wallet: feature: transfer amount with fee included

To transfer ~5 XMR to an address such that your balance drops by exactly 5 XMR, provide a `subtractfeefrom` flag to the `transfer` command. For example:

    transfer 76bDHojqFYiFCCYYtzTveJ8oFtmpNp3X1TgV2oKP7rHmZyFK1RvyE4r8vsJzf7SyNohMnbKT9wbcD3XUTgsZLX8LU5JBCfm 5 subtractfeefrom=all

If my walet balance was exactly 30 XMR before this transaction, it will be exactly 25 XMR afterwards and the destination address will receive slightly
less than 5 XMR. You can manually select which destinations fund the transaction fee and which ones do not by providing the destination index.
For example:

    transfer 75sr8AAr... 3 74M7W4eg... 4 7AbWqDZ6... 5 subtractfeefrom=0,2

This will drop your balance by exactly 12 XMR including fees and will spread the fee cost proportionally (3:5 ratio) over destinations with addresses
`75sr8AAr...` and `7AbWqDZ6...`, respectively.

Disclaimer: This feature was paid for by @LocalMonero.

src/simplewallet/simplewallet.cpp

@@ -196,7 +196,7 @@ namespace
   const char* USAGE_INCOMING_TRANSFERS("incoming_transfers [available|unavailable] [verbose] [uses] [index=<N1>[,<N2>[,...]]]");
   const char* USAGE_PAYMENTS("payments <PID_1> [<PID_2> ... <PID_N>]");
   const char* USAGE_PAYMENT_ID("payment_id");
-  const char* USAGE_TRANSFER("transfer [index=<N1>[,<N2>,...]] [<priority>] [<ring_size>] (<URI> | <address> <amount>) [<payment_id>]");
+  const char* USAGE_TRANSFER("transfer [index=<N1>[,<N2>,...]] [<priority>] [<ring_size>] (<URI> | <address> <amount>) [subtractfeefrom=<D0>[,<D1>,all,...]] [<payment_id>]");
   const char* USAGE_LOCKED_TRANSFER("locked_transfer [index=<N1>[,<N2>,...]] [<priority>] [<ring_size>] (<URI> | <addr> <amount>) <lockblocks> [<payment_id (obsolete)>]");
   const char* USAGE_LOCKED_SWEEP_ALL("locked_sweep_all [index=<N1>[,<N2>,...] | index=all] [<priority>] [<ring_size>] <address> <lockblocks> [<payment_id (obsolete)>]");
   const char* USAGE_SWEEP_ALL("sweep_all [index=<N1>[,<N2>,...] | index=all] [<priority>] [<ring_size>] [outputs=<N>] <address> [<payment_id (obsolete)>]");
@@ -531,7 +531,52 @@ namespace
       fail_msg_writer() << sw::tr("invalid format for subaddress lookahead; must be <major>:<minor>");
     return r;
   }
-}
+
+  static constexpr const char* SFFD_ARG_NAME{"subtractfeefrom="};
+
+  bool parse_subtract_fee_from_outputs
+  (
+    const std::string& arg,
+    tools::wallet2::unique_index_container& subtract_fee_from_outputs,
+    bool& subtract_fee_from_all,
+    bool& matches
+  )
+  {
+    matches = false;
+    if (!boost::string_ref{arg}.starts_with(SFFD_ARG_NAME)) // if arg doesn't match
+      return true;
+    matches = true;
+
+    const char* arg_end = arg.c_str() + arg.size();
+    for (const char* p = arg.c_str() + strlen(SFFD_ARG_NAME); p < arg_end;)
+    {
+      const char* new_p = nullptr;
+      const unsigned long dest_index = strtoul(p, const_cast<char**>(&new_p), 10);
+      if (dest_index == 0 && new_p == p) // numerical conversion failed
+      {
+        if (0 != strncmp(p, "all", 3))
+        {
+          fail_msg_writer() << tr("Failed to parse subtractfeefrom list");
+          return false;
+        }
+        subtract_fee_from_all = true;
+        break;
+      }
+      else if (dest_index > std::numeric_limits<uint32_t>::max())
+      {
+        fail_msg_writer() << tr("Destination index is too large") << ": " << dest_index;
+        return false;
+      }
+      else
+      {
+        subtract_fee_from_outputs.insert(dest_index);
+        p = new_p + 1; // skip the comma
+      }
+    }
+
+    return true;
+  }
+} // anonymous namespace
 
 void simple_wallet::handle_transfer_exception(const std::exception_ptr &e, bool trusted_daemon)
 {
@@ -3290,7 +3335,7 @@ simple_wallet::simple_wallet()
                            tr("Show the blockchain height."));
   m_cmd_binder.set_handler("transfer", boost::bind(&simple_wallet::on_command, this, &simple_wallet::transfer, _1),
                            tr(USAGE_TRANSFER),
-                           tr("Transfer <amount> to <address>. If the parameter \"index=<N1>[,<N2>,...]\" is specified, the wallet uses outputs received by addresses of those indices. If omitted, the wallet randomly chooses address indices to be used. In any case, it tries its best not to combine outputs across multiple addresses. <priority> is the priority of the transaction. The higher the priority, the higher the transaction fee. Valid values in priority order (from lowest to highest) are: unimportant, normal, elevated, priority. If omitted, the default value (see the command \"set priority\") is used. <ring_size> is the number of inputs to include for untraceability. Multiple payments can be made at once by adding URI_2 or <address_2> <amount_2> etcetera (before the payment ID, if it's included)"));
+                           tr("Transfer <amount> to <address>. If the parameter \"index=<N1>[,<N2>,...]\" is specified, the wallet uses outputs received by addresses of those indices. If omitted, the wallet randomly chooses address indices to be used. In any case, it tries its best not to combine outputs across multiple addresses. <priority> is the priority of the transaction. The higher the priority, the higher the transaction fee. Valid values in priority order (from lowest to highest) are: unimportant, normal, elevated, priority. If omitted, the default value (see the command \"set priority\") is used. <ring_size> is the number of inputs to include for untraceability. Multiple payments can be made at once by adding URI_2 or <address_2> <amount_2> etcetera (before the payment ID, if it's included). The \"subtractfeefrom=\" list allows you to choose which destinations to fund the tx fee from instead of the change output. The fee will be split across the chosen destinations proportionally equally. For example, to make 3 transfers where the fee is taken from the first and third destinations, one could do: \"transfer <addr1> 3 <addr2> 0.5 <addr3> 1 subtractfeefrom=0,2\". Let's say the tx fee is 0.1. The balance would drop by exactly 4.5 XMR including fees, and addr1 & addr3 would receive 2.925 & 0.975 XMR, respectively. Use \"subtractfeefrom=all\" to spread the fee across all destinations."));
   m_cmd_binder.set_handler("locked_transfer",
                            boost::bind(&simple_wallet::on_command, this, &simple_wallet::locked_transfer,_1),
                            tr(USAGE_LOCKED_TRANSFER),
@@ -6640,6 +6685,27 @@ bool simple_wallet::transfer_main(int transfer_type, const std::vector<std::stri
     local_args.pop_back();
   }
 
