io/fs: add ReadDir and ReadDirFS

Add ReadDir helper function, ReadDirFS interface, and test.
Add ReadDir method to fstest.MapFS.
Add testing of ReadDir method to fstest.TestFS.

For #41190.

Change-Id: Ib860770ec7433ba77b29e626682b238f1b3bf54f
Reviewed-on: https://go-review.googlesource.com/c/go/+/243914
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/io/fs/readdir.go b/src/io/fs/readdir.go
new file mode 100644 (file)
index 0000000..3a5aa6d
--- /dev/null
+++ b/src/io/fs/readdir.go
@@ -0,0 +1,47 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fs
+
+import (
+       "errors"
+       "sort"
+)
+
+// ReadDirFS is the interface implemented by a file system
+// that provides an optimized implementation of ReadDir.
+type ReadDirFS interface {
+       FS
+
+       // ReadDir reads the named directory
+       // and returns a list of directory entries sorted by filename.
+       ReadDir(name string) ([]DirEntry, error)
+}
+
+// ReadDir reads the named directory
+// and returns a list of directory entries sorted by filename.
+//
+// If fs implements ReadDirFS, ReadDir calls fs.ReadDir.
+// Otherwise ReadDir calls fs.Open and uses ReadDir and Close
+// on the returned file.
+func ReadDir(fsys FS, name string) ([]DirEntry, error) {
+       if fsys, ok := fsys.(ReadDirFS); ok {
+               return fsys.ReadDir(name)
+       }
+
+       file, err := fsys.Open(name)
+       if err != nil {
+               return nil, err
+       }
+       defer file.Close()
+
+       dir, ok := file.(ReadDirFile)
+       if !ok {
+               return nil, &PathError{Op: "readdir", Path: name, Err: errors.New("not implemented")}
+       }
+
+       list, err := dir.ReadDir(-1)
+       sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
+       return list, err
+}

diff --git a/src/io/fs/readdir_test.go b/src/io/fs/readdir_test.go
new file mode 100644 (file)
index 0000000..46a4bc2
--- /dev/null
+++ b/src/io/fs/readdir_test.go
@@ -0,0 +1,35 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fs_test
+
+import (
+       . "io/fs"
+       "testing"
+)
+
+type readDirOnly struct{ ReadDirFS }
+
+func (readDirOnly) Open(name string) (File, error) { return nil, ErrNotExist }
+
+func TestReadDir(t *testing.T) {
+       check := func(desc string, dirs []DirEntry, err error) {
+               t.Helper()
+               if err != nil || len(dirs) != 1 || dirs[0].Name() != "hello.txt" {
+                       var names []string
+                       for _, d := range dirs {
+                               names = append(names, d.Name())
+                       }
+                       t.Errorf("ReadDir(%s) = %v, %v, want %v, nil", desc, names, err, []string{"hello.txt"})
+               }
+       }
+
+       // Test that ReadDir uses the method when present.
+       dirs, err := ReadDir(readDirOnly{testFsys}, ".")
+       check("readDirOnly", dirs, err)
+
+       // Test that ReadDir uses Open when the method is not present.
+       dirs, err = ReadDir(openOnly{testFsys}, ".")
+       check("openOnly", dirs, err)
+}

diff --git a/src/testing/fstest/mapfs.go b/src/testing/fstest/mapfs.go
index b01911e5894d47290a056e174384dd58031a93d4..1eaf8f0040f30d028361df832f4e302639c08571 100644 (file)
--- a/src/testing/fstest/mapfs.go
+++ b/src/testing/fstest/mapfs.go
@@ -124,6 +124,10 @@ func (fsys MapFS) Stat(name string) (fs.FileInfo, error) {
        return fs.Stat(fsOnly{fsys}, name)
 }
 
+func (fsys MapFS) ReadDir(name string) ([]fs.DirEntry, error) {
+       return fs.ReadDir(fsOnly{fsys}, name)
+}
+
 // A mapFileInfo implements fs.FileInfo and fs.DirEntry for a given map file.
 type mapFileInfo struct {
        name string

diff --git a/src/testing/fstest/testfs.go b/src/testing/fstest/testfs.go
index 290d2596cc3d8acbc0d5cceeb0c4a918f4da26f8..4ea6ed609597e7140caea6706b724791bbd8f97f 100644 (file)
--- a/src/testing/fstest/testfs.go
+++ b/src/testing/fstest/testfs.go
@@ -196,6 +196,36 @@ func (t *fsTester) checkDir(dir string) {
                }
        }
        t.checkDirList(dir, "first Open+ReadDir(-1) vs third Open+ReadDir(1,2) loop", list, list2)
+
+       // If fsys has ReadDir, check that it matches and is sorted.
+       if fsys, ok := t.fsys.(fs.ReadDirFS); ok {
+               list2, err := fsys.ReadDir(dir)
+               if err != nil {
+                       t.errorf("%s: fsys.ReadDir: %v", dir, err)
+                       return
+               }
+               t.checkDirList(dir, "first Open+ReadDir(-1) vs fsys.ReadDir", list, list2)
+
+               for i := 0; i+1 < len(list2); i++ {
+                       if list2[i].Name() >= list2[i+1].Name() {
+                               t.errorf("%s: fsys.ReadDir: list not sorted: %s before %s", dir, list2[i].Name(), list2[i+1].Name())
+                       }
+               }
+       }
+
+       // Check fs.ReadDir as well.
+       list2, err = fs.ReadDir(t.fsys, dir)
+       if err != nil {
+               t.errorf("%s: fs.ReadDir: %v", dir, err)
+               return
+       }
+       t.checkDirList(dir, "first Open+ReadDir(-1) vs fs.ReadDir", list, list2)
+
+       for i := 0; i+1 < len(list2); i++ {
+               if list2[i].Name() >= list2[i+1].Name() {
+                       t.errorf("%s: fs.ReadDir: list not sorted: %s before %s", dir, list2[i].Name(), list2[i+1].Name())
+               }
+       }
 }
 
 // formatEntry formats an fs.DirEntry into a string for error messages and comparison.
@@ -233,12 +263,22 @@ func (t *fsTester) checkStat(path string, entry fs.DirEntry) {
                t.errorf("%s: mismatch:\n\tentry = %s\n\tfile.Stat() = %s", path, fentry, finfo)
        }
 
+       einfo, err := entry.Info()
+       if err != nil {
+               t.errorf("%s: entry.Info: %v", path, err)
+               return
+       }
+       fentry = formatInfo(einfo)
+       finfo = formatInfo(info)
+       if fentry != finfo {
+               t.errorf("%s: mismatch:\n\tentry.Info() = %s\n\tfile.Stat() = %s\n", path, fentry, finfo)
+       }
+
        info2, err := fs.Stat(t.fsys, path)
        if err != nil {
                t.errorf("%s: fs.Stat: %v", path, err)
                return
        }
-       finfo = formatInfo(info)
        finfo2 := formatInfo(info2)
        if finfo2 != finfo {
                t.errorf("%s: fs.Stat(...) = %s\n\twant %s", path, finfo2, finfo)