diff -r 6c11b48a0695 -r d23b02f37fce src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/internal/ImmutableHeaders.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.incubator.httpclient/share/classes/jdk/incubator/http/internal/ImmutableHeaders.java	Tue Feb 06 14:10:28 2018 +0000
@@ -0,0 +1,94 @@
+/*
+ * 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.incubator.http.internal;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.function.BiPredicate;
+import java.util.function.Predicate;
+import jdk.incubator.http.HttpHeaders;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.unmodifiableList;
+import static java.util.Collections.unmodifiableMap;
+import static java.util.Objects.requireNonNull;
+
+final class ImmutableHeaders extends HttpHeaders {
+
+    private final Map<String, List<String>> map;
+
+    public static ImmutableHeaders empty() {
+        return of(emptyMap());
+    }
+
+    public static ImmutableHeaders of(Map<String, List<String>> src) {
+        return of(src, x -> true);
+    }
+
+    public static ImmutableHeaders of(HttpHeaders headers) {
+        return (headers instanceof ImmutableHeaders)
+                ? (ImmutableHeaders)headers
+                : of(headers.map());
+    }
+
+    public static ImmutableHeaders of(Map<String, List<String>> src,
+                                      Predicate<? super String> keyAllowed) {
+        requireNonNull(src, "src");
+        requireNonNull(keyAllowed, "keyAllowed");
+        return new ImmutableHeaders(src, headerAllowed(keyAllowed));
+    }
+
+    public static ImmutableHeaders of(Map<String, List<String>> src,
+                                      BiPredicate<? super String, ? super List<String>> headerAllowed) {
+        requireNonNull(src, "src");
+        requireNonNull(headerAllowed, "headerAllowed");
+        return new ImmutableHeaders(src, headerAllowed);
+    }
+
+    private ImmutableHeaders(Map<String, List<String>> src,
+                             BiPredicate<? super String, ? super List<String>> headerAllowed) {
+        Map<String, List<String>> m = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+        src.entrySet().stream()
+                .filter(e -> headerAllowed.test(e.getKey(), e.getValue()))
+                .forEach(e ->
+                        {
+                            List<String> values = new ArrayList<>(e.getValue());
+                            m.put(e.getKey(), unmodifiableList(values));
+                        }
+                );
+        this.map = unmodifiableMap(m);
+    }
+
+    private static BiPredicate<String, List<String>> headerAllowed(Predicate<? super String> keyAllowed) {
+        return (n,v) -> keyAllowed.test(n);
+    }
+
+    @Override
+    public Map<String, List<String>> map() {
+        return map;
+    }
+}