diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/PathUtil.java b/gitiles-servlet/src/main/java/com/google/gitiles/PathUtil.java
new file mode 100644
index 0000000..e55b77d
--- /dev/null
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/PathUtil.java
@@ -0,0 +1,64 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// 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 com.google.gitiles;
+
+import com.google.common.base.CharMatcher;
+import com.google.common.base.Splitter;
+import com.google.common.base.Strings;
+import com.google.common.io.Files;
+
+import java.util.StringTokenizer;
+
+/** Static utilities for dealing with pathnames. */
+class PathUtil {
+  private static final CharMatcher MATCHER = CharMatcher.is('/');
+  static final Splitter SPLITTER = Splitter.on(MATCHER);
+
+  static String simplifyPathUpToRoot(String path, String root) {
+    if (path.startsWith("/")) {
+      return null;
+    }
+
+    root = Strings.nullToEmpty(root);
+    // simplifyPath() normalizes "a/../../" to "a", so manually check whether
+    // the path leads above the root.
+    int depth = new StringTokenizer(root, "/").countTokens();
+    for (String part : SPLITTER.split(path)) {
+      if (part.equals("..")) {
+        depth--;
+        if (depth < 0) {
+          return null;
+        }
+      } else if (!part.isEmpty() && !part.equals(".")) {
+        depth++;
+      }
+    }
+
+    String result = Files.simplifyPath(!root.isEmpty() ? root + "/" + path : path);
+    return !result.equals(".") ? result : "";
+  }
+
+  static String basename(String path) {
+    path = MATCHER.trimTrailingFrom(path);
+    int slash = path.lastIndexOf('/');
+    if (slash < 0) {
+      return path;
+    }
+    return path.substring(slash + 1);
+  }
+
+  private PathUtil() {
+  }
+}