Rename should behave like create: avoid conflict.

When we create a file that already exists, we try attaching a suffix
like "(1)" to the filename to avoid the conflict.  The newly added
rename method should do the same, since developers may not have
access to delete the conflicting file.

Test: boots, rename via UI, new unit tests
Bug: 31545404
Change-Id: Ie397eebb0fbf98cf079eee3bbbb6c6b7ca627d91

core/java/android/os/FileUtils.java

@@ -605,6 +605,22 @@ public class FileUtils {
         return null;
     }
 
+    private static File buildUniqueFileWithExtension(File parent, String name, String ext)
+            throws FileNotFoundException {
+        File file = buildFile(parent, name, ext);
+
+        // If conflicting file, try adding counter suffix
+        int n = 0;
+        while (file.exists()) {
+            if (n++ >= 32) {
+                throw new FileNotFoundException("Failed to create unique file");
+            }
+            file = buildFile(parent, name + " (" + n + ")", ext);
+        }
+
+        return file;
+    }
+
     /**
      * Generates a unique file name under the given parent directory. If the display name doesn't
      * have an extension that matches the requested MIME type, the default extension for that MIME
@@ -619,20 +635,29 @@ public class FileUtils {
     public static File buildUniqueFile(File parent, String mimeType, String displayName)
             throws FileNotFoundException {
         final String[] parts = splitFileName(mimeType, displayName);
-        final String name = parts[0];
-        final String ext = parts[1];
-        File file = buildFile(parent, name, ext);
+        return buildUniqueFileWithExtension(parent, parts[0], parts[1]);
+    }
 
-        // If conflicting file, try adding counter suffix
-        int n = 0;
-        while (file.exists()) {
-            if (n++ >= 32) {
-                throw new FileNotFoundException("Failed to create unique file");
-            }
-            file = buildFile(parent, name + " (" + n + ")", ext);
+    /**
+     * Generates a unique file name under the given parent directory, keeping
+     * any extension intact.
+     */
+    public static File buildUniqueFile(File parent, String displayName)
+            throws FileNotFoundException {
+        final String name;
+        final String ext;
+
+        // Extract requested extension from display name
+        final int lastDot = displayName.lastIndexOf('.');
+        if (lastDot >= 0) {
+            name = displayName.substring(0, lastDot);
+            ext = displayName.substring(lastDot + 1);
+        } else {
+            name = displayName;
+            ext = null;
         }
 
-        return file;
+        return buildUniqueFileWithExtension(parent, name, ext);
     }
 
     /**

core/tests/coretests/src/android/os/FileUtilsTest.java

@@ -297,6 +297,20 @@ public class FileUtilsTest extends AndroidTestCase {
                 FileUtils.buildUniqueFile(mTarget, "image/jpeg", "test.jpg"));
     }
 
+    public void testBuildUniqueFile_mimeless() throws Exception {
+        assertNameEquals("test.jpg", FileUtils.buildUniqueFile(mTarget, "test.jpg"));
+        new File(mTarget, "test.jpg").createNewFile();
+        assertNameEquals("test (1).jpg", FileUtils.buildUniqueFile(mTarget, "test.jpg"));
+
+        assertNameEquals("test", FileUtils.buildUniqueFile(mTarget, "test"));
+        new File(mTarget, "test").createNewFile();
+        assertNameEquals("test (1)", FileUtils.buildUniqueFile(mTarget, "test"));
+
+        assertNameEquals("test.foo.bar", FileUtils.buildUniqueFile(mTarget, "test.foo.bar"));
+        new File(mTarget, "test.foo.bar").createNewFile();
+        assertNameEquals("test.foo (1).bar", FileUtils.buildUniqueFile(mTarget, "test.foo.bar"));
+    }
+
     private static void assertNameEquals(String expected, File actual) {
         assertEquals(expected, actual.getName());
     }

packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java

@@ -466,10 +466,7 @@ public class ExternalStorageProvider extends DocumentsProvider {
         displayName = FileUtils.buildValidFatFilename(displayName);
 
         final File before = getFileForDocId(docId);
-        final File after = new File(before.getParentFile(), displayName);
-        if (after.exists()) {
-            throw new IllegalStateException("Already exists " + after);
-        }
+        final File after = FileUtils.buildUniqueFile(before.getParentFile(), displayName);
         if (!before.renameTo(after)) {
             throw new IllegalStateException("Failed to rename to " + after);
         }