pkg: Add fsutil to contian file system utility functions

pkg/fsutil/fsutil.go

@@ -0,0 +1,66 @@
+// Copyright 2018 clair authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package fsutil contains utility functions for file system querying.
+package fsutil
+
+import (
+	"os"
+	"strings"
+)
+
+type dirFilter int
+
+const (
+	// All doesn't filter anything
+	All dirFilter = iota
+	// FilesOnly filters Dir function to return only files
+	FilesOnly
+	// DirectoriesOnly filters Dir function to return only directories
+	DirectoriesOnly
+)
+
+// Readdir lists the files or folders under the given path and filter based on the
+// dirFilter.
+func Readdir(path string, filter dirFilter) ([]string, error) {
+	dir, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	defer dir.Close()
+	finfos, err := dir.Readdir(0)
+	if err != nil {
+		return nil, err
+	}
+
+	var files []string
+	for _, info := range finfos {
+		if filter == DirectoriesOnly && !info.IsDir() {
+			continue
+		}
+
+		if filter == FilesOnly && info.IsDir() {
+			continue
+		}
+
+		if strings.HasPrefix(info.Name(), ".") {
+			continue
+		}
+
+		files = append(files, info.Name())
+	}
+
+	return files, nil
+}