在golang中使用XMLNS声明对XML根令牌进行编码/解码

Question

I am attempting to encode and decode an XML token in Go using the encoding/xml package. The XML token in question has a namespace, an xmlns attribute, and a namespace declaration for the namespace on the tag (the example here is an XMPP stream start element). It is the root element of an XMPP stream:

<?xml version="1.0" encoding="UTF-8"?>
<stream:stream
       from='[e-mail]'
       to='im.example.com'
       version='1.0'
       xml:lang='en'
       xmlns='jabber:client'
       xmlns:stream='http://etherx.jabber.org/streams'>

(Ignore the processing instruction; I merely left that to illustrate that this is the root element)

I want to be able to read/write this token from a struct, so I fetch it as an xml.StartElement with decoder.Token() and manually copy all the attributes over to the struct. I then write it out with encoder.Encode(thestruct), but always get funny results (The xmlns is wrong, and the start tag is never stream:stream even though the XMLName is correct).

How should this struct be modified to be able to encode and decode to and from something like the above XML?

type stream struct {
    STo         string   `xml:"to,attr"`
    SFrom       string   `xml:"from,attr"`
    Version     string   `xml:"version,attr"`
    Xmlns       string   `xml:"xmlns,attr"`
    Lang        string   `xml:"http://www.w3.org/XML/1998/namespace lang,attr"`
    Id          string   `xml:"id,attr"`
    XmlnsStream string   `xml:"xmlns stream,attr"`
    XMLName     xml.Name `xml:"http://etherx.jabber.org/streams stream"`
}

Answer 1

You get correct results, because:

<stream:stream
      xmlns:stream='http://etherx.jabber.org/streams' />

is the same as

<stream xmlns='http://etherx.jabber.org/streams' />

Jabber's XMLs are pretty sophisticated, so if you wan't to end up with correct XMPP XMLs, you probably need to write your own encoder.

By the way, if you look at Golang XMPP implementations you'll see they all use own encoding (and, often, decoding).