Don't fail on listing namespaces (#549)

* Don't fail on listing namespaces

* Remove debugging

* Single HasNamespace()

* Don't log error, return it

* review, and handle ns 'not found'

* Generalise list.Namespace() func

* Doh.

* errors.As and report missing namespace

pkg/kubernetes/client/client.go

@@ -24,6 +24,10 @@ type Client interface {
 
 	// Namespaces the cluster currently has
 	Namespaces() (map[string]bool, error)
+
+	// Namespace retrieves a namespace from the cluster
+	Namespace(namespace string) (manifest.Manifest, error)
+
 	// Resources returns all known api-resources of the cluster
 	Resources() (Resources, error)
 

pkg/kubernetes/client/kubectl.go

@@ -3,6 +3,7 @@ package client
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"os"
 	"regexp"
 
@@ -51,12 +52,13 @@ func (k Kubectl) Namespaces() (map[string]bool, error) {
 	cmd := k.ctl("get", "namespaces", "-o", "json")
 
 	var sout bytes.Buffer
+	var serr bytes.Buffer
 	cmd.Stdout = &sout
-	cmd.Stderr = os.Stderr
+	cmd.Stderr = &serr
 
 	err := cmd.Run()
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err, string(serr.Bytes()))
 	}
 
 	var list manifest.Manifest
@@ -76,6 +78,38 @@ func (k Kubectl) Namespaces() (map[string]bool, error) {
 	return namespaces, nil
 }
 
+type ErrNamespaceNotFound struct {
+	Namespace string
+}
+
+func (e ErrNamespaceNotFound) Error() string {
+	return fmt.Sprintf("Namespace not found: %s", e.Namespace)
+}
+
+// Namespace finds a single namespace in the cluster
+func (k Kubectl) Namespace(namespace string) (manifest.Manifest, error) {
+	cmd := k.ctl("get", "namespaces", namespace, "-o", "json", "--ignore-not-found")
+
+	var sout bytes.Buffer
+	cmd.Stdout = &sout
+	cmd.Stderr = os.Stderr
+
+	err := cmd.Run()
+	if err != nil {
+		return nil, err
+	}
+	if len(sout.Bytes()) == 0 {
+		return nil, ErrNamespaceNotFound{
+			Namespace: namespace,
+		}
+	}
+	var ns manifest.Manifest
+	if err := json.Unmarshal(sout.Bytes(), &ns); err != nil {
+		return nil, err
+	}
+	return ns, nil
+}
+
 // FilterWriter is an io.Writer that discards every message that matches at
 // least one of the regular expressions.
 type FilterWriter struct {

pkg/kubernetes/diff.go

@@ -23,7 +23,18 @@ Please upgrade kubectl to at least version 1.18.1.`)
 	// required for separating
 	namespaces, err := k.ctl.Namespaces()
 	if err != nil {
-		return nil, errors.Wrap(err, "listing namespaces")
+		resourceNamespaces := state.Namespaces()
+		namespaces = map[string]bool{}
+		for _, namespace := range resourceNamespaces {
+			_, err = k.ctl.Namespace(namespace)
+			if err != nil {
+				if errors.As(err, client.ErrNamespaceNotFound{}) {
+					continue
+				}
+				return nil, errors.Wrap(err, "retrieving namespaces")
+			}
+			namespaces[namespace] = true
+		}
 	}
 	resources, err := k.ctl.Resources()
 	if err != nil {

pkg/kubernetes/manifest/manifest.go

@@ -263,6 +263,20 @@ func (m List) String() string {
 	return buf.String()
 }
 
+func (m List) Namespaces() []string {
+	namespaces := map[string]struct{}{}
+	for _, manifest := range m {
+		if namespace := manifest.Metadata().Namespace(); namespace != "" {
+			namespaces[namespace] = struct{}{}
+		}
+	}
+	keys := []string{}
+	for k := range namespaces {
+		keys = append(keys, k)
+	}
+	return keys
+}
+
 func m2o(m interface{}) objx.Map {
 	switch mm := m.(type) {
 	case Metadata: