3 files changed, 196 insertions, 0 deletions
diff --git a/cmd/podman/cliconfig/config.go b/cmd/podman/cliconfig/config.go
index ec08eedb5..cb9d9a338 100644
--- a/cmd/podman/cliconfig/config.go
+++ b/cmd/podman/cliconfig/config.go
@@ -66,6 +66,11 @@ type TagValues struct {
 	PodmanCommand
 }
 
+type TreeValues struct {
+	PodmanCommand
+	WhatRequires bool
+}
+
 type WaitValues struct {
 	PodmanCommand
 	Interval uint
diff --git a/cmd/podman/image.go b/cmd/podman/image.go
index 0e980d4d3..66c141686 100644
--- a/cmd/podman/image.go
+++ b/cmd/podman/image.go
@@ -73,6 +73,7 @@ var imageSubCommands = []*cobra.Command{
 	_rmSubCommand,
 	_saveCommand,
 	_tagCommand,
+	_treeCommand,
 }
 
 func init() {
diff --git a/cmd/podman/tree.go b/cmd/podman/tree.go
new file mode 100644
index 000000000..ebda18cdb
--- /dev/null
+++ b/cmd/podman/tree.go
@@ -0,0 +1,190 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/containers/libpod/cmd/podman/cliconfig"
+	"github.com/containers/libpod/cmd/podman/libpodruntime"
+	"github.com/containers/libpod/libpod/image"
+	units "github.com/docker/go-units"
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+const (
+	middleItem   = "├── "
+	continueItem = "│   "
+	lastItem     = "└── "
+)
+
+var (
+	treeCommand cliconfig.TreeValues
+
+	treeDescription = "Prints layer hierarchy of an image in a tree format"
+	_treeCommand    = &cobra.Command{
+		Use:   "tree",
+		Short: treeDescription,
+		Long:  treeDescription,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			treeCommand.InputArgs = args
+			treeCommand.GlobalFlags = MainGlobalOpts
+			return treeCmd(&treeCommand)
+		},
+		Example: "podman image tree alpine:latest",
+	}
+)
+
+func init() {
+	treeCommand.Command = _treeCommand
+	treeCommand.SetUsageTemplate(UsageTemplate())
+	treeCommand.Flags().BoolVar(&treeCommand.WhatRequires, "whatrequires", false, "Show all child images and layers of the specified image")
+}
+
+// infoImage keep information of Image along with all associated layers
+type infoImage struct {
+	// id of image
+	id string
+	// tags of image
+	tags []string
+	// layers stores all layers of image.
+	layers []image.LayerInfo
+}
+
+func treeCmd(c *cliconfig.TreeValues) error {
+	args := c.InputArgs
+	if len(args) == 0 {
+		return errors.Errorf("an image name must be specified")
+	}
+	if len(args) > 1 {
+		return errors.Errorf("you must provide at most 1 argument")
+	}
+
+	runtime, err := libpodruntime.GetRuntime(&c.PodmanCommand)
+	if err != nil {
+		return errors.Wrapf(err, "error creating libpod runtime")
+	}
+	defer runtime.Shutdown(false)
+
+	img, err := runtime.ImageRuntime().NewFromLocal(args[0])
+	if err != nil {
+		return err
+	}
+
+	// Fetch map of image-layers, which is used for printing output.
+	layerInfoMap, err := image.GetLayersMapWithImageInfo(runtime.ImageRuntime())
+	if err != nil {
+		return errors.Wrapf(err, "error while retriving layers of image %q", img.InputName)
+	}
+
+	// Create an imageInfo and fill the image and layer info
+	imageInfo := &infoImage{
+		id:   img.ID(),
+		tags: img.Names(),
+	}
+
+	size, err := img.Size(context.Background())
+	if err != nil {
+		return errors.Wrapf(err, "error while retriving image size")
+	}
+	fmt.Printf("Image ID: %s\n", imageInfo.id[:12])
+	fmt.Printf("Tags:\t %s\n", imageInfo.tags)
+	fmt.Printf("Size:\t %v\n", units.HumanSizeWithPrecision(float64(*size), 4))
+	fmt.Printf(fmt.Sprintf("Image Layers\n"))
+
+	if !c.WhatRequires {
+		// fill imageInfo with layers associated with image.
