Unmarshaling SOAP messages using Go

Question content

I am relatively new to the go language.

I'm having trouble trying to unmarshal a soap message. My attempt was to abstract the content of the body element and avoid defining the xml structure statically as it changes depending on the requested operation. Unfortunately I can't find the correct way. In the example, the getcontent function should receive a pointer to the structure containing the content and dynamically add it to the body so it can be filled. But the results were not what was expected.

package main

import (
    "encoding/xml"
    "fmt"
)

type Message interface{}

type EnvelopeResponse struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Envelope"`
    Body    Message  `xml:"http://schemas.xmlsoap.org/soap/envelope/ Body"`
}

type Body struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Body"`

    Fault               *Fault  `xml:",omitempty"`
    Content             Message `xml:",omitempty"`
    SOAPBodyContentType string  `xml:"-"`
}

type Fault struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Fault"`

    Code   string `xml:"faultcode,omitempty"`
    String string `xml:"faultstring,omitempty"`
    Actor  string `xml:"faultactor,omitempty"`
    Detail string `xml:"detail,omitempty"`
}

type GetHostNumberOfEntriesResponse struct {
    XMLName                xml.Name `xml:"urn:dslforum-org:service:Hosts:1 GetHostNumberOfEntriesResponse"`
    NewHostNumberOfEntries int64    `xml:"NewHostNumberOfEntries"`
}

func GetContent(rawXml []byte, content interface{}) {
    envelope := EnvelopeResponse{Body: Body{Content: content}}
    xml.Unmarshal(rawXml, &envelope)
}

func main() {
    b := []byte(`
<?xml version="1.0"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<s:Body>
<u:GetHostNumberOfEntriesResponse xmlns:u="urn:dslforum-org:service:Hosts:1">
<NewHostNumberOfEntries>47</NewHostNumberOfEntries>
</u:GetHostNumberOfEntriesResponse>
</s:Body>
</s:Envelope>
`)
    content := &GetHostNumberOfEntriesResponse{}
    GetContent(b, content)
    fmt.Println(*content)
}

Here’s an example from the playground:

https://go.dev/play/p/bbr4vexipbc

Correct Answer

The solution I found was to use generics to represent the variables of the body and parameterized content.

This code works as I expected:

package main

import (
    "encoding/xml"
    "fmt"
)

type EnvelopeResponse[T any] struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Envelope"`
    Body    Body[T]  `xml:"http://schemas.xmlsoap.org/soap/envelope/ Body"`
}

type Body[T any] struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Body"`

    Fault               *Fault `xml:",omitempty"`
    Content             T      `xml:",omitempty"`
    SOAPBodyContentType string `xml:"-"`
}

type Fault struct {
    XMLName xml.Name `xml:"http://schemas.xmlsoap.org/soap/envelope/ Fault"`

    Code   string `xml:"faultcode,omitempty"`
    String string `xml:"faultstring,omitempty"`
    Actor  string `xml:"faultactor,omitempty"`
    Detail string `xml:"detail,omitempty"`
}

type GetHostNumberOfEntriesResponse struct {
    XMLName                xml.Name `xml:"urn:dslforum-org:service:Hosts:1 GetHostNumberOfEntriesResponse"`
    NewHostNumberOfEntries int64    `xml:"NewHostNumberOfEntries"`
}

func GetContent[T any](rawXml []byte, content T) {
    envelope := EnvelopeResponse[T]{Body: Body[T]{Content: content}}
    xml.Unmarshal(rawXml, &envelope)
}

func main() {
    b := []byte(`
<?xml version="1.0"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<s:Body>
<u:GetHostNumberOfEntriesResponse xmlns:u="urn:dslforum-org:service:Hosts:1">
<NewHostNumberOfEntries>47</NewHostNumberOfEntries>
</u:GetHostNumberOfEntriesResponse>
</s:Body>
</s:Envelope>
`)
    content := &GetHostNumberOfEntriesResponse{}
    GetContent(b, content)
    fmt.Println(*content)
}

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