STRV env

Go package for runtime environment configuration.

env package leverage Go's reflection functionality for scanning structures. If the env tag is found, a value of this tag is used for env lookup. If the env variable is set, the value in the structure is overridden. There are two ways how to process structures:

• If a tag value contains ,dive, inner fields of a structure are processed (Session in the example).
• If a structure implements the encoding.TextUnmarshaler interface, UnmarshalText is called for the given structure (AccessTokenExpiration or zap.AtomicLevel in the example).

A good practice when overriding a config with env variables is to use an app prefix. If the env variable APP_PREFIX contains some value (MY_APP for example), each defined env variable has to contain the prefix MY_APP (MY_APP_PORT in the example). There is also an option to choose a custom prefix for env variables by calling MustApplyWithPrefix.

It may happen that the app needs to consume an env variable set by a third party. It's no exception that a cloud provider sets a port your app needs to listen on and you are unable to modify it. In this case, there is an option to enhance the env tag with the ignoreprefix clause (env:"PORT,ignoreprefix"). While other env variables will be searched with a prefix included, PORT not.

Examples

package main

import (
	envx "go.strv.io/env"
	timex "go.strv.io/time"

	"go.uber.org/zap"
)

type config struct {
	Port        uint   `json:"port" env:"PORT"`
	StorageAddr string `json:"storage_addr" env:"STORAGE_ADDR"`
	Session     struct {
		AccessTokenExpiration timex.Duration `json:"access_token_expiration" env:"SESSION_ACCESS_TOKEN_EXPIRATION"`
	} `json:"session" env:",dive"`
	LogLevel zap.AtomicLevel `json:"log_level" env:"LOG_LEVEL"`
}

func main() {
	cfg := config{}
	envx.MustApply(&cfg)
}

See detailed example.