/*

 * Copyright (c) 2000, 2011, 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

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 */

package sun.net.spi.nameservice.dns;

import java.lang.ref.SoftReference;

import java.net.InetAddress;

import java.net.UnknownHostException;

import javax.naming.*;

import javax.naming.directory.*;

import javax.naming.spi.NamingManager;

import java.util.*;

import sun.net.util.IPAddressUtil;

import sun.net.dns.ResolverConfiguration;

import sun.net.spi.nameservice.*;

import java.security.AccessController;

import java.security.PrivilegedAction;

/*

 * A name service provider based on JNDI-DNS.

 */

public final class DNSNameService implements NameService {

    // List of domains specified by property

    private LinkedList<String> domainList = null;

    // JNDI-DNS URL for name servers specified via property

    private String nameProviderUrl = null;

    // Per-thread soft cache of the last temporary context

    private static ThreadLocal<SoftReference<ThreadContext>> contextRef =

            new ThreadLocal<>();

    // Simple class to encapsulate the temporary context

    private static class ThreadContext {

        private DirContext dirCtxt;

        private List<String> nsList;

        public ThreadContext(DirContext dirCtxt, List<String> nsList) {

            this.dirCtxt = dirCtxt;

            this.nsList = nsList;

        }

        public DirContext dirContext() {

            return dirCtxt;

        }

        public List<String> nameservers() {

            return nsList;

        }

    }

    // Returns a per-thread DirContext

    private DirContext getTemporaryContext() throws NamingException {

        SoftReference<ThreadContext> ref = contextRef.get();

        ThreadContext thrCtxt = null;

        List<String> nsList = null;

        // if no property specified we need to obtain the list of servers

        //

        if (nameProviderUrl == null)

            nsList = ResolverConfiguration.open().nameservers();

        // if soft reference hasn't been gc'ed no property has been

        // specified then we need to check if the DNS configuration

        // has changed.

        //

        if ((ref != null) && ((thrCtxt = ref.get()) != null)) {

            if (nameProviderUrl == null) {

                if (!thrCtxt.nameservers().equals(nsList)) {

                    // DNS configuration has changed

                    thrCtxt = null;

                }

            }

        }

        // new thread context needs to be created

        if (thrCtxt == null) {

            final Hashtable<String,Object> env = new Hashtable<>();

            env.put("java.naming.factory.initial",

                    "com.sun.jndi.dns.DnsContextFactory");

            // If no nameservers property specified we create provider URL

            // based on system configured name servers

            //

            String provUrl = nameProviderUrl;

            if (provUrl == null) {

                provUrl = createProviderURL(nsList);

                if (provUrl.length() == 0) {

                    throw new RuntimeException("bad nameserver configuration");

                }

            }

            env.put("java.naming.provider.url", provUrl);

            // Need to create directory context in privileged block

            // as JNDI-DNS needs to resolve the name servers.

            //

            DirContext dirCtxt;

            try {

                dirCtxt = java.security.AccessController.doPrivileged(

                        new java.security.PrivilegedExceptionAction<DirContext>() {

                            public DirContext run() throws NamingException {

                                // Create the DNS context using NamingManager rather than using

                                // the initial context constructor. This avoids having the initial

                                // context constructor call itself.

                                Context ctx = NamingManager.getInitialContext(env);

                                if (!(ctx instanceof DirContext)) {

                                    return null; // cannot create a DNS context

                                }

                                return (DirContext)ctx;

                            }

                    });

            } catch (java.security.PrivilegedActionException pae) {

                throw (NamingException)pae.getException();

            }

            // create new soft reference to our thread context

            //

            thrCtxt = new ThreadContext(dirCtxt, nsList);

            contextRef.set(new SoftReference<ThreadContext>(thrCtxt));

        }

        return thrCtxt.dirContext();

    }

    /**

     * Resolves the specified entry in DNS.

