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typeinfo.go
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typeinfo.go
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// Copyright 2011 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 xml
import (
"fmt"
"reflect"
"strings"
"sync"
)
// typeInfo holds details for the xml representation of a type.
type typeInfo struct {
xmlname *fieldInfo
fields []fieldInfo
}
// fieldInfo holds details for the xml representation of a single field.
type fieldInfo struct {
idx []int
name string
xmlns string
flags fieldFlags
parents []string
}
type fieldFlags int
const (
fElement fieldFlags = 1 << iota
fAttr
fCDATA
fCharData
fInnerXML
fComment
fAny
fOmitEmpty
fTypeAttr
fMode = fElement | fAttr | fCDATA | fCharData | fInnerXML | fComment | fAny
xmlName = "XMLName"
)
var tinfoMap sync.Map // map[reflect.Type]*typeInfo
var nameType = reflect.TypeOf(Name{})
// getTypeInfo returns the typeInfo structure with details necessary
// for marshaling and unmarshaling typ.
func getTypeInfo(typ reflect.Type) (*typeInfo, error) {
if ti, ok := tinfoMap.Load(typ); ok {
return ti.(*typeInfo), nil
}
tinfo := &typeInfo{}
if typ.Kind() == reflect.Struct && typ != nameType {
n := typ.NumField()
for i := 0; i < n; i++ {
f := typ.Field(i)
if (f.PkgPath != "" && !f.Anonymous) || f.Tag.Get("xml") == "-" {
continue // Private field
}
// For embedded structs, embed its fields.
if f.Anonymous {
t := f.Type
if t.Kind() == reflect.Ptr {
t = t.Elem()
}
if t.Kind() == reflect.Struct {
inner, err := getTypeInfo(t)
if err != nil {
return nil, err
}
if tinfo.xmlname == nil {
tinfo.xmlname = inner.xmlname
}
for _, finfo := range inner.fields {
finfo.idx = append([]int{i}, finfo.idx...)
if err := addFieldInfo(typ, tinfo, &finfo); err != nil {
return nil, err
}
}
continue
}
}
finfo, err := structFieldInfo(typ, &f)
if err != nil {
return nil, err
}
if f.Name == xmlName {
tinfo.xmlname = finfo
continue
}
// Add the field if it doesn't conflict with other fields.
if err := addFieldInfo(typ, tinfo, finfo); err != nil {
return nil, err
}
}
}
ti, _ := tinfoMap.LoadOrStore(typ, tinfo)
return ti.(*typeInfo), nil
}
// structFieldInfo builds and returns a fieldInfo for f.
func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, error) {
finfo := &fieldInfo{idx: f.Index}
// Split the tag from the xml namespace if necessary.
tag := f.Tag.Get("xml")
if i := strings.Index(tag, " "); i >= 0 {
finfo.xmlns, tag = tag[:i], tag[i+1:]
}
// Parse flags.
tokens := strings.Split(tag, ",")
if len(tokens) == 1 {
finfo.flags = fElement
} else {
tag = tokens[0]
for _, flag := range tokens[1:] {
switch flag {
case "attr":
finfo.flags |= fAttr
case "cdata":
finfo.flags |= fCDATA
case "chardata":
finfo.flags |= fCharData
case "innerxml":
finfo.flags |= fInnerXML
case "comment":
finfo.flags |= fComment
case "any":
finfo.flags |= fAny
case "omitempty":
finfo.flags |= fOmitEmpty
case "typeattr":
finfo.flags |= fTypeAttr
}
}
// Validate the flags used.
valid := true
switch mode := finfo.flags & fMode; mode {
case 0:
finfo.flags |= fElement
case fAttr, fCDATA, fCharData, fInnerXML, fComment, fAny, fAny | fAttr:
if f.Name == xmlName || tag != "" && mode != fAttr {
valid = false
}
default:
// This will also catch multiple modes in a single field.
valid = false
}
if finfo.flags&fMode == fAny {
finfo.flags |= fElement
}
if finfo.flags&fOmitEmpty != 0 && finfo.flags&(fElement|fAttr) == 0 {
valid = false
}
if !valid {
return nil, fmt.Errorf("xml: invalid tag in field %s of type %s: %q",
f.Name, typ, f.Tag.Get("xml"))
}
}
// Use of xmlns without a name is not allowed.
if finfo.xmlns != "" && tag == "" {
return nil, fmt.Errorf("xml: namespace without name in field %s of type %s: %q",
f.Name, typ, f.Tag.Get("xml"))
}
if f.Name == xmlName {
// The XMLName field records the XML element name. Don't
// process it as usual because its name should default to
// empty rather than to the field name.
finfo.name = tag
return finfo, nil
}
if tag == "" {
// If the name part of the tag is completely empty, get
// default from XMLName of underlying struct if feasible,
// or field name otherwise.
if xmlname := lookupXMLName(f.Type); xmlname != nil {
finfo.xmlns, finfo.name = xmlname.xmlns, xmlname.name
} else {
finfo.name = f.Name
}
return finfo, nil
}
// Prepare field name and parents.
parents := strings.Split(tag, ">")
if parents[0] == "" {
parents[0] = f.Name
}
if parents[len(parents)-1] == "" {
return nil, fmt.Errorf("xml: trailing '>' in field %s of type %s", f.Name, typ)
}
finfo.name = parents[len(parents)-1]
if len(parents) > 1 {
if (finfo.flags & fElement) == 0 {
return nil, fmt.Errorf("xml: %s chain not valid with %s flag", tag, strings.Join(tokens[1:], ","))
}
finfo.parents = parents[:len(parents)-1]
}
// If the field type has an XMLName field, the names must match
// so that the behavior of both marshaling and unmarshaling
// is straightforward and unambiguous.
