115 lines
2.4 KiB
Go
115 lines
2.4 KiB
Go
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package config
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import (
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"os"
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"strings"
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"fmt"
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"reflect"
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"errors"
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"strconv"
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)
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var ConfigFetchMethod = os.Environ
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func Build(prefix string, configStruct interface{}) (err error) {
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defer func() {
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if e := recover(); e != nil {
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switch r := e.(type) {
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case string:
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err = errors.New(r)
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case error:
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err = r
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default:
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err = errors.New("Undefined panic")
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}
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}
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}()
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assertIsPtr(configStruct)
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fieldNames := getConfigStructFieldNames(configStruct)
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config := loadConfig(prefix)
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structRef := reflect.ValueOf(configStruct)
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for _, fieldName := range fieldNames {
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value, ok := config[fieldName]
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if !ok {
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// no such field loaded, avoid overwriting default
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continue
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}
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field := reflect.Indirect(structRef).FieldByName(fieldName)
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typeRef := field.Type()
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ret, err := tryParseString(value, typeRef.Kind())
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if err != nil {
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return err
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}
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field.Set(reflect.ValueOf(ret).Convert(typeRef))
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}
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return nil
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}
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func tryParseString(what string, toType reflect.Kind) (interface{}, error) {
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switch toType {
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case reflect.String:
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return what, nil
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case reflect.Int:
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i, err := strconv.Atoi(what)
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if err != nil {
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return nil, err
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}
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return i, nil
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case reflect.Bool:
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b, err := strconv.ParseBool(what)
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if err != nil {
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return nil, err
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}
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return b, nil
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default:
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return nil, fmt.Errorf("Failed to parse value %v", what)
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}
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}
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func assertIsPtr(what interface{}) {
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r := reflect.ValueOf(what)
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if r.Kind() != reflect.Ptr {
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panic(fmt.Errorf("Supplied value is not a pointer to a struct"))
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}
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}
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func getConfigStructFieldNames(configStruct interface{}) []string {
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configFields := []string{}
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val := reflect.ValueOf(configStruct).Elem()
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for i := 0; i < val.NumField(); i++ {
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configFields = append(configFields, val.Type().Field(i).Name)
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}
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return configFields
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}
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func loadConfig(prefix string) map[string]string {
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prefix = fmt.Sprintf("%s_", prefix)
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config := map[string]string{}
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for _, env := range ConfigFetchMethod() {
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parts := strings.SplitN(env, "=", 2)
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key, value := parts[0], parts[1]
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if strings.HasPrefix(key, prefix) {
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key = strings.TrimPrefix(key, prefix)
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config[key] = value
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}
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}
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return config
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}
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// CheckKeysExist returns an error if not all keys are present in config map
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func CheckKeysExist(config map[string]string, keys ...string) error {
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for _, key := range keys {
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if _, ok := config[key]; ok {
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return fmt.Errorf("Config key '%s' is not set", key)
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}
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}
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return nil
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}
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