lix/src/libutil/config.hh

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#include <cassert>
#include <map>
#include <set>
#include "types.hh"
#include <nlohmann/json_fwd.hpp>
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#pragma once
namespace nix {
/**
* The Config class provides Nix runtime configurations.
*
* What is a Configuration?
* A collection of uniquely named Settings.
*
* What is a Setting?
* Each property that you can set in a configuration corresponds to a
* `Setting`. A setting records value and description of a property
* with a default and optional aliases.
*
* A valid configuration consists of settings that are registered to a
* `Config` object instance:
*
* Config config;
* Setting<std::string> systemSetting{&config, "x86_64-linux", "system", "the current system"};
*
* The above creates a `Config` object and registers a setting called "system"
* via the variable `systemSetting` with it. The setting defaults to the string
* "x86_64-linux", it's description is "the current system". All of the
* registered settings can then be accessed as shown below:
*
* std::map<std::string, Config::SettingInfo> settings;
* config.getSettings(settings);
* config["system"].description == "the current system"
* config["system"].value == "x86_64-linux"
*
*
* The above retrieves all currently known settings from the `Config` object
* and adds them to the `settings` map.
*/
class Args;
class AbstractSetting;
class AbstractConfig
{
protected:
StringMap unknownSettings;
AbstractConfig(const StringMap & initials = {})
: unknownSettings(initials)
{ }
public:
/**
* Sets the value referenced by `name` to `value`. Returns true if the
* setting is known, false otherwise.
*/
virtual bool set(const std::string & name, const std::string & value) = 0;
struct SettingInfo
{
std::string value;
std::string description;
};
/**
* Adds the currently known settings to the given result map `res`.
* - res: map to store settings in
* - overridenOnly: when set to true only overridden settings will be added to `res`
*/
virtual void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) = 0;
/**
* Parses the configuration in `contents` and applies it
* - contents: configuration contents to be parsed and applied
* - path: location of the configuration file
*/
void applyConfig(const std::string & contents, const std::string & path = "<unknown>");
/**
* Applies a nix configuration file
* - path: the location of the config file to apply
*/
void applyConfigFile(const Path & path);
/**
* Resets the `overridden` flag of all Settings
*/
virtual void resetOverriden() = 0;
/**
* Outputs all settings to JSON
* - out: JSONObject to write the configuration to
*/
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virtual nlohmann::json toJSON() = 0;
/**
* Converts settings to `Args` to be used on the command line interface
* - args: args to write to
* - category: category of the settings
*/
virtual void convertToArgs(Args & args, const std::string & category) = 0;
/**
* Logs a warning for each unregistered setting
*/
void warnUnknownSettings();
/**
* Re-applies all previously attempted changes to unknown settings
*/
void reapplyUnknownSettings();
};
/* A class to simplify providing configuration settings. The typical
use is to inherit Config and add Setting<T> members:
class MyClass : private Config
{
Setting<int> foo{this, 123, "foo", "the number of foos to use"};
Setting<std::string> bar{this, "blabla", "bar", "the name of the bar"};
MyClass() : Config(readConfigFile("/etc/my-app.conf"))
{
std::cout << foo << "\n"; // will print 123 unless overriden
}
};
*/
class Config : public AbstractConfig
{
friend class AbstractSetting;
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public:
struct SettingData
{
bool isAlias;
AbstractSetting * setting;
SettingData(bool isAlias, AbstractSetting * setting)
: isAlias(isAlias), setting(setting)
{ }
};
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typedef std::map<std::string, SettingData> Settings;
private:
Settings _settings;
public:
Config(const StringMap & initials = {})
: AbstractConfig(initials)
{ }
bool set(const std::string & name, const std::string & value) override;
void addSetting(AbstractSetting * setting);
void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
void resetOverriden() override;
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nlohmann::json toJSON() override;
void convertToArgs(Args & args, const std::string & category) override;
};
class AbstractSetting
{
friend class Config;
public:
const std::string name;
const std::string description;
const std::set<std::string> aliases;
int created = 123;
bool overriden = false;
void setDefault(const std::string & str);
protected:
AbstractSetting(
const std::string & name,
const std::string & description,
const std::set<std::string> & aliases);
virtual ~AbstractSetting()
{
// Check against a gcc miscompilation causing our constructor
// not to run (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80431).
assert(created == 123);
}
virtual void set(const std::string & value) = 0;
virtual std::string to_string() const = 0;
nlohmann::json toJSON();
virtual std::map<std::string, nlohmann::json> toJSONObject();
virtual void convertToArg(Args & args, const std::string & category);
bool isOverriden() const { return overriden; }
};
/* A setting of type T. */
template<typename T>
class BaseSetting : public AbstractSetting
{
protected:
T value;
const T defaultValue;
public:
BaseSetting(const T & def,
const std::string & name,
const std::string & description,
const std::set<std::string> & aliases = {})
: AbstractSetting(name, description, aliases)
, value(def)
, defaultValue(def)
{ }
operator const T &() const { return value; }
operator T &() { return value; }
const T & get() const { return value; }
bool operator ==(const T & v2) const { return value == v2; }
bool operator !=(const T & v2) const { return value != v2; }
void operator =(const T & v) { assign(v); }
virtual void assign(const T & v) { value = v; }
void set(const std::string & str) override;
virtual void override(const T & v)
{
overriden = true;
value = v;
}
std::string to_string() const override;
void convertToArg(Args & args, const std::string & category) override;
std::map<std::string, nlohmann::json> toJSONObject() override;
};
template<typename T>
std::ostream & operator <<(std::ostream & str, const BaseSetting<T> & opt)
{
str << (const T &) opt;
return str;
}
template<typename T>
bool operator ==(const T & v1, const BaseSetting<T> & v2) { return v1 == (const T &) v2; }
template<typename T>
class Setting : public BaseSetting<T>
{
public:
Setting(Config * options,
const T & def,
const std::string & name,
const std::string & description,
const std::set<std::string> & aliases = {})
: BaseSetting<T>(def, name, description, aliases)
{
options->addSetting(this);
}
void operator =(const T & v) { this->assign(v); }
};
/* A special setting for Paths. These are automatically canonicalised
(e.g. "/foo//bar/" becomes "/foo/bar"). */
class PathSetting : public BaseSetting<Path>
{
bool allowEmpty;
public:
PathSetting(Config * options,
bool allowEmpty,
const Path & def,
const std::string & name,
const std::string & description,
const std::set<std::string> & aliases = {})
: BaseSetting<Path>(def, name, description, aliases)
, allowEmpty(allowEmpty)
{
options->addSetting(this);
}
void set(const std::string & str) override;
Path operator +(const char * p) const { return value + p; }
void operator =(const Path & v) { this->assign(v); }
};
struct GlobalConfig : public AbstractConfig
{
typedef std::vector<Config*> ConfigRegistrations;
static ConfigRegistrations * configRegistrations;
bool set(const std::string & name, const std::string & value) override;
void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
void resetOverriden() override;
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nlohmann::json toJSON() override;
void convertToArgs(Args & args, const std::string & category) override;
struct Register
{
Register(Config * config);
};
};
extern GlobalConfig globalConfig;
}