Introduction

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 anlayze Yaml file and uses built-in golang library to handle JSON file.

Installation

1. Install Yaml library first:

go get gopkg.in/yaml.v2

2. 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

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"`
  }

After that, calls config.ParseDefault(interface{}) to set structure instance with default values. Example codes:

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

3. Defines configruation 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 `json:"username" default:"admin"`
    Password string `json:"password" default:"admin"`
    Log Log         `json:"log"`
  }

Corresponding JSON file:

 {
   "host": "test.db.hostname"
   "port": 8080
   "username": "amdin"
   "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 `yaml:"username" default:"admin"`
    Password string `yaml:"password" default:"admin"`
    Log Log         `yaml:"log"`
  }

Corresponding Yaml file:

 host: test.db.hostname
 port: 8080
 username: amdin
 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 `env:"DB_USER" default:"admin"`
    Password string `env:"DB_PASSWORD" default:"admin"`
    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

6. Defines configuration name for Command line

Using cli keyword to define configuration name

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

III. Reads configurations from JSON and Yaml files

1. Using json to define configuration name

2. Using yaml to define configuration name

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

Parsing configurations from JSON:

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