300 lines
7.6 KiB
Go
300 lines
7.6 KiB
Go
// Copyright 2012 The Gorilla Authors. 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 schema
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import (
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"encoding"
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"errors"
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"fmt"
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"reflect"
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"strings"
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)
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// NewDecoder returns a new Decoder.
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func NewDecoder() *Decoder {
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return &Decoder{cache: newCache()}
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}
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// Decoder decodes values from a map[string][]string to a struct.
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type Decoder struct {
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cache *cache
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zeroEmpty bool
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ignoreUnknownKeys bool
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}
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// SetAliasTag changes the tag used to locate custom field aliases.
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// The default tag is "schema".
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func (d *Decoder) SetAliasTag(tag string) {
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d.cache.tag = tag
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}
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// ZeroEmpty controls the behaviour when the decoder encounters empty values
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// in a map.
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// If z is true and a key in the map has the empty string as a value
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// then the corresponding struct field is set to the zero value.
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// If z is false then empty strings are ignored.
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//
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// The default value is false, that is empty values do not change
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// the value of the struct field.
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func (d *Decoder) ZeroEmpty(z bool) {
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d.zeroEmpty = z
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}
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// IgnoreUnknownKeys controls the behaviour when the decoder encounters unknown
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// keys in the map.
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// If i is true and an unknown field is encountered, it is ignored. This is
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// similar to how unknown keys are handled by encoding/json.
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// If i is false then Decode will return an error. Note that any valid keys
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// will still be decoded in to the target struct.
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//
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// To preserve backwards compatibility, the default value is false.
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func (d *Decoder) IgnoreUnknownKeys(i bool) {
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d.ignoreUnknownKeys = i
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}
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// RegisterConverter registers a converter function for a custom type.
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func (d *Decoder) RegisterConverter(value interface{}, converterFunc Converter) {
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d.cache.regconv[reflect.TypeOf(value)] = converterFunc
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}
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// Decode decodes a map[string][]string to a struct.
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//
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// The first parameter must be a pointer to a struct.
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//
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// The second parameter is a map, typically url.Values from an HTTP request.
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// Keys are "paths" in dotted notation to the struct fields and nested structs.
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//
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// See the package documentation for a full explanation of the mechanics.
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func (d *Decoder) Decode(dst interface{}, src map[string][]string) error {
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v := reflect.ValueOf(dst)
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if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {
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return errors.New("schema: interface must be a pointer to struct")
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}
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v = v.Elem()
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t := v.Type()
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errors := MultiError{}
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for path, values := range src {
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if parts, err := d.cache.parsePath(path, t); err == nil {
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if err = d.decode(v, path, parts, values); err != nil {
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errors[path] = err
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}
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} else if !d.ignoreUnknownKeys {
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errors[path] = fmt.Errorf("schema: invalid path %q", path)
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}
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}
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if len(errors) > 0 {
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return errors
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}
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return nil
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}
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// decode fills a struct field using a parsed path.
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func (d *Decoder) decode(v reflect.Value, path string, parts []pathPart, values []string) error {
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// Get the field walking the struct fields by index.
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for _, name := range parts[0].path {
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if v.Type().Kind() == reflect.Ptr {
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if v.IsNil() {
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v.Set(reflect.New(v.Type().Elem()))
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}
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v = v.Elem()
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}
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v = v.FieldByName(name)
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}
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// Don't even bother for unexported fields.
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if !v.CanSet() {
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return nil
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}
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// Dereference if needed.
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t := v.Type()
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if t.Kind() == reflect.Ptr {
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t = t.Elem()
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if v.IsNil() {
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v.Set(reflect.New(t))
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}
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v = v.Elem()
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}
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// Slice of structs. Let's go recursive.
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if len(parts) > 1 {
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idx := parts[0].index
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if v.IsNil() || v.Len() < idx+1 {
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value := reflect.MakeSlice(t, idx+1, idx+1)
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if v.Len() < idx+1 {
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// Resize it.
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reflect.Copy(value, v)
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}
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v.Set(value)
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}
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return d.decode(v.Index(idx), path, parts[1:], values)
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}
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// Get the converter early in case there is one for a slice type.
