Output to stdout by default

Signed-off-by: Lei Jitang <leijitang@huawei.com>

cmd/oci-create-layer/main.go

@@ -15,31 +15,32 @@
 package main
 
 import (
+	"io"
 	"log"
 	"os"
+	"path/filepath"
 
 	"github.com/opencontainers/image-tools/image"
 	"github.com/spf13/cobra"
 )
 
 type layerCmd struct {
-	stdout *log.Logger
+	stdout io.Writer
 	stderr *log.Logger
 	dest   string
 }
 
 func main() {
-	stdout := log.New(os.Stdout, "", 0)
 	stderr := log.New(os.Stderr, "", 0)
 
-	cmd := newLayerCmd(stdout, stderr)
+	cmd := newLayerCmd(os.Stdout, stderr)
 	if err := cmd.Execute(); err != nil {
 		stderr.Println(err)
 		os.Exit(1)
 	}
 }
 
-func newLayerCmd(stdout, stderr *log.Logger) *cobra.Command {
+func newLayerCmd(stdout io.Writer, stderr *log.Logger) *cobra.Command {
 	v := &layerCmd{
 		stdout: stdout,
 		stderr: stderr,
@@ -66,15 +67,38 @@ func (v *layerCmd) Run(cmd *cobra.Command, args []string) {
 		}
 		os.Exit(1)
 	}
-	var err error
+	var (
+		err error
+		out io.ReadCloser
+	)
 	if len(args) == 1 {
-		err = image.CreateLayer(args[0], "", v.dest)
+		out, err = image.CreateLayer(args[0], "")
 	} else {
-		err = image.CreateLayer(args[0], args[1], v.dest)
+		out, err = image.CreateLayer(args[0], args[1])
 	}
 	if err != nil {
 		v.stderr.Printf("create layer failed: %v", err)
 		os.Exit(1)
 	}
+	if v.dest == "" {
+		_, err := io.Copy(v.stdout, out)
+		if err != nil {
+			v.stderr.Printf("create layer failed: %v", err)
+			os.Exit(1)
+		}
+	} else {
+		filename := filepath.Clean(v.dest)
+		f, err := os.Create(filename)
+		if err != nil {
+			v.stderr.Printf("create layer failed: %v", err)
+			os.Exit(1)
+		}
+		defer f.Close()
+		_, err = io.Copy(f, out)
+		if err != nil {
+			v.stderr.Printf("create layer failed: %v", err)
+			os.Exit(1)
+		}
+	}
 	os.Exit(0)
 }

cmd/oci-create-layer/oci-create-layer.1.md

@@ -8,7 +8,7 @@ oci-create-layer \- Create filesystem changeset
 **oci-create-layer** [child] [parent] [flags]
 
 # DESCRIPTION
-`oci-create-layer` creates a filesystem changeset from two layers. It compares child with parent and generates a filsystem diff, pack the diff into a uncompressed tar archive. The output tar archive name is the child name with .tar suffix by default, use `--dest` to specify a custom one.
+`oci-create-layer` creates a filesystem changeset from two layers. It compares child with parent and generates a filsystem diff, pack the diff into a uncompressed tar archive. The default output is stdout, use `--dest` to specify a custom one.
 
 # OPTIONS
 **--help**
@@ -19,7 +19,7 @@ The dest specify a particular filename where the layer write to
 
 # EXAMPLES
 ```
-$ oci-create-layer rootfs-1-s rootfs-1
+$ oci-create-layer --dest rootfs-1-s.tar rootfs-1-s rootfs-1
 $ ls
 rootfs-1  rootfs-1-s  rootfs-1-s.tar
 

image/layer.go

@@ -15,37 +15,13 @@
 package image
 
 import (
-	"fmt"
 	"io"
-	"os"
-	"path/filepath"
 
 	"github.com/opencontainers/image-tools/utils"
 )
 
 // CreateLayer cretes filesystem changset from child and parent
-func CreateLayer(child, parent, dest string) error {
-	arch, err := Diff(child, parent)
-	if err != nil {
-		return err
-	}
-	defer arch.Close()
-	filename := fmt.Sprintf("%s.tar", filepath.Clean(child))
-	if dest != "" {
-		filename = filepath.Clean(dest)
-	}
-	f, err := os.Create(filename)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-	_, err = io.Copy(f, arch)
-	return err
-}
-
-// Diff produces an archive of the changes between the specified
-// layer and its parent layer which may be "".
-func Diff(child, parent string) (rc io.ReadCloser, err error) {
+func CreateLayer(child, parent string) (io.ReadCloser, error) {
 	changes, err := utils.ChangesDirs(child, parent)
 	if err != nil {
 		return nil, err

image/layer_test.go

@@ -56,7 +56,7 @@ func TestCreateFilesystemChangeset(t *testing.T) {
 	}
 	// create base layer
 	tarfile := filepath.Join(tmp1, "base.tar")
-	err = CreateLayer(basepath, "", tarfile)
+	err = createLayer(basepath, "", tarfile)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -103,7 +103,7 @@ func TestCreateFilesystemChangeset(t *testing.T) {
 
 	// create layer diff
 	tarfile1 := filepath.Join(tmp1, "base.s1.tar")
-	err = CreateLayer(snapshot1path, basepath, tarfile1)
+	err = createLayer(snapshot1path, basepath, tarfile1)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -133,6 +133,25 @@ func TestCreateFilesystemChangeset(t *testing.T) {
 	}
 }
 
+func createLayer(child, parent, dest string) error {
+	filename := filepath.Clean(dest)
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	out, err := CreateLayer(child, parent)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(f, out)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func createFilesystem(path string, files map[string]bool, modify map[string]func(string) error) error {
 	for f, add := range files {
 		// add file