TTuck
Encoding · Example 59

XML

encoding/xml fmt

Go offers built-in support for XML and XML-like formats with the encoding/xml package.

package main

import (
	"encoding/xml"
	"fmt"
)

Plant will be mapped to XML. Similarly to the JSON examples, field tags contain directives for the encoder and decoder. Here we use some special features of the XML package: the XMLName field name dictates the name of the XML element representing this struct; id,attr means that the Id field is an XML attribute rather than a nested element.

type Plant struct {
	XMLName xml.Name `xml:"plant"`
	Id      int      `xml:"id,attr"`
	Name    string   `xml:"name"`
	Origin  []string `xml:"origin"`
}

func (p Plant) String() string {
	return fmt.Sprintf("Plant id=%v, name=%v, origin=%v",
		p.Id, p.Name, p.Origin)
}

func main() {
	coffee := &Plant{Id: 27, Name: "Coffee"}
	coffee.Origin = []string{"Ethiopia", "Brazil"}

Emit XML representing our plant; using MarshalIndent to produce a more human-readable output.

	out, _ := xml.MarshalIndent(coffee, " ", "  ")
	fmt.Println(string(out))

To add a generic XML header to the output, append it explicitly.

	fmt.Println(xml.Header + string(out))

Use Unmarshal to parse a stream of bytes with XML into a data structure. If the XML is malformed or cannot be mapped onto Plant, a descriptive error will be returned.

	var p Plant
	if err := xml.Unmarshal(out, &p); err != nil {
		panic(err)
	}
	fmt.Println(p)

	tomato := &Plant{Id: 81, Name: "Tomato"}
	tomato.Origin = []string{"Mexico", "California"}

The parent>child>plant field tag tells the encoder to nest all plants under <parent><child>...

	type Nesting struct {
		XMLName xml.Name `xml:"nesting"`
		Plants  []*Plant `xml:"parent>child>plant"`
	}

	nesting := &Nesting{}
	nesting.Plants = []*Plant{coffee, tomato}

	out, _ = xml.MarshalIndent(nesting, " ", "  ")
	fmt.Println(string(out))
}
$ go run ./59_xml
 <plant id="27">
   <name>Coffee</name>
   <origin>Ethiopia</origin>
   <origin>Brazil</origin>
 </plant>
<?xml version="1.0" encoding="UTF-8"?>
 <plant id="27">
   <name>Coffee</name>
   <origin>Ethiopia</origin>
   <origin>Brazil</origin>
 </plant>
Plant id=27, name=Coffee, origin=[Ethiopia Brazil]
 <nesting>
   <parent>
     <child>
       <plant id="27">
         <name>Coffee</name>
         <origin>Ethiopia</origin>
         <origin>Brazil</origin>
       </plant>
       <plant id="81">
         <name>Tomato</name>
         <origin>Mexico</origin>
         <origin>California</origin>
       </plant>
     </child>
   </parent>
 </nesting>
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