wallet: make change output address index configurable

src/simplewallet/simplewallet.cpp

@@ -3051,6 +3051,22 @@ bool simple_wallet::set_enable_multisig(const std::vector<std::string> &args/* =
   return true;
 }
 
+bool simple_wallet::set_change_output_index(const std::vector<std::string> &args/* = std::vector<std::string>()*/)
+{
+  const auto pwd_container = get_and_verify_password();
+  if (pwd_container)
+  {
+    uint32_t index;
+    if (!epee::string_tools::get_xtype_from_string(index, args[1]))
+    {
+      fail_msg_writer() << tr("Invalid index");
+      return true;
+    }
+    m_wallet->set_change_output_address_index(index);
+    m_wallet->rewrite(m_wallet_file, pwd_container->password());
+  }
+  return true;
+}
 bool simple_wallet::help(const std::vector<std::string> &args/* = std::vector<std::string>()*/)
 {
   if(args.empty())
@@ -3351,6 +3367,8 @@ simple_wallet::simple_wallet()
                                   "  Device name for hardware wallet.\n "
                                   "export-format <\"binary\"|\"ascii\">\n "
                                   "  Save all exported files as binary (cannot be copied and pasted) or ascii (can be).\n "
+                                  "change-output-index <n>\n "
+                                  "  the destination address index for generating the change output if needed.\n "
                                   "load-deprecated-formats <1|0>\n "
                                   "  Whether to enable importing data in deprecated formats.\n "
                                   "show-wallet-name-when-locked <1|0>\n "
@@ -3751,6 +3769,7 @@ bool simple_wallet::set_variable(const std::vector<std::string> &args)
     success_msg_writer() << "setup-background-mining = " << setup_background_mining_string;
     success_msg_writer() << "device-name = " << m_wallet->device_name();
     success_msg_writer() << "export-format = " << (m_wallet->export_format() == tools::wallet2::ExportFormat::Ascii ? "ascii" : "binary");
+    success_msg_writer() << "change-output-index = " << m_wallet->change_output_address_index();
     success_msg_writer() << "show-wallet-name-when-locked = " << m_wallet->show_wallet_name_when_locked();
     success_msg_writer() << "inactivity-lock-timeout = " << m_wallet->inactivity_lock_timeout()
 #ifdef _WIN32
@@ -3824,6 +3843,7 @@ bool simple_wallet::set_variable(const std::vector<std::string> &args)
     CHECK_SIMPLE_VARIABLE("export-format", set_export_format, tr("\"binary\" or \"ascii\""));
     CHECK_SIMPLE_VARIABLE("load-deprecated-formats", set_load_deprecated_formats, tr("0 or 1"));
     CHECK_SIMPLE_VARIABLE("enable-multisig-experimental", set_enable_multisig, tr("0 or 1"));
+    CHECK_SIMPLE_VARIABLE("change-output-index", set_change_output_index, tr("unsigned integer"));
   }
   fail_msg_writer() << tr("set: unrecognized argument(s)");
   return true;

src/simplewallet/simplewallet.h

@@ -155,6 +155,7 @@ namespace cryptonote
     bool set_export_format(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_load_deprecated_formats(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_enable_multisig(const std::vector<std::string> &args = std::vector<std::string>());
+    bool set_change_output_index(const std::vector<std::string> &args = std::vector<std::string>());
     bool help(const std::vector<std::string> &args = std::vector<std::string>());
     bool apropos(const std::vector<std::string> &args);
     bool scan_tx(const std::vector<std::string> &args);

src/wallet/wallet2.cpp

@@ -1253,6 +1253,7 @@ wallet2::wallet2(network_type nettype, uint64_t kdf_rounds, bool unattended, std
   m_offline(false),
   m_rpc_version(0),
   m_export_format(ExportFormat::Binary),
+  m_change_output_address_index(0),
   m_enable_multisig(false),
   m_pool_info_query_time(0),
   m_has_ever_refreshed_from_node(false),
@@ -4761,6 +4762,9 @@ boost::optional<wallet2::keys_file_data> wallet2::get_keys_file_data(const crypt
   value2.SetInt(false);
   json.AddMember("load_deprecated_formats", value2, json.GetAllocator());
 
+  value2.SetInt(m_change_output_address_index);
+  json.AddMember("change_output_address_index", value2, json.GetAllocator());
+
   value2.SetUint(1);
   json.AddMember("encrypted_secret_keys", value2, json.GetAllocator());
 
@@ -5024,6 +5028,7 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
     m_subaddress_lookahead_minor = SUBADDRESS_LOOKAHEAD_MINOR;
     m_original_keys_available = false;
     m_export_format = ExportFormat::Binary;
+    m_change_output_address_index = 0;
     m_device_name = "";
     m_device_derivation_path = "";
     m_key_device_type = hw::device::device_type::SOFTWARE;
@@ -5208,6 +5213,9 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
     GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, export_format, ExportFormat, Int, false, Binary);
     m_export_format = field_export_format;
 
+    GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, change_output_address_index, uint32_t, Uint, false, 0);
+    m_change_output_address_index = field_change_output_address_index;
+
     GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, device_name, std::string, String, false, std::string());
     if (m_device_name.empty())
     {
@@ -9759,8 +9767,8 @@ void wallet2::transfer_selected(const std::vector<cryptonote::tx_destination_ent
   cryptonote::tx_destination_entry change_dts = AUTO_VAL_INIT(change_dts);
   if (needed_money < found_money)
   {
-    change_dts.addr = get_subaddress({subaddr_account, 0});
-    change_dts.is_subaddress = subaddr_account != 0;
+    change_dts.addr = get_subaddress({subaddr_account, m_change_output_address_index});
+    change_dts.is_subaddress = subaddr_account != 0 || m_change_output_address_index != 0;
     change_dts.amount = found_money - needed_money;
   }
 
@@ -10006,8 +10014,8 @@ void wallet2::transfer_selected_rct(std::vector<cryptonote::tx_destination_entry
   }
   else
   {
-    change_dts.addr = get_subaddress({subaddr_account, 0});
-    change_dts.is_subaddress = subaddr_account != 0;
+    change_dts.addr = get_subaddress({subaddr_account, m_change_output_address_index});
+    change_dts.is_subaddress = subaddr_account != 0 || m_change_output_address_index != 0;
     splitted_dsts.push_back(change_dts);
   }
 

src/wallet/wallet2.h

@@ -1485,6 +1485,8 @@ private:
     void device_derivation_path(const std::string &device_derivation_path) { m_device_derivation_path = device_derivation_path; }
     const ExportFormat & export_format() const { return m_export_format; }
     inline void set_export_format(const ExportFormat& export_format) { m_export_format = export_format; }
+    uint32_t change_output_address_index() const { return m_change_output_address_index; }
+    void set_change_output_address_index(uint32_t value) { m_change_output_address_index = value; }
     bool is_multisig_enabled() const { return m_enable_multisig; }
     void enable_multisig(bool enable) { m_enable_multisig = enable; }
     bool is_mismatched_daemon_version_allowed() const { return m_allow_mismatched_daemon_version; }
@@ -2045,6 +2047,8 @@ private:
 
     ExportFormat m_export_format;
 
+    uint32_t m_change_output_address_index;
+
     bool m_has_ever_refreshed_from_node;
 
     static boost::mutex default_daemon_address_lock;