Add basic application framework and example application to show interaction between events an NBI

Depends on:

• !340 (merged)
• !344 (merged)
• !349 (merged)
• !342 (merged)

controller/northbound/server/topology.go

@@ -9,6 +9,7 @@ import (
 	"code.fbi.h-da.de/danet/gosdn/controller/topology/links"
 	"code.fbi.h-da.de/danet/gosdn/controller/topology/nodes"
 	"code.fbi.h-da.de/danet/gosdn/controller/topology/ports"
+	"code.fbi.h-da.de/danet/gosdn/controller/topology/store"
 	"github.com/google/uuid"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
@@ -103,6 +104,38 @@ func (t *Topology) GetTopology(ctx context.Context, request *apb.GetTopologyRequ
 	}, nil
 }
 
+// DeleteLink deletes a link
+func (t *Topology) DeleteLink(ctx context.Context, request *apb.DeleteLinkRequest) (*apb.DeleteLinkResponse, error) {
+	linkID, err := uuid.Parse(request.Id)
+	if err != nil {
+		return &apb.DeleteLinkResponse{
+			Timestamp: time.Now().UnixNano(),
+			Status:    apb.Status_STATUS_ERROR,
+		}, err
+	}
+
+	foundLink, err := t.topologyService.Get(store.Query{ID: linkID})
+	if err != nil {
+		return &apb.DeleteLinkResponse{
+			Timestamp: time.Now().UnixNano(),
+			Status:    apb.Status_STATUS_ERROR,
+		}, err
+	}
+
+	err = t.topologyService.DeleteLink(foundLink)
+	if err != nil {
+		return &apb.DeleteLinkResponse{
+			Timestamp: time.Now().UnixNano(),
+			Status:    apb.Status_STATUS_ERROR,
+		}, err
+	}
+
+	return &apb.DeleteLinkResponse{
+		Timestamp: time.Now().UnixNano(),
+		Status:    apb.Status_STATUS_OK,
+	}, nil
+}
+
 func (t *Topology) ensureNodeAndPortExists(incomingNode *apb.Node, incomingPort *apb.Port) (nodes.Node, ports.Port, error) {
 	node, err := t.nodeService.EnsureExists(
 		nodes.Node{