PubSub protocol support (#142)

* PubSub protocol support
Added support for :
- XEP-0050   (Command))
- XEP-0060   (PubSub)
- XEP-0004   (Forms)

Fixed the NewClient function by adding parsing of the domain from the JID if no domain is provided in transport config.
Updated xmpp_jukebox example

* Delete useless pubsub errors

* README.md update
Fixed import in echo example

* Typo

* Fixed raw send on client example

* Fixed jukebox example and added a README.md

stanza/commands.go

@@ -0,0 +1,136 @@
+package stanza
+
+import "encoding/xml"
+
+// Implements the XEP-0050 extension
+
+const (
+	CommandActionCancel   = "cancel"
+	CommandActionComplete = "complete"
+	CommandActionExecute  = "execute"
+	CommandActionNext     = "next"
+	CommandActionPrevious = "prev"
+
+	CommandStatusCancelled = "canceled"
+	CommandStatusCompleted = "completed"
+	CommandStatusExecuting = "executing"
+
+	CommandNoteTypeErr  = "error"
+	CommandNoteTypeInfo = "info"
+	CommandNoteTypeWarn = "warn"
+)
+
+type Command struct {
+	XMLName xml.Name `xml:"http://jabber.org/protocol/commands command"`
+
+	CommandElement CommandElement `xml:",any"`
+
+	BadAction       *struct{} `xml:"bad-action,omitempty"`
+	BadLocale       *struct{} `xml:"bad-locale,omitempty"`
+	BadPayload      *struct{} `xml:"bad-payload,omitempty"`
+	BadSessionId    *struct{} `xml:"bad-sessionid,omitempty"`
+	MalformedAction *struct{} `xml:"malformed-action,omitempty"`
+	SessionExpired  *struct{} `xml:"session-expired,omitempty"`
+
+	// Attributes
+	Action    string `xml:"action,attr,omitempty"`
+	Node      string `xml:"node,attr"`
+	SessionId string `xml:"sessionid,attr,omitempty"`
+	Status    string `xml:"status,attr,omitempty"`
+	Lang      string `xml:"lang,attr,omitempty"`
+}
+
+func (c *Command) Namespace() string {
+	return c.XMLName.Space
+}
+
+type CommandElement interface {
+	Ref() string
+}
+
+type Actions struct {
+	Prev     *struct{} `xml:"prev,omitempty"`
+	Next     *struct{} `xml:"next,omitempty"`
+	Complete *struct{} `xml:"complete,omitempty"`
+
+	Execute string `xml:"execute,attr,omitempty"`
+}
+
+func (a *Actions) Ref() string {
+	return "actions"
+}
+
+type Note struct {
+	Text string `xml:",cdata"`
+	Type string `xml:"type,attr,omitempty"`
+}
+
+func (n *Note) Ref() string {
+	return "note"
+}
+
+func (n *Node) Ref() string {
+	return "node"
+}
+
+func (c *Command) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	c.XMLName = start.Name
+
+	// Extract packet attributes
+	for _, attr := range start.Attr {
+		if attr.Name.Local == "action" {
+			c.Action = attr.Value
+		}
+		if attr.Name.Local == "node" {
+			c.Node = attr.Value
+		}
+		if attr.Name.Local == "sessionid" {
+			c.SessionId = attr.Value
+		}
+		if attr.Name.Local == "status" {
+			c.Status = attr.Value
+		}
+		if attr.Name.Local == "lang" {
+			c.Lang = attr.Value
+		}
+	}
+
+	// decode inner elements
+	for {
+		t, err := d.Token()
+		if err != nil {
+			return err
+		}
+
+		switch tt := t.(type) {
+
+		case xml.StartElement:
+			// Decode sub-elements
+			var err error
+			switch tt.Name.Local {
+
+			case "affiliations":
+				a := Actions{}
+				d.DecodeElement(&a, &tt)
+				c.CommandElement = &a
+			case "configure":
+				nt := Note{}
+				d.DecodeElement(&nt, &tt)
+				c.CommandElement = &nt
+			default:
+				n := Node{}
+				e := d.DecodeElement(&n, &tt)
+				_ = e
+				c.CommandElement = &n
+				if err != nil {
+					return err
+				}
+			}
+
+		case xml.EndElement:
+			if tt == start.End() {
+				return nil
+			}
+		}
+	}
+}