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diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -305,6 +305,7 @@
uint256.cpp
util/bytevectorhash.cpp
util/moneystr.cpp
+ util/settings.cpp
util/strencodings.cpp
util/system.cpp
util/threadnames.cpp
diff --git a/src/Makefile.am b/src/Makefile.am
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -233,6 +233,7 @@
util/macros.h \
util/moneystr.h \
util/system.h \
+ util/settings.h \
util/threadnames.h \
util/time.h \
validation.h \
@@ -519,6 +520,7 @@
uint256.h \
util/system.cpp \
util/moneystr.cpp \
+ util/settings.cpp \
util/strencodings.cpp \
util/threadnames.cpp \
util/time.cpp \
diff --git a/src/util/settings.h b/src/util/settings.h
new file mode 100644
--- /dev/null
+++ b/src/util/settings.h
@@ -0,0 +1,98 @@
+// 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.
+
+#ifndef BITCOIN_UTIL_SETTINGS_H
+#define BITCOIN_UTIL_SETTINGS_H
+
+#include <map>
+#include <string>
+#include <vector>
+
+class UniValue;
+
+namespace util {
+
+//! Settings value type (string/integer/boolean/null variant).
+//!
+//! @note UniValue is used here for convenience and because it can be easily
+//! serialized in a readable format. But any other variant type that can
+//! be assigned strings, int64_t, and bool values and has get_str(),
+//! get_int64(), get_bool(), isNum(), isBool(), isFalse(), isTrue() and
+//! isNull() methods can be substituted if there's a need to move away
+//! from UniValue. (An implementation with boost::variant was posted at
+//! 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.
+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 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;
+};
+
+//! Get settings value from combined sources: forced settings, command line
+//! arguments and the read-only config file.
+//!
+//! @param ignore_default_section_config - ignore values in the default section
+//! of the config file (part before any
+//! [section] keywords)
+//! @param get_chain_name - enable special backwards compatible behavior
+//! for GetChainName
+SettingsValue GetSetting(const Settings &settings, const std::string &section,
+ const std::string &name,
+ bool ignore_default_section_config,
+ bool get_chain_name);
+
+//! Get combined setting value similar to GetSetting(), except if setting was
+//! specified multiple times, return a list of all the values specified.
+std::vector<SettingsValue> GetSettingsList(const Settings &settings,
+ const std::string &section,
+ const std::string &name,
+ bool ignore_default_section_config);
+
+//! Return true if a setting is set in the default config file section, and not
+//! overridden by a higher priority command-line or network section value.
+//!
+//! This is used to provide user warnings about values that might be getting
+//! ignored unintentionally.
+bool OnlyHasDefaultSectionSetting(const Settings &settings,
+ const std::string &section,
+ const std::string &name);
+
+//! Accessor for list of settings that skips negated values when iterated over.
+//! The last boolean `false` value in the list and all earlier values are
+//! considered negated.
+struct SettingsSpan {
+ explicit SettingsSpan() = default;
+ explicit SettingsSpan(const SettingsValue &value) noexcept
+ : SettingsSpan(&value, 1) {}
+ explicit SettingsSpan(const SettingsValue *dataIn, size_t sizeIn) noexcept
+ : data(dataIn), size(sizeIn) {}
+ explicit SettingsSpan(const std::vector<SettingsValue> &vec) noexcept;
+ const SettingsValue *begin() const; //<! Pointer to first non-negated value.
+ const SettingsValue *end() const; //<! Pointer to end of values.
+ bool empty() const; //<! True if there are any non-negated values.
+ bool last_negated() const; //<! True if the last value is negated.
+ size_t negated() const; //<! Number of negated values.
+
+ const SettingsValue *data = nullptr;
+ size_t size = 0;
+};
+
+//! Map lookup helper.
+template <typename Map, typename Key>
+auto FindKey(Map &&map, Key &&key) -> decltype(&map.at(key)) {
+ auto it = map.find(key);
+ return it == map.end() ? nullptr : &it->second;
+}
+
+} // namespace util
+
+#endif // BITCOIN_UTIL_SETTINGS_H
diff --git a/src/util/settings.cpp b/src/util/settings.cpp
new file mode 100644
--- /dev/null
+++ b/src/util/settings.cpp
@@ -0,0 +1,210 @@
+// 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 number of negated values (position of last false value)
+ return i;
+ }
+ }
+ return 0;
+}
+
+} // namespace util

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