395         }
 396         else
 397         {
 398             *this << CScriptNum::serialize(n);
 399         }
 400         return *this;
 401     }
 402 public:
 403     CScript() { }
 404     CScript(const_iterator pbegin, const_iterator pend) : CScriptBase(pbegin, pend) { }
 405     CScript(std::vector<unsigned char>::const_iterator pbegin, std::vector<unsigned char>::const_iterator pend) : CScriptBase(pbegin, pend) { }
 406     CScript(const unsigned char* pbegin, const unsigned char* pend) : CScriptBase(pbegin, pend) { }
 407
 408     ADD_SERIALIZE_METHODS;
 409
 410     template <typename Stream, typename Operation>
 411     inline void SerializationOp(Stream& s, Operation ser_action) {
 412         READWRITE(static_cast<CScriptBase&>(*this));
 413     }
 414
 415     CScript& operator+=(const CScript& b)
 416     {
 417         insert(end(), b.begin(), b.end());
 418         return *this;
 419     }
 420
 421     friend CScript operator+(const CScript& a, const CScript& b)
 422     {
 423         CScript ret = a;
 424         ret += b;
 425         return ret;
 426     }
 427
 428     CScript(int64_t b)        { operator<<(b); }
 429
 430     explicit CScript(opcodetype b)     { operator<<(b); }
 431     explicit CScript(const CScriptNum& b) { operator<<(b); }
 432     explicit CScript(const std::vector<unsigned char>& b) { operator<<(b); }
 433
 434
 435     CScript& operator<<(int64_t b) { return push_int64(b); }
 436
 437     CScript& operator<<(opcodetype opcode)
 438     {
 439         if (opcode < 0 || opcode > 0xff)
 440             throw std::runtime_error("CScript::operator<<(): invalid opcode");
 441         insert(end(), (unsigned char)opcode);
 442         return *this;
 443     }
 444
 445     CScript& operator<<(const CScriptNum& b)
 446     {
 447         *this << b.getvch();
 448         return *this;
 449     }
 450
 451     CScript& operator<<(const std::vector<unsigned char>& b)
 452     {
 453         if (b.size() < OP_PUSHDATA1)
 454         {
 455             insert(end(), (unsigned char)b.size());
 456         }
 457         else if (b.size() <= 0xff)
 458         {
 459             insert(end(), OP_PUSHDATA1);
 460             insert(end(), (unsigned char)b.size());
 461         }
 462         else if (b.size() <= 0xffff)
 463         {
 464             insert(end(), OP_PUSHDATA2);
 465             uint8_t _data[2];
 466             WriteLE16(_data, b.size());
 467             insert(end(), _data, _data + sizeof(_data));
 468         }
 469         else
 470         {
 471             insert(end(), OP_PUSHDATA4);
 472             uint8_t _data[4];
 473             WriteLE32(_data, b.size());
 474             insert(end(), _data, _data + sizeof(_data));
 475         }
 476         insert(end(), b.begin(), b.end());
 477         return *this;
 478     }
 479
 480     CScript& operator<<(const CScript& b)
 481     {
 482         // I'm not sure if this should push the script or concatenate scripts.
 483         // If there's ever a use for pushing a script onto a script, delete this member fn
 484         assert(!"Warning: Pushing a CScript onto a CScript with << is probably not intended, use + to concatenate!");
 485         return *this;
 486     }
 487
 488
 489     bool GetOp(iterator& pc, opcodetype& opcodeRet, std::vector<unsigned char>& vchRet)
 490     {
 491          // Wrapper so it can be called with either iterator or const_iterator
 492          const_iterator pc2 = pc;
 493          bool fRet = GetOp2(pc2, opcodeRet, &vchRet);
 494          pc = begin() + (pc2 - begin());
 495          return fRet;
 496     }
 497
 498     bool GetOp(iterator& pc, opcodetype& opcodeRet)
 499     {
 500          const_iterator pc2 = pc;
 501          bool fRet = GetOp2(pc2, opcodeRet, nullptr);
 502          pc = begin() + (pc2 - begin());
 503          return fRet;
 504     }
 505
 506     bool GetOp(const_iterator& pc, opcodetype& opcodeRet, std::vector<unsigned char>& vchRet) const
 507     {
 508         return GetOp2(pc, opcodeRet, &vchRet);
 509     }
 510
 511     bool GetOp(const_iterator& pc, opcodetype& opcodeRet) const
 512     {
 513         return GetOp2(pc, opcodeRet, nullptr);
 514     }
 515
 516     bool GetOp2(const_iterator& pc, opcodetype& opcodeRet, std::vector<unsigned char>* pvchRet) const
 517     {
 518         opcodeRet = OP_INVALIDOPCODE;
 519         if (pvchRet)
 520             pvchRet->clear();
 521         if (pc >= end())
 522             return false;
 523
 524         // Read instruction
 525         if (end() - pc < 1)
 526             return false;
 527         unsigned int opcode = *pc++;
 528
 529         // Immediate operand
 530         if (opcode <= OP_PUSHDATA4)
 531         {
 532             unsigned int nSize = 0;
 533             if (opcode < OP_PUSHDATA1)
 534             {
 535                 nSize = opcode;
 536             }
 537             else if (opcode == OP_PUSHDATA1)
 538             {
