How to Avoid Unmarshaling Only the First Element of an XML Array in Go?

Unmarshal XML Array in Go: Getting Only the First Element

XML, a data format prevalent in enterprise environments, is often represented in complex, nested structures. Go, a versatile programming language, offers robust XML unmarshaling capabilities. However, understanding the nuances of unmarshaling XML arrays can be crucial.

In a particular scenario, a developer encountered an issue when unmarshaling an XML array. The code successfully unmarshaled the first element but failed to retrieve the entire array.

The Problem:

type HostSystemIdentificationInfo []struct {
    IdentiferValue string `xml:"identifierValue"`
    IdentiferType  struct {
        Label   string `xml:"label"`
        Summary string `xml:"summary"`
        Key     string `xml:"key"`
    } `xml:"identifierType"`
}

func main() {
    var t HostSystemIdentificationInfo
    err := xml.Unmarshal([]byte(vv), &t)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(t)
}

const vv = `
  <HostSystemIdentificationInfo xsi:type="HostSystemIdentificationInfo">
    <identifierValue>unknown</identifierValue>
    <identifierType>
      <label>Asset Tag</label>
      <summary>Asset tag of the system</summary>
      <key>AssetTag</key>
    </identifierType>
  </HostSystemIdentificationInfo>
`

The Expected Output:

[{ unknown {Asset Tag Asset tag of the system AssetTag}}]

The Actual Output:

[{ unknown {Asset Tag Asset tag of the system AssetTag}}]

Solution:

The issue arises due to a misunderstanding about the XML unmarshaling process. When unmarshaling an XML array, you cannot simply provide the target struct as the pointer to receive the data. Instead, you must create an xml.Decoder and repeatedly call its Decode method.

package main

import (
    "bytes"
    "encoding/xml"
    "fmt"
    "io"
    "log"
)

type HostSystemIdentificationInfo struct {
    IdentiferValue string `xml:"identifierValue"`
    IdentiferType  struct {
        Label   string `xml:"label"`
        Summary string `xml:"summary"`
        Key     string `xml:"key"`
    } `xml:"identifierType"`
}

func main() {
    d := xml.NewDecoder(bytes.NewBufferString(vv))
    for {
        var t HostSystemIdentificationInfo
        err := d.Decode(&t)
        if err == io.EOF {
            break
        }
        if err != nil {
            log.Fatal(err)
        }
        fmt.Println(t)
    }
}

const vv = `
  <HostSystemIdentificationInfo xsi:type="HostSystemIdentificationInfo">
    <identifierValue>unknown</identifierValue>
    <identifierType>
      <label>Asset Tag</label>
      <summary>Asset tag of the system</summary>
      <key>AssetTag</key>
    </identifierType>
  </HostSystemIdentificationInfo>
`

By utilizing the xml.Decoder, you can correctly iterate over each element in the XML array and unmarshal them individually.

Hence, by following these steps, developers can effectively unmarshal XML arrays in Go, enabling them to parse complex data structures efficiently.

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