290 lines
8.3 KiB
Go
290 lines
8.3 KiB
Go
// Copyright 2013-2022 Frank Schroeder. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package properties
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import (
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"fmt"
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"reflect"
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"strconv"
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"strings"
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"time"
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)
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// Decode assigns property values to exported fields of a struct.
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//
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// Decode traverses v recursively and returns an error if a value cannot be
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// converted to the field type or a required value is missing for a field.
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//
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// The following type dependent decodings are used:
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//
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// String, boolean, numeric fields have the value of the property key assigned.
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// The property key name is the name of the field. A different key and a default
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// value can be set in the field's tag. Fields without default value are
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// required. If the value cannot be converted to the field type an error is
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// returned.
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//
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// time.Duration fields have the result of time.ParseDuration() assigned.
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//
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// time.Time fields have the vaule of time.Parse() assigned. The default layout
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// is time.RFC3339 but can be set in the field's tag.
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//
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// Arrays and slices of string, boolean, numeric, time.Duration and time.Time
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// fields have the value interpreted as a comma separated list of values. The
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// individual values are trimmed of whitespace and empty values are ignored. A
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// default value can be provided as a semicolon separated list in the field's
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// tag.
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//
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// Struct fields are decoded recursively using the field name plus "." as
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// prefix. The prefix (without dot) can be overridden in the field's tag.
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// Default values are not supported in the field's tag. Specify them on the
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// fields of the inner struct instead.
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//
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// Map fields must have a key of type string and are decoded recursively by
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// using the field's name plus ".' as prefix and the next element of the key
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// name as map key. The prefix (without dot) can be overridden in the field's
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// tag. Default values are not supported.
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//
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// Examples:
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//
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// // Field is ignored.
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// Field int `properties:"-"`
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//
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// // Field is assigned value of 'Field'.
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// Field int
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//
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// // Field is assigned value of 'myName'.
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// Field int `properties:"myName"`
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//
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// // Field is assigned value of key 'myName' and has a default
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// // value 15 if the key does not exist.
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// Field int `properties:"myName,default=15"`
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//
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// // Field is assigned value of key 'Field' and has a default
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// // value 15 if the key does not exist.
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// Field int `properties:",default=15"`
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//
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// // Field is assigned value of key 'date' and the date
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// // is in format 2006-01-02
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// Field time.Time `properties:"date,layout=2006-01-02"`
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//
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// // Field is assigned the non-empty and whitespace trimmed
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// // values of key 'Field' split by commas.
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// Field []string
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//
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// // Field is assigned the non-empty and whitespace trimmed
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// // values of key 'Field' split by commas and has a default
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// // value ["a", "b", "c"] if the key does not exist.
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// Field []string `properties:",default=a;b;c"`
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//
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// // Field is decoded recursively with "Field." as key prefix.
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// Field SomeStruct
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//
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// // Field is decoded recursively with "myName." as key prefix.
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// Field SomeStruct `properties:"myName"`
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//
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// // Field is decoded recursively with "Field." as key prefix
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// // and the next dotted element of the key as map key.
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// Field map[string]string
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//
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// // Field is decoded recursively with "myName." as key prefix
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// // and the next dotted element of the key as map key.
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// Field map[string]string `properties:"myName"`
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func (p *Properties) Decode(x interface{}) error {
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t, v := reflect.TypeOf(x), reflect.ValueOf(x)
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if t.Kind() != reflect.Ptr || v.Elem().Type().Kind() != reflect.Struct {
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return fmt.Errorf("not a pointer to struct: %s", t)
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}
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if err := dec(p, "", nil, nil, v); err != nil {
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return err
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}
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return nil
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}
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func dec(p *Properties, key string, def *string, opts map[string]string, v reflect.Value) error {
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t := v.Type()
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// value returns the property value for key or the default if provided.
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value := func() (string, error) {
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if val, ok := p.Get(key); ok {
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return val, nil
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}
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if def != nil {
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return *def, nil
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}
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return "", fmt.Errorf("missing required key %s", key)
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}
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// conv converts a string to a value of the given type.
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conv := func(s string, t reflect.Type) (val reflect.Value, err error) {
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var v interface{}
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switch {
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case isDuration(t):
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v, err = time.ParseDuration(s)
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case isTime(t):
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layout := opts["layout"]
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if layout == "" {
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layout = time.RFC3339
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}
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v, err = time.Parse(layout, s)
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case isBool(t):
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v, err = boolVal(s), nil
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case isString(t):
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v, err = s, nil
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case isFloat(t):
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v, err = strconv.ParseFloat(s, 64)
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case isInt(t):
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v, err = strconv.ParseInt(s, 10, 64)
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case isUint(t):
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v, err = strconv.ParseUint(s, 10, 64)
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default:
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return reflect.Zero(t), fmt.Errorf("unsupported type %s", t)
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}
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if err != nil {
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return reflect.Zero(t), err
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}
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return reflect.ValueOf(v).Convert(t), nil
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}
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// keydef returns the property key and the default value based on the
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// name of the struct field and the options in the tag.
