Interfaces and encoding/xml Unmarshal

I have a soap service I'm writing against. One portion of the soap API is for returning a query result, and I'm hoping to provide the base structs for decoding the envelope, while allow a developer to fill in the interface in which encoding/xml will decode to.

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

type QueryBody struct {
	QueryResult *QueryResult `xml:"queryResponse>result"`
}

type QueryResult struct {
	Done    bool    `xml:"done"`
	Size    int     `xml:"size"`
	Records Record `xml:"records"`
}

type Record interface {
	UnmarshalXML(d *xml.Decoder, start xml.StartElement) error
}

Is it possible to inject an interface like this for unmarhsalling or do I have to accept the interface at the QueryEnvelope{} level?

Ideally client side would act as such:

type Record struct {
     Id int `xml:"id"`,
     Name stirng `xml:"name"`
}

func (r *Record) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
     // unmasrshal here, or best case I dont even need to implment UnmarsahlXML()!
}
res, err := Query("select id from table", Record{})

This would mean that they don't have to reproduce the QueryEnvelope struct (as a developer using the package I'm creating)

The common solution is to ask the client to pass a pointer to his struct instance like so:

// The custom struct of your client
type ClientStruct struct {
	Id   int    `xml:"id"`
	Name string `xml:"name"`
}

// This would be your API
func Query(foo string, v interface{}) {
	fakeXmlResult := "<test><id>012345</id><name>MyName</name></test>"
	xml.Unmarshal([]byte(fakeXmlResult), v)
}

func main() {
	r := ClientStruct{}
	Query("SQL QUERY", &r) // Note the &
	fmt.Println(r)
}

Did I understand your question correctly?

So you can indeed inject an interface partway through, I was failing it allocate memory for the decoder to work:

Package:

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

type QueryBody struct {
	QueryResult *QueryResult `xml:"queryResponse>result"`
}

type QueryResult struct {
	Done    bool        `xml:"done"`
	Size    int         `xml:"size"`
	Records interface{} `xml:"records"`
}

func (r *Resource) Query(sql string, r interface{}) error {
    t := &QueryEnvelope{Body: &QueryBody{QueryResult: &QueryResult{Records: r}}}
    //do query and unmarshal into t
    return err
}

Client / main:

type Record struct {
	Id   string `xml:"id"`
	Name string `xml:"name"`
}

r := new([]*Record) // must allocate memory using new
err = ent.Query("select id, name from account limit 3", r)