+  // Parse subtractfeefrom destination list
+  tools::wallet2::unique_index_container subtract_fee_from_outputs;
+  bool subtract_fee_from_all = false;
+  for (auto it = local_args.begin(); it < local_args.end();)
+  {
+    bool matches = false;
+    if (!parse_subtract_fee_from_outputs(*it, subtract_fee_from_outputs, subtract_fee_from_all, matches))
+    {
+      return false;
+    }
+    else if (matches)
+    {
+      it = local_args.erase(it);
+      break;
+    }
+    else
+    {
+      ++it;
+    }
+  }
+
   vector<cryptonote::address_parse_info> dsts_info;
   vector<cryptonote::tx_destination_entry> dsts;
   for (size_t i = 0; i < local_args.size(); )
@@ -6736,6 +6802,13 @@ bool simple_wallet::transfer_main(int transfer_type, const std::vector<std::stri
     dsts.push_back(de);
   }
 
+  if (subtract_fee_from_all)
+  {
+    subtract_fee_from_outputs.clear();
+    for (decltype(subtract_fee_from_outputs)::value_type i = 0; i < dsts.size(); ++i)
+      subtract_fee_from_outputs.insert(i);
+  }
+
   SCOPED_WALLET_UNLOCK_ON_BAD_PASSWORD(return false;);
 
   try
@@ -6754,13 +6827,13 @@ bool simple_wallet::transfer_main(int transfer_type, const std::vector<std::stri
           return false;
         }
         unlock_block = bc_height + locked_blocks;
-        ptx_vector = m_wallet->create_transactions_2(dsts, fake_outs_count, unlock_block /* unlock_time */, priority, extra, m_current_subaddress_account, subaddr_indices);
+        ptx_vector = m_wallet->create_transactions_2(dsts, fake_outs_count, unlock_block /* unlock_time */, priority, extra, m_current_subaddress_account, subaddr_indices, subtract_fee_from_outputs);
       break;
       default:
         LOG_ERROR("Unknown transfer method, using default");
         /* FALLTHRU */
       case Transfer:
-        ptx_vector = m_wallet->create_transactions_2(dsts, fake_outs_count, 0 /* unlock_time */, priority, extra, m_current_subaddress_account, subaddr_indices);
+        ptx_vector = m_wallet->create_transactions_2(dsts, fake_outs_count, 0 /* unlock_time */, priority, extra, m_current_subaddress_account, subaddr_indices, subtract_fee_from_outputs);
       break;
     }
 

src/wallet/wallet2.cpp

@@ -10523,7 +10523,7 @@ bool wallet2::light_wallet_key_image_is_ours(const crypto::key_image& key_image,
 // This system allows for sending (almost) the entire balance, since it does
 // not generate spurious change in all txes, thus decreasing the instantaneous
 // usable balance.
-std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryptonote::tx_destination_entry> dsts, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices)
+std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryptonote::tx_destination_entry> dsts, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices, const unique_index_container& subtract_fee_from_outputs)
 {
   //ensure device is let in NONE mode in any case
   hw::device &hwdev = m_account.get_device();
@@ -10538,11 +10538,12 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
   }
   std::vector<std::pair<uint32_t, std::vector<size_t>>> unused_transfers_indices_per_subaddr;
   std::vector<std::pair<uint32_t, std::vector<size_t>>> unused_dust_indices_per_subaddr;
-  uint64_t needed_money;
+  uint64_t needed_money, total_needed_money; // 'needed_money' is the sum of the destination amounts, while 'total_needed_money' includes 'needed_money' plus the fee if not 'subtract_fee_from_outputs'
   uint64_t accumulated_fee, accumulated_change;
   struct TX {
     std::vector<size_t> selected_transfers;
     std::vector<cryptonote::tx_destination_entry> dsts;
+    std::vector<bool> dsts_are_fee_subtractable;
     cryptonote::transaction tx;
     pending_tx ptx;
     size_t weight;
@@ -10552,9 +10553,11 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
     TX() : weight(0), needed_fee(0) {}
 
