8266291: (jrtfs) Calling Files.exists may break the JRT filesystem

Reviewed-by: redestad, alanb

Author: sundararajana

src/java.base/share/classes/jdk/internal/jimage/ImageReader.java

@@ -468,6 +468,19 @@ Node handleModulesSubTree(String name, ImageLocation loc) {
 
         Node handleResource(String name) {
             Node n = null;
+            if (!name.startsWith("/modules/")) {
+                return null;
+            }
+            // Make sure that the thing that follows "/modules/" is a module name.
+            int moduleEndIndex = name.indexOf('/', "/modules/".length());
+            if (moduleEndIndex == -1) {
+                return null;
+            }
+            ImageLocation moduleLoc = findLocation(name.substring(0, moduleEndIndex));
+            if (moduleLoc == null || moduleLoc.getModuleOffset() == 0) {
+                return null;
+            }
+
             String locationPath = name.substring("/modules".length());
             ImageLocation resourceLoc = findLocation(locationPath);
             if (resourceLoc != null) {

test/jdk/jdk/internal/jrtfs/Basic.java

@@ -244,22 +244,30 @@ public void testKnownDirectories(String path, boolean theDefault) throws Excepti
         }
     }
 
-    @DataProvider(name = "topLevelPkgDirs")
-    private Object[][] topLevelPkgDirs() {
+    @DataProvider(name = "topLevelNonExistingDirs")
+    private Object[][] topLevelNonExistingDirs() {
         return new Object[][] {
             { "/java/lang" },
             { "java/lang"  },
             { "/java/util" },
             { "java/util"  },
+            { "/modules/modules"  },
+            { "/modules/modules/"  },
+            { "/modules/modules/java.base"  },
+            { "/modules/modules/java.base/"  },
+            { "/modules/modules/java.base/java/lang/Object.class"  },
+            { "/modules/modules/javax.scripting"  },
+            { "/modules/modules/javax.scripting/"  },
+            { "/modules/modules/javax.scripting/javax/script/ScriptEngine.class"  },
         };
     }
 
-    @Test(dataProvider = "topLevelPkgDirs")
+    @Test(dataProvider = "topLevelNonExistingDirs")
     public void testNotExists(String path) throws Exception {
         FileSystem fs = FileSystems.getFileSystem(URI.create("jrt:/"));
         Path dir = fs.getPath(path);
 
-        // package directories should not be there at top level
+        // These directories should not be there at top level
         assertTrue(Files.notExists(dir));
     }
 
@@ -756,5 +764,15 @@ public void objectClassSizeTest() throws Exception {
 
         assertTrue(Files.size(classFile) > 0L);
     }
+
+    // @bug 8266291: (jrtfs) Calling Files.exists may break the JRT filesystem
+    @Test
+    public void fileExistsCallBreaksFileSystem() throws Exception {
+        Path p = FileSystems.getFileSystem(URI.create("jrt:/")).getPath("modules");
+        boolean wasDirectory = Files.isDirectory(p);
+        Path m = p.resolve("modules");
+        Files.exists(m);
+        assertTrue(wasDirectory == Files.isDirectory(p));
+    }
 }