6415373: (cs) UnicodeEncoder emits BOM when there are no bytes to encode

Summary: no BOM output if no byte to encode
Reviewed-by: alanb

src/share/classes/sun/nio/cs/UTF_32Coder.java

@@ -144,7 +144,7 @@ class UTF_32Coder {
 
         protected CoderResult encodeLoop(CharBuffer src, ByteBuffer dst) {
             int mark = src.position();
-            if (!doneBOM) {
+            if (!doneBOM && src.hasRemaining()) {
                 if (dst.remaining() < 4)
                     return CoderResult.OVERFLOW;
                 put(BOM_BIG, dst);

src/share/classes/sun/nio/cs/UnicodeEncoder.java

@@ -70,13 +70,12 @@ public abstract class UnicodeEncoder extends CharsetEncoder {
     protected CoderResult encodeLoop(CharBuffer src, ByteBuffer dst) {
         int mark = src.position();
 
-        if (needsMark) {
+        if (needsMark && src.hasRemaining()) {
             if (dst.remaining() < 2)
                 return CoderResult.OVERFLOW;
             put(BYTE_ORDER_MARK, dst);
             needsMark = false;
         }
-
         try {
             while (src.hasRemaining()) {
                 char c = src.get();

test/sun/nio/cs/EncodingNothing.java

+/*
+ * Copyright (c) 2010, 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 6415373
+ * @summary Encoding nothing should output nothing
+ */
+
+import java.io.*;
+import java.nio.charset.*;
+
+public class EncodingNothing {
+
+    public static void main(String[] args) throws Throwable {
+        int failed = 0;
+        for (Charset cs : Charset.availableCharsets().values()) {
+            if (! cs.canEncode())
+                continue;
+            System.out.printf("%s: ", cs.name());
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            OutputStreamWriter osw = new OutputStreamWriter(baos, cs);
+            osw.close();
+            if (baos.size() != 0) {
+                System.out.printf(" Failed:  output bytes=%d", baos.size());
+                failed++;
+            }
+            System.out.println();
+        }
+        if (failed != 0)
+            throw new AssertionError("Some tests failed");
+    }
+}