     /* Add an output to the transaction.
+     * If merge_destinations is true, when adding a destination with an existing address, to increment the amount of the existing tx output instead of creating a new one
+     * If subtracting_fee is true, when we generate a final list of destinations for transfer_selected[_rct], this destination will be used to fund the tx fee
      * Returns True if the output was added, False if there are no more available output slots.
      */
-    bool add(const cryptonote::tx_destination_entry &de, uint64_t amount, unsigned int original_output_index, bool merge_destinations, size_t max_dsts) {
+    bool add(const cryptonote::tx_destination_entry &de, uint64_t amount, unsigned int original_output_index, bool merge_destinations, size_t max_dsts, bool subtracting_fee) {
       if (merge_destinations)
       {
         std::vector<cryptonote::tx_destination_entry>::iterator i;
@@ -10564,6 +10567,7 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
           if (dsts.size() >= max_dsts)
             return false;
           dsts.push_back(de);
+          dsts_are_fee_subtractable.push_back(subtracting_fee);
           i = dsts.end() - 1;
           i->amount = 0;
         }
@@ -10579,13 +10583,67 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
             return false;
           dsts.push_back(de);
           dsts.back().amount = 0;
+          dsts_are_fee_subtractable.push_back(subtracting_fee);
         }
         THROW_WALLET_EXCEPTION_IF(memcmp(&dsts[original_output_index].addr, &de.addr, sizeof(de.addr)), error::wallet_internal_error, "Mismatched destination address");
         dsts[original_output_index].amount += amount;
       }
       return true;
     }
+
+    // Returns destinations adjusted for given fee if subtract_fee_from_outputs is enabled
+    std::vector<cryptonote::tx_destination_entry> get_adjusted_dsts(uint64_t needed_fee) const
+    {
+      uint64_t dest_total = 0;
+      uint64_t subtractable_dest_total = 0;
+      std::vector<size_t> subtractable_indices;
+      subtractable_indices.reserve(dsts.size());
+      for (size_t i = 0; i < dsts.size(); ++i)
+      {
+        dest_total += dsts[i].amount;
+        if (dsts_are_fee_subtractable[i])
+        {
+          subtractable_dest_total += dsts[i].amount;
+          subtractable_indices.push_back(i);
+        }
+      }
+
+      if (subtractable_indices.empty()) // if subtract_fee_from_outputs is not enabled for this tx
+        return dsts;
+
+      THROW_WALLET_EXCEPTION_IF(subtractable_dest_total < needed_fee, error::tx_not_possible,
+        subtractable_dest_total, dest_total, needed_fee);
+
+      std::vector<cryptonote::tx_destination_entry> res = dsts;
+
+      // subtract fees from destinations equally, rounded down, until dust is left where we subtract 1
+      uint64_t subtractable_remaining = needed_fee;
+      auto si_it = subtractable_indices.cbegin();
+      uint64_t amount_to_subtract = 0;
+      while (subtractable_remaining)
+      {
+        // Set the amount to subtract iterating at the beginning of the list so equal amounts are
+        // subtracted throughout the list of destinations. We use max(x, 1) so that we we still step
+        // forwards even when the amount remaining is less than the number of subtractable indices
+        if (si_it == subtractable_indices.cbegin())
+          amount_to_subtract = std::max<uint64_t>(subtractable_remaining / subtractable_indices.size(), 1);
+
+        cryptonote::tx_destination_entry& d = res[*si_it];
+        THROW_WALLET_EXCEPTION_IF(d.amount <= amount_to_subtract, error::zero_amount);
+
+        subtractable_remaining -= amount_to_subtract;
+        d.amount -= amount_to_subtract;
+        ++si_it;
+
+        // Wrap around to first subtractable index once we hit the end of the list
+        if (si_it == subtractable_indices.cend())
+          si_it = subtractable_indices.cbegin();
+      }
+
+      return res;
+    }
   };
+
   std::vector<TX> txes;
   bool adding_fee; // true if new outputs go towards fee, rather than destinations
   uint64_t needed_fee, available_for_fee = 0;
@@ -10608,6 +10666,14 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
   // throw if attempting a transaction with no destinations
   THROW_WALLET_EXCEPTION_IF(dsts.empty(), error::zero_destination);
 
+  // throw if subtract_fee_from_outputs has a bad index
+  THROW_WALLET_EXCEPTION_IF(subtract_fee_from_outputs.size() && *subtract_fee_from_outputs.crbegin() >= dsts.size(),
+    error::subtract_fee_from_bad_index, *subtract_fee_from_outputs.crbegin());
+
+  // throw if subtract_fee_from_outputs is enabled and we have too many outputs to fit into one tx
+  THROW_WALLET_EXCEPTION_IF(subtract_fee_from_outputs.size() && dsts.size() > BULLETPROOF_MAX_OUTPUTS - 1,
+    error::wallet_internal_error, "subtractfeefrom transfers cannot be split over multiple transactions yet");
+
   // calculate total amount being sent to all destinations
   // throw if total amount overflows uint64_t
   needed_money = 0;
@@ -10635,6 +10701,7 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
   // we could also check for being within FEE_PER_KB, but if the fee calculation
   // ever changes, this might be missed, so let this go through
   const uint64_t min_fee = (base_fee * estimate_tx_size(use_rct, 1, fake_outs_count, 2, extra.size(), bulletproof, clsag, bulletproof_plus, use_view_tags));
+  total_needed_money = needed_money + (subtract_fee_from_outputs.size() ? 0 : min_fee);
   uint64_t balance_subtotal = 0;
   uint64_t unlocked_balance_subtotal = 0;
   for (uint32_t index_minor : subaddr_indices)
@@ -10642,10 +10709,10 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
     balance_subtotal += balance_per_subaddr[index_minor];
     unlocked_balance_subtotal += unlocked_balance_per_subaddr[index_minor].first;
   }
-  THROW_WALLET_EXCEPTION_IF(needed_money + min_fee > balance_subtotal, error::not_enough_money,
+  THROW_WALLET_EXCEPTION_IF(total_needed_money > balance_subtotal || min_fee > balance_subtotal, error::not_enough_money,
     balance_subtotal, needed_money, 0);
   // first check overall balance is enough, then unlocked one, so we throw distinct exceptions
-  THROW_WALLET_EXCEPTION_IF(needed_money + min_fee > unlocked_balance_subtotal, error::not_enough_unlocked_money,
+  THROW_WALLET_EXCEPTION_IF(total_needed_money > unlocked_balance_subtotal || min_fee > unlocked_balance_subtotal, error::not_enough_unlocked_money,
       unlocked_balance_subtotal, needed_money, 0);
 
   for (uint32_t i : subaddr_indices)
@@ -10748,7 +10815,8 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
     // this is used to build a tx that's 1 or 2 inputs, and 2 outputs, which
     // will get us a known fee.
     uint64_t estimated_fee = estimate_fee(use_per_byte_fee, use_rct, 2, fake_outs_count, 2, extra.size(), bulletproof, clsag, bulletproof_plus, use_view_tags, base_fee, fee_quantization_mask);
-    preferred_inputs = pick_preferred_rct_inputs(needed_money + estimated_fee, subaddr_account, subaddr_indices);
+    total_needed_money = needed_money + (subtract_fee_from_outputs.size() ? 0 : estimated_fee);
+    preferred_inputs = pick_preferred_rct_inputs(total_needed_money, subaddr_account, subaddr_indices);
     if (!preferred_inputs.empty())
     {
       string s;
@@ -10781,7 +10849,7 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
   // - we have something to send
   // - or we need to gather more fee
   // - or we have just one input in that tx, which is rct (to try and make all/most rct txes 2/2)
-  unsigned int original_output_index = 0;
+  unsigned int original_output_index = 0, destination_index = 0;
   std::vector<size_t>* unused_transfers_indices = &unused_transfers_indices_per_subaddr[0].second;
   std::vector<size_t>* unused_dust_indices      = &unused_dust_indices_per_subaddr[0].second;
   
