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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package json is forked from the Go standard library to enable us to find the
// field of a struct that a given JSON key maps to.
package json
import (
"bytes"
"fmt"
"reflect"
"sort"
"strings"
"sync"
"unicode"
"unicode/utf8"
)
const (
patchStrategyTagKey = "patchStrategy"
patchMergeKeyTagKey = "patchMergeKey"
)
// Finds the patchStrategy and patchMergeKey struct tag fields on a given
// struct field given the struct type and the JSON name of the field.
// It returns field type, a slice of patch strategies, merge key and error.
// TODO: fix the returned errors to be introspectable.
func LookupPatchMetadataForStruct(t reflect.Type, jsonField string) (
elemType reflect.Type, patchStrategies []string, patchMergeKey string, e error) {
if t.Kind() == reflect.Ptr {
t = t.Elem()
}
if t.Kind() != reflect.Struct {
e = fmt.Errorf("merging an object in json but data type is not struct, instead is: %s",
t.Kind().String())
return
}
jf := []byte(jsonField)
// Find the field that the JSON library would use.
var f *field
fields := cachedTypeFields(t)
for i := range fields {
ff := &fields[i]
if bytes.Equal(ff.nameBytes, jf) {
f = ff
break
}
// Do case-insensitive comparison.
if f == nil && ff.equalFold(ff.nameBytes, jf) {
f = ff
}
}
if f != nil {
// Find the reflect.Value of the most preferential struct field.
tjf := t.Field(f.index[0])
// we must navigate down all the anonymously included structs in the chain
for i := 1; i < len(f.index); i++ {
tjf = tjf.Type.Field(f.index[i])
}
patchStrategy := tjf.Tag.Get(patchStrategyTagKey)
patchMergeKey = tjf.Tag.Get(patchMergeKeyTagKey)
patchStrategies = strings.Split(patchStrategy, ",")
elemType = tjf.Type
return
}
e = fmt.Errorf("unable to find api field in struct %s for the json field %q", t.Name(), jsonField)
return
}
// A field represents a single field found in a struct.
type field struct {
name string
nameBytes []byte // []byte(name)
equalFold func(s, t []byte) bool // bytes.EqualFold or equivalent
tag bool
// index is the sequence of indexes from the containing type fields to this field.
// it is a slice because anonymous structs will need multiple navigation steps to correctly
// resolve the proper fields
index []int
typ reflect.Type
omitEmpty bool
quoted bool
}
func (f field) String() string {
return fmt.Sprintf("{name: %s, type: %v, tag: %v, index: %v, omitEmpty: %v, quoted: %v}", f.name, f.typ, f.tag, f.index, f.omitEmpty, f.quoted)
}
func fillField(f field) field {
f.nameBytes = []byte(f.name)
f.equalFold = foldFunc(f.nameBytes)
return f
}
// byName sorts field by name, breaking ties with depth,
// then breaking ties with "name came from json tag", then
// breaking ties with index sequence.
type byName []field
func (x byName) Len() int { return len(x) }
func (x byName) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x byName) Less(i, j int) bool {
if x[i].name != x[j].name {
return x[i].name < x[j].name
}
if len(x[i].index) != len(x[j].index) {
return len(x[i].index) < len(x[j].index)
}
if x[i].tag != x[j].tag {
return x[i].tag
}
return byIndex(x).Less(i, j)
}
// byIndex sorts field by index sequence.
type byIndex []field
func (x byIndex) Len() int { return len(x) }
func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x byIndex) Less(i, j int) bool {
for k, xik := range x[i].index {
if k >= len(x[j].index) {
return false
}
if xik != x[j].index[k] {
return xik < x[j].index[k]
}
}
return len(x[i].index) < len(x[j].index)
}
// typeFields returns a list of fields that JSON should recognize for the given type.