+		// the layers will be filled such that
+		// (Start)RootLayer->...intermediate Parent Layer(s)-> TopLayer(End)
+		err := buildImageHierarchyMap(imageInfo, layerInfoMap, img.TopLayer())
+		if err != nil {
+			return err
+		}
+		// Build output from imageInfo into buffer
+		printImageHierarchy(imageInfo)
+
+	} else {
+		// fill imageInfo with layers associated with image.
+		// the layers will be filled such that
+		// (Start)TopLayer->...intermediate Child Layer(s)-> Child TopLayer(End)
+		//             (Forks)... intermediate Child Layer(s) -> Child Top Layer(End)
+		err := printImageChildren(layerInfoMap, img.TopLayer(), "", true)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Stores hierarchy of images such that all parent layers using which image is built are stored in imageInfo
+// Layers are added such that  (Start)RootLayer->...intermediate Parent Layer(s)-> TopLayer(End)
+func buildImageHierarchyMap(imageInfo *infoImage, layerMap map[string]*image.LayerInfo, layerID string) error {
+	if layerID == "" {
+		return nil
+	}
+	ll, ok := layerMap[layerID]
+	if !ok {
+		return fmt.Errorf("lookup error: layerid  %s not found", layerID)
+	}
+	if err := buildImageHierarchyMap(imageInfo, layerMap, ll.ParentID); err != nil {
+		return err
+	}
+
+	imageInfo.layers = append(imageInfo.layers, *ll)
+	return nil
+}
+
+// Stores all children layers which are created using given Image.
+// Layers are stored as follows
+// (Start)TopLayer->...intermediate Child Layer(s)-> Child TopLayer(End)
+//             (Forks)... intermediate Child Layer(s) -> Child Top Layer(End)
+func printImageChildren(layerMap map[string]*image.LayerInfo, layerID string, prefix string, last bool) error {
+	if layerID == "" {
+		return nil
+	}
+	ll, ok := layerMap[layerID]
+	if !ok {
+		return fmt.Errorf("lookup error: layerid  %s, not found", layerID)
+	}
+	fmt.Printf(prefix)
+
+	//initialize intend with middleItem to reduce middleItem checks.
+	intend := middleItem
+	if !last {
+		// add continueItem i.e. '|' for next iteration prefix
+		prefix = prefix + continueItem
+	} else if len(ll.ChildID) > 1 || len(ll.ChildID) == 0 {
+		// The above condition ensure, alignment happens for node, which has more then 1 childern.
+		// If node is last in printing hierarchy, it should not be printed as middleItem i.e. ├──
+		intend = lastItem
+		prefix = prefix + " "
+	}
+
+	var tags string
+	if len(ll.RepoTags) > 0 {
+		tags = fmt.Sprintf(" Top Layer of: %s", ll.RepoTags)
+	}
+	fmt.Printf("%sID: %s Size: %7v%s\n", intend, ll.ID[:12], units.HumanSizeWithPrecision(float64(ll.Size), 4), tags)
+	for count, childID := range ll.ChildID {
+		if err := printImageChildren(layerMap, childID, prefix, (count == len(ll.ChildID)-1)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// prints the layers info of image
+func printImageHierarchy(imageInfo *infoImage) {
+	for count, l := range imageInfo.layers {
+		var tags string
+		intend := middleItem
+		if len(l.RepoTags) > 0 {
+			tags = fmt.Sprintf(" Top Layer of: %s", l.RepoTags)
+		}
+		if count == len(imageInfo.layers)-1 {
+			intend = lastItem
+		}
+		fmt.Printf("%s ID: %s Size: %7v%s\n", intend, l.ID[:12], units.HumanSizeWithPrecision(float64(l.Size), 4), tags)
+	}
+}