chipmunk/vendor/github.com/kelseyhightower/envconfig/envconfig.go

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2017-01-24 18:27:39 -08:00
// Copyright (c) 2013 Kelsey Hightower. All rights reserved.
// Use of this source code is governed by the MIT License that can be found in
// the LICENSE file.
package envconfig
import (
"encoding"
"errors"
"fmt"
"reflect"
"strconv"
"strings"
"time"
)
// ErrInvalidSpecification indicates that a specification is of the wrong type.
var ErrInvalidSpecification = errors.New("specification must be a struct pointer")
// A ParseError occurs when an environment variable cannot be converted to
// the type required by a struct field during assignment.
type ParseError struct {
KeyName string
FieldName string
TypeName string
Value string
Err error
}
// Decoder has the same semantics as Setter, but takes higher precedence.
// It is provided for historical compatibility.
type Decoder interface {
Decode(value string) error
}
// Setter is implemented by types can self-deserialize values.
// Any type that implements flag.Value also implements Setter.
type Setter interface {
Set(value string) error
}
func (e *ParseError) Error() string {
return fmt.Sprintf("envconfig.Process: assigning %[1]s to %[2]s: converting '%[3]s' to type %[4]s. details: %[5]s", e.KeyName, e.FieldName, e.Value, e.TypeName, e.Err)
}
// Process populates the specified struct based on environment variables
func Process(prefix string, spec interface{}) error {
s := reflect.ValueOf(spec)
if s.Kind() != reflect.Ptr {
return ErrInvalidSpecification
}
s = s.Elem()
if s.Kind() != reflect.Struct {
return ErrInvalidSpecification
}
typeOfSpec := s.Type()
for i := 0; i < s.NumField(); i++ {
f := s.Field(i)
ftype := typeOfSpec.Field(i)
if !f.CanSet() || ftype.Tag.Get("ignored") == "true" {
continue
}
for f.Kind() == reflect.Ptr {
if f.IsNil() {
if f.Type().Elem().Kind() != reflect.Struct {
// nil pointer to a non-struct: leave it alone
break
}
// nil pointer to struct: create a zero instance
f.Set(reflect.New(f.Type().Elem()))
}
f = f.Elem()
}
alt := ftype.Tag.Get("envconfig")
fieldName := ftype.Name
if alt != "" {
fieldName = alt
}
key := fieldName
if prefix != "" {
key = fmt.Sprintf("%s_%s", prefix, key)
}
key = strings.ToUpper(key)
if f.Kind() == reflect.Struct {
// honor Decode if present
if decoderFrom(f) == nil && setterFrom(f) == nil && textUnmarshaler(f) == nil {
innerPrefix := prefix
if !ftype.Anonymous {
innerPrefix = key
}
embeddedPtr := f.Addr().Interface()
if err := Process(innerPrefix, embeddedPtr); err != nil {
return err
}
f.Set(reflect.ValueOf(embeddedPtr).Elem())
continue
}
}
// `os.Getenv` cannot differentiate between an explicitly set empty value
// and an unset value. `os.LookupEnv` is preferred to `syscall.Getenv`,
// but it is only available in go1.5 or newer. We're using Go build tags
// here to use os.LookupEnv for >=go1.5
value, ok := lookupEnv(key)
if !ok && alt != "" {
key := strings.ToUpper(fieldName)
value, ok = lookupEnv(key)
}
def := ftype.Tag.Get("default")
if def != "" && !ok {
value = def
}
req := ftype.Tag.Get("required")
if !ok && def == "" {
if req == "true" {
return fmt.Errorf("required key %s missing value", key)
}
continue
}
err := processField(value, f)
if err != nil {
return &ParseError{
KeyName: key,
FieldName: fieldName,
TypeName: f.Type().String(),
Value: value,
Err: err,
}
}
}
return nil
}
// MustProcess is the same as Process but panics if an error occurs
func MustProcess(prefix string, spec interface{}) {
if err := Process(prefix, spec); err != nil {
panic(err)
}
}
func processField(value string, field reflect.Value) error {
typ := field.Type()
decoder := decoderFrom(field)
if decoder != nil {
return decoder.Decode(value)
}
// look for Set method if Decode not defined
setter := setterFrom(field)
if setter != nil {
return setter.Set(value)
}
if t := textUnmarshaler(field); t != nil {
return t.UnmarshalText([]byte(value))
}
if typ.Kind() == reflect.Ptr {
typ = typ.Elem()
if field.IsNil() {
field.Set(reflect.New(typ))
}
field = field.Elem()
}
switch typ.Kind() {
case reflect.String:
field.SetString(value)
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
var (
val int64
err error
)
if field.Kind() == reflect.Int64 && typ.PkgPath() == "time" && typ.Name() == "Duration" {
var d time.Duration
d, err = time.ParseDuration(value)
val = int64(d)
} else {
val, err = strconv.ParseInt(value, 0, typ.Bits())
}
if err != nil {
return err
}
field.SetInt(val)
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
val, err := strconv.ParseUint(value, 0, typ.Bits())
if err != nil {
return err
}
field.SetUint(val)
case reflect.Bool:
val, err := strconv.ParseBool(value)
if err != nil {
return err
}
field.SetBool(val)
case reflect.Float32, reflect.Float64:
val, err := strconv.ParseFloat(value, typ.Bits())
if err != nil {
return err
}
field.SetFloat(val)
case reflect.Slice:
vals := strings.Split(value, ",")
sl := reflect.MakeSlice(typ, len(vals), len(vals))
for i, val := range vals {
err := processField(val, sl.Index(i))
if err != nil {
return err
}
}
field.Set(sl)
}
return nil
}
func interfaceFrom(field reflect.Value, fn func(interface{}, *bool)) {
// it may be impossible for a struct field to fail this check
if !field.CanInterface() {
return
}
var ok bool
fn(field.Interface(), &ok)
if !ok && field.CanAddr() {
fn(field.Addr().Interface(), &ok)
}
}
func decoderFrom(field reflect.Value) (d Decoder) {
interfaceFrom(field, func(v interface{}, ok *bool) { d, *ok = v.(Decoder) })
return d
}
func setterFrom(field reflect.Value) (s Setter) {
interfaceFrom(field, func(v interface{}, ok *bool) { s, *ok = v.(Setter) })
return s
}
func textUnmarshaler(field reflect.Value) (t encoding.TextUnmarshaler) {
interfaceFrom(field, func(v interface{}, ok *bool) { t, *ok = v.(encoding.TextUnmarshaler) })
return t
}