Subtract fee from amount

>>> adapts bitcoin/bitcoin@292623a
         + bitcoin/bitcoin@6171826

Adds the autom-subtract-the-fee-from-the-amount-and-send-whats-left
feature to the RPC (sendtoaddress and fundrawtransaction only for now).

src/rpc/client.cpp

@@ -136,6 +136,7 @@ static const CRPCConvertParam vRPCConvertParams[] = {
     { "sendmany", 2, "minconf" },
     { "sendrawtransaction", 1, "allowhighfees" },
     { "sendtoaddress", 1, "amount" },
+    { "sendtoaddress", 4, "subtract_fee" },
     { "setautocombinethreshold", 0, "enable" },
     { "setautocombinethreshold", 1, "threshold" },
     { "setban", 2, "bantime" },

src/rpc/rawtransaction.cpp

@@ -512,7 +512,13 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
             "     \"changePosition\"    (numeric, optional, default random) The index of the change output\n"
             "     \"includeWatching\"   (boolean, optional, default false) Also select inputs which are watch only\n"
             "     \"lockUnspents\"      (boolean, optional, default false) Lock selected unspent outputs\n"
-                " \"feeRate\"           (numeric, optional, default 0=estimate) Set a specific feerate (PIV per KB)\n"
+            "     \"feeRate\"           (numeric, optional, default 0=estimate) Set a specific feerate (PIV per KB)\n"
+            "     \"subtractFeeFromOutputs\" (array, optional) A json array of integers.\n"
+            "                              The fee will be equally deducted from the amount of each specified output.\n"
+            "                              The outputs are specified by their zero-based index, before any change output is added.\n"
+            "                              Those recipients will receive less PIV than you enter in their corresponding amount field.\n"
+            "                              If no outputs are specified here, the sender pays the fee.\n"
+            "                                  [vout_index,...]\n"
             "   }\n"
             "\nResult:\n"
             "{\n"
@@ -542,6 +548,8 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
     int changePosition = -1;
     bool includeWatching = false;
     bool lockUnspents = false;
+    UniValue subtractFeeFromOutputs;
+    std::set<int> setSubtractFeeFromOutputs;
     CFeeRate feeRate = CFeeRate(0);
     bool overrideEstimatedFeerate = false;
 
@@ -555,6 +563,7 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
                 {"includeWatching", UniValueType(UniValue::VBOOL)},
                 {"lockUnspents", UniValueType(UniValue::VBOOL)},
                 {"feeRate", UniValueType()}, // will be checked below
+                {"subtractFeeFromOutputs", UniValueType(UniValue::VARR)},
             },
             true, true);
 
@@ -578,6 +587,10 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
             feeRate = CFeeRate(AmountFromValue(options["feeRate"]));
             overrideEstimatedFeerate = true;
         }
+
+        if (options.exists("subtractFeeFromOutputs")) {
+            subtractFeeFromOutputs = options["subtractFeeFromOutputs"].get_array();
+        }
     }
 
     // parse hex string from parameter
@@ -591,11 +604,25 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
     if (changePosition != -1 && (changePosition < 0 || (unsigned int) changePosition > origTx.vout.size()))
         throw JSONRPCError(RPC_INVALID_PARAMETER, "changePosition out of bounds");
 
+    for (unsigned int idx = 0; idx < subtractFeeFromOutputs.size(); idx++) {
+        int pos = subtractFeeFromOutputs[idx].get_int();
+        if (setSubtractFeeFromOutputs.count(pos))
+            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, duplicated position: %d", pos));
+        if (pos < 0)
+            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, negative position: %d", pos));
+        if (pos >= int(origTx.vout.size()))
+            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, position too large: %d", pos));
+        setSubtractFeeFromOutputs.insert(pos);
+    }
+
     CMutableTransaction tx(origTx);
     CAmount nFeeOut;
     std::string strFailReason;
-    if(!pwallet->FundTransaction(tx, nFeeOut, overrideEstimatedFeerate, feeRate, changePosition, strFailReason, includeWatching, lockUnspents, changeAddress))
+    if(!pwallet->FundTransaction(tx, nFeeOut, overrideEstimatedFeerate, feeRate,
+                                 changePosition, strFailReason, includeWatching,
+                                 lockUnspents, setSubtractFeeFromOutputs, changeAddress)) {
         throw JSONRPCError(RPC_INTERNAL_ERROR, strFailReason);
+    }
 
