xmpp: Implement basic elementBuffer

This is needed to buffer XML elements of a stream until they are
complete and can be given to an element handler.

2 files changed, 76 insertions, 2 deletions

diff --git a/xmpp/element_buffer.go b/xmpp/element_buffer.go
new file mode 100644
index 0000000..c55279b
--- /dev/null
+++ b/xmpp/element_buffer.go
@@ -0,0 +1,58 @@
+package xmpp
+
+import (
+	"encoding/xml"
+)
+
+// elementBuffer is a struct to store multiple values of type xml.Token until
+// they form a complete XML element with opening and closing tag which is
+// suitable to be passed to an appropriate handler function.
+type elementBuffer struct {
+	tokens []xml.Token
+	end    xml.EndElement
+	level  int
+}
+
+// newElementBuffer returns a new initialized elementBuffer struct.
+func newElementBuffer() elementBuffer {
+	buf := elementBuffer{}
+	buf.reset()
+	return buf
+}
+
+// FIXME this function needs essential error handling for corner cases!
+//
+// add is able to add a new xml.Token to the buffer. There are some rules
+// checked to ensure a correct and consistent elementBuffer which are checked.
+// If one of these checks fail the token is not added and a corresponding error
+// is returned.
+func (e *elementBuffer) add(t xml.Token) error {
+	switch t.(type) {
+	case xml.StartElement:
+		e.level += 1
+	case xml.EndElement:
+		e.level -= 1
+	}
+	e.tokens = append(e.tokens, t)
+	return nil
+}
+
+// isComplete returns true if the buffer contains a slice of XML tokens which
+// form a complete XML element starting with an xml.StartElement and closing
+// with the corresponding xml.EndElement.
+func (e *elementBuffer) isComplete() bool {
+	return (len(e.tokens) > 0 && e.level == 0)
+}
+
+// reset returns the content of the buffer as a slice of XML tokens and resets
+// the buffer to the initial state. This function can be used to initialize the
+// elementBuffer struct. In that case the return value can be ignored.
+func (e *elementBuffer) reset() (buf []xml.Token) {
+	retval := e.tokens
+
+	e.tokens = make([]xml.Token, 0)
+	e.end = xml.EndElement{}
+	e.level = 0
+
+	return retval
+}
diff --git a/xmpp/stream_pair.go b/xmpp/stream_pair.go
index e02cca6..b13d8a3 100644
--- a/xmpp/stream_pair.go
+++ b/xmpp/stream_pair.go
@@ -9,6 +9,8 @@ func runStreamPair(s *session) {
 	openStream(s)
 	defer closeStream(s)
 
+	buf := newElementBuffer()
+
 	for {
 		select {
 		case data := <-s.in:
@@ -18,8 +20,22 @@ func runStreamPair(s *session) {
 			default:
 				log.Printf("Unknown data '%d'!\n", data)
 			}
-		case _ = <-s.rx:
-			// TODO route received XML token here
+		case t := <-s.rx:
+			err := buf.add(t)
+			if err != nil {
+				log.Printf("Could not add XML token to buffer: %v\n", err)
+				return
+			}
+			if buf.isComplete() {
+				element := buf.reset()
+				// TODO handle XML element here - this is just a dummy:
+				switch start := element[0].(type) {
+				case xml.StartElement:
+					log.Printf("Got XML element `%s`\n", start.Name.Local)
+				default:
+					log.Println("No xml.StartElement at start of element buffer!")
+				}
+			}
 		}
 	}
 }