@@ -10864,7 +10932,8 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
         // we can fully pay that destination
         LOG_PRINT_L2("We can fully pay " << get_account_address_as_str(m_nettype, dsts[0].is_subaddress, dsts[0].addr) <<
           " for " << print_money(dsts[0].amount));
-        if (!tx.add(dsts[0], dsts[0].amount, original_output_index, m_merge_destinations, BULLETPROOF_MAX_OUTPUTS-1))
+        const bool subtract_fee_from_this_dest = subtract_fee_from_outputs.count(destination_index);
+        if (!tx.add(dsts[0], dsts[0].amount, original_output_index, m_merge_destinations, BULLETPROOF_MAX_OUTPUTS-1, subtract_fee_from_this_dest))
         {
           LOG_PRINT_L2("Didn't pay: ran out of output slots");
           out_slots_exhausted = true;
@@ -10874,6 +10943,7 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
         dsts[0].amount = 0;
         pop_index(dsts, 0);
         ++original_output_index;
+        ++destination_index;
       }
 
       if (!out_slots_exhausted && available_amount > 0 && !dsts.empty() &&
@@ -10881,7 +10951,8 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
         // we can partially fill that destination
         LOG_PRINT_L2("We can partially pay " << get_account_address_as_str(m_nettype, dsts[0].is_subaddress, dsts[0].addr) <<
           " for " << print_money(available_amount) << "/" << print_money(dsts[0].amount));
-        if (tx.add(dsts[0], available_amount, original_output_index, m_merge_destinations, BULLETPROOF_MAX_OUTPUTS-1))
+        const bool subtract_fee_from_this_dest = subtract_fee_from_outputs.count(destination_index);
+        if (tx.add(dsts[0], available_amount, original_output_index, m_merge_destinations, BULLETPROOF_MAX_OUTPUTS-1, subtract_fee_from_this_dest))
         {
           dsts[0].amount -= available_amount;
           available_amount = 0;
@@ -10960,9 +11031,13 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
       // Try to carve the estimated fee from the partial payment (if there is one)
       available_for_fee = try_carving_from_partial_payment(needed_fee, available_for_fee);
 
-      uint64_t inputs = 0, outputs = needed_fee;
+      uint64_t inputs = 0, outputs = 0;
       for (size_t idx: tx.selected_transfers) inputs += m_transfers[idx].amount();
       for (const auto &o: tx.dsts) outputs += o.amount;
+      if (subtract_fee_from_outputs.empty()) // if normal tx that doesn't subtract fees
+      {
+        outputs += needed_fee;
+      }
 
       if (inputs < outputs)
       {
@@ -10973,15 +11048,32 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
 
       LOG_PRINT_L2("Trying to create a tx now, with " << tx.dsts.size() << " outputs and " <<
         tx.selected_transfers.size() << " inputs");
+      auto tx_dsts = tx.get_adjusted_dsts(needed_fee);
       if (use_rct)
-        transfer_selected_rct(tx.dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
+        transfer_selected_rct(tx_dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
           test_tx, test_ptx, rct_config, use_view_tags);
       else
-        transfer_selected(tx.dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
+        transfer_selected(tx_dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
           detail::digit_split_strategy, tx_dust_policy(::config::DEFAULT_DUST_THRESHOLD), test_tx, test_ptx, use_view_tags);
       auto txBlob = t_serializable_object_to_blob(test_ptx.tx);
       needed_fee = calculate_fee(use_per_byte_fee, test_ptx.tx, txBlob.size(), base_fee, fee_quantization_mask);
-      available_for_fee = test_ptx.fee + test_ptx.change_dts.amount + (!test_ptx.dust_added_to_fee ? test_ptx.dust : 0);
+
+      // Depending on the mode, we take extra fees from either our change output or the destination outputs for which subtract_fee_from_outputs is true
+      uint64_t output_available_for_fee = 0;
+      bool tx_has_subtractable_output = false;
+      for (size_t di = 0; di < tx.dsts.size(); ++di)
+      {
+        if (tx.dsts_are_fee_subtractable[di])
+        {
+          output_available_for_fee += tx.dsts[di].amount;
+          tx_has_subtractable_output = true;
+        }
+      }
+      if (!tx_has_subtractable_output)
+      {
+        output_available_for_fee = test_ptx.change_dts.amount;
+      }
+      available_for_fee = test_ptx.fee + output_available_for_fee + (!test_ptx.dust_added_to_fee ? test_ptx.dust : 0);
       LOG_PRINT_L2("Made a " << get_weight_string(test_ptx.tx, txBlob.size()) << " tx, with " << print_money(available_for_fee) << " available for fee (" <<
         print_money(needed_fee) << " needed)");
 
@@ -10997,18 +11089,24 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
       else
       {
         LOG_PRINT_L2("We made a tx, adjusting fee and saving it, we need " << print_money(needed_fee) << " and we have " << print_money(test_ptx.fee));
-        do {
+        size_t fee_tries;
+        for (fee_tries = 0; fee_tries < 10 && needed_fee > test_ptx.fee; ++fee_tries) {
+          tx_dsts = tx.get_adjusted_dsts(needed_fee);
+
           if (use_rct)
-            transfer_selected_rct(tx.dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
+            transfer_selected_rct(tx_dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
               test_tx, test_ptx, rct_config, use_view_tags);
           else
-            transfer_selected(tx.dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
+            transfer_selected(tx_dsts, tx.selected_transfers, fake_outs_count, outs, valid_public_keys_cache, unlock_time, needed_fee, extra,
               detail::digit_split_strategy, tx_dust_policy(::config::DEFAULT_DUST_THRESHOLD), test_tx, test_ptx, use_view_tags);
           txBlob = t_serializable_object_to_blob(test_ptx.tx);
           needed_fee = calculate_fee(use_per_byte_fee, test_ptx.tx, txBlob.size(), base_fee, fee_quantization_mask);
           LOG_PRINT_L2("Made an attempt at a  final " << get_weight_string(test_ptx.tx, txBlob.size()) << " tx, with " << print_money(test_ptx.fee) <<
             " fee  and " << print_money(test_ptx.change_dts.amount) << " change");
-        } while (needed_fee > test_ptx.fee);
+        };
+
+        THROW_WALLET_EXCEPTION_IF(fee_tries == 10, error::wallet_internal_error,
+          "Too many attempts to raise pending tx fee to level of needed fee");
 
