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structfields.go
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structfields.go
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// Copyright (c) Faye Amacker. All rights reserved.
// Licensed under the MIT License. See LICENSE in the project root for license information.
package cbor
import (
"reflect"
"sort"
"strings"
)
type field struct {
name string
nameAsInt int64 // used to decoder to match field name with CBOR int
cborName []byte
idx []int
typ reflect.Type
ef encodeFunc
ief isEmptyFunc
typInfo *typeInfo // used to decoder to reuse type info
tagged bool // used to choose dominant field (at the same level tagged fields dominate untagged fields)
omitEmpty bool // used to skip empty field
keyAsInt bool // used to encode/decode field name as int
}
type fields []*field
// indexFieldSorter sorts fields by field idx at each level, breaking ties with idx depth.
type indexFieldSorter struct {
fields fields
}
func (x *indexFieldSorter) Len() int {
return len(x.fields)
}
func (x *indexFieldSorter) Swap(i, j int) {
x.fields[i], x.fields[j] = x.fields[j], x.fields[i]
}
func (x *indexFieldSorter) Less(i, j int) bool {
iIdx, jIdx := x.fields[i].idx, x.fields[j].idx
for k := 0; k < len(iIdx) && k < len(jIdx); k++ {
if iIdx[k] != jIdx[k] {
return iIdx[k] < jIdx[k]
}
}
return len(iIdx) <= len(jIdx)
}
// nameLevelAndTagFieldSorter sorts fields by field name, idx depth, and presence of tag.
type nameLevelAndTagFieldSorter struct {
fields fields
}
func (x *nameLevelAndTagFieldSorter) Len() int {
return len(x.fields)
}
func (x *nameLevelAndTagFieldSorter) Swap(i, j int) {
x.fields[i], x.fields[j] = x.fields[j], x.fields[i]
}
func (x *nameLevelAndTagFieldSorter) Less(i, j int) bool {
fi, fj := x.fields[i], x.fields[j]
if fi.name != fj.name {
return fi.name < fj.name
}
if len(fi.idx) != len(fj.idx) {
return len(fi.idx) < len(fj.idx)
}
if fi.tagged != fj.tagged {
return fi.tagged
}
return i < j // Field i and j have the same name, depth, and tagged status. Nothing else matters.
}
// getFields returns visible fields of struct type t following visibility rules for JSON encoding.
func getFields(t reflect.Type) (flds fields, structOptions string) {
// Get special field "_" tag options
if f, ok := t.FieldByName("_"); ok {
tag := f.Tag.Get("cbor")
if tag != "-" {
structOptions = tag
}
}
// nTypes contains next level anonymous fields' types and indexes
// (there can be multiple fields of the same type at the same level)
flds, nTypes := appendFields(t, nil, nil, nil)
if len(nTypes) > 0 {
var cTypes map[reflect.Type][][]int // current level anonymous fields' types and indexes
vTypes := map[reflect.Type]bool{t: true} // visited field types at less nested levels
for len(nTypes) > 0 {
cTypes, nTypes = nTypes, nil
for t, idx := range cTypes {
// If there are multiple anonymous fields of the same struct type at the same level, all are ignored.
if len(idx) > 1 {
continue
}
// Anonymous field of the same type at deeper nested level is ignored.
if vTypes[t] {
continue
}
vTypes[t] = true
flds, nTypes = appendFields(t, idx[0], flds, nTypes)
}
}
}
sort.Sort(&nameLevelAndTagFieldSorter{flds})
// Keep visible fields.
j := 0 // index of next unique field
for i := 0; i < len(flds); {
name := flds[i].name
if i == len(flds)-1 || // last field
name != flds[i+1].name || // field i has unique field name
len(flds[i].idx) < len(flds[i+1].idx) || // field i is at a less nested level than field i+1
(flds[i].tagged && !flds[i+1].tagged) { // field i is tagged while field i+1 is not
flds[j] = flds[i]
j++
}
// Skip fields with the same field name.
for i++; i < len(flds) && name == flds[i].name; i++ {
}
}
if j != len(flds) {
flds = flds[:j]
}
// Sort fields by field index
sort.Sort(&indexFieldSorter{flds})
return flds, structOptions
}
// appendFields appends type t's exportable fields to flds and anonymous struct fields to nTypes .
func appendFields(t reflect.Type, idx []int, flds fields, nTypes map[reflect.Type][][]int) (fields, map[reflect.Type][][]int) {
for i := 0; i < t.NumField(); i++ {
f := t.Field(i)
ft := f.Type
for ft.Kind() == reflect.Ptr {
ft = ft.Elem()
}
if !isFieldExportable(f, ft.Kind()) {
continue
}
tag := f.Tag.Get("cbor")
if tag == "" {
tag = f.Tag.Get("json")
}
if tag == "-" {
continue
}
tagged := len(tag) > 0
// Parse field tag options
var tagFieldName string
var omitempty, keyasint bool
for j := 0; len(tag) > 0; j++ {
var token string
idx := strings.IndexByte(tag, ',')
if idx == -1 {
token, tag = tag, ""
} else {
token, tag = tag[:idx], tag[idx+1:]
}
if j == 0 {
tagFieldName = token
} else {
switch token {
case "omitempty":
omitempty = true
case "keyasint":
keyasint = true
}
}
}
fieldName := tagFieldName
if tagFieldName == "" {
fieldName = f.Name
}
fIdx := make([]int, len(idx)+1)
copy(fIdx, idx)
fIdx[len(fIdx)-1] = i
if !f.Anonymous || ft.Kind() != reflect.Struct || len(tagFieldName) > 0 {
flds = append(flds, &field{
name: fieldName,
idx: fIdx,
typ: f.Type,
omitEmpty: omitempty,
keyAsInt: keyasint,
tagged: tagged})
} else {
if nTypes == nil {
nTypes = make(map[reflect.Type][][]int)
}
nTypes[ft] = append(nTypes[ft], fIdx)
}
}
return flds, nTypes
}
// isFieldExportable returns true if f is an exportable (regular or anonymous) field or
// a nonexportable anonymous field of struct type.
// Nonexportable anonymous field of struct type can contain exportable fields.
func isFieldExportable(f reflect.StructField, fk reflect.Kind) bool {
exportable := f.PkgPath == ""
return exportable || (f.Anonymous && fk == reflect.Struct)
}
type embeddedFieldNullPtrFunc func(reflect.Value) (reflect.Value, error)
// getFieldValue returns field value of struct v by index. When encountering null pointer
// to anonymous (embedded) struct field, f is called with the last traversed field value.
func getFieldValue(v reflect.Value, idx []int, f embeddedFieldNullPtrFunc) (fv reflect.Value, err error) {
fv = v
for i, n := range idx {
fv = fv.Field(n)
if i < len(idx)-1 {
if fv.Kind() == reflect.Ptr && fv.Type().Elem().Kind() == reflect.Struct {
if fv.IsNil() {
// Null pointer to embedded struct field
fv, err = f(fv)
if err != nil || !fv.IsValid() {
return fv, err
}
}
fv = fv.Elem()
}
}
}
return fv, nil
}