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keydef := func(f reflect.StructField) (string, *string, map[string]string) {
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_key, _opts := parseTag(f.Tag.Get("properties"))
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var _def *string
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if d, ok := _opts["default"]; ok {
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_def = &d
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}
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if _key != "" {
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return _key, _def, _opts
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}
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return f.Name, _def, _opts
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}
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switch {
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case isDuration(t) || isTime(t) || isBool(t) || isString(t) || isFloat(t) || isInt(t) || isUint(t):
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s, err := value()
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if err != nil {
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return err
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}
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val, err := conv(s, t)
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if err != nil {
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return err
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}
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v.Set(val)
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case isPtr(t):
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return dec(p, key, def, opts, v.Elem())
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case isStruct(t):
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for i := 0; i < v.NumField(); i++ {
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fv := v.Field(i)
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fk, def, opts := keydef(t.Field(i))
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if !fv.CanSet() {
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return fmt.Errorf("cannot set %s", t.Field(i).Name)
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}
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if fk == "-" {
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continue
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}
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if key != "" {
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fk = key + "." + fk
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}
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if err := dec(p, fk, def, opts, fv); err != nil {
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return err
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}
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}
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return nil
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case isArray(t):
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val, err := value()
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if err != nil {
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return err
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}
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vals := split(val, ";")
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a := reflect.MakeSlice(t, 0, len(vals))
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for _, s := range vals {
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val, err := conv(s, t.Elem())
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if err != nil {
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return err
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}
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a = reflect.Append(a, val)
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}
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v.Set(a)
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case isMap(t):
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valT := t.Elem()
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m := reflect.MakeMap(t)
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for postfix := range p.FilterStripPrefix(key + ".").m {
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pp := strings.SplitN(postfix, ".", 2)
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mk, mv := pp[0], reflect.New(valT)
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if err := dec(p, key+"."+mk, nil, nil, mv); err != nil {
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return err
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}
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m.SetMapIndex(reflect.ValueOf(mk), mv.Elem())
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}
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v.Set(m)
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default:
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return fmt.Errorf("unsupported type %s", t)
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}
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return nil
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}
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// split splits a string on sep, trims whitespace of elements
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// and omits empty elements
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func split(s string, sep string) []string {
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var a []string
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for _, v := range strings.Split(s, sep) {
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if v = strings.TrimSpace(v); v != "" {
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a = append(a, v)
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}
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}
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return a
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}
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// parseTag parses a "key,k=v,k=v,..."
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func parseTag(tag string) (key string, opts map[string]string) {
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opts = map[string]string{}
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for i, s := range strings.Split(tag, ",") {
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if i == 0 {
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key = s
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continue
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}
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pp := strings.SplitN(s, "=", 2)
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if len(pp) == 1 {
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opts[pp[0]] = ""
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} else {
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opts[pp[0]] = pp[1]
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}
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}
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return key, opts
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}
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func isArray(t reflect.Type) bool { return t.Kind() == reflect.Array || t.Kind() == reflect.Slice }
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func isBool(t reflect.Type) bool { return t.Kind() == reflect.Bool }
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func isDuration(t reflect.Type) bool { return t == reflect.TypeOf(time.Second) }
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func isMap(t reflect.Type) bool { return t.Kind() == reflect.Map }
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func isPtr(t reflect.Type) bool { return t.Kind() == reflect.Ptr }
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func isString(t reflect.Type) bool { return t.Kind() == reflect.String }
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func isStruct(t reflect.Type) bool { return t.Kind() == reflect.Struct }
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func isTime(t reflect.Type) bool { return t == reflect.TypeOf(time.Time{}) }
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func isFloat(t reflect.Type) bool {
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return t.Kind() == reflect.Float32 || t.Kind() == reflect.Float64
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}
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func isInt(t reflect.Type) bool {
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return t.Kind() == reflect.Int || t.Kind() == reflect.Int8 || t.Kind() == reflect.Int16 || t.Kind() == reflect.Int32 || t.Kind() == reflect.Int64
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}
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func isUint(t reflect.Type) bool {
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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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}
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