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.

1 files changed, 58 insertions, 0 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
+}