Rewrite getting ordered layers, add symlinks support (#1)

* rewrite getting layers

* show symlinks, add test for symlinks

* fix readme

Author: sergkondr

Makefile

@@ -1,4 +1,4 @@
-VERSION := 0.0.1
+VERSION := 0.0.2
 
 build: test
 	go build -ldflags="-X 'main.version=$(VERSION)'" -o docker-tree ./cmd/

README.md

@@ -1,8 +1,9 @@
 # docker-tree
 
+[![License: MIT](https://img.shields.io/badge/License-MIT%202.0-blue.svg)](https://github.com/sergkondr/docker-tree/blob/main/LICENSE)
 [![GitHub release](https://img.shields.io/github/release/sergkondr/docker-tree.svg)](https://github.com/sergkondr/docker-tree/releases/latest)
 [![Go Report Card](https://goreportcard.com/badge/github.com/sergkondr/docker-tree)](https://goreportcard.com/report/github.com/sergkondr/docker-tree)
-[![License: MIT](https://img.shields.io/badge/License-MIT%202.0-blue.svg)](https://github.com/sergkondr/docker-tree/blob/main/LICENSE)
+
 
 This command shows the directory tree of a Docker image, like the 'tree' command. 
 Provide the image name and an optional tag or digest to view the file structure inside the image. 
@@ -13,11 +14,12 @@ Think of this app mainly as an attempt to understand how Docker images work and
 
 ### Install
 ```
-cp ./docker-tree ~/.docker/cli-plugins/docker-tree
+mv ./docker-tree ~/.docker/cli-plugins/docker-tree
 ```
 
 ### Usage
 ```shell
+# Absent image will be pulled automatically
 ➜ docker tree alpine:3.20 /etc/ssl
 3.20: Pulling from library/alpine
 a258b2a6b59a: Pull complete
@@ -33,4 +35,17 @@ ssl/
 ├── openssl.cnf
 ├── openssl.cnf.dist
 └── private/
+
+# Show file tree with symlinks
+➜ docker tree -l alpine:3.20 | head
+precessing image: alpine:3.20
+/
+├── bin/
+│   ├── arch -> /bin/busybox
+│   ├── ash -> /bin/busybox
+│   ├── base64 -> /bin/busybox
+│   ├── bbconfig -> /bin/busybox
+│   ├── busybox
+│   ├── cat -> /bin/busybox
+│   ├── chattr -> /bin/busybox
 ```

cmd/main.go

@@ -20,7 +20,8 @@ func main() {
 	plugin.Run(
 		func(dockerCli command.Cli) *cobra.Command {
 			var (
-				quiet bool
+				quiet     bool
+				showLinks bool
 			)
 
 			cmd := &cobra.Command{
@@ -47,10 +48,11 @@ You can also specify a directory to see the file tree relative to this directory
 					}
 
 					treeStrings, err := docker.GetImageTree(docker.GetTreeOpts{
-						Cli:      dockerCli,
-						ImageID:  imageID,
-						Quiet:    quiet,
-						TreeRoot: treeRoot,
+						Cli:       dockerCli,
+						ImageID:   imageID,
+						Quiet:     quiet,
+						ShowLinks: showLinks,
+						TreeRoot:  treeRoot,
 					})
 					if err != nil {
 						fmt.Fprintf(dockerCli.Err(), "can't get image tree: %s\n", err)
@@ -63,6 +65,7 @@ You can also specify a directory to see the file tree relative to this directory
 
 			flags := cmd.Flags()
 			flags.BoolVarP(&quiet, "quiet", "q", false, "Suppress verbose output")
+			flags.BoolVarP(&showLinks, "links", "l", false, "Show symlinks destination")
 
 			cmd.AddCommand()
 			return cmd

internal/docker/layers.go

@@ -3,22 +3,39 @@ package docker
 import (
 	"archive/tar"
 	"context"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
-	"slices"
 	"strings"
 
 	"github.com/docker/cli/cli/command"
 	"github.com/docker/docker/api/types/image"
 )
 
+const (
+	manifestFileName = "manifest.json"
+	layerTarSuffix   = "layer.tar"
+	blobsPrefix      = "blobs/sha256/"
+)
+
 type layer struct {
 	ID       string
 	FileTree *fileTreeNode
 }
 
-func checkImageExists(cli command.Cli, imageID string) (bool, error) {
-	images, err := cli.Client().ImageList(context.Background(), image.ListOptions{})
+type manifestItem struct {
+	Config   string   `json:"Config"`
+	RepoTags []string `json:"RepoTags"`
+	Layers   []string `json:"Layers"`
+}
+
+var (
+	errNotATar = errors.New("not a tar archive")
+)
+
+func checkImageExists(ctx context.Context, cli command.Cli, imageID string) (bool, error) {
+	images, err := cli.Client().ImageList(ctx, image.ListOptions{})
 	if err != nil {
 		return false, fmt.Errorf("can't list images: %w", err)
 	}
@@ -34,29 +51,11 @@ func checkImageExists(cli command.Cli, imageID string) (bool, error) {
 	return false, nil
 }
 
