pkg/directory: minor refactor of Size()

- separate exported function from implementation, to allow for GoDoc to be
  maintained in a single location.
- don't use named return variables (no "bare" return, and potentially shadowing
  variables)
- reverse the `os.IsNotExist(err) && d != dir` condition, putting  the "lighter"
  `d != dir` first.

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

pkg/directory/directory.go

@@ -1,6 +1,7 @@
 package directory // import "github.com/docker/docker/pkg/directory"
 
 import (
+	"context"
 	"os"
 	"path/filepath"
 )
@@ -22,3 +23,8 @@ func MoveToSubdir(oldpath, subdir string) error {
 	}
 	return nil
 }
+
+// Size walks a directory tree and returns its total size in bytes.
+func Size(ctx context.Context, dir string) (int64, error) {
+	return calcSize(ctx, dir)
+}

pkg/directory/directory_unix.go

@@ -10,14 +10,15 @@ import (
 	"syscall"
 )
 
-// Size walks a directory tree and returns its total size in bytes.
-func Size(ctx context.Context, dir string) (size int64, err error) {
+// calcSize walks a directory tree and returns its total size in bytes.
+func calcSize(ctx context.Context, dir string) (int64, error) {
+	var size int64
 	data := make(map[uint64]struct{})
-	err = filepath.Walk(dir, func(d string, fileInfo os.FileInfo, err error) error {
+	err := filepath.Walk(dir, func(d string, fileInfo os.FileInfo, err error) error {
 		if err != nil {
-			// if dir does not exist, Size() returns the error.
 			// if dir/x disappeared while walking, Size() ignores dir/x.
-			if os.IsNotExist(err) && d != dir {
+			// if dir does not exist, Size() returns the error.
+			if d != dir && os.IsNotExist(err) {
 				return nil
 			}
 			return err
@@ -51,5 +52,5 @@ func Size(ctx context.Context, dir string) (size int64, err error) {
 
 		return nil
 	})
-	return
+	return size, err
 }

pkg/directory/directory_windows.go

@@ -6,13 +6,14 @@ import (
 	"path/filepath"
 )
 
-// Size walks a directory tree and returns its total size in bytes.
-func Size(ctx context.Context, dir string) (size int64, err error) {
-	err = filepath.Walk(dir, func(d string, fileInfo os.FileInfo, err error) error {
+// calcSize walks a directory tree and returns its total calcSize in bytes.
+func calcSize(ctx context.Context, dir string) (int64, error) {
+	var size int64
+	err := filepath.Walk(dir, func(d string, fileInfo os.FileInfo, err error) error {
 		if err != nil {
-			// if dir does not exist, Size() returns the error.
 			// if dir/x disappeared while walking, Size() ignores dir/x.
-			if os.IsNotExist(err) && d != dir {
+			// if dir does not exist, Size() returns the error.
+			if d != dir && os.IsNotExist(err) {
 				return nil
 			}
 			return err
@@ -38,5 +39,5 @@ func Size(ctx context.Context, dir string) (size int64, err error) {
 
 		return nil
 	})
-	return
+	return size, err
 }