feat(publish): add ability to select specific layers to publish

Currently, publish cmd will push every layer in a stacker.yaml file by
default.

This patch adds support to push only required layers.

Signed-off-by: Ramkumar Chinchani <rchincha@cisco.com>

cmd/stacker/publish.go

@@ -69,6 +69,10 @@ var publishCmd = cli.Command{
 			Usage: "set the output layer type (supported values: tar, squashfs); can be supplied multiple times",
 			Value: &cli.StringSlice{"tar"},
 		},
+		cli.StringSliceFlag{
+			Name:  "layer",
+			Usage: "layer to be published; can be specified multiple times",
+		},
 	},
 	Before: beforePublish,
 }
@@ -120,6 +124,7 @@ func doPublish(ctx *cli.Context) error {
 		Progress:       shouldShowProgress(ctx),
 		SkipTLS:        ctx.Bool("skip-tls"),
 		LayerTypes:     layerTypes,
+		Layers:         ctx.StringSlice("layer"),
 	}
 
 	var stackerFiles []string

pkg/stacker/publisher.go

@@ -30,6 +30,7 @@ type PublishArgs struct {
 	Progress       bool
 	SkipTLS        bool
 	LayerTypes     []types.LayerType
+	Layers         []string
 }
 
 // Publisher is responsible for publishing the layers based on stackerfiles
@@ -117,6 +118,19 @@ func (p *Publisher) Publish(file string) error {
 			log.Infof("will not publish: %s build_only %s", file, name)
 			continue
 		}
+		if len(p.opts.Layers) > 0 {
+			found := false
+			for _, lname := range p.opts.Layers {
+				if lname == name {
+					found = true
+					break
+				}
+			}
+
+			if !found {
+				continue
+			}
+		}
 
 		// Verify layer is in build cache
 		_, ok, err = buildCache.Lookup(name)

test/publish.bats

@@ -116,6 +116,19 @@ function teardown() {
     [ -f dest/layer2_test1/rootfs/root/import1 ]
 }
 
+@test "publish selected multiple layers" {
+    stacker recursive-build -d ocibuilds
+    stacker publish -d ocibuilds --url oci:oci_publish --tag test1 --layer layer1 --layer layer6
+
+     # Unpack published image and check content
+    umoci unpack --image oci_publish:layer1_test1 dest/layer1_test1
+    [ -f dest/layer1_test1/rootfs/root/import1 ]
+    umoci unpack --image oci_publish:layer6_test1 dest/layer6_test1
+    [ -f dest/layer6_test1/rootfs/root/import6 ]
+    umoci unpack --image oci_publish:layer2_test1 dest/layer2_test1
+    [ "$status" -eq 1 ]
+}
+
 @test "publish single layer with docker url" {
     stacker build -f ocibuilds/sub1/stacker.yaml
     stacker publish -f ocibuilds/sub1/stacker.yaml --url docker://docker-reg.fake.com/ --username user --password pass --tag test1 --show-only