add support to return list of all instances

docs/swagger.yaml

@@ -26,6 +26,18 @@ paths:
             text/plain:
               schema:
                 type: string
+  /api/v1/instances:
+    get:
+      summary: List of all instances.
+      description: >-
+        Get list of all instances.
+      responses:
+        200:
+          description: ok
+          content:
+            application/json:
+              schema:
+                type: list
   /api/v1/instances/{instance_name}:
     get:
       summary: Status information of an instance.

pkg/controller/model.go

@@ -6,6 +6,8 @@ package controller
 type Repository interface {
 	// ConfigFolder returns the config folder of this controller.
 	ConfigFolder() string
+	// Instances returns a list of all bngblaster instances.
+	Instances() []string
 	// Create a bngblaster instance on the file system.
 	// Does not start an instance.
 	Create(name string, config []byte) error

pkg/controller/repository.go

@@ -127,6 +127,21 @@ func (r *DefaultRepository) cleanupRunFiles(name string) error {
 	return nil
 }
 
+// Instances implements Repository.
+func (r *DefaultRepository) Instances() []string {
+	instances := []string{}
+	entries, err := os.ReadDir(r.configFolder)
+    if err != nil {
+        return instances // Return the empty slice if there's an error.
+    }
+	for _, entry := range entries {
+		if entry.IsDir() {
+			instances = append(instances, entry.Name()) 
+		}
+	}
+	return instances
+}
+
 // Exists implements Repository.
 func (r *DefaultRepository) Exists(name string) bool {
 	folder := path.Join(r.configFolder, name)

pkg/server/server.go

@@ -72,6 +72,7 @@ func (s *Server) routes() {
 			EnableOpenMetrics: true,
 		},
 	))
+	s.router.Path("/api/v1/instances").Methods(http.MethodGet).Handler(s.instances())
 	s.router.
 		Path(
 			fmt.Sprintf("%s/{file_name:%s|%s|%s|%s|%s|%s|%s}",
@@ -102,6 +103,15 @@ func (s *Server) fileServing(directory string) http.HandlerFunc {
 	}
 }
 
+func (s *Server) instances() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		instances := s.repository.Instances()
+		w.Header().Set(contentType, applicationJSON)
+		w.WriteHeader(http.StatusOK)
+		_ = json.NewEncoder(w).Encode(instances)
+	}
+}
+
 func (s *Server) create() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		instanceVariable := mux.Vars(r)[instanceNameParameter]