-func getLayersOrderedArrFromImage(cli command.Cli, imageID string) ([]string, error) {
-	imageInspect, _, err := cli.Client().ImageInspectWithRaw(context.Background(), imageID)
-	if err != nil {
-		return nil, fmt.Errorf("can't inspect image: %w", err)
-	}
-
-	layersOrderedArr := make([]string, len(imageInspect.RootFS.Layers))
-	for i, layer := range imageInspect.RootFS.Layers {
-		layersOrderedArr[i] = fmt.Sprintf("%s", strings.Split(layer, ":")[1])
-	}
-
-	return layersOrderedArr, nil
-}
-
-func readLayers(cli command.Cli, imageID string, layersOrderedArr []string) (map[string]layer, error) {
-	imageReader, err := cli.Client().ImageSave(context.Background(), []string{imageID})
-	if err != nil {
-		return nil, fmt.Errorf("error saving image: %v", err)
-	}
-	defer imageReader.Close()
-
+func getLayersOrderedArrFromImage(imageReader io.ReadCloser) ([]layer, error) {
 	tarReader := tar.NewReader(imageReader)
-	filesInImage := make(map[string]layer, len(layersOrderedArr))
+	manifest := make([]manifestItem, 1)
+	layerInfoMap := make(map[string]layer, 1)
+
 	for {
 		header, err := tarReader.Next()
 		if err == io.EOF {
@@ -67,42 +66,70 @@ func readLayers(cli command.Cli, imageID string, layersOrderedArr []string) (map
 			return nil, fmt.Errorf("error reading tar header: %w", err)
 		}
 
-		fileName := header.Name
-		if header.Typeflag == tar.TypeReg { //|| header.Typeflag == tar.TypeSymlink {
-			fName := strings.TrimPrefix(fileName, "blobs/sha256/")
-			if slices.Contains(layersOrderedArr, fName) {
+		if header.Typeflag == tar.TypeReg || header.Typeflag == tar.TypeSymlink {
+			if header.Name == manifestFileName {
+				fileReader, err := io.ReadAll(tarReader)
+				if err != nil {
+					return nil, fmt.Errorf("error reading tar content: %w", err)
+				}
+
+				if err = json.Unmarshal(fileReader, &manifest); err != nil {
+					return nil, fmt.Errorf("error unmarshalling manifest: %w", err)
+				}
+			} else if strings.HasSuffix(header.Name, layerTarSuffix) {
 				layerReader := tar.NewReader(tarReader)
 				files, err := getFileTreeFromLayer(layerReader)
 				if err != nil {
 					return nil, fmt.Errorf("error getting files from layer: %w", err)
 				}
 
-				filesInImage[fName] = layer{
-					ID:       fileName,
+				layerInfoMap[header.Name] = layer{
+					ID:       header.Name,
+					FileTree: files,
+				}
+			} else if strings.HasPrefix(header.Name, blobsPrefix) {
+				layerReader := tar.NewReader(tarReader)
+				files, err := getFileTreeFromLayer(layerReader)
+				if errors.Is(err, errNotATar) {
+					continue
+				}
+
+				if err != nil {
+					return nil, fmt.Errorf("error getting files from layer: %w", err)
+				}
+
+				layerInfoMap[header.Name] = layer{
+					ID:       header.Name,
 					FileTree: files,
 				}
 			}
 		}
 	}
 
-	return filesInImage, nil
+	orderedLayersArr := make([]layer, len(manifest[0].Layers))
+	for i, layer := range manifest[0].Layers {
+		orderedLayersArr[i] = layerInfoMap[layer]
+	}
+
+	return orderedLayersArr, nil
 }
 
 func getFileTreeFromLayer(layerReader *tar.Reader) (*fileTreeNode, error) {
-	fileTree := &fileTreeNode{"/", true, make([]*fileTreeNode, 0)}
-
+	fileTree := &fileTreeNode{
+		Name:     "/",
+		Symlink:  "",
+		IsDir:    true,
+		Children: make([]*fileTreeNode, 0),
+	}
 	for {
 		header, err := layerReader.Next()
 		if err == io.EOF {
 			break
 		}
-
 		if err != nil {
-			return nil, fmt.Errorf("error reading tar header: %w", err)
+			return nil, errNotATar
 		}
-
 		fileTree.addChild(header)
 	}
-
 	return fileTree, nil
 }

internal/docker/main.go

@@ -1,20 +1,25 @@
 package docker
 
 import (
+	"context"
 	"fmt"
 
 	"github.com/docker/cli/cli/command"
 )
 
 type GetTreeOpts struct {
-	Cli      command.Cli
-	ImageID  string
-	Quiet    bool
-	TreeRoot string
+	Cli command.Cli
+
+	ImageID   string
+	Quiet     bool
+	ShowLinks bool
+	TreeRoot  string
 }
 
 func GetImageTree(opts GetTreeOpts) (string, error) {
-	imageExists, err := checkImageExists(opts.Cli, opts.ImageID)
+	ctx := context.Background()
+
+	imageExists, err := checkImageExists(ctx, opts.Cli, opts.ImageID)
 	if err != nil {
 		return "", fmt.Errorf("can't check if image exists: %w", err)
 	}
@@ -30,26 +35,34 @@ func GetImageTree(opts GetTreeOpts) (string, error) {
 		}
 	}
 
