Add checks for readable kube config

Makefile

@@ -21,7 +21,7 @@ test: TESTFLAGS += -race -v
 test: unit-tests
 
 .PHONY: unit-tests
-unit-tests:
+unit-tests: build
 	@echo "Performing unit test step..."
 	@go test -run $(TESTS) $(PKG) $(TESTFLAGS)
 	@echo "All unit tests passed"

pkg/kube/clientset.go

@@ -7,6 +7,8 @@ import (
 
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/tools/clientcmd"
+
+	"github.com/ian-howell/airshipadm/pkg/util"
 )
 
 // Client is a device which communicates with the Kubernetes API
@@ -24,10 +26,14 @@ func NewForConfig(kubeconfigFilepath string) (*Client, error) {
 		kubeconfigFilepath = filepath.Join(home, ".kube", "config")
 	}
 
+	if err := util.IsReadable(kubeconfigFilepath); err != nil {
+		return nil, errors.New("could not open " + kubeconfigFilepath + ": " + err.Error())
+	}
+
 	// use the current context in kubeconfigFilepath
 	config, err := clientcmd.BuildConfigFromFlags("", kubeconfigFilepath)
 	if err != nil {
-		return nil, err
+		return nil, errors.New("could not build kubernetes config: " + err.Error())
 	}
 
 	// create the clientset

pkg/util/util.go

@@ -0,0 +1,14 @@
+package util
+
+import (
+	"os"
+)
+
+// IsReadable returns nil if the file at path is readable. An error is returned otherwise.
+func IsReadable(path string) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return err.(*os.PathError).Err
+	}
+	return f.Close()
+}

pkg/util/util_test.go

@@ -0,0 +1,40 @@
+package util_test
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/ian-howell/airshipadm/pkg/util"
+)
+
+func TestIsReadable(t *testing.T) {
+	file, err := ioutil.TempFile(os.TempDir(), "airshipadm")
+	if err != nil {
+		t.Fatalf("Unexpected error: %s", err.Error())
+	}
+	defer os.Remove(file.Name())
+
+	if err := util.IsReadable(file.Name()); err != nil {
+		t.Errorf("Unexpected error: %s", err.Error())
+	}
+
+	expected := "permission denied"
+	err = file.Chmod(0000)
+	if err != nil {
+		t.Fatalf("Unexpected error: %s", err.Error())
+	}
+	if err := util.IsReadable(file.Name()); err == nil {
+		t.Errorf("Expected '%s' error", expected)
+	} else if err.Error() != "permission denied" {
+		t.Errorf("Expected '%s' error, got '%s'", expected, err.Error())
+	}
+
+	expected = "no such file or directory"
+	os.Remove(file.Name())
+	if err := util.IsReadable(file.Name()); err == nil {
+		t.Errorf("Expected '%s' error", expected)
+	} else if err.Error() != expected {
+		t.Errorf("Expected '%s' error, got '%s'", expected, err.Error())
+	}
+}