     UniValue result(UniValue::VOBJ);
     result.pushKV("hex", EncodeHexTx(tx));

src/rpc/rpcevo.cpp

@@ -224,7 +224,7 @@ static void FundSpecialTx(CWallet* pwallet, CMutableTransaction& tx, SpecialTxPa
     int nChangePos = -1;
     std::string strFailReason;
     std::set<int> setSubtractFeeFromOutputs;
-    if (!pwallet->FundTransaction(tx, nFee, false, feeRate, nChangePos, strFailReason, false, false))
+    if (!pwallet->FundTransaction(tx, nFee, false, feeRate, nChangePos, strFailReason, false, false, {}))
         throw JSONRPCError(RPC_INTERNAL_ERROR, strFailReason);
 
     if (dummyTxOutAdded && tx.vout.size() > 1) {

src/wallet/rpcwallet.cpp

@@ -997,7 +997,7 @@ UniValue setlabel(const JSONRPCRequest& request)
     return NullUniValue;
 }
 
-static void SendMoney(CWallet* const pwallet, const CTxDestination& address, CAmount nValue, CTransactionRef& tx)
+static void SendMoney(CWallet* const pwallet, const CTxDestination& address, CAmount nValue, bool fSubtractFeeFromAmount, CTransactionRef& tx)
 {
     LOCK2(cs_main, pwallet->cs_wallet);
 
@@ -1018,8 +1018,12 @@ static void SendMoney(CWallet* const pwallet, const CTxDestination& address, CAm
     CReserveKey reservekey(pwallet);
     CAmount nFeeRequired;
     std::string strError;
-    if (!pwallet->CreateTransaction(scriptPubKey, nValue, tx, reservekey, nFeeRequired, strError, nullptr, (CAmount)0)) {
-        if (nValue + nFeeRequired > pwallet->GetAvailableBalance())
+    std::vector<CRecipient> vecSend;
+    int nChangePosRet = -1;
+    CRecipient recipient = {scriptPubKey, nValue, fSubtractFeeFromAmount};
+    vecSend.push_back(recipient);
+    if (!pwallet->CreateTransaction(vecSend, tx, reservekey, nFeeRequired, nChangePosRet, strError)) {
+        if (!fSubtractFeeFromAmount && nValue + nFeeRequired > pwallet->GetAvailableBalance())
             strError = strprintf("Error: This transaction requires a transaction fee of at least %s because of its amount, complexity, or use of recently received funds!", FormatMoney(nFeeRequired));
         LogPrintf("%s: %s\n", __func__, strError);
         throw JSONRPCError(RPC_WALLET_ERROR, strError);
@@ -1086,9 +1090,9 @@ UniValue sendtoaddress(const JSONRPCRequest& request)
     if (!EnsureWalletIsAvailable(pwallet, request.fHelp))
         return NullUniValue;
 
-    if (request.fHelp || request.params.size() < 2 || request.params.size() > 4)
+    if (request.fHelp || request.params.size() < 2 || request.params.size() > 5)
         throw std::runtime_error(
-            "sendtoaddress \"address\" amount ( \"comment\" \"comment-to\" )\n"
+            "sendtoaddress \"address\" amount ( \"comment\" \"comment-to\" subtract_fee )\n"
             "\nSend an amount to a given address. The amount is a real and is rounded to the nearest 0.00000001\n" +
             HelpRequiringPassphrase(pwallet) + "\n"
 
@@ -1100,13 +1104,16 @@ UniValue sendtoaddress(const JSONRPCRequest& request)
             "4. \"comment-to\"  (string, optional) A comment to store the name of the person or organization \n"
             "                             to which you're sending the transaction. This is not part of the \n"
             "                             transaction, just kept in your wallet.\n"
+            "5. subtract_fee    (boolean, optional, default=false) The fee will be deducted from the amount being sent.\n"
+            "                             The recipient will receive less bitcoins than you enter in the amount field.\n"
 
             "\nResult:\n"
             "\"transactionid\"  (string) The transaction id.\n"
 
             "\nExamples:\n" +
             HelpExampleCli("sendtoaddress", "\"DMJRSsuU9zfyrvxVaAEFQqK4MxZg6vgeS6\" 0.1") +
             HelpExampleCli("sendtoaddress", "\"DMJRSsuU9zfyrvxVaAEFQqK4MxZg6vgeS6\" 0.1 \"donation\" \"seans outpost\"") +
+            HelpExampleCli("sendtoaddress", "\"DMJRSsuU9zfyrvxVaAEFQqK4MxZg6vgeS6\" 0.1 \"\" \"\" true") +
             HelpExampleRpc("sendtoaddress", "\"DMJRSsuU9zfyrvxVaAEFQqK4MxZg6vgeS6\", 0.1, \"donation\", \"seans outpost\""));
 
     EnsureWalletIsUnlocked(pwallet);
@@ -1124,6 +1131,7 @@ UniValue sendtoaddress(const JSONRPCRequest& request)
                                    request.params[2].get_str() : "";
     const std::string toStr = (request.params.size() > 3 && !request.params[3].isNull()) ?
                                    request.params[3].get_str() : "";
+    bool fSubtractFeeFromAmount = request.params.size() > 4 && request.params[4].get_bool();
 
     if (isShielded) {
         UniValue sendTo(UniValue::VOBJ);
@@ -1137,7 +1145,7 @@ UniValue sendtoaddress(const JSONRPCRequest& request)
     CAmount nAmount = AmountFromValue(request.params[1]);
 
     CTransactionRef tx;
-    SendMoney(pwallet, address, nAmount, tx);
+    SendMoney(pwallet, address, nAmount, fSubtractFeeFromAmount, tx);
 
     // Wallet comments
     CWalletTx& wtx = pwallet->mapWallet.at(tx->GetHash());
@@ -4556,7 +4564,7 @@ static const CRPCCommand commands[] =
     { "wallet",             "lockunspent",              &lockunspent,              true,  {"unlock","transactions"} },
     { "wallet",             "rawdelegatestake",         &rawdelegatestake,         false, {"staking_addr","amount","owner_addr","ext_owner","include_delegated","from_shield","force"} },
     { "wallet",             "sendmany",                 &sendmany,                 false, {"dummy","amounts","minconf","comment","include_delegated"} },
-    { "wallet",             "sendtoaddress",            &sendtoaddress,            false, {"address","amount","comment","comment-to"} },
+    { "wallet",             "sendtoaddress",            &sendtoaddress,            false, {"address","amount","comment","comment-to","subtract_fee"} },
     { "wallet",             "settxfee",                 &settxfee,                 true,  {"amount"} },
     { "wallet",             "setstakesplitthreshold",   &setstakesplitthreshold,   false, {"value"} },
     { "wallet",             "signmessage",              &signmessage,              true,  {"address","message"} },

src/wallet/wallet.cpp

@@ -2937,13 +2937,14 @@ bool CWallet::CreateBudgetFeeTX(CTransactionRef& tx, const uint256& hash, CReser
     return true;
 }
 
-bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, bool overrideEstimatedFeeRate, const CFeeRate& specificFeeRate, int& nChangePosInOut, std::string& strFailReason, bool includeWatching, bool lockUnspents, const CTxDestination& destChange)
+bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, bool overrideEstimatedFeeRate, const CFeeRate& specificFeeRate, int& nChangePosInOut, std::string& strFailReason, bool includeWatching, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, const CTxDestination& destChange)
 {
     std::vector<CRecipient> vecSend;
 
-    // Turn the txout set into a CRecipient vector
-    for (const CTxOut& txOut : tx.vout) {
-        vecSend.emplace_back(txOut.scriptPubKey, txOut.nValue, false);
+    // Turn the txout set into a CRecipient vector.
+    for (size_t idx = 0; idx < tx.vout.size(); idx++) {
+        const CTxOut& txOut = tx.vout[idx];
+        vecSend.emplace_back(txOut.scriptPubKey, txOut.nValue, setSubtractFeeFromOutputs.count(idx) == 1);
     }
 
     CCoinControl coinControl;
@@ -2977,6 +2978,12 @@ bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, bool ov
         reservekey.KeepKey();
     }
 
