go-auto-cfg    

go-auto-cfg provides a way to access environmental variables as go functions.

go-auto-cfg is a wrapper over viper. It takes a schema file as input and generates a go file, the config loader, with functions named after the env variables.

It is available as a CLI tool. Also, can be used with go generate tool. Go generate example.

Installation

go get -u github.com/sidtharthanan/go-auto-cfg
go-auto-cfg              --help  # depending on your PATH configuration use either of
$GOPATH/bin/go-auto-cfg  --help  # these commands

Usage

go-auto-cfg <schema-file> <output-file>

Example

go-auto-cfg schema.yml config/config.auto.go

The above command will parse schema.yml file and generate config.auto.go file under config package.

Schema file

The schema is defined in a yaml file. It has to be in the following format.

<ENV-variable-name>: <data-type>[,<constraint>]

Schema example

AUTH_FEATURE_ON: bool
CLIENT_ID: string,@optional()
CLIENT_PASS: string,@optional()
POOL_SIZE: integer,@optional(5)
ENVS: strings

Data types

Type	Description
integer	To int.
float	To float64.
string	To string.
bool	To bool.
strings	To []string. Value is either a list of strings or space separated values. example

Constraints

Constraint	Description
@optional()	Makes the variable optional. By default all variables are required.
@optional(default-value)	Makes the variable optional with a default value.

Full example

Sample schema.yml file

AUTH_FEATURE_ON: bool
AUTH_TIMEOUT_IN_HOURS: float
CLIENT_ID: integer
CLIENT_PASS: string
ENVS: strings
SOME_PREFIX: string,@optional(abc)
SOME_SUFFIX: string,@optional()
POOL_SIZE: integer,@optional(20)

Configuration file variables.yml

AUTH_FEATURE_ON: false
AUTH_TIMEOUT_IN_HOURS: 2.5

CLIENT_ID: 20082
CLIENT_PASS: qyUswmix82sw

ENVS: uat prod

Generate the go config loader file

Alternatively this can be automated.

go-auto-cfg schema.yml config/config.auto.go

Use config/config.auto.go to load variables.yml

 import cfg "config"
 
 func main() {
   //load config file "variables.yml" from "." directory
   cfg.Load("variables", ".")
   if cfg.AUTH_FEATURE_ON() {  // false
     middleware.authorize(user)
   }
   poolSize := cfg.POOL_SIZE() // 20
   prefix := cfg.SOME_PREFIX() // "abc"
   suffix := cfg.SOME_SUFFIX() // ""
 }

Use go generate

 //go:generate go-auto-cfg schema.yml config/config.auto.go
 import cfg "config"

 func main() {
   ...
 }

Load multiple configs

 import cfg "config"
 
 func main() {
   cfg.Load("global", ".")
   cfg.SOME_GLOBAL_CONFIG()

   cfgA := cfg.New()
   cfgA.Load("moduleA", ".")
   cfgA.MODULE_A_SPECIFIC_CONFIG()
   
   cfgB := cfg.New()
   cfgB.Load("moduleB", ".")
   cfgB.MODULE_B_SPECIFIC_CONFIG()

 }

FAQ

1. Q: Why functionscfg.SOME_CONFIG() not simple struct memberscfg.SOME_CONFIG?

   A: We want read only configuration and it is not possible to achieve without methods.