 539                 if (end() - pc < 1)
 540                     return false;
 541                 nSize = *pc++;
 542             }
 543             else if (opcode == OP_PUSHDATA2)
 544             {
 545                 if (end() - pc < 2)
 546                     return false;
 547                 nSize = ReadLE16(&pc[0]);
 548                 pc += 2;
 549             }
 550             else if (opcode == OP_PUSHDATA4)
 551             {
 552                 if (end() - pc < 4)
 553                     return false;
 554                 nSize = ReadLE32(&pc[0]);
 555                 pc += 4;
 556             }
 557             if (end() - pc < 0 || (unsigned int)(end() - pc) < nSize)
 558                 return false;
 559             if (pvchRet)
 560                 pvchRet->assign(pc, pc + nSize);
 561             pc += nSize;
 562         }
 563
 564         opcodeRet = (opcodetype)opcode;
 565         return true;
 566     }
 567
 568     /** Encode/decode small integers: */
 569     static int DecodeOP_N(opcodetype opcode)
 570     {
 571         if (opcode == OP_0)
 572             return 0;
 573         assert(opcode >= OP_1 && opcode <= OP_16);
 574         return (int)opcode - (int)(OP_1 - 1);
 575     }
 576     static opcodetype EncodeOP_N(int n)
 577     {
 578         assert(n >= 0 && n <= 16);
 579         if (n == 0)
 580             return OP_0;
 581         return (opcodetype)(OP_1+n-1);
 582     }
 583
 584     int FindAndDelete(const CScript& b)
 585     {
 586         int nFound = 0;
 587         if (b.empty())
 588             return nFound;
 589         CScript result;
 590         iterator pc = begin(), pc2 = begin();
 591         opcodetype opcode;
 592         do
 593         {
 594             result.insert(result.end(), pc2, pc);
 595             while (static_cast<size_t>(end() - pc) >= b.size() && std::equal(b.begin(), b.end(), pc))
 596             {
 597                 pc = pc + b.size();
 598                 ++nFound;
 599             }
 600             pc2 = pc;
 601         }
 602         while (GetOp(pc, opcode));
 603
 604         if (nFound > 0) {
 605             result.insert(result.end(), pc2, end());
 606             *this = result;
 607         }
 608
 609         return nFound;
 610     }
 611     int Find(opcodetype op) const
 612     {
 613         int nFound = 0;
 614         opcodetype opcode;
 615         for (const_iterator pc = begin(); pc != end() && GetOp(pc, opcode);)
 616             if (opcode == op)
 617                 ++nFound;
 618         return nFound;
 619     }
 620
 621     /**
 622      * Pre-version-0.6, Bitcoin always counted CHECKMULTISIGs
 623      * as 20 sigops. With pay-to-script-hash, that changed:
 624      * CHECKMULTISIGs serialized in scriptSigs are
 625      * counted more accurately, assuming they are of the form
 626      *  ... OP_N CHECKMULTISIG ...
 627      */
 628     unsigned int GetSigOpCount(bool fAccurate) const;
 629
 630     /**
 631      * Accurately count sigOps, including sigOps in
 632      * pay-to-script-hash transactions:
 633      */
 634     unsigned int GetSigOpCount(const CScript& scriptSig) const;
 635
 636     bool IsPayToScriptHash() const;
 637     bool IsPayToWitnessScriptHash() const;
 638     bool IsWitnessProgram(int& version, std::vector<unsigned char>& program) const;
 639
 640     /** Called by IsStandardTx and P2SH/BIP62 VerifyScript (which makes it consensus-critical). */
 641     bool IsPushOnly(const_iterator pc) const;
 642     bool IsPushOnly() const;
 643
 644     /** Check if the script contains valid OP_CODES */
 645     bool HasValidOps() const;
 646
 647     /**
 648      * Returns whether the script is guaranteed to fail at execution,
 649      * regardless of the initial stack. This allows outputs to be pruned
 650      * instantly when entering the UTXO set.
 651      */
 652     bool IsUnspendable() const
 653     {
 654         return (size() > 0 && *begin() == OP_RETURN) || (size() > MAX_SCRIPT_SIZE);
 655     }
 656
 657     void clear()
 658     {
 659         // The default prevector::clear() does not release memory
 660         CScriptBase::clear();
 661         shrink_to_fit();
 662     }
 663 };
 664
 665 struct CScriptWitness
 666 {
 667     // Note that this encodes the data elements being pushed, rather than
 668     // encoding them as a CScript that pushes them.
 669     std::vector<std::vector<unsigned char> > stack;
 670
 671     // Some compilers complain without a default constructor
 672     CScriptWitness() { }
 673
 674     bool IsNull() const { return stack.empty(); }
 675
 676     void SetNull() { stack.clear(); stack.shrink_to_fit(); }
 677
 678     std::string ToString() const;
 679 };
 680
 681 class CReserveScript
 682 {
 683 public:
 684     CScript reserveScript;
 685     virtual void KeepScript() {}
 686     CReserveScript() {}
 687     virtual ~CReserveScript() {}
 688 };
 689
 690 #endif // BITCOIN_SCRIPT_SCRIPT_H