Add Load for container and Task with Attach

This adds both container and task loading of running tasks as well as
reattaching to the IO of the task after load.

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

io.go

@@ -1,7 +1,6 @@
 package containerd
 
 import (
-	"bytes"
 	"io"
 	"io/ioutil"
 	"os"
@@ -27,18 +26,17 @@ func (i *IO) Close() error {
 
 type IOCreation func() (*IO, error)
 
-// BufferedIO returns IO that will be logged to an in memory buffer
-func BufferedIO(stdin, stdout, stderr *bytes.Buffer) IOCreation {
+func NewIO(stdin io.Reader, stdout, stderr io.Writer) IOCreation {
 	return func() (*IO, error) {
-		paths, err := fifoPaths()
+		paths, err := NewFifos()
 		if err != nil {
 			return nil, err
 		}
 		i := &IO{
 			Terminal: false,
-			Stdout:   paths.out,
-			Stderr:   paths.err,
-			Stdin:    paths.in,
+			Stdout:   paths.Out,
+			Stderr:   paths.Err,
+			Stdin:    paths.In,
 		}
 		set := &ioSet{
 			in:  stdin,
@@ -54,17 +52,17 @@ func BufferedIO(stdin, stdout, stderr *bytes.Buffer) IOCreation {
 	}
 }
 
-func NewIO(stdin io.Reader, stdout, stderr io.Writer) IOCreation {
+func WithIO(stdin io.Reader, stdout, stderr io.Writer, dir string) IOCreation {
 	return func() (*IO, error) {
-		paths, err := fifoPaths()
+		paths, err := WithFifos(dir)
 		if err != nil {
 			return nil, err
 		}
 		i := &IO{
 			Terminal: false,
-			Stdout:   paths.out,
-			Stderr:   paths.err,
-			Stdin:    paths.in,
+			Stdout:   paths.Out,
+			Stderr:   paths.Err,
+			Stdin:    paths.In,
 		}
 		set := &ioSet{
 			in:  stdin,
@@ -83,7 +81,7 @@ func NewIO(stdin io.Reader, stdout, stderr io.Writer) IOCreation {
 // Stdio returns an IO implementation to be used for a task
 // that outputs the container's IO as the current processes Stdio
 func Stdio() (*IO, error) {
-	paths, err := fifoPaths()
+	paths, err := NewFifos()
 	if err != nil {
 		return nil, err
 	}
@@ -98,14 +96,15 @@ func Stdio() (*IO, error) {
 	}
 	return &IO{
 		Terminal: false,
-		Stdin:    paths.in,
-		Stdout:   paths.out,
-		Stderr:   paths.err,
+		Stdin:    paths.In,
+		Stdout:   paths.Out,
+		Stderr:   paths.Err,
 		closer:   closer,
 	}, nil
 }
 
-func fifoPaths() (*fifoSet, error) {
+// NewFifos returns a new set of fifos for the task
+func NewFifos() (*FifoSet, error) {
 	root := filepath.Join(os.TempDir(), "containerd")
 	if err := os.MkdirAll(root, 0700); err != nil {
 		return nil, err
@@ -114,18 +113,31 @@ func fifoPaths() (*fifoSet, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &fifoSet{
-		dir: dir,
-		in:  filepath.Join(dir, "stdin"),
-		out: filepath.Join(dir, "stdout"),
-		err: filepath.Join(dir, "stderr"),
+	return &FifoSet{
+		Dir: dir,
+		In:  filepath.Join(dir, "stdin"),
+		Out: filepath.Join(dir, "stdout"),
+		Err: filepath.Join(dir, "stderr"),
 	}, nil
 }
 
-type fifoSet struct {
-	// dir is the directory holding the task fifos
-	dir          string
-	in, out, err string
+// WithFifos returns existing or creates new fifos inside an existing dir
+func WithFifos(dir string) (*FifoSet, error) {
+	if err := os.MkdirAll(dir, 0700); err != nil {
+		return nil, err
+	}
+	return &FifoSet{
+		Dir: dir,
+		In:  filepath.Join(dir, "stdin"),
+		Out: filepath.Join(dir, "stdout"),
+		Err: filepath.Join(dir, "stderr"),
+	}, nil
+}
+
+type FifoSet struct {
+	// Dir is the directory holding the task fifos
+	Dir          string
+	In, Out, Err string
 }
 
 type ioSet struct {