-	layersOrderedArr, err := getLayersOrderedArrFromImage(opts.Cli, opts.ImageID)
+	if !opts.Quiet {
+		fmt.Fprintf(opts.Cli.Out(), "precessing image: %s\n", opts.ImageID)
+	}
+
+	imageReader, err := opts.Cli.Client().ImageSave(ctx, []string{opts.ImageID})
 	if err != nil {
-		return "", fmt.Errorf("can't get layersOrderedArr: %w", err)
+		return "", fmt.Errorf("error saving image: %v", err)
 	}
+	defer imageReader.Close()
 
-	layerMap, err := readLayers(opts.Cli, opts.ImageID, layersOrderedArr)
+	layersOrderedArr, err := getLayersOrderedArrFromImage(imageReader)
 	if err != nil {
-		return "", fmt.Errorf("can't read layer: %w", err)
+		return "", fmt.Errorf("can't get layersOrderedArr: %w", err)
 	}
 
-	originalLayer := layerMap[layersOrderedArr[0]].FileTree
+	originalLayer := layersOrderedArr[0].FileTree
 	for i := 1; i <= len(layersOrderedArr)-1; i++ {
-		updatedLayer := layerMap[layersOrderedArr[i]].FileTree
-		originalLayer, _ = mergeFileTrees(originalLayer, updatedLayer)
+		updatedLayer := layersOrderedArr[i].FileTree
+		originalLayer, err = mergeFileTrees(originalLayer, updatedLayer)
+		if err != nil {
+			return "", fmt.Errorf("can't merge layers: %w", err)
+		}
 	}
 
 	node := originalLayer.findNode(opts.TreeRoot)
 	if node == nil {
-		return "", fmt.Errorf("tree is no such path in the image: %s", opts.TreeRoot)
+		return "", fmt.Errorf("there is no such path in the image: %s", opts.TreeRoot)
 	}
 
-	return node.String(), nil
+	return node.getString("", opts.ShowLinks, true, true), nil
 }

internal/docker/run_cli.go

@@ -5,8 +5,9 @@ import (
 	"os/exec"
 )
 
-// unfortunately, we need this to pull an image, because we can't call pull method directly
-// due to unexported parameters of the method, so it is impossible to specify the image outside the docker package
+// Unfortunately, we need this to pull an image, because we can't call pull method directly
+// due to unexported parameters of the method, so it is impossible to specify the image outside the docker package.
+// And I'd like to use this command because of its clear and informative output.
 func runDockerCliCommand(args, env []string) error {
 	cmd := exec.Command("docker", args...)
 	cmd.Env = append(os.Environ(), env...)

internal/docker/tree.go

@@ -13,21 +13,19 @@ const (
 	branch = "│   "
 	middle = "├── "
 	last   = "└── "
+	link   = " -> "
 
 	delFilePrefix = ".wh."
 )
 
 type fileTreeNode struct {
 	Name     string
+	Symlink  string
 	IsDir    bool
 	Children []*fileTreeNode
 }
 
-func (n *fileTreeNode) String() string {
-	return n.getString("", true, true)
-}
-
-func (n *fileTreeNode) getString(prefix string, isFirst, isLast bool) string {
+func (n *fileTreeNode) getString(prefix string, showLinks, isFirst, isLast bool) string {
 	passPrefix := prefix
 	currentPrefix := empty
 
@@ -47,9 +45,12 @@ func (n *fileTreeNode) getString(prefix string, isFirst, isLast bool) string {
 	}
 
 	result := fmt.Sprintf("%s%s%s\n", prefix, currentPrefix, name)
+	if showLinks && n.Symlink != "" {
+		result = fmt.Sprintf("%s%s%s%s%s\n", prefix, currentPrefix, name, link, n.Symlink)
+	}
 
 	for i, child := range n.Children {
-		result += child.getString(passPrefix, false, i == len(n.Children)-1)
+		result += child.getString(passPrefix, showLinks, false, i == len(n.Children)-1)
 	}
 
 	return result
@@ -73,6 +74,11 @@ func (n *fileTreeNode) addChild(file *tar.Header) {
 			Name:  dir,
 			IsDir: file.Typeflag == tar.TypeDir,
 		}
+
+		if file.Typeflag == tar.TypeSymlink {
+			child.Symlink = file.Linkname
+		}
+
 		n.Children = append(n.Children, child)
 	}
 }
@@ -110,10 +116,15 @@ func mergeFileTrees(original, updated *fileTreeNode) (*fileTreeNode, error) {
 		return updated, nil
 	}
 
-	merged := &fileTreeNode{original.Name, original.IsDir, original.Children}
+	merged := &fileTreeNode{
+		Name:     original.Name,
+		Symlink:  "",
+		IsDir:    original.IsDir,
+		Children: original.Children,
+	}
 
 	for _, updatedChild := range updated.Children {
-		// to avoid "/./" in tree for distroless images
+		// to avoid "/./" in tree for some images
 		if updatedChild.Name == "." {
 			continue
 		}