Golang xml key name conflict

Question content

I need to generate a complex xml file in order to load it into another system. Therefore, tags and tag order cannot be changed as they must follow a precise format to load correctly. I'm currently using the encoding/xml package in golang to try to accomplish this.

The problem I'm having is that I can't have two tags with the same name. I get the following error: main.XMLDict Field "Key1" with label "key" conflicts with field "Key2" with label "key". Below is my simplified code:

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

type XMLDict struct {
    XMLName xml.Name    `xml:"dict"`
    Key1    string      `xml:"key"`
    Data1   string      `xml:"data"`
    Key2    string      `xml:"key"`
    StringArray XMLStringArray
}

type XMLStringArray struct {
    XMLName  xml.Name    `xml:"array"̀`
    XMLString   []string `xml:"string"`
}

func main() {

    sa := make([]string, 3)
    sa[0] = "g"
    sa[1] = "h"
    sa[2] = "i"

    arr := XMLStringArray{
        XMLString: sa,
    }

    master := XMLDict{
        Key1: "Color",
        Data1: "Random data",
        Key2: "Curve",
        StringArray: arr,
    }

    output, err := xml.MarshalIndent(master, "  ", "    ")
    if err != nil {
        fmt.Printf("error: %v\n", err)
    }

    os.Stdout.Write(output)

    return
}

Here is an example of the XML file I need to generate:

<dict>
            <key>Color</key>
            <data>
            BAtzdHJlYW10eXBlZIHoA4QBQISEhAdOU0NvbG9yAISECE5TT2Jq
            ZWN0AIWEAWMChARmZmZmg7oehT2DZmYmP4NmZiY/AYY=
            </data>
            <key>Curve</key>
            <dict>
                <key>Interpolation</key>
                <integer>5</integer>
                <key>Points</key>
                <array>
                    <string>{0, 0}</string>
                    <string>{0.05, 0.053871}</string>
                    <string>{0.1, 0.110555}</string>
                    <string>{0.15, 0.166793}</string>
                    <string>{0.2, 0.216919}</string>
                    <string>{0.3, 0.327703}</string>
                    <string>{0.4, 0.440897}</string>
                    <string>{0.5, 0.539322}</string>
                    <string>{0.6, 0.657477}</string>
                    <string>{0.7, 0.763339}</string>
                    <string>{0.75, 0.814082}</string>
                    <string>{0.8, 0.861097}</string>
                    <string>{0.85, 0.904147}</string>
                    <string>{0.9, 0.944079}</string>
                    <string>{0.95, 0.974036}</string>
                    <string>{0.98, 0.990085}</string>
                    <string>{1, 1}</string>
                </array>
            </dict>
            <key>Line Width</key>
            <real>0.0040000001899898052</real>
            <key>Points Diameter</key>
            <real>0.014999999664723873</real>
            <key>Precision</key>
            <real>9.9999997473787516e-05</real>
        </dict>

So, my questions: 1) Is there an easy way to solve this problem, still using the structural approach of building the data and then generating the XML, 2) Is there a better way to build and generate this file than using Stuts or 3) Am I just doing something wrong?

EDIT: Below is the requested input file:

"File created by Curve"
LGOROWLENGTH 3
#
# Curve4 Run Information
#
# Run: Run 1 - Calibration
# Based On: <none>
#
# Values in this file are 'Wanted'
#
# Gray Balance: On
#    reduced after 100%
#    until 100%
#    media white values: Measured
#    media aim points: -0.17 / 0.96
#
NUMBER_OF_FIELDS    6
BEGIN_DATA_FORMAT
SampleID    SAMPLE_NAME CMYK_C  CMYK_M  CMYK_Y  CMYK_K
END_DATA_FORMAT
NUMBER_OF_SETS 17
BEGIN_DATA
A0  "0.00"  0.0000  0.0000  0.0000  0.0000
A1  "5.00"  5.3871  5.1408  5.2761  5.5775
A2  "10.00" 11.0555 10.7418 10.6026 11.0702
A3  "15.00" 16.6793 16.3894 15.8763 16.7064
A4  "20.00" 21.6919 21.7968 21.0234 22.3956
A5  "30.00" 32.7703 32.7458 31.1841 33.6738
A6  "40.00" 44.0897 42.4801 40.0887 44.2966
A7  "50.00" 53.9322 54.2364 49.1680 54.8968
A8  "60.00" 65.7477 64.9423 59.1719 66.4696
A9  "70.00" 76.3339 75.4398 69.4943 77.1661
A10 "75.00" 81.4082 80.5957 75.1423 82.0637
A11 "80.00" 86.1097 84.9296 81.1298 86.7399
A12 "85.00" 90.4147 88.8039 86.7945 90.8142
A13 "90.00" 94.4079 92.6783 92.1110 94.2426
A14 "95.00" 97.4036 96.2097 96.6019 97.2088
A15 "98.00" 99.0085 98.5775 98.7747 98.9000
A16 "100.00"    100.0000    100.0000    100.0000    100.0000
END_DATA

Correct answer

I think there are many solutions to achieve this using XML custom marshaler; this is my attempt.

