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// Copyright 2017 Frank Schroeder. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package properties
import (
"fmt"
"reflect"
"strconv"
"strings"
"time"
)
// Decode assigns property values to exported fields of a struct.
//
// Decode traverses v recursively and returns an error if a value cannot be
// converted to the field type or a required value is missing for a field.
//
// The following type dependent decodings are used:
//
// String, boolean, numeric fields have the value of the property key assigned.
// The property key name is the name of the field. A different key and a default
// value can be set in the field's tag. Fields without default value are
// required. If the value cannot be converted to the field type an error is
// returned.
//
// time.Duration fields have the result of time.ParseDuration() assigned.
//
// time.Time fields have the vaule of time.Parse() assigned. The default layout
// is time.RFC3339 but can be set in the field's tag.
//
// Arrays and slices of string, boolean, numeric, time.Duration and time.Time
// fields have the value interpreted as a comma separated list of values. The
// individual values are trimmed of whitespace and empty values are ignored. A
// default value can be provided as a semicolon separated list in the field's
// tag.
//
// Struct fields are decoded recursively using the field name plus "." as
// prefix. The prefix (without dot) can be overridden in the field's tag.
// Default values are not supported in the field's tag. Specify them on the
// fields of the inner struct instead.
//
// Map fields must have a key of type string and are decoded recursively by
// using the field's name plus ".' as prefix and the next element of the key
// name as map key. The prefix (without dot) can be overridden in the field's
// tag. Default values are not supported.
//
// Examples:
//
// // Field is ignored.
// Field int `properties:"-"`
//
// // Field is assigned value of 'Field'.
// Field int
//
// // Field is assigned value of 'myName'.
// Field int `properties:"myName"`
//
// // Field is assigned value of key 'myName' and has a default
// // value 15 if the key does not exist.
// Field int `properties:"myName,default=15"`
//
// // Field is assigned value of key 'Field' and has a default
// // value 15 if the key does not exist.
// Field int `properties:",default=15"`
//
// // Field is assigned value of key 'date' and the date
// // is in format 2006-01-02
// Field time.Time `properties:"date,layout=2006-01-02"`
//
// // Field is assigned the non-empty and whitespace trimmed
// // values of key 'Field' split by commas.
// Field []string
//
// // Field is assigned the non-empty and whitespace trimmed
// // values of key 'Field' split by commas and has a default
// // value ["a", "b", "c"] if the key does not exist.
// Field []string `properties:",default=a;b;c"`
//
// // Field is decoded recursively with "Field." as key prefix.
// Field SomeStruct
//
// // Field is decoded recursively with "myName." as key prefix.
// Field SomeStruct `properties:"myName"`
//
// // Field is decoded recursively with "Field." as key prefix
// // and the next dotted element of the key as map key.
// Field map[string]string
//
// // Field is decoded recursively with "myName." as key prefix
// // and the next dotted element of the key as map key.
// Field map[string]string `properties:"myName"`
func (p *Properties) Decode(x interface{}) error {
t, v := reflect.TypeOf(x), reflect.ValueOf(x)
if t.Kind() != reflect.Ptr || v.Elem().Type().Kind() != reflect.Struct {
return fmt.Errorf("not a pointer to struct: %s", t)
}
if err := dec(p, "", nil, nil, v); err != nil {
return err
}
return nil
}
func dec(p *Properties, key string, def *string, opts map[string]string, v reflect.Value) error {
t := v.Type()
// value returns the property value for key or the default if provided.
value := func() (string, error) {
if val, ok := p.Get(key); ok {
return val, nil
}
if def != nil {
return *def, nil
}
return "", fmt.Errorf("missing required key %s", key)
}
// conv converts a string to a value of the given type.
conv := func(s string, t reflect.Type) (val reflect.Value, err error) {
var v interface{}
switch {
case isDuration(t):
v, err = time.ParseDuration(s)
case isTime(t):
layout := opts["layout"]
if layout == "" {
layout = time.RFC3339
}
v, err = time.Parse(layout, s)
case isBool(t):
v, err = boolVal(s), nil
case isString(t):
v, err = s, nil
case isFloat(t):
v, err = strconv.ParseFloat(s, 64)
case isInt(t):
v, err = strconv.ParseInt(s, 10, 64)
case isUint(t):
v, err = strconv.ParseUint(s, 10, 64)
default:
return reflect.Zero(t), fmt.Errorf("unsupported type %s", t)
}
if err != nil {
return reflect.Zero(t), err
}
return reflect.ValueOf(v).Convert(t), nil
}
// keydef returns the property key and the default value based on the
// name of the struct field and the options in the tag.
