Add Interface to Kanister/kube pkg to support write to a file in pod …

…(#5465)

* Add Interface to kube for  write to file in pod

* Address review suggestions

* Nit fix

pkg/kube/pod_writer.go

@@ -0,0 +1,50 @@
+package kube
+
+import (
+	"context"
+	"io"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+	"k8s.io/client-go/kubernetes"
+
+	"github.com/kanisterio/kanister/pkg/format"
+)
+
+// PodWriter specifies Kubernetes Client and the other params needed for writing content to a file
+type PodWriter struct {
+	cli           kubernetes.Interface
+	namespace     string
+	path          string
+	podName       string
+	containerName string
+}
+
+// NewPodWriter returns a new PodWriter given Kubernetes Client, Namespace, path of file, name of pod and container
+func NewPodWriter(cli kubernetes.Interface, namespace, path, podName, containerName string) *PodWriter {
+	return &PodWriter{
+		cli:           cli,
+		namespace:     namespace,
+		path:          filepath.Clean(path),
+		podName:       podName,
+		containerName: containerName,
+	}
+}
+
+// Write will create a new file(if not present) and write the provided content to the file
+func (p *PodWriter) Write(ctx context.Context, content io.Reader) error {
+	cmd := []string{"sh", "-c", "cat - > " + p.path}
+	stdout, stderr, err := Exec(p.cli, p.namespace, p.podName, p.containerName, cmd, content)
+	format.Log(p.podName, p.containerName, stdout)
+	format.Log(p.podName, p.containerName, stderr)
+	return errors.Wrap(err, "Failed to write contents to file")
+}
+
+// Remove will delete the file created by Write() func
+func (p *PodWriter) Remove(ctx context.Context) error {
+	cmd := []string{"sh", "-c", "rm " + p.path}
+	stdout, stderr, err := Exec(p.cli, p.namespace, p.podName, p.containerName, cmd, nil)
+	format.Log(p.podName, p.containerName, stdout)
+	format.Log(p.podName, p.containerName, stderr)
+	return errors.Wrap(err, "Failed to delete file")
+}

pkg/kube/pod_writer_test.go

@@ -0,0 +1,79 @@
+// +build !unit
+
+package kube
+
+import (
+	"bytes"
+	"context"
+	"time"
+
+	. "gopkg.in/check.v1"
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+)
+
+type PodWriteSuite struct {
+	cli       kubernetes.Interface
+	namespace string
+	pod       *v1.Pod
+}
+
+var _ = Suite(&PodWriteSuite{})
+
+func (p *PodWriteSuite) SetUpSuite(c *C) {
+	var err error
+	p.cli, err = NewClient()
+	c.Assert(err, IsNil)
+	ns := &v1.Namespace{
+		ObjectMeta: metav1.ObjectMeta{
+			GenerateName: "podwritertest-",
+		},
+	}
+	ns, err = p.cli.Core().Namespaces().Create(ns)
+	c.Assert(err, IsNil)
+	p.namespace = ns.Name
+	pod := &v1.Pod{
+		ObjectMeta: metav1.ObjectMeta{Name: "testpod"},
+		Spec: v1.PodSpec{
+			Containers: []v1.Container{
+				v1.Container{
+					Name:    "testcontainer",
+					Image:   "busybox",
+					Command: []string{"sh", "-c", "tail -f /dev/null"},
+				},
+			},
+		},
+	}
+	p.pod, err = p.cli.Core().Pods(p.namespace).Create(pod)
+	c.Assert(err, IsNil)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Minute)
+	defer cancel()
+	c.Assert(WaitForPodReady(ctx, p.cli, p.namespace, p.pod.Name), IsNil)
+	p.pod, err = p.cli.Core().Pods(p.namespace).Get(p.pod.Name, metav1.GetOptions{})
+	c.Assert(err, IsNil)
+}
+
+func (p *PodWriteSuite) TearDownSuite(c *C) {
+	if p.namespace != "" {
+		err := p.cli.Core().Namespaces().Delete(p.namespace, nil)
+		c.Assert(err, IsNil)
+	}
+}
+func (p *PodWriteSuite) TestPodWriter(c *C) {
+	path := "/tmp/test.txt"
+	c.Assert(p.pod.Status.Phase, Equals, v1.PodRunning)
+	c.Assert(len(p.pod.Status.ContainerStatuses) > 0, Equals, true)
+	for _, cs := range p.pod.Status.ContainerStatuses {
+		pw := NewPodWriter(p.cli, p.pod.Namespace, path, p.pod.Name, cs.Name)
+		err := pw.Write(context.Background(), bytes.NewBufferString("badabing"))
+		c.Assert(err, IsNil)
+		cmd := []string{"sh", "-c", "cat " + pw.path}
+		stdout, stderr, err := Exec(p.cli, p.pod.Namespace, p.pod.Name, cs.Name, cmd, nil)
+		c.Assert(err, IsNil)
+		c.Assert(stdout, Equals, "badabing")
+		c.Assert(stderr, Equals, "")
+		err = pw.Remove(context.Background())
+		c.Assert(err, IsNil)
+	}
+}