         LOG_PRINT_L2("Made a final " << get_weight_string(test_ptx.tx, txBlob.size()) << " tx, with " << print_money(test_ptx.fee) <<
           " fee  and " << print_money(test_ptx.change_dts.amount) << " change");
@@ -11061,10 +11159,13 @@ skip_tx:
   for (std::vector<TX>::iterator i = txes.begin(); i != txes.end(); ++i)
   {
     TX &tx = *i;
+
+    const auto tx_dsts = tx.get_adjusted_dsts(tx.needed_fee);
+
     cryptonote::transaction test_tx;
     pending_tx test_ptx;
     if (use_rct) {
-      transfer_selected_rct(tx.dsts,                    /* NOMOD std::vector<cryptonote::tx_destination_entry> dsts,*/
+      transfer_selected_rct(tx_dsts,                    /* NOMOD std::vector<cryptonote::tx_destination_entry> dsts,*/
                             tx.selected_transfers,      /* const std::list<size_t> selected_transfers */
                             fake_outs_count,            /* CONST size_t fake_outputs_count, */
                             tx.outs,                    /* MOD   std::vector<std::vector<tools::wallet2::get_outs_entry>> &outs, */
@@ -11077,7 +11178,7 @@ skip_tx:
                             rct_config,
                             use_view_tags);             /* const bool use_view_tags */
     } else {
-      transfer_selected(tx.dsts,
+      transfer_selected(tx_dsts,
                         tx.selected_transfers,
                         fake_outs_count,
                         tx.outs,
@@ -11111,23 +11212,38 @@ skip_tx:
     ptx_vector.push_back(tx.ptx);
   }
 
-  THROW_WALLET_EXCEPTION_IF(!sanity_check(ptx_vector, original_dsts), error::wallet_internal_error, "Created transaction(s) failed sanity check");
+  THROW_WALLET_EXCEPTION_IF(!sanity_check(ptx_vector, original_dsts, subtract_fee_from_outputs), error::wallet_internal_error, "Created transaction(s) failed sanity check");
 
   // if we made it this far, we're OK to actually send the transactions
   return ptx_vector;
 }
 
-bool wallet2::sanity_check(const std::vector<wallet2::pending_tx> &ptx_vector, std::vector<cryptonote::tx_destination_entry> dsts) const
+bool wallet2::sanity_check(const std::vector<wallet2::pending_tx> &ptx_vector, const std::vector<cryptonote::tx_destination_entry>& dsts, const unique_index_container& subtract_fee_from_outputs) const
 {
-  MDEBUG("sanity_check: " << ptx_vector.size() << " txes, " << dsts.size() << " destinations");
+  MDEBUG("sanity_check: " << ptx_vector.size() << " txes, " << dsts.size() << " destinations, subtract_fee_from_outputs " <<
+    (subtract_fee_from_outputs.size() ? "enabled" : "disabled"));
 
   THROW_WALLET_EXCEPTION_IF(ptx_vector.empty(), error::wallet_internal_error, "No transactions");
+  THROW_WALLET_EXCEPTION_IF(!subtract_fee_from_outputs.empty() && ptx_vector.size() != 1,
+    error::wallet_internal_error, "feature subtractfeefrom not supported for split transactions");
+
+  // For destinations from where the fee is subtracted, the required amount has to be at least
+  // target amount - (tx fee / num_subtractable + 1). +1 since fee might not be evenly divisble by
+  // the number of subtractble destinations. For non-subtractable destinations, we need at least
+  // the target amount.
+  const size_t num_subtractable_dests = subtract_fee_from_outputs.size();
+  const uint64_t fee0 = ptx_vector[0].fee;
+  const uint64_t subtractable_fee_deduction = fee0 / std::max<size_t>(num_subtractable_dests, 1) + 1;
 
   // check every party in there does receive at least the required amount
   std::unordered_map<account_public_address, std::pair<uint64_t, bool>> required;
-  for (const auto &d: dsts)
+  for (size_t i = 0; i < dsts.size(); ++i)
   {
-    required[d.addr].first += d.amount;
+    const cryptonote::tx_destination_entry& d = dsts[i];
+    const bool dest_is_subtractable = subtract_fee_from_outputs.count(i);
+    const uint64_t fee_deduction = dest_is_subtractable ? subtractable_fee_deduction : 0;
+    const uint64_t required_amount = d.amount - std::min(fee_deduction, d.amount);
+    required[d.addr].first += required_amount;
     required[d.addr].second = d.is_subaddress;
   }
 

src/wallet/wallet2.h

@@ -598,6 +598,7 @@ private:
 
     typedef std::vector<transfer_details> transfer_container;
     typedef serializable_unordered_multimap<crypto::hash, payment_details> payment_container;
+    typedef std::set<uint32_t> unique_index_container;
 
     struct multisig_sig
     {
@@ -1111,11 +1112,11 @@ private:
     bool parse_unsigned_tx_from_str(const std::string &unsigned_tx_st, unsigned_tx_set &exported_txs) const;
     bool load_tx(const std::string &signed_filename, std::vector<tools::wallet2::pending_tx> &ptx, std::function<bool(const signed_tx_set&)> accept_func = NULL);
     bool parse_tx_from_str(const std::string &signed_tx_st, std::vector<tools::wallet2::pending_tx> &ptx, std::function<bool(const signed_tx_set &)> accept_func);
-    std::vector<wallet2::pending_tx> create_transactions_2(std::vector<cryptonote::tx_destination_entry> dsts, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices);     // pass subaddr_indices by value on purpose
+    std::vector<wallet2::pending_tx> create_transactions_2(std::vector<cryptonote::tx_destination_entry> dsts, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices, const unique_index_container& subtract_fee_from_outputs = {});     // pass subaddr_indices by value on purpose
     std::vector<wallet2::pending_tx> create_transactions_all(uint64_t below, const cryptonote::account_public_address &address, bool is_subaddress, const size_t outputs, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices);
     std::vector<wallet2::pending_tx> create_transactions_single(const crypto::key_image &ki, const cryptonote::account_public_address &address, bool is_subaddress, const size_t outputs, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra);
     std::vector<wallet2::pending_tx> create_transactions_from(const cryptonote::account_public_address &address, bool is_subaddress, const size_t outputs, std::vector<size_t> unused_transfers_indices, std::vector<size_t> unused_dust_indices, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra);
-    bool sanity_check(const std::vector<wallet2::pending_tx> &ptx_vector, std::vector<cryptonote::tx_destination_entry> dsts) const;
+    bool sanity_check(const std::vector<wallet2::pending_tx> &ptx_vector, const std::vector<cryptonote::tx_destination_entry>& dsts, const unique_index_container& subtract_fee_from_outputs = {}) const;
     void cold_tx_aux_import(const std::vector<pending_tx>& ptx, const std::vector<std::string>& tx_device_aux);
     void cold_sign_tx(const std::vector<pending_tx>& ptx_vector, signed_tx_set &exported_txs, std::vector<cryptonote::address_parse_info> &dsts_info, std::vector<std::string> & tx_device_aux);
     uint64_t cold_key_image_sync(uint64_t &spent, uint64_t &unspent);