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conv := d.cache.converter(t)
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if conv == nil && t.Kind() == reflect.Slice {
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var items []reflect.Value
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elemT := t.Elem()
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isPtrElem := elemT.Kind() == reflect.Ptr
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if isPtrElem {
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elemT = elemT.Elem()
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}
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// Try to get a converter for the element type.
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conv := d.cache.converter(elemT)
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if conv == nil {
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// As we are not dealing with slice of structs here, we don't need to check if the type
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// implements TextUnmarshaler interface
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return fmt.Errorf("schema: converter not found for %v", elemT)
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}
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for key, value := range values {
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if value == "" {
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if d.zeroEmpty {
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items = append(items, reflect.Zero(elemT))
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}
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} else if item := conv(value); item.IsValid() {
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if isPtrElem {
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ptr := reflect.New(elemT)
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ptr.Elem().Set(item)
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item = ptr
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}
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if item.Type() != elemT && !isPtrElem {
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item = item.Convert(elemT)
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}
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items = append(items, item)
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} else {
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if strings.Contains(value, ",") {
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values := strings.Split(value, ",")
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for _, value := range values {
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if value == "" {
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if d.zeroEmpty {
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items = append(items, reflect.Zero(elemT))
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}
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} else if item := conv(value); item.IsValid() {
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if isPtrElem {
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ptr := reflect.New(elemT)
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ptr.Elem().Set(item)
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item = ptr
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}
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if item.Type() != elemT && !isPtrElem {
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item = item.Convert(elemT)
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}
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items = append(items, item)
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} else {
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return ConversionError{
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Key: path,
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Type: elemT,
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Index: key,
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}
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}
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}
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} else {
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return ConversionError{
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Key: path,
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Type: elemT,
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Index: key,
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}
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}
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}
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}
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value := reflect.Append(reflect.MakeSlice(t, 0, 0), items...)
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v.Set(value)
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} else {
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val := ""
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// Use the last value provided if any values were provided
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if len(values) > 0 {
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val = values[len(values)-1]
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}
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if val == "" {
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if d.zeroEmpty {
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v.Set(reflect.Zero(t))
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}
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} else if conv != nil {
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if value := conv(val); value.IsValid() {
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v.Set(value.Convert(t))
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} else {
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return ConversionError{
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Key: path,
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Type: t,
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Index: -1,
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}
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}
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} else {
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// When there's no registered conversion for the custom type, we will check if the type
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// implements the TextUnmarshaler interface. As the UnmarshalText function should be applied
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// to the pointer of the type, we convert the value to pointer.
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if v.CanAddr() {
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v = v.Addr()
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}
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if u, ok := v.Interface().(encoding.TextUnmarshaler); ok {
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if err := u.UnmarshalText([]byte(val)); err != nil {
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return ConversionError{
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Key: path,
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Type: t,
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Index: -1,
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Err: err,
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}
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}
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} else {
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return fmt.Errorf("schema: converter not found for %v", t)
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}
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}
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}
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return nil
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}
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// Errors ---------------------------------------------------------------------
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// ConversionError stores information about a failed conversion.
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type ConversionError struct {
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Key string // key from the source map.
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Type reflect.Type // expected type of elem
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Index int // index for multi-value fields; -1 for single-value fields.
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Err error // low-level error (when it exists)
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}
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func (e ConversionError) Error() string {
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var output string
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if e.Index < 0 {
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output = fmt.Sprintf("schema: error converting value for %q", e.Key)
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} else {
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output = fmt.Sprintf("schema: error converting value for index %d of %q",
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e.Index, e.Key)
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}
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if e.Err != nil {
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output = fmt.Sprintf("%s. Details: %s", output, e.Err)
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}
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return output
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}
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// MultiError stores multiple decoding errors.
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//
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// Borrowed from the App Engine SDK.
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type MultiError map[string]error
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func (e MultiError) Error() string {
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s := ""
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for _, err := range e {
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s = err.Error()
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break
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}
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switch len(e) {
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case 0:
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return "(0 errors)"
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case 1:
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return s
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case 2:
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return s + " (and 1 other error)"
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}
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return fmt.Sprintf("%s (and %d other errors)", s, len(e)-1)
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}
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