8292043: Incorrect decoding near EOF for stateful decoders like UTF-16

Reviewed-by: joehw, alanb, lancea

Author: naotoj

src/java.base/share/classes/sun/nio/cs/StreamDecoder.java

@@ -378,7 +378,6 @@ int implRead(char[] cbuf, int off, int end) throws IOException {
                     eof = true;
                     if ((cb.position() == 0) && (!bb.hasRemaining()))
                         break;
-                    decoder.reset();
                 }
                 continue;
             }

test/jdk/java/io/InputStreamReader/StatefulDecoderNearEOF.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2022, 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.
+ */
+
+/* @test
+ * @bug 8292043
+ * @run testng StatefulDecoderNearEOF
+ * @summary Check MalformedInputException is thrown with stateful decoders
+ *      with malformed input before EOF
+ */
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.UncheckedIOException;
+import java.nio.charset.CodingErrorAction;
+import java.nio.charset.MalformedInputException;
+import java.nio.charset.StandardCharsets;
+import java.util.stream.IntStream;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertThrows;
+
+@Test
+public class StatefulDecoderNearEOF {
+
+    @DataProvider
+    public Object[][] inputs() {
+        return new Object[][] {
+            // BOM, followed by High surrogate (in UTF-16LE).
+            // First read() should throw an exception.
+            {new byte[] {(byte)0xff, (byte)0xfe, 0, (byte)0xd8}, 0},
+
+            // BOM, followed by 'A', 'B', 'C', then by High surrogate (in UTF-16LE).
+            // Fourth read() should throw an exception.
+            {new byte[] {(byte)0xff, (byte)0xfe, (byte)0x41, 0, (byte)0x42, 0, (byte)0x43, 0, 0, (byte)0xd8}, 3},
+        };
+    }
+
+    @Test (dataProvider = "inputs")
+    public void testStatefulDecoderNearEOF(byte[] ba, int numSucessReads) throws IOException {
+        try (var r = new InputStreamReader(
+                new ByteArrayInputStream(ba),
+                StandardCharsets.UTF_16.newDecoder().onMalformedInput(CodingErrorAction.REPORT))) {
+            // Issue read() as many as numSucessReads which should not fail
+            IntStream.rangeClosed(1, numSucessReads).forEach(i -> {
+                try {
+                    assertEquals(r.read(), (int)ba[i * 2]);
+                } catch (IOException e) {
+                    throw new UncheckedIOException(e);
+                }
+            });
+
+            // Final dangling high surrogate should throw an exception
+            assertThrows(MalformedInputException.class, () -> r.read());
+        }
+    }
+}