     *

     * Canonical name records are recursively resolved (to a maximum

     * of 5 to avoid performance hit and potential CNAME loops).

     *

     * @param   ctx     JNDI directory context

     * @param   name    name to resolve

     * @param   ids     record types to search

     * @param   depth   call depth - pass as 0.

     *

     * @return  array list with results (will have at least on entry)

     *

     * @throws  UnknownHostException if lookup fails or other error.

     */

    private ArrayList<String> resolve(final DirContext ctx, final String name,

                                      final String[] ids, int depth)

            throws UnknownHostException

    {

        ArrayList<String> results = new ArrayList<>();

        Attributes attrs;

        // do the query

        try {

            attrs = java.security.AccessController.doPrivileged(

                    new java.security.PrivilegedExceptionAction<Attributes>() {

                        public Attributes run() throws NamingException {

                            return ctx.getAttributes(name, ids);

                        }

                });

        } catch (java.security.PrivilegedActionException pae) {

            throw new UnknownHostException(pae.getException().getMessage());

        }

        // non-requested type returned so enumeration is empty

        NamingEnumeration<? extends Attribute> ne = attrs.getAll();

        if (!ne.hasMoreElements()) {

            throw new UnknownHostException("DNS record not found");

        }

        // iterate through the returned attributes

        UnknownHostException uhe = null;

        try {

            while (ne.hasMoreElements()) {

                Attribute attr = ne.next();

                String attrID = attr.getID();

                for (NamingEnumeration<?> e = attr.getAll(); e.hasMoreElements();) {

                    String addr = (String)e.next();

                    // for canoncical name records do recursive lookup

                    // - also check for CNAME loops to avoid stack overflow

                    if (attrID.equals("CNAME")) {

                        if (depth > 4) {

                            throw new UnknownHostException(name + ": possible CNAME loop");

                        }

                        try {

                            results.addAll(resolve(ctx, addr, ids, depth+1));

                        } catch (UnknownHostException x) {

                            // canonical name can't be resolved.

                            if (uhe == null)

                                uhe = x;

                        }

                    } else {

                        results.add(addr);

                    }

                }

            }

        } catch (NamingException nx) {

            throw new UnknownHostException(nx.getMessage());

        }

        // pending exception as canonical name could not be resolved.

        if (results.isEmpty() && uhe != null) {

            throw uhe;

        }

        return results;

    }

    public DNSNameService() throws Exception {

        // default domain

        String domain = AccessController.doPrivileged(

            (PrivilegedAction<String>) () -> System.getProperty("sun.net.spi.nameservice.domain"));

        if (domain != null && domain.length() > 0) {

            domainList = new LinkedList<String>();

            domainList.add(domain);

        }

        // name servers

        String nameservers = AccessController.doPrivileged(

            (PrivilegedAction<String>) () -> System.getProperty("sun.net.spi.nameservice.nameservers"));

        if (nameservers != null && nameservers.length() > 0) {

            nameProviderUrl = createProviderURL(nameservers);

            if (nameProviderUrl.length() == 0) {

                throw new RuntimeException("malformed nameservers property");

            }

        } else {

            // no property specified so check host DNS resolver configured

            // with at least one nameserver in dotted notation.

            //

            List<String> nsList = ResolverConfiguration.open().nameservers();

            if (nsList.isEmpty()) {

                throw new RuntimeException("no nameservers provided");

            }

            boolean found = false;

            for (String addr: nsList) {

                if (IPAddressUtil.isIPv4LiteralAddress(addr) ||

                    IPAddressUtil.isIPv6LiteralAddress(addr)) {

                    found = true;

                    break;

                }

            }

            if (!found) {

                throw new RuntimeException("bad nameserver configuration");

            }

        }

    }

    public InetAddress[] lookupAllHostAddr(String host) throws UnknownHostException {

        // DNS records that we search for

        String[] ids = {"A", "AAAA", "CNAME"};

