Add ctr attach for reattaching to running task

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/ctr/attach.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"os"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/containerd/console"
+	"github.com/containerd/containerd"
+	"github.com/urfave/cli"
+)
+
+var attachCommand = cli.Command{
+	Name:      "attach",
+	Usage:     "attach to the IO of a running container",
+	ArgsUsage: "CONTAINER",
+	Action: func(context *cli.Context) error {
+		ctx, cancel := appContext(context)
+		defer cancel()
+		client, err := newClient(context)
+		if err != nil {
+			return err
+		}
+		container, err := client.LoadContainer(ctx, context.Args().First())
+		if err != nil {
+			return err
+		}
+		spec, err := container.Spec()
+		if err != nil {
+			return err
+		}
+		var (
+			con console.Console
+			tty = spec.Process.Terminal
+		)
+		if tty {
+			con = console.Current()
+			defer con.Reset()
+			if err := con.SetRaw(); err != nil {
+				return err
+			}
+		}
+		task, err := container.Task(ctx, containerd.WithAttach(os.Stdin, os.Stdout, os.Stderr))
+		if err != nil {
+			return err
+		}
+		defer task.Delete(ctx)
+		if tty {
+			if err := handleConsoleResize(ctx, task, con); err != nil {
+				logrus.WithError(err).Error("console resize")
+			}
+		} else {
+			sigc := forwardAllSignals(ctx, task)
+			defer stopCatch(sigc)
+		}
+		status, err := task.Wait(ctx)
+		if err != nil {
+			return err
+		}
+		if status != 0 {
+			return cli.NewExitError("", int(status))
+		}
+		return nil
+	},
+}

cmd/ctr/delete.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 
+	"github.com/containerd/containerd"
 	"github.com/urfave/cli"
 )
 
@@ -21,9 +22,20 @@ var deleteCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		if _, err := container.Task(ctx, nil); err == nil {
-			return fmt.Errorf("cannot delete a container with a running task")
+		task, err := container.Task(ctx, nil)
+		if err != nil {
+			return container.Delete(ctx)
+		}
+		status, err := task.Status(ctx)
+		if err != nil {
+			return err
+		}
+		if status == containerd.Stopped {
+			if _, err := task.Delete(ctx); err != nil {
+				return err
 			}
 			return container.Delete(ctx)
+		}
+		return fmt.Errorf("cannot delete a container with an existing task")
 	},
 }

cmd/ctr/main.go

@@ -52,6 +52,7 @@ containerd CLI
 		},
 	}
 	app.Commands = append([]cli.Command{
+		attachCommand,
 		checkpointCommand,
 		runCommand,
 		deleteCommand,

container.go

@@ -193,11 +193,16 @@ func (c *container) loadTask(ctx context.Context, ioAttach IOAttach) (Task, erro
 			return nil, err
 		}
 	}
+	// create and close a channel on load as we already have the pid
+	// and don't want to block calls to Wait(), etc...
+	ps := make(chan struct{})
+	close(ps)
 	t := &task{
 		client:      c.client,
 		io:          i,
 		containerID: response.Task.ContainerID,
 		pid:         response.Task.Pid,
+		pidSync:     ps,
 	}
 	c.task = t
 	return t, nil

task.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"runtime"
+	"strings"
 	"syscall"
 
 	"github.com/containerd/containerd/api/services/containers"
@@ -127,7 +128,7 @@ func (t *task) Status(ctx context.Context) (TaskStatus, error) {
 	if err != nil {
 		return "", err
 	}
-	return TaskStatus(r.Task.Status.String()), nil
+	return TaskStatus(strings.ToLower(r.Task.Status.String())), nil
 }
 
 // Wait is a blocking call that will wait for the task to exit and return the exit status