example_test.go

// NOTE: os.Clearenv must be called before each test that uses env vars to avoid false positives with env bleeding over.
package config_test

import (
	"fmt"
	"os"
	"strings"

	"github.com/JeremyLoy/config"
)

type MySubConfig struct {
	IPWhitelist []string
}

type MyConfig struct {
	DatabaseURL string `config:"DATABASE_URL"`
	Port        int
	FeatureFlag bool `config:"FEATURE_FLAG"`
	SubConfig   MySubConfig
}

func Example() {
	os.Clearenv()
	os.Setenv("DATABASE_URL", "db://")
	os.Setenv("PORT", "1234")
	os.Setenv("FEATURE_FLAG", "true") // also accepts t, f, 0, 1 etc. see strconv package.
	// Double underscore for sub structs. Space separation for slices.
	os.Setenv("SUBCONFIG__IPWHITELIST", "0.0.0.0 1.1.1.1 2.2.2.2")

	var c MyConfig
	config.FromEnv().To(&c)

	fmt.Println(c.DatabaseURL)
	fmt.Println(c.Port)
	fmt.Println(c.FeatureFlag)
	fmt.Println(c.SubConfig.IPWhitelist, len(c.SubConfig.IPWhitelist))

	// Output:
	// db://
	// 1234
	// true
	// [0.0.0.0 1.1.1.1 2.2.2.2] 3
}

func Example_subconfig() {
	os.Clearenv()
	os.Setenv("SUBCONFIG__IPWHITELIST", "0.0.0.0 1.1.1.1 2.2.2.2")

	var c MySubConfig
	config.FromEnv().Sub(&c, "SUBCONFIG")

	fmt.Println(c.IPWhitelist, len(c.IPWhitelist))

	// Output:
	// [0.0.0.0 1.1.1.1 2.2.2.2] 3
}

func Example_defaults() {
	os.Clearenv()
	os.Setenv("DATABASE_URL", "production://")

	// existing values on the struct are maintained if unset in the env
	c := MyConfig{
		DatabaseURL: "development://",
		Port:        1234,
	}
	config.FromEnv().To(&c)

	fmt.Println(c.DatabaseURL)
	fmt.Println(c.Port)

	// Output:
	// production://
	// 1234
}

func Example_errorHandling() {
	os.Clearenv()
	os.Setenv("PORT", "X")

	var c MyConfig
	err := config.FromEnv().To(&c)
	fmt.Println(err)

	// Output:
	// config: the following fields had errors: [port]
}

func Example_fromFileWithOverride() {
	tempFile, _ := os.CreateTemp("", "temp")
	tempFile.Write([]byte(strings.Join([]string{"PORT=1234", "FEATURE_FLAG=true"}, "\n")))
	tempFile.Close()

	os.Clearenv()
	os.Setenv("DATABASE_URL", "db://")
	os.Setenv("PORT", "5678")

	var c MyConfig
	config.From(tempFile.Name()).FromEnv().To(&c)

	// db:// was only set in ENV
	fmt.Println(c.DatabaseURL)
	// 1234 was overridden by 5678
	fmt.Println(c.Port)
	// FeatureFlag was was only set in file
	fmt.Println(c.FeatureFlag)

	// Output:
	// db://
	// 5678
	// true
}

func Example_structTags() {
	type MyConfig struct {
		// NOTE: even when using tags, lookup is still case insensitive.
		// dAtABase_urL would still work.
		DatabaseURL string `config:"DATABASE_URL"`
	}

	os.Clearenv()
	os.Setenv("DATABASE_URL", "db://")

	var c MyConfig
	config.FromEnv().To(&c)

	fmt.Println(c.DatabaseURL)

	// Output:
	// db://
}