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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 (
"bufio"
"bytes"
"fmt"
"io"
"reflect"
"strconv"
"strings"
)
const (
// A generic XML header suitable for use with the output of Marshal and
// MarshalIndent. This is not automatically added to any output of this
// package, it is provided as a convenience.
Header = `<?xml version="1.0" encoding="UTF-8"?>` + "\n"
)
// A Marshaler can produce well-formatted XML representing its internal state.
// It is used by both Marshal and MarshalIndent.
type Marshaler interface {
MarshalXML() ([]byte, error)
}
type printer struct {
*bufio.Writer
}
// Marshal writes an XML-formatted representation of v to w.
//
// If v implements Marshaler, then Marshal calls its MarshalXML method.
// Otherwise, Marshal uses the following procedure to create the XML.
//
// Marshal handles an array or slice by marshalling each of the elements.
// Marshal handles a pointer by marshalling the value it points at or, if the
// pointer is nil, by writing nothing. Marshal handles an interface value by
// marshalling the value it contains or, if the interface value is nil, by
// writing nothing. Marshal handles all other data by writing one or more XML
// elements containing the data.
//
// The name for the XML elements is taken from, in order of preference:
// - the tag on the XMLName field, if the data is a struct
// - the value of the XMLName field of type xml.Name
// - the tag of the struct field used to obtain the data
// - the name of the struct field used to obtain the data
// - the name of the marshalled type
//
// The XML element for a struct contains marshalled elements for each of the
// exported fields of the struct, with these exceptions:
// - the XMLName field, described above, is omitted.
// - a field with tag "name,attr" becomes an attribute with
// the given name in the XML element.
// - a field with tag ",attr" becomes an attribute with the
// field name in the in the XML element.
// - a field with tag ",chardata" is written as character data,
// not as an XML element.
// - a field with tag ",innerxml" is written verbatim, not subject
// to the usual marshalling procedure.
// - a field with tag ",comment" is written as an XML comment, not
// subject to the usual marshalling procedure. It must not contain
// the "--" string within it.
//
// If a field uses a tag "a>b>c", then the element c will be nested inside
// parent elements a and b. Fields that appear next to each other that name
// the same parent will be enclosed in one XML element. For example:
//
// type Result struct {
// XMLName xml.Name `xml:"result"`
// Id int `xml:"id,attr"`
// FirstName string `xml:"person>name>first"`
// LastName string `xml:"person>name>last"`
// Age int `xml:"person>age"`
// }
//
// xml.Marshal(w, &Result{Id: 13, FirstName: "John", LastName: "Doe", Age: 42})
//
// would be marshalled as:
//
// <result>
// <person id="13">
// <name>
// <first>John</first>
// <last>Doe</last>
// </name>
// <age>42</age>
// </person>
// </result>
//
// Marshal will return an error if asked to marshal a channel, function, or map.
func Marshal(w io.Writer, v interface{}) (err error) {
p := &printer{bufio.NewWriter(w)}
err = p.marshalValue(reflect.ValueOf(v), nil)
p.Flush()
return err
}
func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo) error {
if !val.IsValid() {
return nil
}
kind := val.Kind()
typ := val.Type()
// Try Marshaler
if typ.NumMethod() > 0 {
if marshaler, ok := val.Interface().(Marshaler); ok {
bytes, err := marshaler.MarshalXML()
if err != nil {
return err
}
p.Write(bytes)
return nil
}
}
// Drill into pointers/interfaces
if kind == reflect.Ptr || kind == reflect.Interface {
if val.IsNil() {
return nil
}
return p.marshalValue(val.Elem(), finfo)
}
// Slices and arrays iterate over the elements. They do not have an enclosing tag.
if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
for i, n := 0, val.Len(); i < n; i++ {
if err := p.marshalValue(val.Index(i), finfo); err != nil {
return err
}
}
return nil
}
tinfo, err := getTypeInfo(typ)
if err != nil {
return err
}
// Precedence for the XML element name is:
// 1. XMLName field in underlying struct;
// 2. field name/tag in the struct field; and
// 3. type name
var xmlns, name string
if tinfo.xmlname != nil {
xmlname := tinfo.xmlname
if xmlname.name != "" {
xmlns, name = xmlname.xmlns, xmlname.name
} else if v, ok := val.FieldByIndex(xmlname.idx).Interface().(Name); ok && v.Local != "" {
xmlns, name = v.Space, v.Local
}
}
if name == "" && finfo != nil {
xmlns, name = finfo.xmlns, finfo.name
}
if name == "" {
name = typ.Name()
if name == "" {
return &UnsupportedTypeError{typ}
}
}
p.WriteByte('<')
p.WriteString(name)
if xmlns != "" {
p.WriteString(` xmlns="`)
// TODO: EscapeString, to avoid the allocation.
