Clean Env
Minimalistic configuration reader
Overview
This is a simple configuration reading tool. It just does the following:
- reads and parses configuration structure from the file
- reads and overwrites configuration structure from environment variables
- writes a detailed variable list to help output
Content
- Installation
- Usage
- Model Format
- Supported types
- Custom Functions
- Supported File Formats
- Integration
- Examples
- Contribution
- Thanks
Installation
To install the package run
go get -u github.com/ilyakaznacheev/cleanenv
Usage
The package is oriented to be simple in use and explicitness.
The main idea is to use a structured configuration variable instead of any sort of dynamic set of configuration fields like some libraries does, to avoid unnecessary type conversions and move the configuration through the program as a simple structure, not as an object with complex behavior.
There are just several actions you can do with this tool and probably only things you want to do with your config if your application is not too complicated.
- read configuration file
- read environment variables
- read some environment variables again
Read Configuration
You can read a configuration file and environment variables in a single function call.
import github.com/ilyakaznacheev/cleanenv
type ConfigDatabase struct {
Port string `yaml:"port" env:"PORT" env-default:"5432"`
Host string `yaml:"host" env:"HOST" env-default:"localhost"`
Name string `yaml:"name" env:"NAME" env-default:"postgres"`
User string `yaml:"user" env:"USER" env-default:"user"`
Password string `yaml:"password" env:"PASSWORD"`
}
var cfg ConfigDatabase
err := cleanenv.ReadConfig("config.yml", &cfg)
if err != nil {
...
}
This will do the following:
- parse configuration file according to YAML format (
yamltag in this case); - reads environment variables and overwrites values from the file with the values which was found in the environment (
envtag); - if no value was found on the first two steps, the field will be filled with the default value (
env-defaulttag) if it is set.
Read Environment Variables Only
Sometimes you don't want to use configuration files at all, or you may want to use .env file format instead. Thus, you can limit yourself with only reading environment variables:
import github.com/ilyakaznacheev/cleanenv
type ConfigDatabase struct {
Port string `env:"PORT" env-default:"5432"`
Host string `env:"HOST" env-default:"localhost"`
Name string `env:"NAME" env-default:"postgres"`
User string `env:"USER" env-default:"user"`
Password string `env:"PASSWORD"`
}
var cfg ConfigDatabase
err := cleanenv.ReadEnv(&cfg)
if err != nil {
...
}
Update Environment Variables
Some environment variables may change during the application run. To get the new values you need to mark these variables as updatable with the tag env-upd and then run the update function:
import github.com/ilyakaznacheev/cleanenv
type ConfigRemote struct {
Port string `env:"PORT" env-upd`
Host string `env:"HOST" env-upd`
UserName string `env:"USERNAME"`
}
var cfg ConfigRemote
cleanenv.ReadEnv(&cfg)
// ... some actions in-between
err := cleanenv.UpdateEnv(&cfg)
if err != nil {
...
}
Here remote host and port may change in a distributed system architecture. Fields cfg.Port and cfg.Host can be updated in the runtime from corresponding environment variables. You can update them before the remote service call. Field cfg.UserName will not be changed after the initial read, though.
Description
You can get descriptions of all environment variables to use them in the help documentation.
import github.com/ilyakaznacheev/cleanenv
type ConfigServer struct {
Port string `env:"PORT" env-description:"server port"`
Host string `env:"HOST" env-description:"server host"`
}
var cfg ConfigRemote
help, err := cleanenv.GetDescription(&cfg, nil)
if err != nil {
...
}
You will get the following:
Environment variables:
PORT server port
HOST server host
Model Format
Library uses tags to configure the model of configuration structure. There are the following tags:
env="<name>"- environment variable name (e.g.env="PORT");env-upd- flag to mark a field as updatable. RunUpdateEnv(&cfg)to refresh updatable variables from environment;env-required- flag to mark a field as required. If set will return an error during environment parsing when the flagged as required field is empty (default Go value). Tagenv-defaultis ignored in this case;env-default="<value>"- default value. If the field wasn't filled from the environment variable default value will be used instead;env-separator="<value>"- custom list and map separator. If not set, the default separator,will be used;env-description="<value>"- environment variable description;env-layout="<value>"- parsing layout (for types liketime.Time);
Supported types
There are following supported types:
int(any kind);float(any kind);string;boolean;- slices (of any other supported type);
- maps (of any other supported type);
time.Duration;time.Time(layout by default is RFC3339, may be overridden byenv-layout);- any type implementing
cleanenv.Setterinterface.
Custom Functions
To enhance package abilities you can use some custom functions.
Custom Value Setter
To make custom type allows to set the value from the environment variable, you need to implement the Setter interface on the field level:
type MyField string
func (f *MyField) SetValue(s string) error {
if s == "" {
return fmt.Errorf("field value can't be empty")
}
*f = MyField("my field is: "+ s)
return nil
}
type Config struct {
Field MyField `env="MY_VALUE"`
}
SetValue method should implement conversion logic from string to custom type.
Custom Value Update
You may need to execute some custom field update logic, e.g. for remote config load.
Thus, you need to implement the Updater interface on the structure level:
type Config struct {
Field string
}
func (c *Config) Update() error {
newField, err := SomeCustomUpdate()
f.Field = newField
return err
}
Supported File Formats
There are several most popular config file formats supported:
- YAML
- JSON
- TOML
- ENV
- EDN
Integration
The package can be used with many other solutions. To make it more useful, we made some helpers.
Flag
You can use the cleanenv help together with Golang flag package.
// create some config structure
var cfg config
// create flag set using `flag` package
fset := flag.NewFlagSet("Example", flag.ContinueOnError)
// get config usage with wrapped flag usage
fset.Usage = cleanenv.FUsage(fset.Output(), &cfg, nil, fset.Usage)
fset.Parse(os.Args[1:])
Examples
type Config struct {
Port string `yaml:"port" env:"PORT" env-default:"8080"`
Host string `yaml:"host" env:"HOST" env-default:"localhost"`
}
var cfg Config
err := ReadConfig("config.yml", &cfg)
if err != nil {
...
}
This code will try to read and parse the configuration file config.yml as the structure is described in the Config structure. Then it will overwrite fields from available environment variables (PORT, HOST).
For more details check the example directory.
Contribution
The tool is open-sourced under the MIT license.
If you will find some error, want to add something or ask a question - feel free to create an issue and/or make a pull request.
Any contribution is welcome.
Thanks
Big thanks to a project kelseyhightower/envconfig for inspiration.
The logo was made by alexchoffy.
![Does this support parsing `map[string]CustomStruct` using the `env` tag?](https://avatars.githubusercontent.com/u/31163334?v=4)
