Add msg.Get method to match and extract message extensions

message.go

@@ -2,6 +2,7 @@ package xmpp
 
 import (
 	"encoding/xml"
+	"reflect"
 )
 
 // ============================================================================
@@ -30,6 +31,37 @@ func NewMessage(a Attrs) Message {
 	}
 }
 
+// Get search and extracts a specific extension on a message.
+// It receives a pointer to an MsgExtension. It will panic if the caller
+// does not pass a pointer.
+// It will return true if the passed extension is found and set the pointer
+// to the extension passed as parameter to the found extension.
+// It will return false if the extension is not found on the message.
+//
+// Example usage:
+//   var oob xmpp.OOB
+//   if ok := msg.Get(&oob); ok {
+//     // oob extension has been found
+//	 }
+func (msg *Message) Get(ext MsgExtension) bool {
+	target := reflect.ValueOf(ext)
+	if target.Kind() != reflect.Ptr {
+		panic("you must pass a pointer to the message Get method")
+	}
+
+	for _, e := range msg.Extensions {
+		if reflect.TypeOf(e) == target.Type() {
+			source := reflect.ValueOf(e)
+			if source.Kind() != reflect.Ptr {
+				source = source.Elem()
+			}
+			target.Elem().Set(source.Elem())
+			return true
+		}
+	}
+	return false
+}
+
 type messageDecoder struct{}
 
 var message messageDecoder

message_test.go

@@ -47,3 +47,30 @@ func TestDecodeError(t *testing.T) {
 		t.Errorf("incorrect error type: %s", parsedMessage.Error.Type)
 	}
 }
+
+func TestGetOOB(t *testing.T) {
+	image := "https://localhost/image.png"
+	msg := xmpp.NewMessage(xmpp.Attrs{To: "test@localhost"})
+	ext := xmpp.OOB{
+		XMLName: xml.Name{Space: "jabber:x:oob", Local: "x"},
+		URL:     image,
+	}
+	msg.Extensions = append(msg.Extensions, &ext)
+
+	// OOB can properly be found
+	var oob xmpp.OOB
+	// Try to find and
+	if ok := msg.Get(&oob); !ok {
+		t.Error("could not find oob extension")
+		return
+	}
+	if oob.URL != image {
+		t.Errorf("OOB URL was not properly extracted: ''%s", oob.URL)
+	}
+
+	// Markable is not found
+	var m xmpp.Markable
+	if ok := msg.Get(&m); ok {
+		t.Error("we should not have found markable extension")
+	}
+}