jdk-24/test/jdk/java/lang/String/CompactString/MaxSizeUTF16String.java

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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 >= 8g & vm.bits == 64
 * @requires vm.flagless
 * @run junit/othervm -XX:+CompactStrings -Xmx8g MaxSizeUTF16String
 * @run junit/othervm -XX:-CompactStrings -Xmx8g MaxSizeUTF16String
 * @run junit/othervm -Xcomp -Xmx8g 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";
    private final static String EXPECTED_VM_LIMIT_MESSAGE = "Requested array size exceeds VM limit";
    private final static String UNEXPECTED_JAVA_HEAP_SPACE = "Java heap space";

    // 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().equals(UNEXPECTED_JAVA_HEAP_SPACE)) {
                    // Insufficient heap size
                    throw ex;
                }
                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE) &&
                        !ex.getMessage().startsWith(EXPECTED_VM_LIMIT_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().equals(UNEXPECTED_JAVA_HEAP_SPACE)) {
                    // Insufficient heap size
                    throw ex;
                }
                if (!ex.getMessage().startsWith(EXPECTED_OOME_MESSAGE) &&
                        !ex.getMessage().startsWith(EXPECTED_VM_LIMIT_MESSAGE)) {
                    throw new RuntimeException("Wrong exception message: " + ex.getMessage(), ex);
                }
            }
        }
    }

    /*
     * Test that UTF-8 of too large strings throws OOME, (not NegativeArraySizeException).
     */
    @Test
    public void testMaxUTF8_UTF16Encode() {
        String s = "\uFFFF";
        final byte[] bytes1 = s.getBytes(StandardCharsets.UTF_8);
        assertEquals(3, bytes1.length, "UTF_8 encoded length of 0xffff");

        int min = Integer.MAX_VALUE / bytes1.length - 1;
        int max = min + 3;

        // String of size min can be UTF_8 encoded.
        System.out.println("testing size: " + min);
        String s1 = s.repeat(min);
        byte[] bytes = s1.getBytes(StandardCharsets.UTF_8);
        int remaining = Integer.MAX_VALUE - bytes.length;
        assertTrue(remaining >= bytes1.length, "remainder too large: " + remaining);

        // Strings of size min+1...min+2, throw OOME
        // The resulting byte array would exceed implementation limits
        for (int count = min + 1; count < max; count++) {
            System.out.println("testing size: " + count);
            final String s2 = s.repeat(count);
            OutOfMemoryError ex = assertThrows(OutOfMemoryError.class, () -> s2.getBytes(StandardCharsets.UTF_8));
            ex.printStackTrace();
        };
    }
}