src/wallet/wallet_errors.h

@@ -85,6 +85,7 @@ namespace tools
     //         tx_too_big
     //         zero_amount
     //         zero_destination
+    //         subtract_fee_from_bad_index
     //       wallet_rpc_error *
     //         daemon_busy
     //         no_connection_to_daemon
@@ -779,6 +780,15 @@ namespace tools
       }
     };
     //----------------------------------------------------------------------------------------------------
+    struct subtract_fee_from_bad_index : public transfer_error
+    {
+      explicit subtract_fee_from_bad_index(std::string&& loc, long bad_index)
+        : transfer_error(std::move(loc),
+          "subtractfeefrom: bad index: " + std::to_string(bad_index) + " (indexes are 0-based)")
+      {
+      }
+    };
+    //----------------------------------------------------------------------------------------------------
     struct wallet_rpc_error : public wallet_logic_error
     {
       const std::string& request() const { return m_request; }

src/wallet/wallet_rpc_server.cpp

@@ -988,9 +988,9 @@ namespace tools
     return amount;
   }
   //------------------------------------------------------------------------------------------------------------------------------
-  template<typename Ts, typename Tu, typename Tk>
+  template<typename Ts, typename Tu, typename Tk, typename Ta>
   bool wallet_rpc_server::fill_response(std::vector<tools::wallet2::pending_tx> &ptx_vector,
-      bool get_tx_key, Ts& tx_key, Tu &amount, Tu &fee, Tu &weight, std::string &multisig_txset, std::string &unsigned_txset, bool do_not_relay,
+      bool get_tx_key, Ts& tx_key, Tu &amount, Ta &amounts_by_dest, Tu &fee, Tu &weight, std::string &multisig_txset, std::string &unsigned_txset, bool do_not_relay,
       Ts &tx_hash, bool get_tx_hex, Ts &tx_blob, bool get_tx_metadata, Ts &tx_metadata, Tk &spent_key_images, epee::json_rpc::error &er)
   {
     for (const auto & ptx : ptx_vector)
@@ -1007,6 +1007,12 @@ namespace tools
       fill(fee, ptx.fee);
       fill(weight, cryptonote::get_transaction_weight(ptx.tx));
 
+      // add amounts by destination
+      tools::wallet_rpc::amounts_list abd;
+      for (const auto& dst : ptx.dests)
+        abd.amounts.push_back(dst.amount);
+      fill(amounts_by_dest, abd);
+
       // add spent key images
       tools::wallet_rpc::key_image_list key_image_list;
       bool all_are_txin_to_key = std::all_of(ptx.tx.vin.begin(), ptx.tx.vin.end(), [&](const cryptonote::txin_v& s_e) -> bool
@@ -1087,7 +1093,7 @@ namespace tools
     {
       uint64_t mixin = m_wallet->adjust_mixin(req.ring_size ? req.ring_size - 1 : 0);
       uint32_t priority = m_wallet->adjust_priority(req.priority);
-      std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_transactions_2(dsts, mixin, req.unlock_time, priority, extra, req.account_index, req.subaddr_indices);
+      std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_transactions_2(dsts, mixin, req.unlock_time, priority, extra, req.account_index, req.subaddr_indices, req.subtract_fee_from_outputs);
 
       if (ptx_vector.empty())
       {
@@ -1104,7 +1110,7 @@ namespace tools
         return false;
       }
 
-      return fill_response(ptx_vector, req.get_tx_key, res.tx_key, res.amount, res.fee, res.weight, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
+      return fill_response(ptx_vector, req.get_tx_key, res.tx_key, res.amount, res.amounts_by_dest, res.fee, res.weight, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
           res.tx_hash, req.get_tx_hex, res.tx_blob, req.get_tx_metadata, res.tx_metadata, res.spent_key_images, er);
     }
     catch (const std::exception& e)
@@ -1152,7 +1158,7 @@ namespace tools
         return false;
       }
 
-      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
+      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.amounts_by_dest_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
           res.tx_hash_list, req.get_tx_hex, res.tx_blob_list, req.get_tx_metadata, res.tx_metadata_list, res.spent_key_images_list, er);
     }
     catch (const std::exception& e)
@@ -1541,7 +1547,7 @@ namespace tools
     {
       std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_unmixable_sweep_transactions();
 
-      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
+      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.amounts_by_dest_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
           res.tx_hash_list, req.get_tx_hex, res.tx_blob_list, req.get_tx_metadata, res.tx_metadata_list, res.spent_key_images_list, er);
     }
     catch (const std::exception& e)
@@ -1601,7 +1607,7 @@ namespace tools
       uint32_t priority = m_wallet->adjust_priority(req.priority);
       std::vector<wallet2::pending_tx> ptx_vector = m_wallet->create_transactions_all(req.below_amount, dsts[0].addr, dsts[0].is_subaddress, req.outputs, mixin, req.unlock_time, priority, extra, req.account_index, subaddr_indices);
 
-      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
+      return fill_response(ptx_vector, req.get_tx_keys, res.tx_key_list, res.amount_list, res.amounts_by_dest_list, res.fee_list, res.weight_list, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
           res.tx_hash_list, req.get_tx_hex, res.tx_blob_list, req.get_tx_metadata, res.tx_metadata_list, res.spent_key_images_list, er);
     }
     catch (const std::exception& e)
@@ -1678,7 +1684,7 @@ namespace tools
         return false;
       }
 