Escape(p, []byte(xmlns))
p.WriteByte('"')
}
// Attributes
for i := range tinfo.fields {
finfo := &tinfo.fields[i]
if finfo.flags&fAttr == 0 {
continue
}
var str string
if fv := val.FieldByIndex(finfo.idx); fv.Kind() == reflect.String {
str = fv.String()
} else {
str = fmt.Sprint(fv.Interface())
}
if str != "" {
p.WriteByte(' ')
p.WriteString(finfo.name)
p.WriteString(`="`)
Escape(p, []byte(str))
p.WriteByte('"')
}
}
p.WriteByte('>')
switch k := val.Kind(); k {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
p.WriteString(strconv.FormatInt(val.Int(), 10))
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
p.WriteString(strconv.FormatUint(val.Uint(), 10))
case reflect.Float32, reflect.Float64:
p.WriteString(strconv.FormatFloat(val.Float(), 'g', -1, 64))
case reflect.String:
Escape(p, []byte(val.String()))
case reflect.Bool:
p.WriteString(strconv.FormatBool(val.Bool()))
case reflect.Array:
// will be [...]byte
bytes := make([]byte, val.Len())
for i := range bytes {
bytes[i] = val.Index(i).Interface().(byte)
}
Escape(p, bytes)
case reflect.Slice:
// will be []byte
bytes := val.Interface().([]byte)
Escape(p, bytes)
case reflect.Struct:
if err := p.marshalStruct(tinfo, val); err != nil {
return err
}
default:
return &UnsupportedTypeError{typ}
}
p.WriteByte('<')
p.WriteByte('/')
p.WriteString(name)
p.WriteByte('>')
return nil
}
var ddBytes = []byte("--")
func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
s := parentStack{printer: p}
for i := range tinfo.fields {
finfo := &tinfo.fields[i]
if finfo.flags&(fAttr|fAny) != 0 {
continue
}
vf := val.FieldByIndex(finfo.idx)
switch finfo.flags & fMode {
case fCharData:
switch vf.Kind() {
case reflect.String:
Escape(p, []byte(vf.String()))
case reflect.Slice:
if elem, ok := vf.Interface().([]byte); ok {
Escape(p, elem)
}
}
continue
case fComment:
k := vf.Kind()
if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
}
if vf.Len() == 0 {
continue
}
p.WriteString("<!--")
dashDash := false
dashLast := false
switch k {
case reflect.String:
s := vf.String()
dashDash = strings.Index(s, "--") >= 0
dashLast = s[len(s)-1] == '-'
if !dashDash {
p.WriteString(s)
}
case reflect.Slice:
b := vf.Bytes()
dashDash = bytes.Index(b, ddBytes) >= 0
dashLast = b[len(b)-1] == '-'
if !dashDash {
p.Write(b)
}
default:
panic("can't happen")
}
if dashDash {
return fmt.Errorf(`xml: comments must not contain "--"`)
}
if dashLast {
// "--->" is invalid grammar. Make it "- -->"
p.WriteByte(' ')
}
p.WriteString("-->")
continue
case fInnerXml:
iface := vf.Interface()
switch raw := iface.(type) {
case []byte:
p.Write(raw)
continue
case string:
p.WriteString(raw)
continue
}
case fElement:
s.trim(finfo.parents)
if len(finfo.parents) > len(s.stack) {
if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
s.push(finfo.parents[len(s.stack):])
}
}
}
if err := p.marshalValue(vf, finfo); err != nil {
return err
}
}
s.trim(nil)
return nil
}
type parentStack struct {
*printer
stack []string
}
// trim updates the XML context to match the longest common prefix of the stack
// and the given parents. A closing tag will be written for every parent
// popped. Passing a zero slice or nil will close all the elements.
func (s *parentStack) trim(parents []string) {
split := 0
for ; split < len(parents) && split < len(s.stack); split++ {
if parents[split] != s.stack[split] {
break
}
}
for i := len(s.stack) - 1; i >= split; i-- {
s.WriteString("</")
s.WriteString(s.stack[i])
s.WriteByte('>')
}
s.stack = parents[:split]
}
// push adds parent elements to the stack and writes open tags.
func (s *parentStack) push(parents []string) {
for i := 0; i < len(parents); i++ {
s.WriteString("<")
s.WriteString(parents[i])
s.WriteByte('>')
}
s.stack = append(s.stack, parents...)
}
// A MarshalXMLError is returned when Marshal or MarshalIndent encounter a type
// that cannot be converted into XML.
type UnsupportedTypeError struct {
Type reflect.Type
}
func (e *UnsupportedTypeError) Error() string {
return "xml: unsupported type: " + e.Type.String()
}
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