pkg/fileutils: move ReadSymlinkedDirectory to daemon

It has no external consumers, is written with specific behavior, making
it not a good candidate to carry in the module.

This moves it to the daemon as a non-exported `resolveSymlinkedDirectory`
utility, so that it's only accessible where it's currently used.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/daemon.go

@@ -63,7 +63,6 @@ import (
 	volumesservice "github.com/docker/docker/daemon/volume/service"
 	"github.com/docker/docker/dockerversion"
 	"github.com/docker/docker/pkg/authorization"
-	"github.com/docker/docker/pkg/fileutils"
 	"github.com/docker/docker/pkg/plugingetter"
 	"github.com/docker/docker/pkg/sysinfo"
 	"github.com/moby/buildkit/util/grpcerrors"
@@ -804,7 +803,7 @@ func NewDaemon(ctx context.Context, config *config.Config, pluginStore *plugin.S
 	if err != nil {
 		return nil, fmt.Errorf("Unable to get the TempDir under %s: %s", config.Root, err)
 	}
-	realTmp, err := fileutils.ReadSymlinkedDirectory(tmp)
+	realTmp, err := resolveSymlinkedDirectory(tmp)
 	if err != nil {
 		return nil, fmt.Errorf("Unable to get the full path to the TempDir (%s): %s", tmp, err)
 	}
@@ -1540,9 +1539,9 @@ func CreateDaemonRoot(config *config.Config) error {
 	if _, err := os.Stat(config.Root); err != nil && os.IsNotExist(err) {
 		realRoot = config.Root
 	} else {
-		realRoot, err = fileutils.ReadSymlinkedDirectory(config.Root)
+		realRoot, err = resolveSymlinkedDirectory(config.Root)
 		if err != nil {
-			return fmt.Errorf("Unable to get the full path to root (%s): %s", config.Root, err)
+			return fmt.Errorf("unable to get the full path to root (%s): %s", config.Root, err)
 		}
 	}
 
@@ -1672,3 +1671,25 @@ func (i *imageBackend) GetRepositories(ctx context.Context, ref reference.Named,
 		},
 	})
 }
+
+// resolveSymlinkedDirectory returns the target directory of a symlink and
+// checks if it resolves to a directory (not a file).
+func resolveSymlinkedDirectory(path string) (realPath string, _ error) {
+	var err error
+	realPath, err = filepath.Abs(path)
+	if err != nil {
+		return "", fmt.Errorf("unable to get absolute path for %s: %w", path, err)
+	}
+	realPath, err = filepath.EvalSymlinks(realPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to canonicalise path for %s: %w", path, err)
+	}
+	realPathInfo, err := os.Stat(realPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to stat target '%s' of '%s': %w", realPath, path, err)
+	}
+	if !realPathInfo.Mode().IsDir() {
+		return "", fmt.Errorf("canonical path points to a file '%s'", realPath)
+	}
+	return realPath, nil
+}

