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// Copyright (C) 2022 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package lowmemjson
import (
"reflect"
)
type structField struct {
Name string
Path []int
Tagged bool
OmitEmpty bool
Quote bool
}
type structIndex struct {
byPos []structField
byName map[string]int
}
func indexStruct(typ reflect.Type) structIndex {
byName := make(map[string][]structField)
var byPos []string
indexStructInner(typ, nil, byName, &byPos)
ret := structIndex{
byName: make(map[string]int),
}
for _, name := range byPos {
fields := byName[name]
delete(byName, name)
switch len(fields) {
case 0:
// do nothing
case 1:
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, fields[0])
default:
// To quote the encoding/json docs (version 1.18.4):
//
// If there are multiple fields at the same level, and that level is the
// least nested (and would therefore be the nesting level selected by the
// usual Go rules), the following extra rules apply:
//
// 1) Of those fields, if any are JSON-tagged, only tagged fields are
// considered, even if there are multiple untagged fields that would
// otherwise conflict.
//
// 2) If there is exactly one field (tagged or not according to the first
// rule), that is selected.
//
// 3) Otherwise there are multiple fields, and all are ignored; no error
// occurs.
leastLevel := len(fields[0].Path)
for _, field := range fields[1:] {
if len(field.Path) < leastLevel {
leastLevel = len(field.Path)
}
}
var numUntagged, numTagged int
var untaggedIdx, taggedIdx int
for i, field := range fields {
if len(field.Path) != leastLevel {
continue
}
if field.Tagged {
numTagged++
taggedIdx = i
if numTagged > 1 {
break // optimization
}
} else {
numUntagged++
untaggedIdx = i
}
}
switch numTagged {
case 0:
switch numUntagged {
case 0:
// do nothing
case 1:
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, fields[untaggedIdx])
}
case 1:
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, fields[taggedIdx])
}
}
}
return ret
}
func indexStructInner(typ reflect.Type, prefix []int, byName map[string][]structField, byPos *[]string) {
n := typ.NumField()
for i := 0; i < n; i++ {
path := append(append([]int(nil), prefix...), i)
fTyp := typ.Field(i)
var embed bool
if fTyp.Anonymous {
t := fTyp.Type
if t.Kind() == reflect.Pointer {
t = t.Elem()
}
if !fTyp.IsExported() && t.Kind() != reflect.Struct {
continue
}
embed = t.Kind() == reflect.Struct
} else if !fTyp.IsExported() {
continue
}
tag := fTyp.Tag.Get("json")
if tag == "-" {
continue
}
tagName, opts := parseTag(tag)
name := tagName
if name == "" {
name = fTyp.Name
}
if embed {
t := fTyp.Type
if t.Kind() == reflect.Pointer {
t = t.Elem()
}
indexStructInner(t, path, byName, byPos)
} else {
byName[name] = append(byName[name], structField{
Name: name,
Path: path,
Tagged: tagName != "",
OmitEmpty: opts.Contains("omitempty"),
Quote: opts.Contains("string") && isQuotable(fTyp.Type),
})
*byPos = append(*byPos, name)
}
}
}
func isQuotable(typ reflect.Type) bool {
for typ.Kind() == reflect.Pointer {
typ = typ.Elem()
}
switch typ.Kind() {
case reflect.Bool,
reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
reflect.Uintptr,
reflect.Float32, reflect.Float64,
reflect.String:
return true
default:
return false
}
}
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