settings: Add resetSettings() method

Allows the GUI to clear settings.json file and save settings.json.bak file when
GUI "Reset Options" button is pressed or -resetguisettings command line option
is used. (GUI code already backs up and resets the "guisettings.ini" file this
way, so this just makes the same behavior possible for "settings.json")

src/interfaces/node.h

@@ -112,6 +112,10 @@ public:
     //! source, but not being persisted.
     virtual void forceSetting(const std::string& name, const util::SettingsValue& value) = 0;
 
+    //! Clear all settings in <datadir>/settings.json and store a backup of
+    //! previous settings in <datadir>/settings.json.bak.
+    virtual void resetSettings() = 0;
+
     //! Map port.
     virtual void mapPort(bool use_upnp, bool use_natpmp) = 0;
 

src/node/interfaces.cpp

@@ -144,6 +144,14 @@ public:
             }
         });
     }
+    void resetSettings() override
+    {
+        gArgs.WriteSettingsFile(/*errors=*/nullptr, /*backup=*/true);
+        gArgs.LockSettings([&](util::Settings& settings) {
+            settings.rw_settings.clear();
+        });
+        gArgs.WriteSettingsFile();
+    }
     void mapPort(bool use_upnp, bool use_natpmp) override { StartMapPort(use_upnp, use_natpmp); }
     bool getProxy(Network net, Proxy& proxy_info) override { return GetProxy(net, proxy_info); }
     size_t getNodeCount(ConnectionDirection flags) override

src/util/system.cpp

@@ -526,12 +526,15 @@ bool ArgsManager::InitSettings(std::string& error)
     return true;
 }
 
-bool ArgsManager::GetSettingsPath(fs::path* filepath, bool temp) const
+bool ArgsManager::GetSettingsPath(fs::path* filepath, bool temp, bool backup) const
 {
     fs::path settings = GetPathArg("-settings", fs::path{BITCOIN_SETTINGS_FILENAME});
     if (settings.empty()) {
         return false;
     }
+    if (backup) {
+        settings += ".bak";
+    }
     if (filepath) {
         *filepath = fsbridge::AbsPathJoin(GetDataDirNet(), temp ? settings + ".tmp" : settings);
     }
@@ -572,10 +575,10 @@ bool ArgsManager::ReadSettingsFile(std::vector<std::string>* errors)
     return true;
 }
 
-bool ArgsManager::WriteSettingsFile(std::vector<std::string>* errors) const
+bool ArgsManager::WriteSettingsFile(std::vector<std::string>* errors, bool backup) const
 {
     fs::path path, path_tmp;
-    if (!GetSettingsPath(&path, /* temp= */ false) || !GetSettingsPath(&path_tmp, /* temp= */ true)) {
+    if (!GetSettingsPath(&path, /*temp=*/false, backup) || !GetSettingsPath(&path_tmp, /*temp=*/true, backup)) {
         throw std::logic_error("Attempt to write settings file when dynamic settings are disabled.");
     }
 

src/util/system.h

@@ -440,7 +440,7 @@ protected:
      * Get settings file path, or return false if read-write settings were
      * disabled with -nosettings.
      */
-    bool GetSettingsPath(fs::path* filepath = nullptr, bool temp = false) const;
+    bool GetSettingsPath(fs::path* filepath = nullptr, bool temp = false, bool backup = false) const;
 
     /**
      * Read settings file. Push errors to vector, or log them if null.
@@ -448,9 +448,10 @@ protected:
     bool ReadSettingsFile(std::vector<std::string>* errors = nullptr);
 
     /**
-     * Write settings file. Push errors to vector, or log them if null.
+     * Write settings file or backup settings file. Push errors to vector, or
+     * log them if null.
      */
-    bool WriteSettingsFile(std::vector<std::string>* errors = nullptr) const;
+    bool WriteSettingsFile(std::vector<std::string>* errors = nullptr, bool backup = false) const;
 
     /**
      * Get current setting from config file or read/write settings file,