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util.go
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util.go
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package config
import (
"encoding/json"
"fmt"
"reflect"
"strconv"
"strings"
"time"
)
type decoder interface {
Decode(value string) error
}
type fieldInfo struct {
Name string
Default string
Field reflect.Value
}
// StringTemplate is a convenience alias
type StringTemplate string
func decoderFrom(field reflect.Value) (d decoder) {
// it may be impossible for a struct field to fail this check
if !field.CanInterface() {
return
}
d, ok := field.Interface().(decoder)
if !ok && field.CanAddr() {
d, _ = field.Addr().Interface().(decoder)
}
return d
}
// taken from github.com/kelseyhightower/envconfig
func structFields(spec interface{}) ([]fieldInfo, error) {
s := reflect.ValueOf(spec).Elem()
// over allocate an info array, we will extend if needed later
infos := make([]fieldInfo, 0, s.NumField())
for i := 0; i < s.NumField(); i++ {
f := s.Field(i)
ftype := s.Type().Field(i)
fieldName := ftype.Tag.Get("name")
if fieldName == "" {
fieldName = strings.ToLower(ftype.Name)
}
// Capture information about the config variable
info := fieldInfo{
Name: fieldName,
Field: f,
Default: ftype.Tag.Get("default"),
}
infos = append(infos, info)
if f.Kind() == reflect.Struct {
// honor Decode if present
if decoderFrom(f) == nil {
embeddedPtr := f.Addr().Interface()
embeddedInfos, err := structFields(embeddedPtr)
if err != nil {
return nil, err
}
infos = append(infos[:len(infos)-1], embeddedInfos...)
continue
}
}
}
return infos, nil
}
func processField(value string, field reflect.Value) error {
typ := field.Type()
decoder := decoderFrom(field)
if decoder != nil {
return decoder.Decode(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)
case reflect.Map:
pairs, err := getMapPairsFromString(value)
if err != nil {
return fmt.Errorf("could not split value %q into map items: %v", value, err)
}
mp := reflect.MakeMap(typ)
for _, pair := range pairs {
kvpair := strings.Split(pair, ":")
if len(kvpair) != 2 {
return fmt.Errorf("invalid map item: %q", pair)
}
k := reflect.New(typ.Key()).Elem()
err := processField(kvpair[0], k)
if err != nil {
return err
}
v := reflect.New(typ.Elem()).Elem()
err = processField(kvpair[1], v)
if err != nil {
return err
}
mp.SetMapIndex(k, v)
}
field.Set(mp)
}
return nil
}
type parserState int
const (
plain parserState = iota
doubleQuoted
singleQuoted
)
// Split the pair candidates by commas not located inside open quotes
// Escape characters are not supported for simplicity, as we don't
// expect to find them inside the map values for our use cases
func getMapPairsFromString(value string) (pairs []string, err error) {
pairs = make([]string, 0)
state := plain
var start, quote int
for i, ch := range strings.Split(value, "") {
if (ch == `"` || ch == `'`) && i > 0 && value[i-1] == '\\' {
fmt.Printf("Parser warning: ecape character '\\' have no effect on quotes inside the configuration value %s\n", value)
}
if ch == `"` {
if state == plain {
state = doubleQuoted
quote = i
} else if state == doubleQuoted {
state = plain
quote = 0
}
}
if ch == "'" {
if state == plain {
state = singleQuoted
quote = i
} else if state == singleQuoted {
state = plain
quote = 0
}
}
if ch == "," && state == plain {
pairs = append(pairs, strings.Trim(value[start:i], " \t"))
start = i + 1
}
}
if state != plain {
err = fmt.Errorf("unmatched quote starting at position %d", quote+1)
pairs = nil
} else {
pairs = append(pairs, strings.Trim(value[start:], " \t"))
}
return
}
// Decode cast value to StringTemplate
func (f *StringTemplate) Decode(value string) error {
*f = StringTemplate(value)
return nil
}
// Format formatted string from StringTemplate
func (f *StringTemplate) Format(a ...string) string {
res := string(*f)
for i := 0; i < len(a); i += 2 {
res = strings.Replace(res, "{"+a[i]+"}", a[i+1], -1)
}
return res
}
// MarshalJSON converts a StringTemplate to byte slice
func (f StringTemplate) MarshalJSON() ([]byte, error) {
return json.Marshal(string(f))
}