Allow creation of FARMap with a FAR that have no Forwarding Parameter…

… and no FORW Flag

Closes #5

pfcp/far_map.go

@@ -154,26 +154,37 @@ func NewFARMap(fars []*ie.IE) (farmap *FARMap, err error, cause uint8, offending
 			}
 		}
 
-		fp, err := far.ForwardingParameters()
 		// This IE shall be present when the Apply Action requests
 		// the packets to be forwarded. It may be present otherwise.
-		if err != nil {
-			// XXX: Updating FAR should not be done like that
-			fp, err = far.UpdateForwardingParameters()
+		mustHaveFP := false
+		hasFP := false
+		if far.HasFORW() {
+			mustHaveFP = true
+		}
+		fp, err := far.ForwardingParameters()
 
+		if err != nil && mustHaveFP {
+			fp, err = far.ForwardingParameters()
 			if err != nil {
 				//XXX:  workaround for a free5gc-smf bug: Forwarding Parameters are missing sometimes
 				fp = make([]*ie.IE, 0)
+				hasFP = true
 				//			if err == io.ErrUnexpectedEOF {
 				//				return nil, err, ie.CauseInvalidLength, ie.ForwardingParameters
 				//			}
 				//			if ie.NewApplyAction(aa).HasFORW() && err == ie.ErrIENotFound {
 				//				return nil, err, ie.CauseConditionalIEMissing, ie.ForwardingParameters
 				//			}
+			} else if err == nil {
+				hasFP = true
 			}
 		}
 
-		err = f.Add(NewFAR(ie.NewFARID(id), ie.NewApplyAction(aa...), ie.NewForwardingParameters(fp...)))
+		if !hasFP {
+			err = f.Add(NewFAR(ie.NewFARID(id), ie.NewApplyAction(aa...), nil))
+		} else {
+			err = f.Add(NewFAR(ie.NewFARID(id), ie.NewApplyAction(aa...), ie.NewForwardingParameters(fp...)))
+		}
 		if err != nil {
 			return nil, err, ie.CauseMandatoryIEIncorrect, ie.CreateFAR
 		}