daemon/daemon_test.go

@@ -3,8 +3,10 @@ package daemon
 import (
 	"net/netip"
 	"os"
+	"path"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 
 	cerrdefs "github.com/containerd/errdefs"
@@ -341,3 +343,100 @@ func TestDeriveULABaseNetwork(t *testing.T) {
 		})
 	}
 }
+
+// Reading a symlink to a directory must return the directory
+func TestResolveSymlinkedDirectoryExistingDirectory(t *testing.T) {
+	// TODO Windows: Port this test
+	if runtime.GOOS == "windows" {
+		t.Skip("Needs porting to Windows")
+	}
+
+	// On macOS, tmp itself is symlinked, so resolve this one upfront;
+	// see https://github.com/golang/go/issues/56259
+	tmpDir, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	srcPath := filepath.Join(tmpDir, "/testReadSymlinkToExistingDirectory")
+	dstPath := filepath.Join(tmpDir, "/dirLinkTest")
+	if err = os.Mkdir(srcPath, 0o777); err != nil {
+		t.Errorf("failed to create directory: %s", err)
+	}
+
+	if err = os.Symlink(srcPath, dstPath); err != nil {
+		t.Errorf("failed to create symlink: %s", err)
+	}
+
+	var symlinkedPath string
+	if symlinkedPath, err = resolveSymlinkedDirectory(dstPath); err != nil {
+		t.Fatalf("failed to read symlink to directory: %s", err)
+	}
+
+	if symlinkedPath != srcPath {
+		t.Fatalf("symlink returned unexpected directory: %s", symlinkedPath)
+	}
+
+	if err = os.Remove(srcPath); err != nil {
+		t.Errorf("failed to remove temporary directory: %s", err)
+	}
+
+	if err = os.Remove(dstPath); err != nil {
+		t.Errorf("failed to remove symlink: %s", err)
+	}
+}
+
+// Reading a non-existing symlink must fail
+func TestResolveSymlinkedDirectoryNonExistingSymlink(t *testing.T) {
+	tmpDir := t.TempDir()
+	symLinkedPath, err := resolveSymlinkedDirectory(path.Join(tmpDir, "/Non/ExistingPath"))
+	if err == nil {
+		t.Errorf("error expected for non-existing symlink")
+	}
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Errorf("Expected an os.ErrNotExist, got: %v", err)
+	}
+	if symLinkedPath != "" {
+		t.Fatalf("expected empty path, but '%s' was returned", symLinkedPath)
+	}
+}
+
+// Reading a symlink to a file must fail
+func TestResolveSymlinkedDirectoryToFile(t *testing.T) {
+	// TODO Windows: Port this test
+	if runtime.GOOS == "windows" {
+		t.Skip("Needs porting to Windows")
+	}
+	var err error
+	var file *os.File
+
+	// #nosec G303
+	if file, err = os.Create("/tmp/testSymlinkToFile"); err != nil {
+		t.Fatalf("failed to create file: %s", err)
+	}
+
+	_ = file.Close()
+
+	if err = os.Symlink("/tmp/testSymlinkToFile", "/tmp/fileLinkTest"); err != nil {
+		t.Errorf("failed to create symlink: %s", err)
+	}
+
+	symlinkedPath, err := resolveSymlinkedDirectory("/tmp/fileLinkTest")
+	if err == nil {
+		t.Errorf("resolveSymlinkedDirectory on a symlink to a file should've failed")
+	} else if !strings.HasPrefix(err.Error(), "canonical path points to a file") {
+		t.Errorf("unexpected error: %v", err)
+	}
+
+	if symlinkedPath != "" {
+		t.Errorf("path should've been empty: %s", symlinkedPath)
+	}
+
+	if err = os.Remove("/tmp/testSymlinkToFile"); err != nil {
+		t.Errorf("failed to remove file: %s", err)
+	}
+
+	if err = os.Remove("/tmp/fileLinkTest"); err != nil {
+		t.Errorf("failed to remove symlink: %s", err)
+	}
+}

pkg/fileutils/fileutils.go

@@ -1,29 +0,0 @@
-package fileutils
-
-import (
-	"fmt"
-	"os"
-	"path/filepath"
-)
-
-// ReadSymlinkedDirectory returns the target directory of a symlink.
-// The target of the symbolic link may not be a file.
-func ReadSymlinkedDirectory(path string) (realPath string, _ error) {
-	var err error
-	realPath, err = filepath.Abs(path)
-	if err != nil {
-		return "", fmt.Errorf("unable to get absolute path for %s: %w", path, err)
-	}
-	realPath, err = filepath.EvalSymlinks(realPath)
-	if err != nil {
-		return "", fmt.Errorf("failed to canonicalise path for %s: %w", path, err)
-	}
-	realPathInfo, err := os.Stat(realPath)
-	if err != nil {
-		return "", fmt.Errorf("failed to stat target '%s' of '%s': %w", realPath, path, err)
-	}
-	if !realPathInfo.Mode().IsDir() {
-		return "", fmt.Errorf("canonical path points to a file '%s'", realPath)
-	}
-	return realPath, nil
-}

