Merge #991: [RPC][Wallet] Create multiple transactions with one command.

a872b41 Create multiple transactions with one command. (Zannick)

Pull request description:

  ## Details

  RPC send commands have a new argument `inputs_per_tx` that controls whether the amount specified can be split across multiple transactions. This value ranges from 0 (default) to 32 (an upper bound designed to prevent transactions larger than can be accepted). When set to 0, attempts to fit the send in one transaction as per previous behavior.

  The sends are interpreted to mean that the recipient will receive the sent amount, but under the hood the transactions are created as if `subtractfeefromamount` was specified. In particular, if the send needs to be split into `n > 1` transactions, the outputs of the first `n - 1` are randomly reduced to account for the fee (and the shortfall from the inputs).

  Coins are selected using a sliding window that prioritizes cleaning up small utxos (dust) over using fewer inputs, and thus transactions built this way will tend toward having more inputs. This is beneficial for ringct staking (keeping larger coins intact and reducing the amount of small utxos). The smallest utxo is always included if possible to prevent the amount of small utxos from increasing with usage.

  ## Tested
  On regtest some months ago.

Tree-SHA512: 8b6b0b7fccdb16507da321c371b8075fdecae5f53ca2fb95a49a8d8edb6104c3c7d26270c0f029a99bf0aff4fe6a15c9e0b0fdfad372ab8166b619ce2ac38f98

src/interfaces/wallet.cpp

@@ -502,12 +502,12 @@ class WalletImpl : public Wallet
                 break;
             }
             case OUTPUT_CT:
-                if (0 != pwalletAnon->AddBlindedInputs(wtx, rtx, recipients, !fCheckFeeOnly, nFeeRet, &coin_control, fail_reason))
+                if (0 != pwalletAnon->AddBlindedInputs(wtx, rtx, recipients, !fCheckFeeOnly, 0, nFeeRet, &coin_control, fail_reason))
                     fFailed = true;
                 break;
             case OUTPUT_RINGCT:
                 if (!pwalletAnon->AddAnonInputs(wtx, rtx, recipients, !fCheckFeeOnly, nRingSize,
-                                                nInputsPerSig, nFeeRet, &coin_control, fail_reason))
+                                                nInputsPerSig, 0, nFeeRet, &coin_control, fail_reason))
                     fFailed = true;
                 break;
             default:

src/veil/ringct/anonwallet.h

@@ -227,9 +227,9 @@ class AnonWallet
             CAmount &nFeeRet, const CCoinControl *coinControl, std::string &sError, bool fZerocoinInputs, CAmount nInputValue);
 
     int AddBlindedInputs(CWalletTx &wtx, CTransactionRecord &rtx, std::vector<CTempRecipient> &vecSend, bool sign,
-            CAmount &nFeeRet, const CCoinControl *coinControl, std::string &sError);
+            size_t nMaximumInputs, CAmount &nFeeRet, const CCoinControl *coinControl, std::string &sError);
     int AddBlindedInputs_Inner(CWalletTx &wtx, CTransactionRecord &rtx, std::vector<CTempRecipient> &vecSend, bool sign,
-            CAmount &nFeeRet, const CCoinControl *coinControl, std::string &sError);
+            size_t nMaximumInputs, CAmount &nFeeRet, const CCoinControl *coinControl, std::string &sError);
 
 
     bool PlaceRealOutputs(std::vector<std::vector<int64_t> > &vMI, size_t &nSecretColumn, size_t nRingSize, std::set<int64_t> &setHave,
@@ -240,10 +240,10 @@ class AnonWallet
 
     bool IsMyAnonInput(const CTxIn& txin, COutPoint& myOutpoint);
     bool AddAnonInputs_Inner(CWalletTx &wtx, CTransactionRecord &rtx, std::vector<CTempRecipient> &vecSend,
-         bool sign, size_t nRingSize, size_t nInputsPerSig, CAmount &nFeeRet,
+         bool sign, size_t nRingSize, size_t nInputsPerSig, size_t nMaximumInputs, CAmount &nFeeRet,
          const CCoinControl *coinControl, std::string &sError, bool fZerocoinInputs, CAmount nInputValue);
     bool AddAnonInputs(CWalletTx &wtx, CTransactionRecord &rtx, std::vector<CTempRecipient> &vecSend,
-         bool sign, size_t nRingSize, size_t nInputsPerSig, CAmount &nFeeRet,
+         bool sign, size_t nRingSize, size_t nInputsPerSig, size_t nMaximumInputs, CAmount &nFeeRet,
          const CCoinControl *coinControl, std::string &sError, bool fZerocoinInputs = false,
          CAmount nInputValue = 0);
 
@@ -322,15 +322,23 @@ class AnonWallet
      * populate vCoins with vector of available COutputs.
      */
     void AvailableBlindedCoins(std::vector<COutputR>& vCoins, bool fOnlySafe=true, const CCoinControl *coinControl = nullptr, const CAmount& nMinimumAmount = 1, const CAmount& nMaximumAmount = MAX_MONEY, const CAmount& nMinimumSumAmount = MAX_MONEY, const uint64_t& nMaximumCount = 0, const int& nMinDepth = 0, const int& nMaxDepth = 0x7FFFFFFF, bool fIncludeImmature=false) const;
-    bool SelectBlindedCoins(const std::vector<COutputR>& vAvailableCoins, const CAmount& nTargetValue, std::vector<std::pair<MapRecords_t::const_iterator,unsigned int> > &setCoinsRet, CAmount &nValueRet, const CCoinControl *coinControl = nullptr) const;
+    /**
+     * Returns a list of coins for a single transaction based on the target value and allowed number of inputs.
+     */
+    bool SelectBlindedCoins(const std::vector<COutputR>& vAvailableCoins, const CAmount& nTargetValue, size_t nMaximumCount, std::vector<std::pair<MapRecords_t::const_iterator,unsigned int> > &setCoinsRet, CAmount &nValueRet, const CCoinControl *coinControl = nullptr) const;
 
     void AvailableAnonCoins(std::vector<COutputR> &vCoins, bool fOnlySafe=true, const CCoinControl *coinControl = nullptr, const CAmount& nMinimumAmount = 1, const CAmount& nMaximumAmount = MAX_MONEY, const CAmount& nMinimumSumAmount = MAX_MONEY, const uint64_t& nMaximumCount = 0, const int& nMinDepth = 0, const int& nMaxDepth = 0x7FFFFFFF, bool fIncludeImmature=false) const;
 
     /**
      * Return list of available coins and locked coins grouped by non-change output address.
      */
 
-    bool SelectCoinsMinConf(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutputR> vCoins, std::vector<std::pair<MapRecords_t::const_iterator,unsigned int> > &setCoinsRet, CAmount &nValueRet) const;
+    bool SelectCoinsMinConf(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutputR> &vCoins, std::vector<std::pair<MapRecords_t::const_iterator,unsigned int> > &setCoinsRet, CAmount &nValueRet) const;
+    /**
+     * Like SelectCoinsMinConf, but always selects at most nMaximumCount coins,
+     * with the intention of being put in a single tx that partially accomplishes the target to be sent.
+     */
+    bool SelectCoinsForOneTx(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutputR> &vCoins, size_t nMaximumCount, std::vector<std::pair<MapRecords_t::const_iterator,unsigned int> > &setCoinsRet, CAmount &nValueRet) const;
 
     bool IsSpent(const uint256& hash, unsigned int n) const EXCLUSIVE_LOCKS_REQUIRED(cs_main);