text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2018 The Bitcoin developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  // NOTE: This file is intended to be customised by the end user, and includes only local node policy logic
  
  #include "policy/policy.h"
  
  #include "validation.h"
  #include "tinyformat.h"
  #include "util.h"
  #include "utilstrencodings.h"
  
  #include <boost/foreach.hpp>
  
      /**
       * Check transaction inputs to mitigate two
       * potential denial-of-service attacks:
       * 
       * 1. scriptSigs with extra data stuffed into them,
       *    not consumed by scriptPubKey (or P2SH script)
       * 2. P2SH scripts with a crazy number of expensive
       *    CHECKSIG/CHECKMULTISIG operations
       *
       * Check transaction inputs, and make sure any
       * pay-to-script-hash transactions are evaluating IsStandard scripts
       * 
       * Why bother? To avoid denial-of-service attacks; an attacker
       * can submit a standard HASH... OP_EQUAL transaction,
       * which will get accepted into blocks. The redemption
       * script can be anything; an attacker could use a very
       * expensive-to-check-upon-redemption script like:
       *   DUP CHECKSIG DROP ... repeated 100 times... OP_1
       */
  
  bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType)
  {
      std::vector<std::vector<unsigned char> > vSolutions;
      if (!Solver(scriptPubKey, whichType, vSolutions))
          return false;
  
      if (whichType == TX_MULTISIG)
      {
          unsigned char m = vSolutions.front()[0];
          unsigned char n = vSolutions.back()[0];
          // Support up to x-of-3 multisig txns as standard
          if (n < 1 || n > 3)
              return false;
          if (m < 1 || m > n)
              return false;
      } else if (whichType == TX_NULL_DATA &&
                 (!fAcceptDatacarrier || scriptPubKey.size() > nMaxDatacarrierBytes))
            return false;
  
      return whichType != TX_NONSTANDARD;
  }
  
  bool IsStandardTx(const CTransaction& tx, std::string& reason)
  {
      if (tx.nVersion > CTransaction::MAX_STANDARD_VERSION || tx.nVersion < 1) {
          reason = "version";
          return false;
      }
  
      // Extremely large transactions with lots of inputs can cost the network
      // almost as much to process as they cost the sender in fees, because
      // computing signature hashes is O(ninputs*txsize). Limiting transactions
      // to MAX_STANDARD_TX_SIZE mitigates CPU exhaustion attacks.
      unsigned int sz = tx.GetSerializeSize(SER_NETWORK, CTransaction::CURRENT_VERSION);
      if (sz >= MAX_STANDARD_TX_SIZE) {
          reason = "tx-size";
          return false;
      }
  
      BOOST_FOREACH(const CTxIn& txin, tx.vin)
      {
          // Biggest 'standard' txin is a 15-of-15 P2SH multisig with compressed
          // keys. (remember the 520 byte limit on redeemScript size) That works
          // out to a (15*(33+1))+3=513 byte redeemScript, 513+1+15*(73+1)+3=1627
          // bytes of scriptSig, which we round off to 1650 bytes for some minor
          // future-proofing. That's also enough to spend a 20-of-20
          // CHECKMULTISIG scriptPubKey, though such a scriptPubKey is not
          // considered standard)
          if (txin.scriptSig.size() > 1650) {
              reason = "scriptsig-size";
              return false;
          }
          if (!txin.scriptSig.IsPushOnly()) {
              reason = "scriptsig-not-pushonly";
              return false;
          }
      }
  
      unsigned int nDataOut = 0;
      txnouttype whichType;
      BOOST_FOREACH(const CTxOut& txout, tx.vout) {
          if (!::IsStandard(txout.scriptPubKey, whichType)) {
              reason = "scriptpubkey";
              return false;
          }
  
          if (whichType == TX_NULL_DATA)
              nDataOut++;
          else if ((whichType == TX_MULTISIG) && (!fIsBareMultisigStd)) {
              reason = "bare-multisig";
              return false;
          } else if (txout.IsDust(::minRelayTxFee)) {
              reason = "dust";
              return false;
          }
      }
  
      // only one OP_RETURN txout is permitted
      if (nDataOut > 1) {
          reason = "multi-op-return";
          return false;
      }
  
      return true;
  }
  
  bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
  {
      if (tx.IsCoinBase())
          return true; // Coinbases don't use vin normally
  
      for (unsigned int i = 0; i < tx.vin.size(); i++)
      {
          const CTxOut& prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;
  
          std::vector<std::vector<unsigned char> > vSolutions;
          txnouttype whichType;
          // get the scriptPubKey corresponding to this input:
          const CScript& prevScript = prev.scriptPubKey;
          if (!Solver(prevScript, whichType, vSolutions))
              return false;
  
          if (whichType == TX_SCRIPTHASH)
          {
              std::vector<std::vector<unsigned char> > stack;
              // convert the scriptSig into a stack, so we can inspect the redeemScript
              if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), 0))
                  return false;
              if (stack.empty())
                  return false;
              CScript subscript(stack.back().begin(), stack.back().end());
              if (subscript.GetSigOpCount(true) > MAX_P2SH_SIGOPS) {
                  return false;
              }
          }
      }
  
      return true;
  }
  