如何在Golang中创建自定义类型（字符串）的元数据CDATA格式？

Question

WeChat message reply requires such a format, CDATA is to resolve the special characters.

<xml>
<ToUserName><![CDATA[toUser]]></ToUserName>
<FromUserName><![CDATA[fromUser]]></FromUserName>
<CreateTime>12345678</CreateTime>
<MsgType><![CDATA[text]]></MsgType>
<Content><![CDATA[hello world]]></Content>
</xml>

When using golang to achieve the specification,I found that the xml.Marshal () can be used with the struct tag xml:",cdata" . Define a struct to deal with, the codes seems like:

package main

import (
    "encoding/xml"
    "fmt"
    "time"
)

type TextMsg struct {
    XMLName      xml.Name `xml:"xml"`
    ToUserName   CDATA
    FromUserName CDATA
    CreateTime   int64
    MsgType      CDATA
    Content      CDATA
}

type CDATA struct {
    Text string `xml:",cdata"`
}

func main() {
    msg := TextMsg{
        ToUserName:   CDATA{"userId"},
        FromUserName: CDATA{"appId"},
        CreateTime:   time.Now().Unix(),
        MsgType:      CDATA{"text"},
        Content:      CDATA{"some message like <hello>"}}

    b, _ := xml.MarshalIndent(msg, "", "    ")
    fmt.Println(string(b))
}

Output results:

<xml>
    <ToUserName><![CDATA[userId]]></ToUserName>
    <FromUserName><![CDATA[appId]]></FromUserName>
    <CreateTime>1485837083</CreateTime>
    <MsgType><![CDATA[text]]></MsgType>
    <Content><![CDATA[some message like <hello>]]></Content>
</xml>

But I think it's not perfect, since variable assignment is not as convenient as the normal string type, so I change the CDATA into string type, and try to achieve MarshalXML ():

package main

import (
    "encoding/xml"
    "fmt"
    "time"
)

type TextMsg struct {
    XMLName      xml.Name `xml:"xml"`
    ToUserName   CDATA
    FromUserName CDATA
    CreateTime   int64
    MsgType      CDATA
    Content      CDATA
}

type CDATA string

func (c CDATA) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
    e.EncodeElement("<![CDATA["+string(c)+"]]>", start)
    return nil
}

func main() {
    msg := TextMsg{
        ToUserName:   "userId",
        FromUserName: "appId",
        CreateTime:   time.Now().Unix(),
        MsgType:      "text",
        Content:      "some message like <hello>"}

    b, _ := xml.MarshalIndent(msg, "", "    ")
    fmt.Println(string(b))
}

But the output results do not meet expectations, "<" or ">" is escaped:

<xml>
    <ToUserName>&lt;![CDATA[userId]]&gt;</ToUserName>
    <FromUserName>&lt;![CDATA[appId]]&gt;</FromUserName>
    <CreateTime>1485837470</CreateTime>
    <MsgType>&lt;![CDATA[text]]&gt;</MsgType>
    <Content>&lt;![CDATA[some message like &lt;hello&gt;]]&gt;</Content>
</xml>

Do you have any good suggestions for me, thank you.

Answer 1

You can create another structure CDATA2 which has tag xml:",cdata", and pass it to EncodeElement().

EncodeElement() would correctly encode CDATA2{"foo<>"} to <![CDATA[foo<>]]>.

type CDATA2 struct {
    Text string `xml:",cdata"`
}

func (c CDATA) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
    e.EncodeElement(CDATA2{string(c)}, start)
    return nil
}

Check it in: Go Playground

Edit: you can use anonymous struct if you don't want to define named type

func (c CDATA) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
    e.EncodeElement(struct {
        string `xml:",cdata"`
    }{string(c)}, start)
    return nil
}

Check it in: Go Playground