Add xmpp/router.go

This implements a routing function for XML elements received by an XML
stream.

2 files changed, 60 insertions, 7 deletions

diff --git a/xmpp/router.go b/xmpp/router.go
new file mode 100644
index 0000000..839f870
--- /dev/null
+++ b/xmpp/router.go
@@ -0,0 +1,59 @@
+package xmpp
+
+import (
+	"encoding/xml"
+	"log"
+)
+
+// routingTable is a data structure which contains routing information for XML
+// elements. The xml.StartElement at the beginning of an XML element has a name
+// containing the XML namespace and a local name. Based on this compisition
+// which forms the xml.Name the appropriate handler function is defined by each
+// entry of the routingTable.
+type routingTable []struct {
+	name    xml.Name
+	handler func([]xml.Token)
+}
+
+// getRoutingTable returns the routing table used in
+// xengineering.eu/limox/xmpp. Since Go does not allow such a datatype as a
+// constant such a function is a simple yet inefficient approach to guarantee
+// that an unmodified routing table is delivered to each user. A global
+// variable would have the problem that it could be altered during execution.
+func getRoutingTable() routingTable {
+	return routingTable{
+		// TODO fill with entries
+	}
+}
+
+// route determines the correct handler function for the given XML element by a
+// given routingTable. In addition it executes the determined handler function.
+// If no handler function is found an error message is send via the log module.
+func route(e []xml.Token, t routingTable) {
+	var name xml.Name
+
+	// TODO a stronger definition of an XML element (as here
+	// https://www.w3schools.com/xml/xml_elements.asp) would define that the
+	// first Token of an element is a StartElement token. This would make this
+	// code easier.
+	escape := false
+	for _, token := range e {
+		switch s := token.(type) {
+		case xml.StartElement:
+			name = s.Name
+			escape = true
+		}
+		if escape {
+			break
+		}
+	}
+
+	for _, r := range t {
+		if name == r.name {
+			r.handler(e)
+			return
+		}
+	}
+
+	log.Println("Could not route XML element")
+}
diff --git a/xmpp/stream_pair.go b/xmpp/stream_pair.go
index b13d8a3..c9108d1 100644
--- a/xmpp/stream_pair.go
+++ b/xmpp/stream_pair.go
@@ -28,13 +28,7 @@ func runStreamPair(s *session) {
 			}
 			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!")
-				}
+				route(element, getRoutingTable())
 			}
 		}
 	}