if finfo.flags&fElement != 0 {
ftyp := f.Type
xmlname := lookupXMLName(ftyp)
if xmlname != nil && xmlname.name != finfo.name {
return nil, fmt.Errorf("xml: name %q in tag of %s.%s conflicts with name %q in %s.XMLName",
finfo.name, typ, f.Name, xmlname.name, ftyp)
}
}
return finfo, nil
}
// lookupXMLName returns the fieldInfo for typ's XMLName field
// in case it exists and has a valid xml field tag, otherwise
// it returns nil.
func lookupXMLName(typ reflect.Type) (xmlname *fieldInfo) {
for typ.Kind() == reflect.Ptr {
typ = typ.Elem()
}
if typ.Kind() != reflect.Struct {
return nil
}
for i, n := 0, typ.NumField(); i < n; i++ {
f := typ.Field(i)
if f.Name != xmlName {
continue
}
finfo, err := structFieldInfo(typ, &f)
if err == nil && finfo.name != "" {
return finfo
}
// Also consider errors as a non-existent field tag
// and let getTypeInfo itself report the error.
break
}
return nil
}
func min(a, b int) int {
if a <= b {
return a
}
return b
}
// addFieldInfo adds finfo to tinfo.fields if there are no
// conflicts, or if conflicts arise from previous fields that were
// obtained from deeper embedded structures than finfo. In the latter
// case, the conflicting entries are dropped.
// A conflict occurs when the path (parent + name) to a field is
// itself a prefix of another path, or when two paths match exactly.
// It is okay for field paths to share a common, shorter prefix.
func addFieldInfo(typ reflect.Type, tinfo *typeInfo, newf *fieldInfo) error {
var conflicts []int
Loop:
// First, figure all conflicts. Most working code will have none.
for i := range tinfo.fields {
oldf := &tinfo.fields[i]
if oldf.flags&fMode != newf.flags&fMode {
continue
}
if oldf.xmlns != "" && newf.xmlns != "" && oldf.xmlns != newf.xmlns {
continue
}
minl := min(len(newf.parents), len(oldf.parents))
for p := 0; p < minl; p++ {
if oldf.parents[p] != newf.parents[p] {
continue Loop
}
}
if len(oldf.parents) > len(newf.parents) {
if oldf.parents[len(newf.parents)] == newf.name {
conflicts = append(conflicts, i)
}
} else if len(oldf.parents) < len(newf.parents) {
if newf.parents[len(oldf.parents)] == oldf.name {
conflicts = append(conflicts, i)
}
} else {
if newf.name == oldf.name {
conflicts = append(conflicts, i)
}
}
}
// Without conflicts, add the new field and return.
if conflicts == nil {
tinfo.fields = append(tinfo.fields, *newf)
return nil
}
// If any conflict is shallower, ignore the new field.
// This matches the Go field resolution on embedding.
for _, i := range conflicts {
if len(tinfo.fields[i].idx) < len(newf.idx) {
return nil
}
}
// Otherwise, if any of them is at the same depth level, it's an error.
for _, i := range conflicts {
oldf := &tinfo.fields[i]
if len(oldf.idx) == len(newf.idx) {
f1 := typ.FieldByIndex(oldf.idx)
f2 := typ.FieldByIndex(newf.idx)
return &TagPathError{typ, f1.Name, f1.Tag.Get("xml"), f2.Name, f2.Tag.Get("xml")}
}
}
// Otherwise, the new field is shallower, and thus takes precedence,
// so drop the conflicting fields from tinfo and append the new one.
for c := len(conflicts) - 1; c >= 0; c-- {
i := conflicts[c]
copy(tinfo.fields[i:], tinfo.fields[i+1:])
tinfo.fields = tinfo.fields[:len(tinfo.fields)-1]
}
tinfo.fields = append(tinfo.fields, *newf)
return nil
}
// A TagPathError represents an error in the unmarshaling process
// caused by the use of field tags with conflicting paths.
type TagPathError struct {
Struct reflect.Type
Field1, Tag1 string
Field2, Tag2 string
}
func (e *TagPathError) Error() string {
return fmt.Sprintf("%s field %q with tag %q conflicts with field %q with tag %q", e.Struct, e.Field1, e.Tag1, e.Field2, e.Tag2)
}
const (
initNilPointers = true
dontInitNilPointers = false
)
// value returns v's field value corresponding to finfo.
// It's equivalent to v.FieldByIndex(finfo.idx), but when passed
// initNilPointers, it initializes and dereferences pointers as necessary.
// When passed dontInitNilPointers and a nil pointer is reached, the function
// returns a zero reflect.Value.
func (finfo *fieldInfo) value(v reflect.Value, shouldInitNilPointers bool) reflect.Value {
for i, x := range finfo.idx {
if i > 0 {
t := v.Type()
if t.Kind() == reflect.Ptr && t.Elem().Kind() == reflect.Struct {
if v.IsNil() {
if !shouldInitNilPointers {
return reflect.Value{}
}
v.Set(reflect.New(v.Type().Elem()))
}
v = v.Elem()
}
}
v = v.Field(x)
}
return v
}