8329623: NegativeArraySizeException encoding large String to UTF-8

Reviewed-by: naoto, rgiulietti

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

@@ -1335,7 +1335,13 @@ public final class String
         int dp = 0;
         int sp = 0;
         int sl = val.length >> 1;
-        byte[] dst = new byte[sl * 3];
+        // UTF-8 encoded can be as much as 3 times the string length
+        // For very large estimate, (as in overflow of 32 bit int), precompute the exact size
+        long allocLen = (sl * 3 < 0) ? computeSizeUTF8_UTF16(val, doReplace) : sl * 3;
+        if (allocLen > (long)Integer.MAX_VALUE) {
+            throw new OutOfMemoryError("Required length exceeds implementation limit");
+        }
+        byte[] dst = new byte[(int) allocLen];
         while (sp < sl) {
             // ascii fast loop;
             char c = StringUTF16.getChar(val, sp);
@@ -1385,6 +1391,47 @@ public final class String
         return Arrays.copyOf(dst, dp);
     }
 
+    /**
+     * {@return the exact size required to UTF_8 encode this UTF16 string}
+     * @param val UTF16 encoded byte array
+     * @param doReplace true to replace unmappable characters
+     */
+    private static long computeSizeUTF8_UTF16(byte[] val, boolean doReplace) {
+        long dp = 0L;
+        int sp = 0;
+        int sl = val.length >> 1;
+
+        while (sp < sl) {
+            char c = StringUTF16.getChar(val, sp++);
+            if (c < 0x80) {
+                dp++;
+            } else if (c < 0x800) {
+                dp += 2;
+            } else if (Character.isSurrogate(c)) {
+                int uc = -1;
+                char c2;
+                if (Character.isHighSurrogate(c) && sp < sl &&
+                        Character.isLowSurrogate(c2 = StringUTF16.getChar(val, sp))) {
+                    uc = Character.toCodePoint(c, c2);
+                }
+                if (uc < 0) {
+                    if (doReplace) {
+                        dp++;
+                    } else {
+                        throwUnmappable(sp - 1);
+                    }
+                } else {
+                    dp += 4;
+                    sp++;  // 2 chars
+                }
+            } else {
+                // 3 bytes, 16 bits
+                dp += 3;
+            }
+        }
+        return dp;
+    }
+
     /**
      * Constructs a new {@code String} by decoding the specified array of bytes
      * using the specified {@linkplain java.nio.charset.Charset charset}.  The

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2024, 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
@@ -118,4 +118,33 @@ public class MaxSizeUTF16String {
             }
         }
     }
+
+    /*
+     * 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();
+        };
+    }
 }