Xconf

---

Package xconf provides a configuration registry for an application.
Configurations can be extracted from a file / env / flag set / remote system.
Supported formats are json, yaml, ini, (java) properties, toml, plain.

Installation

$ go get github.com/actforgood/xconf

Configuration loaders

You can create your own configuration retriever implementing Loader interface. Package provides these Loaders for you:

• EnvLoader - loads environment variables.
• DotEnvFileLoader, DotEnvReaderLoader - loads configuration from a .env file / io.Reader.
• JSONFileLoader, JSONReaderLoader - loads json configuration from a file / io.Reader.
• YAMLFileLoader, YAMLReaderLoader - loads yaml configuration from a file / io.Reader.
• IniFileLoader - loads ini configuration from a file.
• PropertiesFileLoader, PropertiesBytesLoader - loads java style properties configuration from a file / bytes slice.
• TOMLFileLoader, TOMLReaderLoader - loads toml configuration from a file / io.Reader.
• ConsulLoader - loads json/yaml/plain configuration from a remote Consul KV Store.
• EtcdLoader - loads json/yaml/plain configuration from a remote Etcd KV Store.
• PlainLoader - explicit configuration provider.
• FileLoader - factory for <JSON|YAML|Ini|DotEnv|Properties|TOML>FileLoaders based on file extension.
• FlagSetLoader - extracts configuration from a flag.FlagSet.
• MultiLoader - loads (and merges, if configured) configuration from multiple loaders.

Upon above loaders there are available decorators which can help you achieve more sophisticated outcome:

• FilterKVLoader - filters other loader's configurations (based on keys and or their values).
  Example of applicability: I load configurations from environment, but I only want the ones prefixed with "MY_APP_" - I can apply this loader with FilterKVWhitelistFunc(FilterKeyWithPrefix("MY_APP_") filter function.
• AlterValueLoader - changes the value for a configuration key.
  Example of applicability: I load configurations from environment and for a given key I want its value to be a slice (not a string as envs are read/stored by default) - I can apply this loader with ToStringList altering function.
• IgnoreErrorLoader - ignores the error returned by another loader.
  Example of applicability: I load configuration from environment and from file (using a MultiLoader), but it's not mandatory for that file to exist (file it's just an auxiliary source for my configurations, that may exist) - I can use this loader to ignore "file does not exist" error.
• FileCacheLoader - caches configuration from a [X]FileLoader until file gets modified (to be used if loader is called multiple times).
• FlattenLoader - creates easy to access nested configuration leaf keys symlinks.
• AliasLoader - creates aliases for other keys.

Configuration contract

The main configuration contract this package provides looks like:

type Config interface {
	Get(key string, def ...any) any
}

with a default implementation obtained with:

// NewDefaultConfig instantiates a new default config object.
// The first parameter is the loader used as a source of getting the key-value configuration map.
// The second parameter represents a list of optional functions to configure the object.
func NewDefaultConfig(loader Loader, opts ...DefaultConfigOption) (*DefaultConfig, error)

The DefaultConfig has an option of reloading configurations (interval based), if you want to retrieve updated configuration at runtime. There are 2 (proposed) ways of working with it:

• injecting a Config reference and calling Get(key) every time you need a configuration.
• registering your class as an observer to get notified about config changes.

Example of usage (first case) (note: code does not compile):

// cart_service.go
const (
	defaultMaxQtyCfgVal uint = 100
	maxQtyCfgKey             = "MAX_ALLOWED_QTY_TO_ORDER"
)

type CartService struct {
	config xconf.Config
}

func NewCartService(config xconf.Config) *CartService {
	return &CartService{
		config: config,
	}
}

func (cartSvc *CartService) AddProduct(sku string, qty uint) error {
	// ...
	if customerType != B2B {
		totalQty := currentQty + qty
		maxQty := cartSvc.config.Get(maxQtyCfgKey, defaultMaxQtyCfgVal).(uint)
		if totalQty > maxQty {
			return ErrMaxQtyExceeded
		}
	}
	// ...
	return nil
}

func main() {
	// somewhere in the bootstrap of your application ...
	var (
		loader  xconf.Loader // = ... your desired source(s)
		config  xconf.Config
		cartSvc *CartService
	)
	config, err := xconf.NewDefaultConfig(
		loader,
		xconf.DefaultConfigWithReloadInterval(time.Minute), // reload every minute
	)
	if err != nil {
		panic(err)
	}
	cartSvc = NewCartService(config)

	// somewhere in the application business flow ...
	_ = cartSvc.AddProduct("IPHONE", 1)

	// somewhere in the shutdown of your application ...
	if closableConfig, ok := config.(io.Closer); ok {
		_ = closableConfig.Close()
	}
}

Example of usage (second case) (note: code does not compile):

