Merge bitcoin/bitcoin#15936: interfaces: Expose settings.json methods to GUI

f9fdcec7e932843a91ddf7f377e00bd2a6efb82a settings: Add resetSettings() method (Ryan Ofsky)
77fabffef4ea840ee15c97061048fe8443d74658 init: Remove Shutdown() node.args reset (Ryan Ofsky)
0e55bc6e7fe439404dc56093a0949395dae51e6b settings: Add update/getPersistent/isIgnored methods (Ryan Ofsky)

Pull request description:

  Add `interfaces::Node` `updateSetting`, `forceSetting`, `resetSettings`, `isSettingIgnored`, and `getPersistentSetting` methods so GUI is able to manipulate `settings.json` file and use and modify node settings.

  (Originally this PR also contained GUI changes to unify bitcoin-qt and bitcoind persistent settings and call these methods, but the GUI commits have been dropped from this PR and moved to bitcoin-core/gui/pull/602)

ACKs for top commit:
  vasild:
    ACK f9fdcec7e932843a91ddf7f377e00bd2a6efb82a
  hebasto:
    re-ACK f9fdcec7e932843a91ddf7f377e00bd2a6efb82a, only a function renamed since my recent [review](https://github.com/bitcoin/bitcoin/pull/15936#pullrequestreview-979324357).

Tree-SHA512: 4cac853ee29be96d2ff38404165b9dfb7c622b2a9c99a15979596f3484ffde0da3d9c9c372677dff5119ca7cffa6383d81037fd9889a29cc9285882a8dc0c268

1 files changed, 40 insertions, 0 deletions

diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index decc347954..4810ae1f68 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -112,6 +112,46 @@ public:
         }
     }
     bool shutdownRequested() override { return ShutdownRequested(); }
+    bool isSettingIgnored(const std::string& name) override
+    {
+        bool ignored = false;
+        gArgs.LockSettings([&](util::Settings& settings) {
+            if (auto* options = util::FindKey(settings.command_line_options, name)) {
+                ignored = !options->empty();
+            }
+        });
+        return ignored;
+    }
+    util::SettingsValue getPersistentSetting(const std::string& name) override { return gArgs.GetPersistentSetting(name); }
+    void updateRwSetting(const std::string& name, const util::SettingsValue& value) override
+    {
+        gArgs.LockSettings([&](util::Settings& settings) {
+            if (value.isNull()) {
+                settings.rw_settings.erase(name);
+            } else {
+                settings.rw_settings[name] = value;
+            }
+        });
+        gArgs.WriteSettingsFile();
+    }
+    void forceSetting(const std::string& name, const util::SettingsValue& value) override
+    {
+        gArgs.LockSettings([&](util::Settings& settings) {
+            if (value.isNull()) {
+                settings.forced_settings.erase(name);
+            } else {
+                settings.forced_settings[name] = value;
+            }
+        });
+    }
+    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