// The algorithm is breadth-first search over the set of structs to include - the top struct
// and then any reachable anonymous structs.
func typeFields(t reflect.Type) []field {
// Anonymous fields to explore at the current level and the next.
current := []field{}
next := []field{{typ: t}}
// Count of queued names for current level and the next.
count := map[reflect.Type]int{}
nextCount := map[reflect.Type]int{}
// Types already visited at an earlier level.
visited := map[reflect.Type]bool{}
// Fields found.
var fields []field
for len(next) > 0 {
current, next = next, current[:0]
count, nextCount = nextCount, map[reflect.Type]int{}
for _, f := range current {
if visited[f.typ] {
continue
}
visited[f.typ] = true
// Scan f.typ for fields to include.
for i := 0; i < f.typ.NumField(); i++ {
sf := f.typ.Field(i)
if sf.PkgPath != "" { // unexported
continue
}
tag := sf.Tag.Get("json")
if tag == "-" {
continue
}
name, opts := parseTag(tag)
if !isValidTag(name) {
name = ""
}
index := make([]int, len(f.index)+1)
copy(index, f.index)
index[len(f.index)] = i
ft := sf.Type
if ft.Name() == "" && ft.Kind() == reflect.Ptr {
// Follow pointer.
ft = ft.Elem()
}
// Record found field and index sequence.
if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
tagged := name != ""
if name == "" {
name = sf.Name
}
fields = append(fields, fillField(field{
name: name,
tag: tagged,
index: index,
typ: ft,
omitEmpty: opts.Contains("omitempty"),
quoted: opts.Contains("string"),
}))
if count[f.typ] > 1 {
// If there were multiple instances, add a second,
// so that the annihilation code will see a duplicate.
// It only cares about the distinction between 1 or 2,
// so don't bother generating any more copies.
fields = append(fields, fields[len(fields)-1])
}
continue
}
// Record new anonymous struct to explore in next round.
nextCount[ft]++
if nextCount[ft] == 1 {
next = append(next, fillField(field{name: ft.Name(), index: index, typ: ft}))
}
}
}
}
sort.Sort(byName(fields))
// Delete all fields that are hidden by the Go rules for embedded fields,
// except that fields with JSON tags are promoted.
// The fields are sorted in primary order of name, secondary order
// of field index length. Loop over names; for each name, delete
// hidden fields by choosing the one dominant field that survives.
out := fields[:0]
for advance, i := 0, 0; i < len(fields); i += advance {
// One iteration per name.
// Find the sequence of fields with the name of this first field.
fi := fields[i]
name := fi.name
for advance = 1; i+advance < len(fields); advance++ {
fj := fields[i+advance]
if fj.name != name {
break
}
}
if advance == 1 { // Only one field with this name
out = append(out, fi)
continue
}
dominant, ok := dominantField(fields[i : i+advance])
if ok {
out = append(out, dominant)
}
}
fields = out
sort.Sort(byIndex(fields))
return fields
}
// dominantField looks through the fields, all of which are known to
// have the same name, to find the single field that dominates the
// others using Go's embedding rules, modified by the presence of
// JSON tags. If there are multiple top-level fields, the boolean
// will be false: This condition is an error in Go and we skip all
// the fields.
func dominantField(fields []field) (field, bool) {
// The fields are sorted in increasing index-length order. The winner
// must therefore be one with the shortest index length. Drop all
// longer entries, which is easy: just truncate the slice.
length := len(fields[0].index)
tagged := -1 // Index of first tagged field.
for i, f := range fields {
if len(f.index) > length {
fields = fields[:i]
break
}
if f.tag {
if tagged >= 0 {
// Multiple tagged fields at the same level: conflict.
// Return no field.
return field{}, false
}
tagged = i
}
}
if tagged >= 0 {
return fields[tagged], true
}
// All remaining fields have the same length. If there's more than one,
// we have a conflict (two fields named "X" at the same level) and we
// return no field.
if len(fields) > 1 {
return field{}, false
}
return fields[0], true
}
var fieldCache struct {
sync.RWMutex
m map[reflect.Type][]field
}
// cachedTypeFields is like typeFields but uses a cache to avoid repeated work.
func cachedTypeFields(t reflect.Type) []field {
fieldCache.RLock()
f := fieldCache.m[t]
fieldCache.RUnlock()
if f != nil {
return f
}
// Compute fields without lock.
// Might duplicate effort but won't hold other computations back.
f = typeFields(t)
if f == nil {
f = []field{}
}
fieldCache.Lock()
if fieldCache.m == nil {
fieldCache.m = map[reflect.Type][]field{}
}
fieldCache.m[t] = f
fieldCache.Unlock()
return f
}
func isValidTag(s string) bool {
if s == "" {
return false
}
for _, c := range s {
switch {
case strings.ContainsRune("!#$%&()*+-./:<=>?@[]^_{|}~ ", c):
// Backslash and quote chars are reserved, but
// otherwise any punctuation chars are allowed
// in a tag name.
default:
if !unicode.IsLetter(c) && !unicode.IsDigit(c) {
return false
}
}
}
return true
}
const (
caseMask = ^byte(0x20) // Mask to ignore case in ASCII.
kelvin = '\u212a'
smallLongEss = '\u017f'
)
// foldFunc returns one of four different case folding equivalence
// functions, from most general (and slow) to fastest:
//
// 1) bytes.EqualFold, if the key s contains any non-ASCII UTF-8
// 2) equalFoldRight, if s contains special folding ASCII ('k', 'K', 's', 'S')
// 3) asciiEqualFold, no special, but includes non-letters (including _)
// 4) simpleLetterEqualFold, no specials, no non-letters.
