Our own cross-platform implementation of Path.isAbsolute()

Author: ldematte

libs/entitlement/src/main/java/org/elasticsearch/entitlement/runtime/policy/entitlements/FilesEntitlement.java

@@ -21,6 +21,8 @@
 import java.util.Objects;
 import java.util.stream.Stream;
 
+import static java.lang.Character.isLetter;
+
 /**
  * Describes a file entitlement with a path and mode.
  */
@@ -60,6 +62,49 @@ static FileData ofPathSetting(String setting, Mode mode) {
         static FileData ofRelativePathSetting(String setting, BaseDir baseDir, Mode mode) {
             return new RelativePathSettingFileData(setting, baseDir, mode);
         }
+
+        /**
+         * Tests if a path is absolute or relative, taking into consideration both Unix and Windows conventions
+         */
+        static boolean isAbsolutePath(String path) {
+            if (path.isEmpty()) {
+                return false;
+            }
+            if (path.charAt(0) == '/') {
+                // Unix/BSD absolute
+                return true;
+            }
+
+            return isWindowsAbsolutePath(path);
+        }
+
+        private static boolean isSlash(char c) {
+            return (c == '\\') || (c == '/');
+        }
+
+        private static boolean isWindowsAbsolutePath(String input) {
+            // if a prefix is present, we expected (long) UNC or (long) absolute
+            if (input.startsWith("\\\\?\\")) {
+                return true;
+            }
+
+            if (input.length() > 1) {
+                char c0 = input.charAt(0);
+                char c1 = input.charAt(1);
+                char c = 0;
+                int next = 2;
+                if (isSlash(c0) && isSlash(c1)) {
+                    // Two slashes or more: UNC
+                    return true;
+                }
+                if (isLetter(c0) && c1 == ':') {
+                    // A drive: absolute
+                    return true;
+                }
+            }
+            // Otherwise relative
+            return false;
+        }
     }
 
     private sealed interface RelativeFileData extends FileData {

libs/entitlement/src/test/java/org/elasticsearch/entitlement/runtime/policy/entitlements/FileDataTests.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.entitlement.runtime.policy.entitlements;
+
+import org.elasticsearch.test.ESTestCase;
+import static org.hamcrest.Matchers.is;
+
+import static org.elasticsearch.entitlement.runtime.policy.entitlements.FilesEntitlement.FileData.isAbsolutePath;
+
+public class FileDataTests  extends ESTestCase {
+
+    public void testPathIsAbsolute() {
+        var windowsNamedPipe = "\\\\.\\pipe";
+        var windowsDosAbsolutePath = "C:\\temp";
+        var unixAbsolutePath = "/tmp/foo";
+        var unixStyleUncPath = "//C/temp";
+        var uncPath = "\\\\C\\temp";
+        var longPath = "\\\\?\\C:\\temp";
+
+        var relativePath = "foo";
+        var headingSlashRelativePath = "\\foo";
+
+        assertThat(isAbsolutePath(windowsNamedPipe), is(true));
+        assertThat(isAbsolutePath(windowsDosAbsolutePath), is(true));
+        assertThat(isAbsolutePath(unixAbsolutePath), is(true));
+        assertThat(isAbsolutePath(unixStyleUncPath), is(true));
+        assertThat(isAbsolutePath(uncPath), is(true));
+        assertThat(isAbsolutePath(longPath), is(true));
+
+        assertThat(isAbsolutePath(relativePath), is(false));
+        assertThat(isAbsolutePath(headingSlashRelativePath), is(false));
+        assertThat(isAbsolutePath(""), is(false));
+    }
+}