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// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package lowmemjson
import (
"reflect"
"git.lukeshu.com/go/typedsync"
"git.lukeshu.com/go/lowmemjson/internal"
)
type structField struct {
Name string
Path []int
Tagged bool
OmitEmpty bool
Quote bool
}
// A structIndex is used by Decoder.Decode() and Encoder.Encode() when
// decoding-to or encoding-from a struct.
type structIndex struct {
byPos []structField
byName map[string]int
}
var structIndexCache typedsync.CacheMap[reflect.Type, structIndex]
// indexStruct takes a struct Type, and indexes its fields for use by
// Decoder.Decode() and Encoder.Encode(). indexStruct caches its
// results.
func indexStruct(typ reflect.Type) structIndex {
ret, _ := structIndexCache.LoadOrCompute(typ, indexStructReal)
return ret
}
// indexStructReal is like indexStruct, but is the real indexer,
// bypassing the cache.
func indexStructReal(typ reflect.Type) structIndex {
var byPos []structField
byName := make(map[string][]int)
indexStructInner(typ, &byPos, byName, nil, map[reflect.Type]struct{}{})
ret := structIndex{
byName: make(map[string]int),
}
for curPos, _field := range byPos {
name := _field.Name
fieldPoss := byName[name]
switch len(fieldPoss) {
case 0:
// do nothing
case 1:
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, _field)
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(byPos[fieldPoss[0]].Path)
for _, fieldPos := range fieldPoss[1:] {
field := byPos[fieldPos]
if len(field.Path) < leastLevel {
leastLevel = len(field.Path)
}
}
var numUntagged, numTagged int
var untaggedPos, taggedPos int
for _, fieldPos := range fieldPoss {
field := byPos[fieldPos]
if len(field.Path) != leastLevel {
continue
}
if field.Tagged {
numTagged++
taggedPos = fieldPos
if numTagged > 1 {
break // optimization
}
} else {
numUntagged++
untaggedPos = fieldPos
}
}
switch numTagged {
case 0:
switch numUntagged {
case 0:
// do nothing
case 1:
if curPos == untaggedPos {
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, byPos[curPos])
}
}
case 1:
if curPos == taggedPos {
ret.byName[name] = len(ret.byPos)
ret.byPos = append(ret.byPos, byPos[curPos])
}
}
}
}
return ret
}
// indexStructInner crawls the struct `typ`, storing information on
// all struct fields foun in to `byPos` and `byName`. If `typ`
// contains other structs as fields, indexStructInner will recurse and
// call itself; keeping track of stack information with `stackPath`
// (which identifies where we are in the parent struct) and
// `stackSeen` (which is used for detecting loops).
func indexStructInner(typ reflect.Type, byPos *[]structField, byName map[string][]int, stackPath []int, stackSeen map[reflect.Type]struct{}) {
if _, ok := stackSeen[typ]; ok {
return
}
stackSeen[typ] = struct{}{}
defer delete(stackSeen, typ)
n := typ.NumField()
for i := 0; i < n; i++ {
stackPath := append(stackPath, 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 := internal.ParseTag(tag)
name := tagName
if !isValidTag(name) {
name = ""
}
if name == "" {
name = fTyp.Name
}
if embed && tagName == "" {
t := fTyp.Type
if t.Kind() == reflect.Pointer {
t = t.Elem()
}
indexStructInner(t, byPos, byName, stackPath, stackSeen)
} else {
byName[name] = append(byName[name], len(*byPos))
*byPos = append(*byPos, structField{
Name: name,
Path: append([]int(nil), stackPath...),
Tagged: tagName != "",
OmitEmpty: opts.Contains("omitempty"),
Quote: opts.Contains("string") && isQuotable(fTyp.Type),
})
}
}
}
// isQuotable returns whether a type is eligible for `json:,string`
// quoting.
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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