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config.go
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config.go
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package config
import (
"bytes"
"errors"
"fmt"
"io"
"os"
"reflect"
"strings"
"github.com/spf13/viper"
)
// MetaConfig holds configuration for environment name and service name
type MetaConfig struct {
Environment string
ServiceName string `mapstructure:"service_name"`
Region string `mapstructure:"region"`
}
type fileSystem interface {
ReadFile(name string) ([]byte, error)
}
// Load config from file then from environment variables
func Load(fs fileSystem, config interface{}) error {
configType := "json"
viper.SetConfigType(configType)
configName := "config"
if isTesting() {
configName = "config_test"
}
viper.SetConfigName(configName)
configFile := configName + "." + configType
contents, err := fs.ReadFile(configFile)
if err != nil {
return fmt.Errorf("unable to read config from %s: %w", configFile, err)
}
return ReadJSON(bytes.NewReader(contents), config)
}
func ReadJSON(in io.Reader, config interface{}) error {
configType := "json"
viper.SetConfigType(configType)
if err := viper.ReadConfig(in); err != nil {
return fmt.Errorf("unable to read config: %v", err)
}
return unmarshalConfig(config)
}
func unmarshalConfig(config interface{}) error {
viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
viper.AutomaticEnv()
// Read the config file again and consider environment variables at the same time
if err := viper.Unmarshal(config); err != nil {
return fmt.Errorf(
"unable to unmarshal config at %s: %w",
viper.ConfigFileUsed(),
err,
)
}
// Set the environment to be "test" if tests are being run.
meta := getMetaConfig(config)
if meta == nil {
return errors.New("meta config not available")
}
if isTesting() {
meta.Environment = "test"
} else {
env := os.Getenv("ENV")
if env != "" {
meta.Environment = env
}
}
return nil
}
func isTesting() bool {
for _, arg := range os.Args {
if strings.HasPrefix(arg, "-test.v=") {
return true
}
}
return false || os.Getenv("ENV") == "test"
}
func getMetaConfig(config interface{}) *MetaConfig {
v := reflect.ValueOf(config).Elem()
for i := 0; i < v.NumField(); i++ {
field := v.Field(i)
typ := field.Type()
if typ.AssignableTo(reflect.TypeOf(MetaConfig{})) {
return field.Addr().Interface().(*MetaConfig)
}
}
for i := 0; i < v.NumField(); i++ {
field := v.Field(i)
if field.CanAddr() {
if meta := getMetaConfig(field.Addr().Interface()); meta != nil {
return meta
}
}
}
return nil
}