util: Add ReadSettings and WriteSettings functions

Currently unused, but includes tests.

3 files changed, 149 insertions, 0 deletions

diff --git a/src/test/settings_tests.cpp b/src/test/settings_tests.cpp
index fcd831ccda..1a2d775f49 100644
--- a/src/test/settings_tests.cpp
+++ b/src/test/settings_tests.cpp
@@ -12,10 +12,90 @@
 #include <univalue.h>
 #include <util/strencodings.h>
 #include <util/string.h>
+#include <util/system.h>
 #include <vector>
 
+inline bool operator==(const util::SettingsValue& a, const util::SettingsValue& b)
+{
+    return a.write() == b.write();
+}
+
+inline std::ostream& operator<<(std::ostream& os, const util::SettingsValue& value)
+{
+    os << value.write();
+    return os;
+}
+
+inline std::ostream& operator<<(std::ostream& os, const std::pair<std::string, util::SettingsValue>& kv)
+{
+    util::SettingsValue out(util::SettingsValue::VOBJ);
+    out.__pushKV(kv.first, kv.second);
+    os << out.write();
+    return os;
+}
+
+inline void WriteText(const fs::path& path, const std::string& text)
+{
+    fsbridge::ofstream file;
+    file.open(path);
+    file << text;
+}
+
 BOOST_FIXTURE_TEST_SUITE(settings_tests, BasicTestingSetup)
 
+BOOST_AUTO_TEST_CASE(ReadWrite)
+{
+    fs::path path = GetDataDir() / "settings.json";
+
+    WriteText(path, R"({
+        "string": "string",
+        "num": 5,
+        "bool": true,
+        "null": null
+    })");
+
+    std::map<std::string, util::SettingsValue> expected{
+        {"string", "string"},
+        {"num", 5},
+        {"bool", true},
+        {"null", {}},
+    };
+
+    // Check file read.
+    std::map<std::string, util::SettingsValue> values;
+    std::vector<std::string> errors;
+    BOOST_CHECK(util::ReadSettings(path, values, errors));
+    BOOST_CHECK_EQUAL_COLLECTIONS(values.begin(), values.end(), expected.begin(), expected.end());
+    BOOST_CHECK(errors.empty());
+
+    // Check no errors if file doesn't exist.
+    fs::remove(path);
+    BOOST_CHECK(util::ReadSettings(path, values, errors));
+    BOOST_CHECK(values.empty());
+    BOOST_CHECK(errors.empty());
+
+    // Check duplicate keys not allowed
+    WriteText(path, R"({
+        "dupe": "string",
+        "dupe": "dupe"
+    })");
+    BOOST_CHECK(!util::ReadSettings(path, values, errors));
+    std::vector<std::string> dup_keys = {strprintf("Found duplicate key dupe in settings file %s", path.string())};
+    BOOST_CHECK_EQUAL_COLLECTIONS(errors.begin(), errors.end(), dup_keys.begin(), dup_keys.end());
+
+    // Check non-kv json files not allowed
+    WriteText(path, R"("non-kv")");
+    BOOST_CHECK(!util::ReadSettings(path, values, errors));
+    std::vector<std::string> non_kv = {strprintf("Found non-object value \"non-kv\" in settings file %s", path.string())};
+    BOOST_CHECK_EQUAL_COLLECTIONS(errors.begin(), errors.end(), non_kv.begin(), non_kv.end());
+
+    // Check invalid json not allowed
+    WriteText(path, R"(invalid json)");
+    BOOST_CHECK(!util::ReadSettings(path, values, errors));
+    std::vector<std::string> fail_parse = {strprintf("Unable to parse settings file %s", path.string())};
+    BOOST_CHECK_EQUAL_COLLECTIONS(errors.begin(), errors.end(), fail_parse.begin(), fail_parse.end());
+}
+
 //! Check settings struct contents against expected json strings.
 static void CheckValues(const util::Settings& settings, const std::string& single_val, const std::string& list_val)
 {
diff --git a/src/util/settings.cpp b/src/util/settings.cpp
index e4979df755..34894e994e 100644
--- a/src/util/settings.cpp
+++ b/src/util/settings.cpp
@@ -4,6 +4,7 @@
 
 #include <util/settings.h>
 
+#include <tinyformat.h>
 #include <univalue.h>
 
 namespace util {
@@ -49,6 +50,62 @@ static void MergeSettings(const Settings& settings, const std::string& section,
 }
 } // namespace
 
+bool ReadSettings(const fs::path& path, std::map<std::string, SettingsValue>& values, std::vector<std::string>& errors)
+{
+    values.clear();
+    errors.clear();
+
+    fsbridge::ifstream file;
+    file.open(path);
+    if (!file.is_open()) return true; // Ok for file not to exist.
+
+    SettingsValue in;
+    if (!in.read(std::string{std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>()})) {
+        errors.emplace_back(strprintf("Unable to parse settings file %s", path.string()));
+        return false;
+    }
+
+    if (file.fail()) {
+        errors.emplace_back(strprintf("Failed reading settings file %s", path.string()));
+        return false;
+    }
+    file.close(); // Done with file descriptor. Release while copying data.
+
+    if (!in.isObject()) {
+        errors.emplace_back(strprintf("Found non-object value %s in settings file %s", in.write(), path.string()));
+        return false;
+    }
+
+    const std::vector<std::string>& in_keys = in.getKeys();
+    const std::vector<SettingsValue>& in_values = in.getValues();
+    for (size_t i = 0; i < in_keys.size(); ++i) {
+        auto inserted = values.emplace(in_keys[i], in_values[i]);
+        if (!inserted.second) {
+            errors.emplace_back(strprintf("Found duplicate key %s in settings file %s", in_keys[i], path.string()));
+        }
+    }
+    return errors.empty();
+}
+
+bool WriteSettings(const fs::path& path,
+    const std::map<std::string, SettingsValue>& values,
+    std::vector<std::string>& errors)
+{
+    SettingsValue out(SettingsValue::VOBJ);
+    for (const auto& value : values) {
+        out.__pushKV(value.first, value.second);
+    }
+    fsbridge::ofstream file;
+    file.open(path);
+    if (file.fail()) {
+        errors.emplace_back(strprintf("Error: Unable to open settings file %s for writing", path.string()));
+        return false;
+    }
+    file << out.write(/* prettyIndent= */ 1, /* indentLevel= */ 4) << std::endl;
+    file.close();
+    return true;
+}
+
 SettingsValue GetSetting(const Settings& settings,
     const std::string& section,
     const std::string& name,
diff --git a/src/util/settings.h b/src/util/settings.h
index 1d03639fa2..ee160e1ac8 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>
@@ -35,6 +37,16 @@ struct Settings {
     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.
 //!