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https://github.com/ilyakaznacheev/cleanenv

✨Clean and minimalistic environment configuration reader for Golang
https://github.com/ilyakaznacheev/cleanenv

configuration environment-configuration environment-variables hacktoberfest

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✨Clean and minimalistic environment configuration reader for Golang

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![Clean Env](logo.svg)



# Clean Env



Minimalistic configuration reader



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## 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](#installation)

- [Usage](#usage)

    - [Read Configuration](#read-configuration)

    - [Read Environment Variables Only](#read-environment-variables-only)

    - [Update Environment Variables](#update-environment-variables)

    - [Description](#description)

- [Model Format](#model-format)

- [Supported types](#supported-types)

- [Custom Functions](#custom-functions)

    - [Custom Value Setter](#custom-value-setter)

    - [Custom Value Update](#custom-value-update)

- [Supported File Formats](#supported-file-formats)

- [Integration](#integration)

    - [Flag](#flag)

- [Examples](#examples)

- [Contribution](#contribution)

- [Thanks](#thanks)



## Installation



To install the package run



```bash

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.



```go

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:



1. parse configuration file according to YAML format (`yaml` tag in this case);

1. reads environment variables and overwrites values from the file with the values which was found in the environment (`env` tag);

1. if no value was found on the first two steps, the field will be filled with the default value (`env-default` tag) 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:



```go 

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:



```go

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.



```go

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=""` - environment variable name (e.g. `env="PORT"`);

- `env-upd` - flag to mark a field as updatable. Run `UpdateEnv(&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). Tag `env-default` is ignored in this case;

- `env-default=""` - default value. If the field wasn't filled from the environment variable default value will be used instead;

- `env-separator=""` - custom list and map separator. If not set, the default separator `,` will be used;

- `env-description=""` - environment variable description;

- `env-layout=""` - parsing layout (for types like `time.Time`);

- `env-prefix=""` - prefix for all fields of nested structure (only for nested structures);



## 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 by `env-layout`);

- `*time.Location` (time zone parsing [depends](https://pkg.go.dev/time#LoadLocation) on running machine);

- any type that implements `encoding.TextUnmarshaler`;

- any type implementing `cleanenv.Setter` interface.



## 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:



```go

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:



```go

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 (`.yaml`, `.yml`)

- JSON (`.json`)

- TOML (`.toml`)

- EDN (`.edn`)

- ENV (`.env`)



**Note**:

- while using `.env` file the library will set corresponding data to process environment variables.

  It will override existing variables with the same keys in the process environment.



## 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.



```go

// 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



```go

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](/example) directory.



## Version Support Policy



We support the last 7 versions of Golang. E.g. if the current version is 1.19, we test compatibility with all versions from 1.19 to 1.13.



If you use an older version of Golang in your project, please use an older library version.



## Contribution



The tool is open-sourced under the [MIT](LICENSE) license.



If you find some error, want to add something or ask a question - feel free to create an issue and/or make a pull request.



Guidelines for contribution may be found in [CONTRIBUTING.md](CONTRIBUTING.md).



Any contribution is welcome.



## Thanks



Big thanks to a project [kelseyhightower/envconfig](https://github.com/kelseyhightower/envconfig) for inspiration.



The logo was made by [alexchoffy](https://www.instagram.com/alexchoffy/).



## Blog Posts



[Clean Configuration Management in Golang](https://dev.to/ilyakaznacheev/clean-configuration-management-in-golang-1c89).