+    // Copy output sizes from new transaction; they may have had the fee
+    // subtracted from them.
+    for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
+        tx.vout[idx].nValue = wtx->vout[idx].nValue;
+    }
+
     // Add new txins while keeping original txin scriptSig/order.
     for (const CTxIn& txin : wtx->vin) {
         if (!coinControl.IsSelected(txin.prevout)) {
@@ -3003,16 +3010,18 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend,
 {
     CAmount nValue = 0;
     int nChangePosRequest = nChangePosInOut;
-
+    unsigned int nSubtractFeeFromAmount = 0;
     for (const CRecipient& rec : vecSend) {
-        if (rec.nAmount < 0) {
+        if (nValue < 0 || rec.nAmount < 0) {
             strFailReason = _("Transaction amounts must be positive");
             return false;
         }
         nValue += rec.nAmount;
+        if (rec.fSubtractFeeFromAmount)
+            nSubtractFeeFromAmount++;
     }
-    if (vecSend.empty() || nValue < 0) {
-        strFailReason = _("Transaction amounts must be positive");
+    if (vecSend.empty()) {
+        strFailReason = _("Transaction must have at least one recipient");
         return false;
     }
 
@@ -3036,11 +3045,25 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend,
                 nChangePosInOut = nChangePosRequest;
                 txNew.vin.clear();
                 txNew.vout.clear();
-                CAmount nTotalValue = nValue + nFeeRet;
+                bool fFirst = true;
+
+                CAmount nValueToSelect = nValue;
+                if (nSubtractFeeFromAmount == 0)
+                    nValueToSelect += nFeeRet;
 
                 // Fill outputs
                 for (const CRecipient& rec : vecSend) {
                     CTxOut txout(rec.nAmount, rec.scriptPubKey);
+                    if (rec.fSubtractFeeFromAmount) {
+                        assert(nSubtractFeeFromAmount != 0);
+                        txout.nValue -= nFeeRet / nSubtractFeeFromAmount; // Subtract fee equally from each selected recipient
+
+                        if (fFirst) {
+                            // first receiver pays the remainder not divisible by output count
+                            fFirst = false;
+                            txout.nValue -= nFeeRet % nSubtractFeeFromAmount;
+                        }
+                    }
                     if (IsDust(txout, dustRelayFee)) {
                         strFailReason = _("Transaction amount too small");
                         return false;
@@ -3052,13 +3075,13 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend,
                 CAmount nValueIn = 0;
                 setCoins.clear();
 
-                if (!SelectCoinsToSpend(vAvailableCoins, nTotalValue, setCoins, nValueIn, coinControl)) {
+                if (!SelectCoinsToSpend(vAvailableCoins, nValueToSelect, setCoins, nValueIn, coinControl)) {
                     strFailReason = _("Insufficient funds.");
                     return false;
                 }
 
                 // Change
-                CAmount nChange = nValueIn - nValue - nFeeRet;
+                CAmount nChange = nValueIn - nValueToSelect;
                 if (nChange > 0) {
                     // Fill a vout to ourself
                     // TODO: pass in scriptChange instead of reservekey so

src/wallet/wallet.h

@@ -1026,7 +1026,7 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
     CAmount GetUnconfirmedWatchOnlyBalance() const;
     CAmount GetImmatureWatchOnlyBalance() const;
     CAmount GetLegacyBalance(const isminefilter& filter, int minDepth) const;
-    bool FundTransaction(CMutableTransaction& tx, CAmount &nFeeRet, bool overrideEstimatedFeeRate, const CFeeRate& specificFeeRate, int& nChangePosInOut, std::string& strFailReason, bool includeWatching, bool lockUnspents, const CTxDestination& destChange = CNoDestination());
+    bool FundTransaction(CMutableTransaction& tx, CAmount &nFeeRet, bool overrideEstimatedFeeRate, const CFeeRate& specificFeeRate, int& nChangePosInOut, std::string& strFailReason, bool includeWatching, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, const CTxDestination& destChange = CNoDestination());
     /**
      * Create a new transaction paying the recipients with a set of coins
      * selected by SelectCoins(); Also create the change output, when needed

test/functional/wallet_basic.py

@@ -138,10 +138,11 @@ def run_test(self):
         assert_equal(node_2_bal, node_2_expected_bal)
 