-      return fill_response(ptx_vector, req.get_tx_key, res.tx_key, res.amount, res.fee, res.weight, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
+      return fill_response(ptx_vector, req.get_tx_key, res.tx_key, res.amount, res.amounts_by_dest, res.fee, res.weight, res.multisig_txset, res.unsigned_txset, req.do_not_relay,
           res.tx_hash, req.get_tx_hex, res.tx_blob, req.get_tx_metadata, res.tx_metadata, res.spent_key_images, er);
     }
     catch (const std::exception& e)

src/wallet/wallet_rpc_server.h

@@ -263,9 +263,9 @@ namespace tools
       bool not_open(epee::json_rpc::error& er);
       void handle_rpc_exception(const std::exception_ptr& e, epee::json_rpc::error& er, int default_error_code);
 
-      template<typename Ts, typename Tu, typename Tk>
+      template<typename Ts, typename Tu, typename Tk, typename Ta>
       bool fill_response(std::vector<tools::wallet2::pending_tx> &ptx_vector,
-          bool get_tx_key, Ts& tx_key, Tu &amount, Tu &fee, Tu &weight, std::string &multisig_txset, std::string &unsigned_txset, bool do_not_relay,
+          bool get_tx_key, Ts& tx_key, Tu &amount, Ta &amounts_by_dest, Tu &fee, Tu &weight, std::string &multisig_txset, std::string &unsigned_txset, bool do_not_relay,
           Ts &tx_hash, bool get_tx_hex, Ts &tx_blob, bool get_tx_metadata, Ts &tx_metadata, Tk &spent_key_images, epee::json_rpc::error &er);
 
       bool validate_transfer(const std::list<wallet_rpc::transfer_destination>& destinations, const std::string& payment_id, std::vector<cryptonote::tx_destination_entry>& dsts, std::vector<uint8_t>& extra, bool at_least_one_destination, epee::json_rpc::error& er);

src/wallet/wallet_rpc_server_commands_defs.h

@@ -47,7 +47,7 @@
 // advance which version they will stop working with
 // Don't go over 32767 for any of these
 #define WALLET_RPC_VERSION_MAJOR 1
-#define WALLET_RPC_VERSION_MINOR 26
+#define WALLET_RPC_VERSION_MINOR 27
 #define MAKE_WALLET_RPC_VERSION(major,minor) (((major)<<16)|(minor))
 #define WALLET_RPC_VERSION MAKE_WALLET_RPC_VERSION(WALLET_RPC_VERSION_MAJOR, WALLET_RPC_VERSION_MINOR)
 namespace tools
@@ -530,11 +530,23 @@ namespace wallet_rpc
     END_KV_SERIALIZE_MAP()
   };
 
+  struct amounts_list
+  {
+    std::list<uint64_t> amounts;
+
+    bool operator==(const amounts_list& other) const { return amounts == other.amounts; }
+
+    BEGIN_KV_SERIALIZE_MAP()
+      KV_SERIALIZE(amounts)
+    END_KV_SERIALIZE_MAP()
+  };
+
   struct single_transfer_response
   {
     std::string tx_hash;
     std::string tx_key;
     uint64_t amount;
+    amounts_list amounts_by_dest;
     uint64_t fee;
     uint64_t weight;
     std::string tx_blob;
@@ -547,6 +559,7 @@ namespace wallet_rpc
       KV_SERIALIZE(tx_hash)
       KV_SERIALIZE(tx_key)
       KV_SERIALIZE(amount)
+      KV_SERIALIZE_OPT(amounts_by_dest, decltype(amounts_by_dest)())
       KV_SERIALIZE(fee)
       KV_SERIALIZE(weight)
       KV_SERIALIZE(tx_blob)
@@ -564,6 +577,7 @@ namespace wallet_rpc
       std::list<transfer_destination> destinations;
       uint32_t account_index;
       std::set<uint32_t> subaddr_indices;
+      std::set<uint32_t> subtract_fee_from_outputs;
       uint32_t priority;
       uint64_t ring_size;
       uint64_t unlock_time;
@@ -577,6 +591,7 @@ namespace wallet_rpc
         KV_SERIALIZE(destinations)
         KV_SERIALIZE(account_index)
         KV_SERIALIZE(subaddr_indices)
+        KV_SERIALIZE_OPT(subtract_fee_from_outputs, decltype(subtract_fee_from_outputs)())
         KV_SERIALIZE(priority)
         KV_SERIALIZE_OPT(ring_size, (uint64_t)0)
         KV_SERIALIZE(unlock_time)
@@ -598,6 +613,7 @@ namespace wallet_rpc
     std::list<std::string> tx_hash_list;
     std::list<std::string> tx_key_list;
     std::list<uint64_t> amount_list;
+    std::list<amounts_list> amounts_by_dest_list;
     std::list<uint64_t> fee_list;
     std::list<uint64_t> weight_list;
     std::list<std::string> tx_blob_list;
@@ -610,6 +626,7 @@ namespace wallet_rpc
       KV_SERIALIZE(tx_hash_list)
       KV_SERIALIZE(tx_key_list)
       KV_SERIALIZE(amount_list)
+      KV_SERIALIZE_OPT(amounts_by_dest_list, decltype(amounts_by_dest_list)())
       KV_SERIALIZE(fee_list)
       KV_SERIALIZE(weight_list)
       KV_SERIALIZE(tx_blob_list)

tests/functional_tests/transfer.py

@@ -62,6 +62,7 @@ class TransferTest():
         self.check_rescan()
         self.check_is_key_image_spent()
         self.check_scan_tx()
+        self.check_subtract_fee_from_outputs()
 
     def reset(self):
         print('Resetting blockchain')
@@ -1046,5 +1047,85 @@ class TransferTest():
         diff_transfers(receiver_wallet.get_transfers(), res)
         assert receiver_wallet.get_balance().balance == expected_receiver_balance
 