First of all, in your root <dict> it always seems to be a "list" of items like this:

<key>a-string</key>
<data|integer|real|array|dict>a-value</data|integer|real|array|dict>

<key>another-string</key>
<data|integer|real|array|dict>another-value</data|integer|real|array|dict>

To represent each of these, we can define a KeyValue structure, where Value is just an interface to represent anything it can hold (data , integer,...)

type KeyValue struct {
    Key   string
    Value Value
}

type Value interface {
    getXMLName() string // this will return data, integer, array, etc, depending on the implementation
}

We can then implement Value using the different types provided in the example:

type ValueData struct {
    Data string `xml:",chardata"`
}

func (v ValueData) getXMLName() string { return "data" }

type ValueInteger struct {
    Integer int `xml:",chardata"`
}

func (v ValueInteger) getXMLName() string { return "integer" }

type ValueStringArray struct {
    Array []string `xml:"string"`
}

func (v ValueStringArray) getXMLName() string { return "array" }

type ValueReal struct {
    Real float64 `xml:",chardata"`
}

func (v ValueReal) getXMLName() string { return "real" }

Within the XML tag, chardata is used to avoid including extra levels in our XML document; for ValueStringArray, we use string because your The project is named this way.

Finally, to allow recursion (dict internal dict), we can also define this structure:

type ValueDict struct {
    XMLName    xml.Name `xml:"dict"`
    KeysValues []KeyValue
}

func (v ValueDict) getXMLName() string { return "dict" }

After completing all operations, we can implement a custom marshaler:

func (kv KeyValue) MarshalXML(e *xml.Encoder, _ xml.StartElement) error {
    if err := e.EncodeElement(kv.Key, xml.StartElement{Name: xml.Name{Local: "key"}}); err != nil {
        return err
    }
    if err := e.EncodeElement(kv.Value, xml.StartElement{Name: xml.Name{Local: kv.Value.getXMLName()}}); err != nil {
        return err
    }
    return nil
}

This will allow the generation of projects like this:

<key>Line Width</key>
<real>0.004000000189989805</real>

The name of the

tag (here real) is based on what is returned by the getXMLName() method.

Finally, you can define Go structs and marshals like this:

master := ValueDict{
    KeysValues: []KeyValue{
        {
            Key: "Color",
            Value: ValueData{
                Data: "BAtzdHJlYW10eXBlZIHoA4QBQISEhAdOU0NvbG9yAISECE5TT2JqZWN0AIWEAWMChARmZmZmg7oehT2DZmYmP4NmZiY/AYY=",
            },
        },
        {
            Key: "Curve",
            Value: ValueDict{
                KeysValues: []KeyValue{
                    {
                        Key: "Interpolation",
                        Value: ValueInteger{
                            Integer: 5,
                        },
                    },
                    {
                        Key: "Points",
                        Value: ValueStringArray{
                            Array: []string{
                                "{0, 0}",
                                "{0.05, 0.053871}",
                                "{0.1, 0.110555}",
                                "{0.15, 0.166793}",
                                "{0.2, 0.216919}",
                                "{0.3, 0.327703}",
                                "{0.4, 0.440897}",
                                "{0.5, 0.539322}",
                                "{0.6, 0.657477}",
                                "{0.7, 0.763339}",
                                "{0.75, 0.814082}",
                                "{0.8, 0.861097}",
                                "{0.85, 0.904147}",
                                "{0.9, 0.944079}",
                                "{0.95, 0.974036}",
                                "{0.98, 0.990085}",
                                "{1, 1}",
                            },
                        },
                    },
                },
            },
        },
        {
            Key: "Line Width",
            Value: ValueReal{
                Real: 0.0040000001899898052,
            },
        },
        {
            Key: "Points Diameter",
            Value: ValueReal{
                Real: 0.014999999664723873,
            },
        },
        {
            Key: "Precision",
            Value: ValueReal{
                Real: 9.9999997473787516e-05,
            },
        },
    },
}

output, err := xml.MarshalIndent(master, "  ", "    ")
if err != nil {
    fmt.Printf("error: %v\n", err)
}

os.Stdout.Write(output)

This will print exactly what is in the sample XML provided in your question.

You can test the complete code in the Go Playground: https://go.dev/play/p /k8cEIywx3UB.

The main advantages of this solution are:

• We just need to implement a custom XML marshaler
• It can be easily extended if you have other structures in your XML document (let's say a boolean value, we can create a ValueBool implementation Value)

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