Add a "copy" command for copying images

This copies an image from ImageSource to ImageDestination, e.g.

skopeo copy atomic:mitr/busybox:latest dir:t-down # pull
skopeo copy dir:t-up atomic:mitr/busybox:latest # push

copy.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/codegangsta/cli"
+)
+
+// FIXME: Also handle schema2, and put this elsewhere:
+// docker.go contains similar code, more sophisticated
+// (at the very least the deduplication should be reused from there).
+func manifestLayers(manifest []byte) ([]string, error) {
+	man := manifestSchema1{}
+	if err := json.Unmarshal(manifest, &man); err != nil {
+		return nil, err
+	}
+
+	layers := []string{}
+	for _, layer := range man.FSLayers {
+		layers = append(layers, layer.BlobSum)
+	}
+	return layers, nil
+}
+
+func copyHandler(context *cli.Context) {
+	if len(context.Args()) != 2 {
+		logrus.Fatal("Usage: copy source destination")
+	}
+
+	src, err := parseImageSource(context, context.Args()[0])
+	if err != nil {
+		logrus.Fatalf("Error initializing %s: %s", context.Args()[0], err.Error())
+	}
+
+	dest, err := parseImageDestination(context, context.Args()[1])
+	if err != nil {
+		logrus.Fatalf("Error initializing %s: %s", context.Args()[1], err.Error())
+	}
+
+	manifest, digest, err := src.GetManifest()
+	if err != nil {
+		logrus.Fatalf("Error reading manifest: %s", err.Error())
+	}
+	fmt.Printf("Canonical manifest digest: %s\n", digest)
+
+	layers, err := manifestLayers(manifest)
+	if err != nil {
+		logrus.Fatalf("Error parsing manifest: %s", err.Error())
+	}
+	for _, layer := range layers {
+		stream, err := src.GetLayer(layer)
+		if err != nil {
+			logrus.Fatalf("Error reading layer %s: %s", layer, err.Error())
+		}
+		defer stream.Close()
+		if err := dest.PutLayer(layer, stream); err != nil {
+			logrus.Fatalf("Error writing layer: %s", err.Error())
+		}
+	}
+
+	sigs, err := src.GetSignatures()
+	if err != nil {
+		logrus.Fatalf("Error reading signatures: %s", err.Error())
+	}
+	if err := dest.PutSignatures(sigs); err != nil {
+		logrus.Fatalf("Error writing signatures: %s", err.Error())
+	}
+
+	// FIXME: We need to call PutManifest after PutLayer and PutSignatures. This seems ugly; move to a "set properties" + "commit" model?
+	if err := dest.PutManifest(manifest); err != nil {
+		logrus.Fatalf("Error writing manifest: %s", err.Error())
+	}
+}
+
+var copyCmd = cli.Command{
+	Name:   "copy",
+	Action: copyHandler,
+}

main.go

@@ -60,6 +60,7 @@ func main() {
 		return nil
 	}
 	app.Commands = []cli.Command{
+		copyCmd,
 		inspectCmd,
 		layersCmd,
 		standaloneSignCmd,

man1/skopeo.1

@@ -8,6 +8,8 @@
 .SH NAME
 skopeo \(em Inspect Docker images and repositories on registries
 .SH SYNOPSIS
+\fBskopeo copy\fR source-location destination-location
+.PP
 \fBskopeo inspect\fR image-name [\fB--raw\fR]
 .PP
 \fBskopeo layers\fR image-name
@@ -45,6 +47,15 @@ Show help
 .B "--version, -v"
 print the version number
 .SH COMMANDS
+.TP
+.B copy
+Copy an image (manifest, filesystem layers, signatures) from one location to another.
+.sp
+.B source-location
+and
+.B destination-location
+can be \fBdocker://\fRdocker-reference, \fBdir:\fRlocal-path, or \fBatomic:\fRimagestream-name\fB:\fRtag .
+
 .TP
 .B inspect
 Return low-level information on images in a registry