         # Send 10 PIV normal
+        self.log.info("test sendtoaddress")
         address = self.nodes[0].getnewaddress("test")
         self.nodes[2].settxfee(float(fee_per_kbyte))
         txid = self.nodes[2].sendtoaddress(address, 10, "", "")
-        fee = self.nodes[2].gettransaction(txid)["fee"]
+        fee = self.nodes[2].gettransaction(txid)["fee"]     # fee < 0
         node_2_bal -= (Decimal('10') - fee)
         assert_equal(self.nodes[2].getbalance(), node_2_bal)
         self.nodes[2].generate(1)
@@ -150,6 +151,7 @@ def run_test(self):
         assert_equal(node_0_bal, Decimal('10'))
 
         # Sendmany 10 PIV
+        self.log.info("test sendmany")
         txid = self.nodes[2].sendmany('', {address: 10}, 0, "")
         fee = self.nodes[2].gettransaction(txid)["fee"]
         self.nodes[2].generate(1)
@@ -160,9 +162,6 @@ def run_test(self):
         assert_equal(self.nodes[0].getbalance(), node_0_bal)
         assert_fee_amount(-fee, self.get_vsize(self.nodes[2].getrawtransaction(txid)), fee_per_kbyte)
 
-        # This will raise an exception since generate does not accept a string
-        assert_raises_rpc_error(-1, "not an integer", self.nodes[0].generate, "2")
-
         # Import address and private key to check correct behavior of spendable unspents
         # 1. Send some coins to generate new UTXO
         address_to_import = self.nodes[2].getnewaddress()
@@ -171,6 +170,7 @@ def run_test(self):
         self.sync_all(self.nodes[0:3])
 
         # 2. Import address from node2 to node1
+        self.log.info("test importaddress")
         self.nodes[1].importaddress(address_to_import)
 
         # 3. Validate that the imported address is watch-only on node1
@@ -184,6 +184,7 @@ def run_test(self):
 
         # 5. Import private key of the previously imported address on node1
         priv_key = self.nodes[2].dumpprivkey(address_to_import)
+        self.log.info("test importprivkey")
         self.nodes[1].importprivkey(priv_key)
 
         # 6. Check that the unspents are now spendable on node1
@@ -258,7 +259,5 @@ def run_test(self):
         assert_equal(9, self.len_listunspent({"minimumSumAmount": 2500.00}))
 
 
-
-
 if __name__ == '__main__':
     WalletTest().main()

test/functional/wallet_listtransactions.py

@@ -10,6 +10,7 @@
 from test_framework.test_framework import PivxTestFramework
 from test_framework.util import (
     assert_array_result,
+    assert_equal,
     hex_str_to_bytes,
 )
 
@@ -94,6 +95,26 @@ def run_test(self):
         txs = [tx for tx in self.nodes[0].listtransactions("*", 100, 0, True) if "label" in tx and tx['label'] == 'watchonly']
         assert_array_result(txs, {"category": "receive", "amount": Decimal("0.1")}, {"txid": txid})
 
+        node_0_bal = self.nodes[0].getbalance()
+        node_1_bal = self.nodes[1].getbalance()
+
+        # Send 10 PIV with subtract fee from amount
+        self.log.info("test sendtoaddress with subtract-fee-from-amt")
+        txid = self.nodes[0].sendtoaddress(self.nodes[1].getnewaddress(), 10, "", "", True)
+        node_0_bal -= Decimal('10')
+        assert_equal(self.nodes[0].getbalance(), node_0_bal)
+        self.nodes[0].generate(1)
+        self.sync_all()
+        fee = self.nodes[0].gettransaction(txid)["fee"]     # fee < 0
+        node_1_bal += (Decimal('10') + fee)
+        assert_equal(self.nodes[1].getbalance(), node_1_bal)
+        assert_array_result(self.nodes[0].listtransactions(),
+                           {"txid": txid},
+                           {"category": "send", "amount": - Decimal('10') - fee, "confirmations": 1})
+        assert_array_result(self.nodes[1].listtransactions(),
+                           {"txid": txid},
+                           {"category": "receive", "amount": + Decimal('10') + fee, "confirmations": 1})
+
 
 if __name__ == '__main__':
     ListTransactionsTest().main()