8321180: Condition for non-latin1 string size too large exception is off by one

Reviewed-by: rgiulietti

src/java.base/share/classes/java/lang/StringUTF16.java

@@ -42,15 +42,10 @@ import static java.lang.String.LATIN1;
 
 final class StringUTF16 {
 
+    // Return a new byte array for a UTF16-coded string for len chars
+    // Throw an exception if out of range
     public static byte[] newBytesFor(int len) {
-        if (len < 0) {
-            throw new NegativeArraySizeException();
-        }
-        if (len > MAX_LENGTH) {
-            throw new OutOfMemoryError("UTF16 String size is " + len +
-                                       ", should be less than " + MAX_LENGTH);
-        }
-        return new byte[len << 1];
+        return new byte[newBytesLength(len)];
     }
 
     // Check the size of a UTF16-coded string
@@ -59,7 +54,7 @@ final class StringUTF16 {
         if (len < 0) {
             throw new NegativeArraySizeException();
         }
-        if (len > MAX_LENGTH) {
+        if (len >= MAX_LENGTH) {
             throw new OutOfMemoryError("UTF16 String size is " + len +
                                        ", should be less than " + MAX_LENGTH);
         }

test/jdk/java/lang/String/CompactString/MaxSizeUTF16String.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.nio.charset.StandardCharsets;
+
+/*
+ * @test
+ * @bug 8077559 8321180
+ * @summary Tests Compact String for maximum size strings
+ * @requires os.maxMemory >= 7g & vm.bits == 64
+ * @run junit/othervm -XX:+CompactStrings -Xmx7g MaxSizeUTF16String
+ * @run junit/othervm -XX:-CompactStrings -Xmx7g MaxSizeUTF16String
+ */
+
+public class MaxSizeUTF16String {
+
+    private final static int MAX_UTF16_STRING_LENGTH = Integer.MAX_VALUE / 2;
+
+    private final static String EXPECTED_OOME_MESSAGE = "UTF16 String size is";
+
+    // Create a large UTF-8 byte array with a single non-latin1 character
+    private static byte[] generateUTF8Data(int byteSize) {
+        byte[] nonAscii = "\u0100".getBytes(StandardCharsets.UTF_8);
+        byte[] arr = new byte[byteSize];
+        System.arraycopy(nonAscii, 0, arr, 0, nonAscii.length); // non-latin1 at start
+        return arr;
+    }
+
+    // Create a large char array with a single non-latin1 character
+    private static char[] generateCharData(int size) {
+        char[] nonAscii = "\u0100".toCharArray();
+        char[] arr = new char[size];
+        System.arraycopy(nonAscii, 0, arr, 0, nonAscii.length); // non-latin1 at start
+        return arr;
+    }
+
+    @Test
+    public void testMaxUTF8() {
+        // Overly large UTF-8 data with 1 non-latin1 char
+        final byte[] large_utf8_bytes = generateUTF8Data(MAX_UTF16_STRING_LENGTH + 1);
+        int[] sizes = new int[] {
+                MAX_UTF16_STRING_LENGTH + 1,
+                MAX_UTF16_STRING_LENGTH,
+                MAX_UTF16_STRING_LENGTH - 1};
+        for (int size : sizes) {
+            System.err.println("Checking max UTF16 string len: " + size);
+            try {
+                // Use only part of the UTF-8 byte array
+                new String(large_utf8_bytes, 0, size, StandardCharsets.UTF_8);
+                if (size >= MAX_UTF16_STRING_LENGTH) {
+                    fail("Expected OutOfMemoryError with message prefix: " + EXPECTED_OOME_MESSAGE);
+                }
+            } catch (OutOfMemoryError ex) {
+                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE)) {
+                    fail("Failed: Not the OutOfMemoryError expected", ex);
+                }
+            }
+        }
+    }
+
+    @Test
+    public void testMaxCharArray() {
+        // Overly large UTF-8 data with 1 non-latin1 char
+        final char[] large_char_array = generateCharData(MAX_UTF16_STRING_LENGTH + 1);
+        int[] sizes = new int[]{
+                MAX_UTF16_STRING_LENGTH + 1,
+                MAX_UTF16_STRING_LENGTH,
+                MAX_UTF16_STRING_LENGTH - 1};
+        for (int size : sizes) {
+            System.err.println("Checking max UTF16 string len: " + size);
+            try {
+                // Large char array with 1 non-latin1 char
+                new String(large_char_array, 0, size);
+                if (size >= MAX_UTF16_STRING_LENGTH) {
+                    fail("Expected OutOfMemoryError with message prefix: " + EXPECTED_OOME_MESSAGE);
+                }
+            } catch (OutOfMemoryError ex) {
+                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE)) {
+                    throw new RuntimeException("Wrong exception message: " + ex.getMessage(), ex);
+                }
+            }
+        }
+    }
+}