如何解析具有相同名称的嵌套节点的XML？

Question

I'm new to Golang and parsing XML with nested nodes of the same name is too difficult to me. This is a XML pulled from a third party API:

<?xml version="1.0" encoding="UTF-8"?>
<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
    <gesmes:subject>Reference rates</gesmes:subject>
    <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time="2019-01-28">
            <Cube currency="USD" rate="1.1418"/>
            <Cube currency="JPY" rate="124.94"/>
            <Cube currency="BGN" rate="1.9558"/>
        </Cube>
        <Cube time="2019-01-25">
            <Cube currency="USD" rate="1.1346"/>
            <Cube currency="JPY" rate="124.72"/>
            <Cube currency="BGN" rate="1.9558"/>
        </Cube>
    </Cube>
</gesmes:Envelope>

I need to parse it so I have an output like this:

&{Rates:[{Currency:USD Rate:1.1418 Date:2019-01-28} {Currency:JPY Rate:124.94 Date:2019-01-28} {Currency:BGN Rate:1.9558 Date:2019-01-28} {Currency:USD Rate:1.1346 Date:2019-01-25} {Currency:JPY Rate:124.72 Date:2019-01-25} {Currency:BGN Rate:1.9558 Date:2019-01-25}]}

And here's my code:

package main

import (
    "encoding/xml"
    "fmt"
)


type Rate struct {
    Currency  string `xml:"currency,attr"`
    Rate      string `xml:"rate,attr"`
    Date    string `xml:"time,attr"`
}

type Rates struct {
    Rates []Rate `xml:"Cube>Cube>Cube"`
}

func main() {
    v := &Rates{}
    if err := xml.Unmarshal([]byte(src), v); err != nil {
        panic(err)
    }
    fmt.Printf("%+v

", v)
}

const src = `<?xml version="1.0" encoding="UTF-8"?>
<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
    <gesmes:subject>Reference rates</gesmes:subject>
    <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time="2019-01-28">
            <Cube currency="USD" rate="1.1418"/>
            <Cube currency="JPY" rate="124.94"/>
            <Cube currency="BGN" rate="1.9558"/>
        </Cube>
        <Cube time="2019-01-25">
            <Cube currency="USD" rate="1.1346"/>
            <Cube currency="JPY" rate="124.72"/>
            <Cube currency="BGN" rate="1.9558"/>
        </Cube>
    </Cube>
</gesmes:Envelope>`

I'm out of ideas how to insert time attribute into Rates object. Any help would be appreciated.

Here it is in golang playground

Answer 1

You could implement a custom xml.Unmarshaler to get the results you want.

type Rate struct {
    Currency string `xml:"currency,attr"`
    Rate     string `xml:"rate,attr"`
    Date     string `xml:"time,attr"`
}

type Rates struct {
    Rates RateList `xml:"Cube>Cube"`
}

type RateList []Rate

func (ls *RateList) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
    date := start.Attr[0].Value

    for {
        tok, err := d.Token()
        if err != nil {
            if err == io.EOF {
                return nil
            }
            return err
        }

        if se, ok := tok.(xml.StartElement); ok {
            rate := Rate{Date: date}
            if err := d.DecodeElement(&rate, &se); err != nil {
                return err
            }

            *ls = append(*ls, rate)
        }
    }
}

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