//
// The letters S and K are special because they map to 3 runes, not just 2:
// * S maps to s and to U+017F 'ſ' Latin small letter long s
// * k maps to K and to U+212A 'K' Kelvin sign
// See http://play.golang.org/p/tTxjOc0OGo
//
// The returned function is specialized for matching against s and
// should only be given s. It's not curried for performance reasons.
func foldFunc(s []byte) func(s, t []byte) bool {
nonLetter := false
special := false // special letter
for _, b := range s {
if b >= utf8.RuneSelf {
return bytes.EqualFold
}
upper := b & caseMask
if upper < 'A' || upper > 'Z' {
nonLetter = true
} else if upper == 'K' || upper == 'S' {
// See above for why these letters are special.
special = true
}
}
if special {
return equalFoldRight
}
if nonLetter {
return asciiEqualFold
}
return simpleLetterEqualFold
}
// equalFoldRight is a specialization of bytes.EqualFold when s is
// known to be all ASCII (including punctuation), but contains an 's',
// 'S', 'k', or 'K', requiring a Unicode fold on the bytes in t.
// See comments on foldFunc.
func equalFoldRight(s, t []byte) bool {
for _, sb := range s {
if len(t) == 0 {
return false
}
tb := t[0]
if tb < utf8.RuneSelf {
if sb != tb {
sbUpper := sb & caseMask
if 'A' <= sbUpper && sbUpper <= 'Z' {
if sbUpper != tb&caseMask {
return false
}
} else {
return false
}
}
t = t[1:]
continue
}
// sb is ASCII and t is not. t must be either kelvin
// sign or long s; sb must be s, S, k, or K.
tr, size := utf8.DecodeRune(t)
switch sb {
case 's', 'S':
if tr != smallLongEss {
return false
}
case 'k', 'K':
if tr != kelvin {
return false
}
default:
return false
}
t = t[size:]
}
if len(t) > 0 {
return false
}
return true
}
// asciiEqualFold is a specialization of bytes.EqualFold for use when
// s is all ASCII (but may contain non-letters) and contains no
// special-folding letters.
// See comments on foldFunc.
func asciiEqualFold(s, t []byte) bool {
if len(s) != len(t) {
return false
}
for i, sb := range s {
tb := t[i]
if sb == tb {
continue
}
if ('a' <= sb && sb <= 'z') || ('A' <= sb && sb <= 'Z') {
if sb&caseMask != tb&caseMask {
return false
}
} else {
return false
}
}
return true
}
// simpleLetterEqualFold is a specialization of bytes.EqualFold for
// use when s is all ASCII letters (no underscores, etc) and also
// doesn't contain 'k', 'K', 's', or 'S'.
// See comments on foldFunc.
func simpleLetterEqualFold(s, t []byte) bool {
if len(s) != len(t) {
return false
}
for i, b := range s {
if b&caseMask != t[i]&caseMask {
return false
}
}
return true
}
// tagOptions is the string following a comma in a struct field's "json"
// tag, or the empty string. It does not include the leading comma.
type tagOptions string
// parseTag splits a struct field's json tag into its name and
// comma-separated options.
func parseTag(tag string) (string, tagOptions) {
if idx := strings.Index(tag, ","); idx != -1 {
return tag[:idx], tagOptions(tag[idx+1:])
}
return tag, tagOptions("")
}
// Contains reports whether a comma-separated list of options
// contains a particular substr flag. substr must be surrounded by a
// string boundary or commas.
func (o tagOptions) Contains(optionName string) bool {
if len(o) == 0 {
return false
}
s := string(o)
for s != "" {
var next string
i := strings.Index(s, ",")
if i >= 0 {
s, next = s[:i], s[i+1:]
}
if s == optionName {
return true
}
s = next
}
return false
}
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