Config

config is a simple golang library and designed to read configurations from JSON, Yaml files, environment variables and command line. config depends on go-yaml to analyze Yaml file and uses built-in golang library to handle JSON file.

Installation

1. Install Yaml library first:

go get gopkg.in/yaml.v3

1. Install config library:

go get github.com/eschao/config

Usage

I. Define configuration name in structure tags

Like JSON, Yaml, config uses tags to define configurations:

Tag	Example	Function
json	Host string json:"host"	Maps Host to a JSON field: host
yaml	Host string yaml:"host"	Maps Host to a Yaml field: host
env	Host string env:"HOST"	Maps Host to a Environment variable: HOST
cli	Host string cli:"host database host"	Maps Host to a command line argument: -host or --host
default	Port int default:"8080"	Defines the port with default value: 8080
separator	Path string json:"path" separator:";"	Separator is used to split string to a slice
usage	Usage string usage:"host address"	Usage description

1. Data types

config supports the following golang data types:

• bool
• string
• int8, int16, int, int32, int64
• uint8, uint16, uint, uint32, uint64
• float32, float64
• slice type. e.g: []string, []int ...

2. Defines default values

Using default keyword in structure tags to define default value:

type Log struct {
    Path  string `default:"/var/logs"`
    Level string `default:"debug"`
}

3. Defines configuration name for JSON

Like parsing JSON object, using json keyword to define configuration name:

  type Database struct {
    Host     string `json:"host"`
    Port     int    `json:"port"`
    Username string `default:"admin" json:"username"`
    Password string `default:"admin" json:"password"`
    Log      Log    `json:"log"`
  }

Corresponding JSON file:

 {
   "host": "test.db.hostname",
   "port": 8080,
   "username": "admin",
   "password": "admin",
   "log": {
     "path": "/var/logs/db",
     "level": "debug"
   }
 }

4. Defines configuration name for Yaml

Like parsing Yaml object, using yaml keyword to define configuration name

  type Database struct {
    Host     string `yaml:"host"`
    Port     int    `yaml:"port"`
    Username string `default:"admin" yaml:"username"`
    Password string `default:"admin" yaml:"password"`
    Log      Log    `yaml:"log"`
  }

Corresponding Yaml file:

  host: test.db.hostname
  port: 8080
  username: admin
  password: admin
  log:
    path: /var/logs/db
    level: debug

5. Defines configuration name for Environment variable

Using env keyword to define configuration name

  type Database struct {
    Host     string `env:"DB_HOST"`
    Port     int    `env:"DB_PORT"`
    Username string `default:"admin" env:"DB_USER"`
    Password string `default:"admin" env:"DB_PASSWORD"`
    Log      Log    `env:"DB_LOG_"`
  }

Corresponding Environment variables:

 export DB_HOST=test.db.hostname
 export DB_PORT=8080
 export DB_USER=admin
 export DB_PASSWORD=admin
 export DB_LOG_PATH=/var/logs/db
 export DB_LOG_LEVEL=debug

Since the Log is a structure and nested in Database structure, the tag of Log and tags of its structure members will be combined to be an unique environment variable, for example: Path will be mapped to environment var: DB_LOG_PATH. But if the Log has no tag definition, only tags of its structure members will be used, that means the Path will be mapped to PATH.

6. Defines configuration name for Command line

Using cli keyword to define configuration name:

  type Database struct {
    Host     string `cli:"host" usage:"database host name"`
    Port     int    `cli:"port" usage:"database port"`
    Username string `cli:"username" default:"admin" usage:"database username"`
    Password string `cli:"password" default:"admin" usage:"database password"`
    Log      Log    `cli:"log" usage:"database log configurations"`
  }

For cli definition, the string is command line argument, and the usage tag are the command line usage and will be outputted when printing usage.

Corresponding command line:

  ./main --host test.db.hostname --port 8080 --username admin --password admin --log-path /var/logs/db --log-level debug

or

  ./main --host=test.db.hostname --port=8080 --username=admin --password=admin --log-path=/var/logs/db --log-level=debug

7. Defines configuration name as a slice type

Using separator to split string as a slice:

  type Log struct {
    Levels []string `env:"LEVELS" cli:"levels" separator:";" usage:"log levels"`
  }

If the separator is not given, its default is :, The separator only works on env and cli tags.

  logConfig := Log{}
  // export LEVELS=debug;error;info
  config.ParseEnv(&logConfig)
  // logConfig[0] == debug
  // logConfig[1] == error
  // logConfig[2] == info

II. Parses configurations

1. Parses default values

When default values are defined in tags, calls config.ParseDefault(interface{}) to assign them to given structure instance BEFORE parsing any other configuration types:

  logConfig := Log{}
  config.ParseDefault(&logConfig)

Note: Other parsing functions don't set structure instance with default values whatever if the configuration value is provided or not

2. Parses from Environment variables

  dbConfig := Database{}
  config.ParseEnv(&dbConfig)

3. Parses from Command line

  dbConfig := Database{}
  config.ParseCli(&dbConfig)

4. Parses from default configuration files

Calls ParseConfigFile(interface{}, string) to parse given configuration file:

  dbConfig := Database{}
  config.ParseConfigFile(&dbConfig, "config.json")

If the configuration file is not given, the default configuration files: config.json and config.yaml will be located under the same folder with fixed searching order.

The config.json will always be located first, if it doesn't exist, then checks
config.yaml. If all of them are not found, parsing will fail.

  dbConfig := Database{}
  config.ParseConfigFile(&dbConfig, "")

4. Parses from configuration file specified by command line

Calls ParseConfig(interface{}, string) to parse the configuration file given by command line. The second parameter is a command line argument which is used to specify config file:

  dbConfig := Database{}
  config.ParseConfig(&dbConfig, "c")

Run application like:

  ./main -c config.json

ParseConfig() will analyze command line arguments and get configure file: config.json from argument -c

III. Multi-Configurations

You can define all supported configuration tags in a structure and call corresponding functions in your desired order to parse.

Examples:

  type Log struct {
    Path   string `cli:"path"   default:"/var/logs"   env:"PATH"   json:"path"   usage:"log path"   yaml:"path"`
    Levels string `cli:"levels" default:"debug;error" env:"LEVELS" json:"levels" usage:"log levels" yaml:"levels"`
  }
  
  type Database struct {
    Host     string `cli:"host" env:"DB_HOST" json:"host" usage:"database host name" yaml:"host"`
    Port     int    `cli:"port" env:"DB_PORT" json:"port" usage:"database port"      yaml:"port"`
    Username string `cli:"username" default:"admin" env:"DB_USER"   json:"user"   usage:"database username" yaml" user"`
    Password string `cli:"password" default:"admin" env:"DB_PASSWD" json:"passwd" usage:"database password" yaml:"passwd"`
    Log      Log    `cli:"log" env:"DB_LOG_" json:"log" usage:"database log configurations" yaml:"log"`
  }

Then, you can parse as below:

 dbConfig := Database{}
 
 // parse default values
 if err := config.ParseDefault(&dbConfig); err != nil {
   // error handling
 }

 // parse configuration file from command line
 err := config.ParseConfig(&dbConfig, "c")
 
 // parse default configurations
 if err != nil {
   err = config.ParseConfigFile(&dbConfig), "")
 }
 
 // parse environment variables
 if err != nil {
   err = config.ParseEnv(&dbConfig)
 }
 
 // parse command line
 if err != nil {
   err = config.ParseCli(&dbConfig)
 }
 
 // check if all required configurations are set
 ...

You don't need to call all of them. Just invokes parsing function that your need.

License

This project is licensed under the Apache License Version 2.0.