1 files changed, 169 insertions, 0 deletions
diff --git a/src/util/settings.cpp b/src/util/settings.cpp
new file mode 100644
index 0000000000..af75fef310
--- /dev/null
+++ b/src/util/settings.cpp
@@ -0,0 +1,169 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/settings.h>
+
+#include <univalue.h>
+
+namespace util {
+namespace {
+
+enum class Source {
+   FORCED,
+   COMMAND_LINE,
+   CONFIG_FILE_NETWORK_SECTION,
+   CONFIG_FILE_DEFAULT_SECTION
+};
+
+//! Merge settings from multiple sources in precedence order:
+//! Forced config > command line > config file network-specific section > config file default section
+//!
+//! This function is provided with a callback function fn that contains
+//! specific logic for how to merge the sources.
+template <typename Fn>
+static void MergeSettings(const Settings& settings, const std::string& section, const std::string& name, Fn&& fn)
+{
+    // Merge in the forced settings
+    if (auto* value = FindKey(settings.forced_settings, name)) {
+        fn(SettingsSpan(*value), Source::FORCED);
+    }
+    // Merge in the command-line options
+    if (auto* values = FindKey(settings.command_line_options, name)) {
+        fn(SettingsSpan(*values), Source::COMMAND_LINE);
+    }
+    // Merge in the network-specific section of the config file
+    if (!section.empty()) {
+        if (auto* map = FindKey(settings.ro_config, section)) {
+            if (auto* values = FindKey(*map, name)) {
+                fn(SettingsSpan(*values), Source::CONFIG_FILE_NETWORK_SECTION);
+            }
+        }
+    }
+    // Merge in the default section of the config file
+    if (auto* map = FindKey(settings.ro_config, "")) {
+        if (auto* values = FindKey(*map, name)) {
+            fn(SettingsSpan(*values), Source::CONFIG_FILE_DEFAULT_SECTION);
+        }
+    }
+}
+} // namespace
+
+SettingsValue GetSetting(const Settings& settings,
+    const std::string& section,
+    const std::string& name,
+    bool ignore_default_section_config,
+    bool get_chain_name)
+{
+    SettingsValue result;
+    MergeSettings(settings, section, name, [&](SettingsSpan span, Source source) {
+        // Weird behavior preserved for backwards compatibility: Apply negated
+        // setting even if non-negated setting would be ignored. A negated
+        // value in the default section is applied to network specific options,
+        // even though normal non-negated values there would be ignored.
+        const bool never_ignore_negated_setting = span.last_negated();
+
+        // Weird behavior preserved for backwards compatibility: Take first
+        // assigned value instead of last. In general, later settings take
+        // precedence over early settings, but for backwards compatibility in
+        // the config file the precedence is reversed for all settings except
+        // chain name settings.
+        const bool reverse_precedence = (source == Source::CONFIG_FILE_NETWORK_SECTION || source == Source::CONFIG_FILE_DEFAULT_SECTION) && !get_chain_name;
+
+        // Weird behavior preserved for backwards compatibility: Negated
+        // -regtest and -testnet arguments which you would expect to override
+        // values set in the configuration file are currently accepted but
+        // silently ignored. It would be better to apply these just like other
+        // negated values, or at least warn they are ignored.
+        const bool skip_negated_command_line = get_chain_name;
+
+        // Ignore settings in default config section if requested.
+        if (ignore_default_section_config && source == Source::CONFIG_FILE_DEFAULT_SECTION && !never_ignore_negated_setting) return;
+
+        // Skip negated command line settings.
+        if (skip_negated_command_line && span.last_negated()) return;
+
+        // Stick with highest priority value, keeping result if already set.
+        if (!result.isNull()) return;
+
+        if (!span.empty()) {
+            result = reverse_precedence ? span.begin()[0] : span.end()[-1];
+        } else if (span.last_negated()) {
+            result = false;
+        }
+    });
+    return result;
+}
+
+std::vector<SettingsValue> GetSettingsList(const Settings& settings,
+    const std::string& section,
+    const std::string& name,
+    bool ignore_default_section_config)
+{
+    std::vector<SettingsValue> result;
+    bool result_complete = false;
+    bool prev_negated_empty = false;
+    MergeSettings(settings, section, name, [&](SettingsSpan span, Source source) {
+        // Weird behavior preserved for backwards compatibility: Apply config
+        // file settings even if negated on command line. Negating a setting on
+        // command line will ignore earlier settings on the command line and
+        // ignore settings in the config file, unless the negated command line
+        // value is followed by non-negated value, in which case config file
+        // settings will be brought back from the dead (but earlier command
+        // line settings will still be ignored).
+        const bool add_zombie_config_values = (source == Source::CONFIG_FILE_NETWORK_SECTION || source == Source::CONFIG_FILE_DEFAULT_SECTION) && !prev_negated_empty;
+
+        // Ignore settings in default config section if requested.
+        if (ignore_default_section_config && source == Source::CONFIG_FILE_DEFAULT_SECTION) return;
+
+        // Add new settings to the result if isn't already complete, or if the
+        // values are zombies.
+        if (!result_complete || add_zombie_config_values) {
+            for (const auto& value : span) {
+                if (value.isArray()) {
+                    result.insert(result.end(), value.getValues().begin(), value.getValues().end());
+                } else {
+                    result.push_back(value);
+                }
+            }
+        }
+
+        // If a setting was negated, or if a setting was forced, set
+        // result_complete to true to ignore any later lower priority settings.
+        result_complete |= span.negated() > 0 || source == Source::FORCED;
+
+        // Update the negated and empty state used for the zombie values check.
+        prev_negated_empty |= span.last_negated() && result.empty();
+    });
+    return result;
+}
+
+bool OnlyHasDefaultSectionSetting(const Settings& settings, const std::string& section, const std::string& name)
+{
+    bool has_default_section_setting = false;
+    bool has_other_setting = false;
+    MergeSettings(settings, section, name, [&](SettingsSpan span, Source source) {
+        if (span.empty()) return;
+        else if (source == Source::CONFIG_FILE_DEFAULT_SECTION) has_default_section_setting = true;
+        else has_other_setting = true;
+    });
+    // If a value is set in the default section and not explicitly overwritten by the
+    // user on the command line or in a different section, then we want to enable
+    // warnings about the value being ignored.
+    return has_default_section_setting && !has_other_setting;
+}
+
+SettingsSpan::SettingsSpan(const std::vector<SettingsValue>& vec) noexcept : SettingsSpan(vec.data(), vec.size()) {}
+const SettingsValue* SettingsSpan::begin() const { return data + negated(); }
+const SettingsValue* SettingsSpan::end() const { return data + size; }
+bool SettingsSpan::empty() const { return size == 0 || last_negated(); }
+bool SettingsSpan::last_negated() const { return size > 0 && data[size - 1].isFalse(); }
+size_t SettingsSpan::negated() const
+{
+    for (size_t i = size; i > 0; --i) {
+        if (data[i - 1].isFalse()) return i; // Return number of negated values (position of last false value)
+    }
+    return 0;
+}
+
+} // namespace util