--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.dns.client/share/classes/jdk/dns/client/internal/DnsResolver.java	Thu Nov 07 18:46:06 2019 +0000
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2019, 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.dns.client.internal;
+
+import jdk.dns.client.ex.DnsResolverException;
+import jdk.dns.conf.DnsResolverConfiguration;
+
+import java.net.InetAddress;
+import java.security.PrivilegedAction;
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+
+public class DnsResolver implements AutoCloseable {
+    private DnsClient dnsClient;
+
+    /*
+     * Constructs a new Resolver given package oracle.dns.client.standalone;its servers and timeout parameters.
+     * Each server is of the form "server[:port]".
+     * IPv6 literal host names include delimiting brackets.
+     * There must be at least one server.
+     * "timeout" is the initial timeout interval (in ms) for UDP queries,
+     * and "retries" gives the number of retries per server.
+     */
+    public DnsResolver() {
+        dnsClient = new DnsClient(dnsResolverConfiguration.nameservers(), 1000, 4);
+    }
+
+    @Override
+    public void close() {
+        dnsClient.close();
+        dnsClient = null;
+    }
+
+    public Set<String> getDomainsSearchList() {
+        var domainsToSearch = new LinkedHashSet<String>();
+        var domain = dnsResolverConfiguration.domain();
+        // First, try the domain
+        if (!domain.isBlank()) {
+            domainsToSearch.add(domain);
+        }
+        // Then iterate over the search list
+        domainsToSearch.addAll(dnsResolverConfiguration.searchlist());
+        if (DEBUG) {
+            System.out.printf("Domains search list:%s%n", domainsToSearch);
+        }
+        return domainsToSearch;
+    }
+
+    /*
+     * Queries resource records of a particular class and type for a
+     * given domain name.
+     * Useful values of rrtype are ResourceRecord.[Q]TYPE_xxx.
+     */
+    public ResourceRecords query(String fqdn, int rrtype)
+            throws DnsResolverException {
+        return dnsClient.query(new DnsName(fqdn), ResourceRecord.CLASS_INTERNET, rrtype, true, false);
+    }
+
+    public List<String> rlookup(String literalIP, InetAddress address) throws DnsResolverException {
+
+        switch (AddressFamily.fromInetAddress(address)) {
+            case IPv4:
+                return ipv4rlookup(literalIP);
+            case IPv6:
+                return ipv6rlookup(literalIP);
+            default:
+                throw new RuntimeException("Only IPv4 and IPv6 addresses are supported");
+        }
+    }
+
+    private List<String> ipv4rlookup(String literalIP) throws DnsResolverException {
+        var request = literalIP + "IN-ADDR.ARPA.";
+        var hostNames = new ArrayList<String>();
+        var rrs = query(request, ResourceRecord.TYPE_PTR);
+        for (int i = 0; i < rrs.answer.size(); i++) {
+            ResourceRecord rr = rrs.answer.elementAt(i);
+            hostNames.add(rr.getRdata().toString());
+        }
+        return hostNames;
+    }
+
+    private List<String> ipv6rlookup(String literalIP) throws DnsResolverException {
+        List<String> hostNames = new ArrayList<>();
+        ResourceRecords rrs = query(literalIP + "IP6.ARPA.", ResourceRecord.TYPE_PTR);
+        /**
+         * Because RFC 3152 changed the root domain name for reverse
+         * lookups from IP6.INT. to IP6.ARPA., we need to check
+         * both. I.E. first the new one, IP6.ARPA, then if it fails
+         * the older one, IP6.INT
+         */
+        if (rrs.answer.isEmpty()) {
+            rrs = query(literalIP + "IP6.INT.", ResourceRecord.TYPE_PTR);
+        }
+        for (int i = 0; i < rrs.answer.size(); i++) {
+            ResourceRecord rr = rrs.answer.elementAt(i);
+            hostNames.add(rr.getRdata().toString());
+        }
+        return hostNames;
+    }
+
+
+    // Configuration file tracker
+    private static DnsResolverConfiguration dnsResolverConfiguration = new DnsResolverConfiguration();
+    private static final boolean DEBUG = java.security.AccessController.doPrivileged(
+            (PrivilegedAction<Boolean>) () -> Boolean.getBoolean("jdk.dns.client.debug"));
+}