feat: add LoadTaskProcess api in containerd client

This commit aims to add an api to get the task process of the containerd
client.
We have a use case where we are trying to consume the exited containers
and get their exit code however the current implementation of the cliet
dosn't expose this api.
The broader issue and usecase is captured here
#3722.

Author: sambhav-jain-16

container/containerd/client.go

@@ -25,6 +25,7 @@ import (
 	containersapi "github.com/containerd/containerd/api/services/containers/v1"
 	tasksapi "github.com/containerd/containerd/api/services/tasks/v1"
 	versionapi "github.com/containerd/containerd/api/services/version/v1"
+	"github.com/containerd/containerd/api/types/task"
 	tasktypes "github.com/containerd/containerd/api/types/task"
 	"github.com/containerd/errdefs/pkg/errgrpc"
 	"google.golang.org/grpc"
@@ -45,6 +46,7 @@ type client struct {
 type ContainerdClient interface {
 	LoadContainer(ctx context.Context, id string) (*containers.Container, error)
 	TaskPid(ctx context.Context, id string) (uint32, error)
+	LoadTaskProcess(ctx context.Context, id string) (*task.Process, error)
 	Version(ctx context.Context) (string, error)
 }
 
@@ -132,6 +134,17 @@ func (c *client) TaskPid(ctx context.Context, id string) (uint32, error) {
 	return response.Process.Pid, nil
 }
 
+func (c *client) LoadTaskProcess(ctx context.Context, id string) (*task.Process, error) {
+	response, err := c.taskService.Get(ctx, &tasksapi.GetRequest{
+		ContainerID: id,
+	})
+	if err != nil {
+		return nil, errgrpc.ToNative(err)
+	}
+
+	return response.Process, nil
+}
+
 func (c *client) Version(ctx context.Context) (string, error) {
 	response, err := c.versionService.Version(ctx, &emptypb.Empty{})
 	if err != nil {

container/containerd/client_test.go

@@ -18,12 +18,14 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/containerd/containerd/api/types/task"
 	"github.com/google/cadvisor/container/containerd/containers"
 )
 
 type containerdClientMock struct {
 	cntrs     map[string]*containers.Container
 	returnErr error
+	tasks     map[string]*task.Process
 }
 
 func (c *containerdClientMock) LoadContainer(ctx context.Context, id string) (*containers.Container, error) {
@@ -45,9 +47,27 @@ func (c *containerdClientMock) TaskPid(ctx context.Context, id string) (uint32,
 	return 2389, nil
 }
 
+func (c *containerdClientMock) LoadTaskProcess(ctx context.Context, id string) (*task.Process, error) {
+	if c.returnErr != nil {
+		return nil, c.returnErr
+	}
+	task, ok := c.tasks[id]
+	if !ok {
+		return nil, fmt.Errorf("unable to find task for container %q", id)
+	}
+	return task, nil
+}
+
 func mockcontainerdClient(cntrs map[string]*containers.Container, returnErr error) ContainerdClient {
+	tasks := make(map[string]*task.Process)
+
+	for _, cntr := range cntrs {
+		tasks[cntr.ID] = &task.Process{}
+	}
+
 	return &containerdClientMock{
 		cntrs:     cntrs,
 		returnErr: returnErr,
+		tasks:     tasks,
 	}
 }