// redis_wrapper.go
const (
	RedisHostCfgKey = "REDIS_HOST"
	DefaultRedisHostCfgVal = "127.0.0.1:6379"
)

type RedisClient interface {
	Ping() error
	Get(key string) (string, error)
	Set(key string, value any, expiration time.Duration) (string, error)
	Close() error
}

type RedisClientWrapper struct {
	client *redis.Client // official client
	mu     sync.RWMutex
}

func NewRedisClientWrapper(host string) *RedisClientWrapper {
	officialClient = ...
	return &RedisClientWrapper {
		client: officialClient,
	}
}

func (wrapper *RedisClientWrapper) Get(key string) (string, error) {
	wrapper.mu.RLock()
	defer wrapper.mu.RUnlock()

	return wrapper.client.Get(key).Result()
}

func (wrapper *RedisClientWrapper) OnConfigChange(config xconf.Config, changedKeys ...string) {
	for _, changedKey := range changedKeys {
		if changedKey == RedisHostCfgKey { // or use strings.EqualFold() if you enabled DefaultConfigWithIgnoreCaseSensitivity.
			wrapper.mu.Lock()
			_ = wrapper.client.Close() // close previous client
			newClient := ... // reinitialize client based on config.Get(RedisHostCfgKey).(string)
			wrapper.client = newClient
			wrapper.mu.Unlock()
		}
	}
}

func main() {
	// somewhere in the bootstrap of your application ...
	var (
		loader      xconf.Loader // = ... your desired source(s)
		config      xconf.Config
		redisClient RedisClient
	)
	config, err := xconf.NewDefaultConfig(
		loader,
		xconf.DefaultConfigWithReloadInterval(30 * time.Second), // reload every 30 seconds
	)
	if err != nil {
		panic(err)
	}
	redisHost := config.Get(RedisHostCfgKey, DefaultRedisHostCfgVal).(string)
	redisClient = NewRedisClient(redisHost)
	config.RegisterObserver(redisClient.OnConfigChange) // register redis wrapper as an observer

	// somewhere in the application business flow ...
	_, _ = redisClient.Get("something")

	// somewhere in the shutdown of your application ...
	if closableConfig, ok := config.(io.Closer); ok {
		_ = closableConfig.Close()
	}
	_ = redisClient.Close()
}

Unmarshal configuration map to structs

This is not the subject of this package, but as a mention, you can achieve that if needed, with a package like github.com/mitchellh/mapstructure.
Example:

package main

import (
	"bytes"
	"fmt"

	"github.com/actforgood/xconf"
	"github.com/mitchellh/mapstructure"
)

type DBConfig struct {
	Host string
	Port int
	Auth Auth
}

type Auth struct {
	Username string
	Password string
}

func main() {
	var (
		jsonConfig = `{
	"db": {
		"host": "127.0.0.1",
		"port": 3306,
		"auth": {
			"username": "JohnDoe",
			"password": "verySecretPwd"
		}
	}		
}`
		dbConfig    DBConfig               // the struct to populate with configuration
		dbConfigMap map[string]any // the configuration map for "db" key
		loader      = xconf.JSONReaderLoader(bytes.NewReader([]byte(jsonConfig)))
	)

	// example using directly a Loader:
	configMap, err := loader.Load()
	if err != nil {
		panic(err)
	}
	dbConfigMap = configMap["db"].(map[string]any)
	if err := mapstructure.Decode(dbConfigMap, &dbConfig); err != nil {
		panic(err)
	}
	fmt.Printf("%+v", dbConfig)

	// example using the Config contract:
	config, err := xconf.NewDefaultConfig(loader)
	if err != nil {
		panic(err)
	}
	dbConfigMap = config.Get("db").(map[string]any)
	if err := mapstructure.Decode(dbConfigMap, &dbConfig); err != nil {
		panic(err)
	}
	fmt.Printf("%+v", dbConfig)

	// both Printf will produce: {Host:127.0.0.1 Port:3306 Auth:{Username:JohnDoe Password:verySecretPwd}}
}

TODOs

Things that can be added to package, extended:

• Support more formats (like HCL)
• Add also a writer/persister functionality (currently you can only read configurations) to different sources and formats (JSONFileWriter/YAMLFileWriter/EtcdWriter/ConsulWriter/...) implementing a common contract like:

type ConfigWriter interface {
	Write(configMap map[string]any) error
}

• Add a typed struct with methods like GetString, GetInt...

Misc

• Feel free to use this pkg if you like it and fits your needs. Check also other packages like spf13/viper ...
• To run unit tests: make test / make cover .
• To run integration tests: make test-integration / make cover-integration : will setup Consul and Etcd docker containers with some keys in them, run ./scripts/teardown_dockers.sh at the end to stop and remove containers).
• To run benchmarks: make bench.
• Project's class diagram can be found here.

License

This package is released under a MIT license. See LICENSE.
Other 3rd party packages directly used by this package are released under their own licenses.

• github.com/joho/godotenv - MIT License
• github.com/magiconair/properties - BSD (2 Clause) License
• gopkg.in/ini.v1 - Apache 2.0 License
• gopkg.in/yaml.v3 - MIT And Apache License
• github.com/pelletier/go-toml/v2 - MIT License
• go.etcd.io/etcd/client/v3 - Apache 2.0 License
• github.com/spf13/cast - MIT License
• github.com/actforgood/xerr - MIT License
• github.com/actforgood/xlog - MIT License