1 files changed, 119 insertions, 0 deletions
diff --git a/pkg/sentry/fs/path.go b/pkg/sentry/fs/path.go
new file mode 100644
index 000000000..e4dc02dbb
--- /dev/null
+++ b/pkg/sentry/fs/path.go
@@ -0,0 +1,119 @@
+// Copyright 2018 The gVisor 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 fs
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// TrimTrailingSlashes trims any trailing slashes.
+//
+// The returned boolean indicates whether any changes were made.
+//
+//go:nosplit
+func TrimTrailingSlashes(dir string) (trimmed string, changed bool) {
+	// Trim the trailing slash, except for root.
+	for len(dir) > 1 && dir[len(dir)-1] == '/' {
+		dir = dir[:len(dir)-1]
+		changed = true
+	}
+	return dir, changed
+}
+
+// SplitLast splits the given path into a directory and a file.
+//
+// The "absoluteness" of the path is preserved, but dir is always stripped of
+// trailing slashes.
+//
+//go:nosplit
+func SplitLast(path string) (dir, file string) {
+	path, _ = TrimTrailingSlashes(path)
+	if path == "" {
+		return ".", "."
+	} else if path == "/" {
+		return "/", "."
+	}
+
+	var slash int // Last location of slash in path.
+	for slash = len(path) - 1; slash >= 0 && path[slash] != '/'; slash-- {
+	}
+	switch {
+	case slash < 0:
+		return ".", path
+	case slash == 0:
+		// Directory of the form "/foo", or just "/". We need to
+		// preserve the first slash here, since it indicates an
+		// absolute path.
+		return "/", path[1:]
+	default:
+		// Drop the trailing slash.
+		dir, _ = TrimTrailingSlashes(path[:slash])
+		return dir, path[slash+1:]
+	}
+}
+
+// SplitFirst splits the given path into a first directory and the remainder.
+//
+// If remainder is empty, then the path is a single element.
+//
+//go:nosplit
+func SplitFirst(path string) (current, remainder string) {
+	path, _ = TrimTrailingSlashes(path)
+	if path == "" {
+		return ".", ""
+	}
+
+	var slash int // First location of slash in path.
+	for slash = 0; slash < len(path) && path[slash] != '/'; slash++ {
+	}
+	switch {
+	case slash >= len(path):
+		return path, ""
+	case slash == 0:
+		// See above.
+		return "/", path[1:]
+	default:
+		current = path[:slash]
+		remainder = path[slash+1:]
+		// Strip redundant slashes.
+		for len(remainder) > 0 && remainder[0] == '/' {
+			remainder = remainder[1:]
+		}
+		return current, remainder
+	}
+}
+
+// IsSubpath checks whether the first path is a (strict) descendent of the
+// second. If it is a subpath, then true is returned along with a clean
+// relative path from the second path to the first. Otherwise false is
+// returned.
+func IsSubpath(subpath, path string) (string, bool) {
+	cleanPath := filepath.Clean(path)
+	cleanSubpath := filepath.Clean(subpath)
+
+	// Add a trailing slash to the path if it does not already have one.
+	if len(cleanPath) == 0 || cleanPath[len(cleanPath)-1] != '/' {
+		cleanPath += "/"
+	}
+	if cleanPath == cleanSubpath {
+		// Paths are equal, thus not a strict subpath.
+		return "", false
+	}
+	if strings.HasPrefix(cleanSubpath, cleanPath) {
+		return strings.TrimPrefix(cleanSubpath, cleanPath), true
+	}
+	return "", false
+}