Implement label selector for lists

Fixes #68.

Author: ahmetb

README.md

@@ -9,7 +9,7 @@
 A kubectl plugin to explore ownership relationships between Kubernetes objects
 through `ownersReferences` on the objects.
 
-The [`kubectl lineage`](https://github.com/tohjustin/kube-lineage) plugin is very similar to `kubectl tree`, but it 
+The [`kubectl lineage`](https://github.com/tohjustin/kube-lineage) plugin is very similar to `kubectl tree`, but it
 [understands](https://github.com/tohjustin/kube-lineage#supported-relationships)
 logical relationships between some API objects without needing ownerReferences.
 
@@ -39,8 +39,16 @@ Example (Agones Fleet):
 By default, the plugin will only search "namespaced" objects in the same
 namespace as the specified object.
 
-You can use the `-A` or `--all-namespaces` flag to search namespaced and
-non-namespaced objects in all namespaces.
+- `-A`, `--all-namespaces`: Search namespaced and non-namespaced objects in all namespaces.
+
+- `-l`, `--selector`: Selector (label query) to filter on. Supports equality (`=`, `==`, `!=`), set-based (`in`, `notin`), and existence operators. Examples:
+  - `-l key1=value1,key2=value2` (equality)
+  - `-l "env in (prod,staging)"` (set-based)
+  - `-l "tier=frontend,env!=test"` (mixed)
+
+  This helps reduce workload and data volume when working with large clusters.
+
+- `--condition-types`: Comma-separated list of condition types to check (default: Ready). Example: `Ready,Processed,Scheduled`.
 
 ## Author
 

cmd/kubectl-tree/query.go

@@ -15,7 +15,7 @@ import (
 )
 
 // getAllResources finds all API objects in specified API resources in all namespaces (or non-namespaced).
-func getAllResources(client dynamic.Interface, apis []apiResource, allNs bool) ([]unstructured.Unstructured, error) {
+func getAllResources(client dynamic.Interface, apis []apiResource, allNs bool, labelSelector string) ([]unstructured.Unstructured, error) {
 	var mu sync.Mutex
 	var wg sync.WaitGroup
 	var out []unstructured.Unstructured
@@ -33,7 +33,7 @@ func getAllResources(client dynamic.Interface, apis []apiResource, allNs bool) (
 		go func(a apiResource) {
 			defer wg.Done()
 			klog.V(4).Infof("[query api] start: %s", a.GroupVersionResource())
-			v, err := queryAPI(client, a, allNs)
+			v, err := queryAPI(client, a, allNs, labelSelector)
 			if err != nil {
 				if errors.IsForbidden(err) {
 					// should not fail the overall process, but print an info message indicating the permission issue
@@ -59,7 +59,7 @@ func getAllResources(client dynamic.Interface, apis []apiResource, allNs bool) (
 	return out, errResult
 }
 
-func queryAPI(client dynamic.Interface, api apiResource, allNs bool) ([]unstructured.Unstructured, error) {
+func queryAPI(client dynamic.Interface, api apiResource, allNs bool, labelSelector string) ([]unstructured.Unstructured, error) {
 	var out []unstructured.Unstructured
 
 	var next string
@@ -76,10 +76,14 @@ func queryAPI(client dynamic.Interface, api apiResource, allNs bool) ([]unstruct
 		} else {
 			intf = nintf
 		}
-		resp, err := intf.List(context.TODO(), metav1.ListOptions{
+		listOptions := metav1.ListOptions{
 			Limit:    250,
 			Continue: next,
-		})
+		}
+		if labelSelector != "" {
+			listOptions.LabelSelector = labelSelector
+		}
+		resp, err := intf.List(context.TODO(), listOptions)
 		if err != nil {
 			return nil, fmt.Errorf("listing resources failed (%s): %w", api.GroupVersionResource(), err)
 		}

cmd/kubectl-tree/rootcmd.go

@@ -40,6 +40,7 @@ const (
 	allNamespacesFlag  = "all-namespaces"
 	colorFlag          = "color"
 	conditionTypesFlag = "condition-types"
+	selectorFlag       = "selector"
 )
 
 var (
@@ -95,6 +96,11 @@ func run(command *cobra.Command, args []string) error {
 		return err
 	}
 
+	labelSelector, err := command.Flags().GetString(selectorFlag)
+	if err != nil {
+		return err
+	}
+
 	restConfig, err := cf.ToRESTConfig()
 	if err != nil {
 		return err
@@ -175,7 +181,7 @@ func run(command *cobra.Command, args []string) error {
 	klog.V(5).Infof("target parent object: %#v", obj)
 
 	klog.V(2).Infof("querying all api objects")
-	apiObjects, err := getAllResources(dyn, apis.resources(), allNs)
+	apiObjects, err := getAllResources(dyn, apis.resources(), allNs, labelSelector)
 	if err != nil {
 		return fmt.Errorf("error while querying api objects: %w", err)
 	}
@@ -207,6 +213,7 @@ func init() {
 	rootCmd.Flags().BoolP(allNamespacesFlag, "A", false, "query all objects in all API groups, both namespaced and non-namespaced")
 	rootCmd.Flags().StringP(colorFlag, "c", "auto", "Enable or disable color output. This can be 'always', 'never', or 'auto' (default = use color only if using tty). The flag is overridden by the NO_COLOR env variable if set.")
 	rootCmd.Flags().StringSlice(conditionTypesFlag, []string{"Ready"}, "Comma-separated list of condition types to check (default: Ready). Example: Ready,Processed,Scheduled")
+	rootCmd.Flags().StringP(selectorFlag, "l", "", "Selector (label query) to filter on, supports '=', '==', and '!='. (e.g. -l key1=value1,key2=value2)")
 
 	cf.AddFlags(rootCmd.Flags())
 	if err := flag.Set("logtostderr", "true"); err != nil {