From e847ec7474736661b8153dfadd6b84d3f84ec946 Mon Sep 17 00:00:00 2001
From: Natasha Sarkar <natashasarkar@google.com>
Date: Tue, 8 Jun 2021 11:18:11 -0700
Subject: [PATCH] ReadDir method for filesys

---
 api/filesys/filesystem.go |  2 ++
 api/filesys/fsnode.go     | 23 +++++++++++++++++++++++
 api/filesys/fsondisk.go   | 13 +++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/api/filesys/filesystem.go b/api/filesys/filesystem.go
index 2d8caf2b8..e5034092b 100644
--- a/api/filesys/filesystem.go
+++ b/api/filesys/filesystem.go
@@ -28,6 +28,8 @@ type FileSystem interface {
 	Open(path string) (File, error)
 	// IsDir returns true if the path is a directory.
 	IsDir(path string) bool
+	// ReadDir returns a list of files and directories within a directory.
+	ReadDir(path string) ([]string, error)
 	// CleanedAbs converts the given path into a
 	// directory and a file name, where the directory
 	// is represented as a ConfirmedDir and all that implies.
diff --git a/api/filesys/fsnode.go b/api/filesys/fsnode.go
index 97e0408e0..f3c1d3878 100644
--- a/api/filesys/fsnode.go
+++ b/api/filesys/fsnode.go
@@ -349,6 +349,29 @@ func (n *fsNode) IsDir(path string) bool {
 	return result.isNodeADir()
 }
 
+// ReadDir implements FileSystem.
+func (n *fsNode) ReadDir(path string) ([]string, error) {
+	if !n.IsDir(path) {
+		return nil, fmt.Errorf("%s is not a directory", path)
+	}
+
+	dir, err := n.Find(path)
+	if err != nil {
+		return nil, err
+	}
+	if dir == nil {
+		return nil, fmt.Errorf("could not find directory %s", path)
+	}
+
+	keys := make([]string, len(dir.dir))
+	i := 0
+	for k := range dir.dir {
+		keys[i] = k
+		i++
+	}
+	return keys, nil
+}
+
 // Size returns the size of the node.
 func (n *fsNode) Size() int64 {
 	if n.isNodeADir() {
diff --git a/api/filesys/fsondisk.go b/api/filesys/fsondisk.go
index 6becbb6f1..86cd26d75 100644
--- a/api/filesys/fsondisk.go
+++ b/api/filesys/fsondisk.go
@@ -100,6 +100,19 @@ func (fsOnDisk) IsDir(name string) bool {
 	return info.IsDir()
 }
 
+// ReadDir delegates to os.ReadDir
+func (fsOnDisk) ReadDir(name string) ([]string, error) {
+	dirEntries, err := os.ReadDir(name)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]string, len(dirEntries))
+	for i := range dirEntries {
+		result[i] = dirEntries[i].Name()
+	}
+	return result, nil
+}
+
 // ReadFile delegates to ioutil.ReadFile.
 func (fsOnDisk) ReadFile(name string) ([]byte, error) { return ioutil.ReadFile(name) }