+    def check_subtract_fee_from_outputs(self):
+        daemon = Daemon()
+
+        print('Testing fee-included transfers')
+
+        def inner_test_external_transfer(dsts, subtract_fee_from_outputs):
+            # refresh wallet and get balance
+            self.wallet[0].refresh()
+            balance1 = self.wallet[0].get_balance().balance
+
+            # Check that this transaction is possible with our current balance + other preconditions
+            dst_sum = sum(map(lambda x: x['amount'], dsts))
+            assert balance1 >= dst_sum
+            if subtract_fee_from_outputs:
+                assert max(subtract_fee_from_outputs) < len(dsts)
+
+            # transfer with subtractfeefrom=all
+            transfer_res = self.wallet[0].transfer(dsts, subtract_fee_from_outputs = subtract_fee_from_outputs, get_tx_metadata = True)
+            tx_hex = transfer_res.tx_metadata
+            tx_fee = transfer_res.fee
+            amount_spent = transfer_res.amount
+            amounts_by_dest = transfer_res.amounts_by_dest.amounts
+
+            # Assert that fee and amount spent to outputs adds up
+            assert tx_fee != 0
+            if subtract_fee_from_outputs:
+                assert tx_fee + amount_spent == dst_sum
+            else:
+                assert amount_spent == dst_sum
+
+            # Check the amounts by each destination that only the destinations set as subtractable
+            # got subtracted and that the subtracted dests are approximately correct
+            assert len(amounts_by_dest) == len(dsts) # if this fails... idk
+            for i in range(len(dsts)):
+                if i in subtract_fee_from_outputs: # dest is subtractable
+                    approx_subtraction = tx_fee // len(subtract_fee_from_outputs)
+                    assert amounts_by_dest[i] < dsts[i]['amount']
+                    assert dsts[i]['amount'] - amounts_by_dest[i] - approx_subtraction <= 1
+                else:
+                    assert amounts_by_dest[i] == dsts[i]['amount']
+
+            # relay tx and generate block (not to us, to simplify balance change calculations)
+            relay_res = self.wallet[0].relay_tx(tx_hex)
+            daemon.generateblocks('44Kbx4sJ7JDRDV5aAhLJzQCjDz2ViLRduE3ijDZu3osWKBjMGkV1XPk4pfDUMqt1Aiezvephdqm6YD19GKFD9ZcXVUTp6BW', 1)
+
+            # refresh and get balance again
+            self.wallet[0].refresh()
+            balance2 = self.wallet[0].get_balance().balance
+
+            # Check that the wallet balance dropped by the correct amount
+            balance_drop = balance1 - balance2
+            if subtract_fee_from_outputs:
+                assert balance_drop == dst_sum
+            else:
+                assert balance_drop == dst_sum + tx_fee
+
+        dst1 = {'address': '44Kbx4sJ7JDRDV5aAhLJzQCjDz2ViLRduE3ijDZu3osWKBjMGkV1XPk4pfDUMqt1Aiezvephdqm6YD19GKFD9ZcXVUTp6BW', 'amount': 1100000000001}
+        dst2 = {'address': '46r4nYSevkfBUMhuykdK3gQ98XDqDTYW1hNLaXNvjpsJaSbNtdXh1sKMsdVgqkaihChAzEy29zEDPMR3NHQvGoZCLGwTerK', 'amount': 1200000000000}
+        dst3 = {'address': '46r4nYSevkfBUMhuykdK3gQ98XDqDTYW1hNLaXNvjpsJaSbNtdXh1sKMsdVgqkaihChAzEy29zEDPMR3NHQvGoZCLGwTerK', 'amount': 1}
+
+        inner_test_external_transfer([dst1, dst2], [0, 1])
+        inner_test_external_transfer([dst1, dst2], [0])
+        inner_test_external_transfer([dst1, dst2], [1])
+        inner_test_external_transfer([dst1, dst2], [])
+        inner_test_external_transfer([dst1], [0])
+        inner_test_external_transfer([dst1], [])
+        inner_test_external_transfer([dst3], [])
+        try:
+            inner_test_external_transfer([dst1, dst3], [0, 1]) # Test subtractfeefrom if one of the outputs would underflow w/o good checks
+            raise ValueError('transfer request with tiny subtractable destination should have thrown')
+        except:
+            pass
+
+        # Check for JSONRPC error on bad index
+        try:
+            transfer_res = self.wallet[0].transfer([dst1], subtract_fee_from_outputs = [1])
+            raise ValueError('transfer request with index should have thrown')
+        except AssertionError:
+            pass
+
 if __name__ == '__main__':
     TransferTest().run_test()

tests/unit_tests/epee_utils.cpp

@@ -1836,3 +1836,60 @@ TEST(parsing, unicode)
   epee::misc_utils::parse::match_string2(si, s.end(), bs);
   EXPECT_EQ(bs, "あまやかす");
 }
+
+TEST(parsing, strtoul)
+{
+  long ul;
+  const char* p;
+  const char* endp;
+
+  errno = 0; // Some libc's only set errno on failure, some set it to 0 on success
+
+  p = "0";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(0, ul);
+  EXPECT_EQ(p + 1, endp);
+
+  p = "000000";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(0, ul);
+  EXPECT_EQ(p + 6, endp);
+
+  p = "1";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(1, ul);
+  EXPECT_EQ(p + 1, endp);
+
+  p = "0q";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(0, ul);
+  EXPECT_EQ(p + 1, endp);
+
+  p = "    \t   0";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(0, ul);
+  EXPECT_EQ(p + 9, endp);
+
+  p = "q";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(0, errno);
+  EXPECT_EQ(0, ul);
+  EXPECT_EQ(p, endp);
+
+  p = "999999999999999999999999999999999999999";
+  endp = nullptr;
+  ul = std::strtoul(p, const_cast<char**>(&endp), 10);
+  EXPECT_EQ(ERANGE, errno);
+  EXPECT_EQ(ULLONG_MAX, ul);
+}

utils/python-rpc/framework/wallet.py

@@ -38,13 +38,14 @@ class Wallet(object):
         self.port = port
         self.rpc = JSONRPC('{protocol}://{host}:{port}'.format(protocol=protocol, host=host, port=port if port else 18090+idx))
 
-    def transfer(self, destinations, account_index = 0, subaddr_indices = [], priority = 0, ring_size = 0, unlock_time = 0, payment_id = '', get_tx_key = True, do_not_relay = False, get_tx_hex = False, get_tx_metadata = False):
+    def transfer(self, destinations, account_index = 0, subaddr_indices = [], priority = 0, ring_size = 0, unlock_time = 0, payment_id = '', get_tx_key = True, do_not_relay = False, get_tx_hex = False, get_tx_metadata = False, subtract_fee_from_outputs = []):
         transfer = {
             'method': 'transfer',
             'params': {
                 'destinations': destinations,
                 'account_index': account_index,
                 'subaddr_indices': subaddr_indices,
+                'subtract_fee_from_outputs': subtract_fee_from_outputs,
                 'priority': priority,
                 'ring_size' : ring_size,
                 'unlock_time' : unlock_time,