pkg/fileutils/fileutils_test.go

@@ -1,109 +0,0 @@
-package fileutils
-
-import (
-	"errors"
-	"os"
-	"path"
-	"path/filepath"
-	"runtime"
-	"strings"
-	"testing"
-)
-
-// Reading a symlink to a directory must return the directory
-func TestReadSymlinkedDirectoryExistingDirectory(t *testing.T) {
-	// TODO Windows: Port this test
-	if runtime.GOOS == "windows" {
-		t.Skip("Needs porting to Windows")
-	}
-
-	// On macOS, tmp itself is symlinked, so resolve this one upfront;
-	// see https://github.com/golang/go/issues/56259
-	tmpDir, err := filepath.EvalSymlinks(t.TempDir())
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	srcPath := filepath.Join(tmpDir, "/testReadSymlinkToExistingDirectory")
-	dstPath := filepath.Join(tmpDir, "/dirLinkTest")
-	if err = os.Mkdir(srcPath, 0o777); err != nil {
-		t.Errorf("failed to create directory: %s", err)
-	}
-
-	if err = os.Symlink(srcPath, dstPath); err != nil {
-		t.Errorf("failed to create symlink: %s", err)
-	}
-
-	var symlinkedPath string
-	if symlinkedPath, err = ReadSymlinkedDirectory(dstPath); err != nil {
-		t.Fatalf("failed to read symlink to directory: %s", err)
-	}
-
-	if symlinkedPath != srcPath {
-		t.Fatalf("symlink returned unexpected directory: %s", symlinkedPath)
-	}
-
-	if err = os.Remove(srcPath); err != nil {
-		t.Errorf("failed to remove temporary directory: %s", err)
-	}
-
-	if err = os.Remove(dstPath); err != nil {
-		t.Errorf("failed to remove symlink: %s", err)
-	}
-}
-
-// Reading a non-existing symlink must fail
-func TestReadSymlinkedDirectoryNonExistingSymlink(t *testing.T) {
-	tmpDir := t.TempDir()
-	symLinkedPath, err := ReadSymlinkedDirectory(path.Join(tmpDir, "/Non/ExistingPath"))
-	if err == nil {
-		t.Errorf("error expected for non-existing symlink")
-	}
-	if !errors.Is(err, os.ErrNotExist) {
-		t.Errorf("Expected an os.ErrNotExist, got: %v", err)
-	}
-	if symLinkedPath != "" {
-		t.Fatalf("expected empty path, but '%s' was returned", symLinkedPath)
-	}
-}
-
-// Reading a symlink to a file must fail
-func TestReadSymlinkedDirectoryToFile(t *testing.T) {
-	// TODO Windows: Port this test
-	if runtime.GOOS == "windows" {
-		t.Skip("Needs porting to Windows")
-	}
-	var err error
-	var file *os.File
-
-	// #nosec G303
-	if file, err = os.Create("/tmp/testReadSymlinkToFile"); err != nil {
-		t.Fatalf("failed to create file: %s", err)
-	}
-
-	_ = file.Close()
-
-	if err = os.Symlink("/tmp/testReadSymlinkToFile", "/tmp/fileLinkTest"); err != nil {
-		t.Errorf("failed to create symlink: %s", err)
-	}
-
-	symlinkedPath, err := ReadSymlinkedDirectory("/tmp/fileLinkTest")
-	if err == nil {
-		t.Errorf("ReadSymlinkedDirectory on a symlink to a file should've failed")
-	}
-	if !strings.HasPrefix(err.Error(), "canonical path points to a file") {
-		t.Errorf("unexpected error: %v", err)
-	}
-
-	if symlinkedPath != "" {
-		t.Errorf("path should've been empty: %s", symlinkedPath)
-	}
-
-	if err = os.Remove("/tmp/testReadSymlinkToFile"); err != nil {
-		t.Errorf("failed to remove file: %s", err)
-	}
-
-	if err = os.Remove("/tmp/fileLinkTest"); err != nil {
-		t.Errorf("failed to remove symlink: %s", err)
-	}
-}