How to parse xml correctly

I want to create structs = each type of command.

Commands have common part of xml - CommandResult. I created interface Command. I need to SomeCommand implements Command and can to be parsed as xml, also IsError must be realized in CommandResult, other functions must be realized by SomeCommand.

Code:

type Command interface {
    IsError() bool

    Request(buf *bufio.Writer, params interface{}) error
    ...
}

// Result of request
type CommandResult struct {
    Code    int    `xml:"code,attr" json:"code"`
    Message string `xml:"msg" json:"msg"`
}

// this Command's func is realized by CommandResult 
func (self CommandResult) IsError() bool {
    return true
}


// some command
type SomeCommand struct {
    CommandResult // CommandResult `xml:"response>result" json:"result"`
}

// this Command's func is realized by SomeCommand 
func (self SomeCommand) Request(buf *bufio.Writer, params interface{}) error {
    return nil
}

// other Command's functions are realized by CommandResult too

XML:

<epp>
  <response>
    <result code="1000">
      <msg>Command completed successfully</msg>
    </result>
    <trID>
      <svTRID>asd</svTRID>
    </trID>
  </response>
</epp>

Expected result:

a := SomeCommand
xml.NewDecoder(reader).Decode(&a)
// a.CommandResult.Code = 1000
// a.CommandResult.Message = 'Command completed successfully'

// a implements Command

Solution

I think paths in embedded structure should be absolute as all "parent's" structures are part of the "child". So your

 type CommandResult struct {
     Code    int    `xml:"code,attr" json:"code"`
     Message string `xml:"msg" json:"msg"`
 }

Should be more like

 type CommandResult struct {
     Code    int    `xml:"response>result>code,attr" json:"code"`
     Message string `xml:"response>result>msg" json:"msg"`
 }

BUT! There we are facing Go's limitation.

You can't use attr with chaining. There is issue on Github but looks like it is not in priority list. So if I right understand shortest version of your CommandResult declaration would be:

type CommandResult struct {
    Result struct {
        Code    int    `xml:"code,attr" json:"code"`
        Message string `xml:"msg" json:"msg"`
    } `xml:"response>result" json:"response"`
}

Not a real problem but in case if you will decide to convert Command back to XML would be nice to declare its XMLName. Something like
```
type CommandResult struct {
    XMLName xml.Name `xml:"epp"`
    Result  struct {
        Code    int    `xml:"code,attr" json:"code"`
        Message string `xml:"msg" json:"msg"`
    } `xml:"response>result" json:"response"`
}
```
Because without it XML encoder will produce something like <SomeCommand><response>...</response></SomeCommand>

Update with full example

package main

import (
    "bufio"
    "encoding/xml"
    "log"
)

type Command interface {
    IsError() bool

    Request(buf *bufio.Writer, params interface{}) error
}

// Result of request
type CommandResult struct {
    XMLName xml.Name `xml:"epp"`
    Result  struct {
        Code    int    `xml:"code,attr" json:"code"`
        Message string `xml:"msg" json:"msg"`
    } `xml:"response>result" json:"response"`
}

// this Command's func is realized by CommandResult
func (self CommandResult) IsError() bool {
    return true
}

// some command
type SomeCommand struct {
    CommandResult
}

// this Command's func is realized by SomeCommand
func (self SomeCommand) Request(buf *bufio.Writer, params interface{}) error {
    return nil
}

type AnotherCommand struct {
    CommandResult
}

func (self AnotherCommand) Request(buf *bufio.Writer, params interface{}) error {
    return nil
}

func main() {
    var c Command

    c = SomeCommand{}
    log.Println(c.IsError())

    c = AnotherCommand{}
    log.Println(c.IsError())
}