Merge #15935: Add <datadir>/settings.json persistent settings storage

9c69cfe4c54e38edd2f54303be2f8a53dcf5bad8 Add <datadir>/settings.json persistent settings storage. (Russell Yanofsky)
eb682c5700e7a9176d0104d470b83ff9aa3589e8 util: Add ReadSettings and WriteSettings functions (Russell Yanofsky)

Pull request description:

  Persistent settings are used in followup PRs #15936 to unify gui settings between bitcoin-qt and bitcoind, and #15937 to add a load_on_startup flag to the loadwallet RPC and maintain a dynamic list of wallets that should be loaded on startup that also can be shared between bitcoind and bitcoin-qt.

ACKs for top commit:
  MarcoFalke:
    Approach re-ACK 9c69cfe4c54e38edd2f54303be2f8a53dcf5bad8 🌾
  jnewbery:
    utACK 9c69cfe4c54e38edd2f54303be2f8a53dcf5bad8

Tree-SHA512: 39fcc6051717117c9141e934de1d0d3f739484be4685cdf97d54de967c8c816502b4fd0de12114433beaa5c5b7060c810fd8ae4e2b3ce7c371eb729ac01ba2e1

1 files changed, 17 insertions, 3 deletions

diff --git a/src/util/settings.h b/src/util/settings.h
index 1d03639fa2..ed36349232 100644
--- a/src/util/settings.h
+++ b/src/util/settings.h
@@ -5,6 +5,8 @@
 #ifndef BITCOIN_UTIL_SETTINGS_H
 #define BITCOIN_UTIL_SETTINGS_H
 
+#include <fs.h>
+
 #include <map>
 #include <string>
 #include <vector>
@@ -24,19 +26,31 @@ namespace util {
 //!       https://github.com/bitcoin/bitcoin/pull/15934/files#r337691812)
 using SettingsValue = UniValue;
 
-//! Stored bitcoin settings. This struct combines settings from the command line
-//! and a read-only configuration file.
+//! Stored settings. This struct combines settings from the command line, a
+//! read-only configuration file, and a read-write runtime settings file.
 struct Settings {
     //! Map of setting name to forced setting value.
     std::map<std::string, SettingsValue> forced_settings;
     //! Map of setting name to list of command line values.
     std::map<std::string, std::vector<SettingsValue>> command_line_options;
+    //! Map of setting name to read-write file setting value.
+    std::map<std::string, SettingsValue> rw_settings;
     //! Map of config section name and setting name to list of config file values.
     std::map<std::string, std::map<std::string, std::vector<SettingsValue>>> ro_config;
 };
 
+//! Read settings file.
+bool ReadSettings(const fs::path& path,
+    std::map<std::string, SettingsValue>& values,
+    std::vector<std::string>& errors);
+
+//! Write settings file.
+bool WriteSettings(const fs::path& path,
+    const std::map<std::string, SettingsValue>& values,
+    std::vector<std::string>& errors);
+
 //! Get settings value from combined sources: forced settings, command line
-//! arguments and the read-only config file.
+//! arguments, runtime read-write settings, and the read-only config file.
 //!
 //! @param ignore_default_section_config - ignore values in the default section
 //!                                        of the config file (part before any