backend: refactor listing valid contexts and error

This removes the dependacy of manually parsing of k8s resources. It was
a problem as we had to be in sync with k8s API changes, which is not a
good way. This change removes that and it splits kubeconfig into
seperate contexts and validates them.

Fixes: #2347
Co-Authored-By: Santhosh Nagaraj <sannagaraj@microsoft.com>
Signed-off-by: Kautilya Tripathi <ktripathi@microsoft.com>

backend/cmd/cluster.go

@@ -9,6 +9,7 @@ type Cluster struct {
 	Server   string                 `json:"server,omitempty"`
 	AuthType string                 `json:"auth_type"`
 	Metadata map[string]interface{} `json:"meta_data"`
+	Error    string                 `json:"error,omitempty"`
 }
 
 type ClusterReq struct {

backend/cmd/headlamp.go

@@ -1013,6 +1013,14 @@ func handleClusterAPI(c *HeadlampConfig, router *mux.Router) {
 			return
 		}
 
+		if kContext.Error != "" {
+			logger.Log(logger.LevelError, map[string]string{"key": contextKey},
+				errors.New(kContext.Error), "context has error")
+			http.Error(w, kContext.Error, http.StatusBadRequest)
+
+			return
+		}
+
 		clusterURL, err := url.Parse(kContext.Cluster.Server)
 		if err != nil {
 			logger.Log(logger.LevelError, map[string]string{"ClusterURL": kContext.Cluster.Server},
@@ -1062,6 +1070,15 @@ func (c *HeadlampConfig) getClusters() []Cluster {
 	for _, context := range contexts {
 		context := context
 
+		if context.Error != "" {
+			clusters = append(clusters, Cluster{
+				Name:  context.Name,
+				Error: context.Error,
+			})
+
+			continue
+		}
+
 		// Dynamic clusters should not be visible to other users.
 		if context.Internal {
 			continue
@@ -1143,27 +1160,7 @@ func parseClusterFromKubeConfig(kubeConfigs []string) ([]Cluster, []error) {
 	var setupErrors []error
 
 	for _, kubeConfig := range kubeConfigs {
-		var contexts []kubeconfig.Context
-
-		kubeConfigByte, err := base64.StdEncoding.DecodeString(kubeConfig)
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "decoding kubeconfig")
-
-			setupErrors = append(setupErrors, err)
-
-			continue
-		}
-
-		config, err := clientcmd.Load(kubeConfigByte)
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "loading kubeconfig")
-
-			setupErrors = append(setupErrors, err)
-
-			continue
-		}
-
-		contexts, errs := kubeconfig.LoadContextsFromAPIConfig(config, true)
+		contexts, errs := kubeconfig.LoadContextsFromBase64String(kubeConfig, kubeconfig.DynamicCluster)
 		if len(errs) > 0 {
 			setupErrors = append(setupErrors, errs...)
 			continue
@@ -1221,39 +1218,42 @@ func (c *HeadlampConfig) addCluster(w http.ResponseWriter, r *http.Request) {
 	var setupErrors []error
 
 	if clusterReq.KubeConfig != nil {
-		kubeConfigByte, err := base64.StdEncoding.DecodeString(*clusterReq.KubeConfig)
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "decoding kubeconfig")
-			http.Error(w, "decoding kubeconfig", http.StatusBadRequest)
+		// get contexts from kubeconfig earlier to skip proxy setup and parse errors.
+		contexts, setupErrors = kubeconfig.LoadContextsFromBase64String(*clusterReq.KubeConfig, kubeconfig.DynamicCluster)
 
-			return
-		}
+		if len(setupErrors) == 0 {
+			kubeConfigByte, err := base64.StdEncoding.DecodeString(*clusterReq.KubeConfig)
+			if err != nil {
+				logger.Log(logger.LevelError, nil, err, "decoding kubeconfig")
+				http.Error(w, "decoding kubeconfig", http.StatusBadRequest)
 
-		config, err := clientcmd.Load(kubeConfigByte)
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "loading kubeconfig")
-			http.Error(w, "loading kubeconfig", http.StatusBadRequest)
+				return
+			}
 
-			return
-		}
+			config, err := clientcmd.Load(kubeConfigByte)
+			if err != nil {
+				logger.Log(logger.LevelError, nil, err, "loading kubeconfig")
+				http.Error(w, "loading kubeconfig", http.StatusBadRequest)
 
-		kubeConfigPersistenceDir, err := defaultKubeConfigPersistenceDir()
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "getting default kubeconfig persistence dir")
-			http.Error(w, "getting default kubeconfig persistence dir", http.StatusInternalServerError)
+				return
+			}
 
-			return
-		}
+			kubeConfigPersistenceDir, err := defaultKubeConfigPersistenceDir()
+			if err != nil {
+				logger.Log(logger.LevelError, nil, err, "getting default kubeconfig persistence dir")
+				http.Error(w, "getting default kubeconfig persistence dir", http.StatusInternalServerError)
 
-		err = kubeconfig.WriteToFile(*config, kubeConfigPersistenceDir)
-		if err != nil {
-			logger.Log(logger.LevelError, nil, err, "writing kubeconfig")
-			http.Error(w, "writing kubeconfig", http.StatusBadRequest)
+				return
+			}
 
-			return
-		}
+			err = kubeconfig.WriteToFile(*config, kubeConfigPersistenceDir)
+			if err != nil {
+				logger.Log(logger.LevelError, nil, err, "writing kubeconfig")
+				http.Error(w, "writing kubeconfig", http.StatusBadRequest)
 
-		contexts, setupErrors = kubeconfig.LoadContextsFromAPIConfig(config, false)
+				return
+			}
+		}
 	} else {
 		conf := &api.Config{
 			Clusters: map[string]*api.Cluster{