How Can I Unmarshal XML with Dynamic Attributes in Go?

Unmarshaling XML with Dynamic Attributes in Go

In Go, unmarshaling XML with dynamic attributes can be a challenge. However, with the recent resolution of Issue 3633, there is now a simple and efficient way to handle this situation.

The Issue: Unknown Attributes

Traditionally, when unmarshaling XML in Go, you would define a struct with specific fields to match the expected XML elements. However, what happens when you encounter XML tags with attributes that you cannot predict?

The Solution: The ",any,attr" Tag

The solution lies in using the ",any,attr" tag in your Go struct definition. This tag instructs the XML unmarshaler to collect all attributes of the specified element into a slice of xml.Attr structs.

Example

Consider the following XML snippet:

<TAG ATTR1="VALUE1" ATTR2="VALUE2" />

To unmarshal this XML into a Go struct, you can use the following code:

package main

import (
    "encoding/xml"
    "fmt"
)

func main() {
    var v struct {
        Attributes []xml.Attr `xml:",any,attr"`
    }

    data := `<TAG ATTR1="VALUE1" ATTR2="VALUE2" />`

    err := xml.Unmarshal([]byte(data), &v)
    if err != nil {
        panic(err)
    }
    fmt.Println(v)
}

When you run this code, the v struct will be populated with the following data:

{[]xml.Attr{
    {Name: {Local: "ATTR1"}, Value: "VALUE1"},
    {Name: {Local: "ATTR2"}, Value: "VALUE2"},
}}

The Attributes slice contains two xml.Attr structs, each representing one of the attributes from the XML tag.

Conclusion

The ",any,attr" tag provides a powerful and flexible way to unmarshal XML tags with dynamic attributes in Go. By utilizing this feature, you can easily handle unpredictable XML structures and extract the data you need into custom structs.

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