keydef := func(f reflect.StructField) (string, *string, map[string]string) {
_key, _opts := parseTag(f.Tag.Get("properties"))
var _def *string
if d, ok := _opts["default"]; ok {
_def = &d
}
if _key != "" {
return _key, _def, _opts
}
return f.Name, _def, _opts
}
switch {
case isDuration(t) || isTime(t) || isBool(t) || isString(t) || isFloat(t) || isInt(t) || isUint(t):
s, err := value()
if err != nil {
return err
}
val, err := conv(s, t)
if err != nil {
return err
}
v.Set(val)
case isPtr(t):
return dec(p, key, def, opts, v.Elem())
case isStruct(t):
for i := 0; i < v.NumField(); i++ {
fv := v.Field(i)
fk, def, opts := keydef(t.Field(i))
if !fv.CanSet() {
return fmt.Errorf("cannot set %s", t.Field(i).Name)
}
if fk == "-" {
continue
}
if key != "" {
fk = key + "." + fk
}
if err := dec(p, fk, def, opts, fv); err != nil {
return err
}
}
return nil
case isArray(t):
val, err := value()
if err != nil {
return err
}
vals := split(val, ";")
a := reflect.MakeSlice(t, 0, len(vals))
for _, s := range vals {
val, err := conv(s, t.Elem())
if err != nil {
return err
}
a = reflect.Append(a, val)
}
v.Set(a)
case isMap(t):
valT := t.Elem()
m := reflect.MakeMap(t)
for postfix := range p.FilterStripPrefix(key + ".").m {
pp := strings.SplitN(postfix, ".", 2)
mk, mv := pp[0], reflect.New(valT)
if err := dec(p, key+"."+mk, nil, nil, mv); err != nil {
return err
}
m.SetMapIndex(reflect.ValueOf(mk), mv.Elem())
}
v.Set(m)
default:
return fmt.Errorf("unsupported type %s", t)
}
return nil
}
// split splits a string on sep, trims whitespace of elements
// and omits empty elements
func split(s string, sep string) []string {
var a []string
for _, v := range strings.Split(s, sep) {
if v = strings.TrimSpace(v); v != "" {
a = append(a, v)
}
}
return a
}
// parseTag parses a "key,k=v,k=v,..."
func parseTag(tag string) (key string, opts map[string]string) {
opts = map[string]string{}
for i, s := range strings.Split(tag, ",") {
if i == 0 {
key = s
continue
}
pp := strings.SplitN(s, "=", 2)
if len(pp) == 1 {
opts[pp[0]] = ""
} else {
opts[pp[0]] = pp[1]
}
}
return key, opts
}
func isArray(t reflect.Type) bool { return t.Kind() == reflect.Array || t.Kind() == reflect.Slice }
func isBool(t reflect.Type) bool { return t.Kind() == reflect.Bool }
func isDuration(t reflect.Type) bool { return t == reflect.TypeOf(time.Second) }
func isMap(t reflect.Type) bool { return t.Kind() == reflect.Map }
func isPtr(t reflect.Type) bool { return t.Kind() == reflect.Ptr }
func isString(t reflect.Type) bool { return t.Kind() == reflect.String }
func isStruct(t reflect.Type) bool { return t.Kind() == reflect.Struct }
func isTime(t reflect.Type) bool { return t == reflect.TypeOf(time.Time{}) }
func isFloat(t reflect.Type) bool {
return t.Kind() == reflect.Float32 || t.Kind() == reflect.Float64
}
func isInt(t reflect.Type) bool {
return t.Kind() == reflect.Int || t.Kind() == reflect.Int8 || t.Kind() == reflect.Int16 || t.Kind() == reflect.Int32 || t.Kind() == reflect.Int64
}
func isUint(t reflect.Type) bool {
return t.Kind() == reflect.Uint || t.Kind() == reflect.Uint8 || t.Kind() == reflect.Uint16 || t.Kind() == reflect.Uint32 || t.Kind() == reflect.Uint64
}
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