--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.net.http/share/classes/java/net/http/internal/common/HttpHeadersImpl.java	Wed Feb 07 14:17:24 2018 +0000
@@ -0,0 +1,73 @@
+/*
+ * 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 java.net.http.internal.common;
+
+import java.net.http.HttpHeaders;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+
+/**
+ * Implementation of HttpHeaders.
+ */
+public class HttpHeadersImpl extends HttpHeaders {
+
+    private final TreeMap<String,List<String>> headers;
+
+    public HttpHeadersImpl() {
+        headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    @Override
+    public Map<String, List<String>> map() {
+        return Collections.unmodifiableMap(headers);
+    }
+
+    // package private mutators
+
+    public HttpHeadersImpl deepCopy() {
+        HttpHeadersImpl h1 = new HttpHeadersImpl();
+        for (Map.Entry<String,List<String>> entry : headers.entrySet()) {
+            List<String> valuesCopy = new ArrayList<>(entry.getValue());
+            h1.headers.put(entry.getKey(), valuesCopy);
+        }
+        return h1;
+    }
+
+    public void addHeader(String name, String value) {
+        headers.computeIfAbsent(name, k -> new ArrayList<>(1))
+               .add(value);
+    }
+
+    public void setHeader(String name, String value) {
+        List<String> values = new ArrayList<>(1); // most headers has one value
+        values.add(value);
+        headers.put(name, values);
+    }
+}