--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/websocket/UTF8AccumulatingDecoder.java	Wed Feb 07 21:45:37 2018 +0000
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2015, 2018, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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.
+ */
+
+package jdk.internal.net.http.websocket;
+
+import jdk.internal.net.http.common.Log;
+
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.CharsetDecoder;
+import java.nio.charset.CoderResult;
+import java.nio.charset.CodingErrorAction;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static jdk.internal.net.http.common.Utils.EMPTY_BYTEBUFFER;
+
+final class UTF8AccumulatingDecoder {
+
+    private final CharsetDecoder decoder = UTF_8.newDecoder();
+
+    {
+        decoder.onMalformedInput(CodingErrorAction.REPORT);
+        decoder.onUnmappableCharacter(CodingErrorAction.REPORT);
+    }
+
+    private ByteBuffer leftovers = EMPTY_BYTEBUFFER;
+
+    CharBuffer decode(ByteBuffer in, boolean endOfInput)
+            throws CharacterCodingException
+    {
+        ByteBuffer b;
+        int rem = leftovers.remaining();
+        if (rem != 0) {
+            // We won't need this wasteful allocation & copying when JDK-8155222
+            // has been resolved
+            b = ByteBuffer.allocate(rem + in.remaining());
+            b.put(leftovers).put(in).flip();
+        } else {
+            b = in;
+        }
+        CharBuffer out = CharBuffer.allocate(b.remaining());
+        CoderResult r = decoder.decode(b, out, endOfInput);
+        if (r.isError()) {
+            r.throwException();
+        }
+        if (b.hasRemaining()) {
+            leftovers = ByteBuffer.allocate(b.remaining()).put(b).flip();
+        } else {
+            leftovers = EMPTY_BYTEBUFFER;
+        }
+        // Since it's UTF-8, the assumption is leftovers.remaining() < 4
+        // (i.e. small). Otherwise a shared buffer should be used
+        if (!(leftovers.remaining() < 4)) {
+            Log.logError("The size of decoding leftovers is greater than expected: {0}",
+                         leftovers.remaining());
+        }
+        b.position(b.limit()); // As if we always read to the end
+        // Decoder promises that in the case of endOfInput == true:
+        // "...any remaining undecoded input will be treated as being
+        // malformed"
+        assert !(endOfInput && leftovers.hasRemaining()) : endOfInput + ", " + leftovers;
+        if (endOfInput) {
+            r = decoder.flush(out);
+            decoder.reset();
+            if (r.isOverflow()) {
+                // FIXME: for now I know flush() does nothing. But the
+                // implementation of UTF8 decoder might change. And if now
+                // flush() is a no-op, it is not guaranteed to remain so in
+                // the future
+                throw new InternalError("Not yet implemented");
+            }
+        }
+        return out.flip();
+    }
+}