        // first get directory context

        DirContext ctx;

        try {

            ctx = getTemporaryContext();

        } catch (NamingException nx) {

            throw new Error(nx);

        }

        ArrayList<String> results = null;

        UnknownHostException uhe = null;

        // If host already contains a domain name then just look it up

        if (host.indexOf('.') >= 0) {

            try {

                results = resolve(ctx, host, ids, 0);

            } catch (UnknownHostException x) {

                uhe = x;

            }

        }

        // Here we try to resolve the host using the domain suffix or

        // the domain suffix search list. If the host cannot be resolved

        // using the domain suffix then we attempt devolution of

        // the suffix - eg: if we are searching for "foo" and our

        // domain suffix is "eng.sun.com" we will try to resolve

        // "foo.eng.sun.com" and "foo.sun.com".

        // It's not normal to attempt devolation with domains on the

        // domain suffix search list - however as ResolverConfiguration

        // doesn't distinguish domain or search list in the list it

        // returns we approximate by doing devolution on the domain

        // suffix if the list has one entry.

        if (results == null) {

            List<String> searchList = null;

            Iterator<String> i;

            boolean usingSearchList = false;

            if (domainList != null) {

                i = domainList.iterator();

            } else {

                searchList = ResolverConfiguration.open().searchlist();

                if (searchList.size() > 1) {

                    usingSearchList = true;

                }

                i = searchList.iterator();

            }

            // iterator through each domain suffix

            while (i.hasNext()) {

                String parentDomain = i.next();

                int start = 0;

                while ((start = parentDomain.indexOf('.')) != -1

                       && start < parentDomain.length() -1) {

                    try {

                        results = resolve(ctx, host+"."+parentDomain, ids, 0);

                        break;

                    } catch (UnknownHostException x) {

                        uhe = x;

                        if (usingSearchList) {

                            break;

                        }

                        // devolve

                        parentDomain = parentDomain.substring(start+1);

                    }

                }

                if (results != null) {

                    break;

                }

            }

        }

        // finally try the host if it doesn't have a domain name

        if (results == null && (host.indexOf('.') < 0)) {

            results = resolve(ctx, host, ids, 0);

        }

        // if not found then throw the (last) exception thrown.

        if (results == null) {

            assert uhe != null;

            throw uhe;

        }

        /**

         * Convert the array list into a byte aray list - this

         * filters out any invalid IPv4/IPv6 addresses.

         */

        assert results.size() > 0;

        InetAddress[] addrs = new InetAddress[results.size()];

        int count = 0;

        for (int i=0; i<results.size(); i++) {

            String addrString = results.get(i);

            byte addr[] = IPAddressUtil.textToNumericFormatV4(addrString);

            if (addr == null) {

                addr = IPAddressUtil.textToNumericFormatV6(addrString);

            }

            if (addr != null) {

                addrs[count++] = InetAddress.getByAddress(host, addr);

            }

        }

        /**

         * If addresses are filtered then we need to resize the

         * array. Additionally if all addresses are filtered then

         * we throw an exception.

         */

        if (count == 0) {

            throw new UnknownHostException(host + ": no valid DNS records");

        }

        if (count < results.size()) {

            InetAddress[] tmp = new InetAddress[count];

            for (int i=0; i<count; i++) {

                tmp[i] = addrs[i];

            }

            addrs = tmp;

        }

        return addrs;

    }

    /**

     * Reverse lookup code. I.E: find a host name from an IP address.

     * IPv4 addresses are mapped in the IN-ADDR.ARPA. top domain, while

     * IPv6 addresses can be in IP6.ARPA or IP6.INT.

     * In both cases the address has to be converted into a dotted form.

     */

    public String getHostByAddr(byte[] addr) throws UnknownHostException {

        String host = null;

        try {

            String literalip = "";

            String[] ids = { "PTR" };

            DirContext ctx;

            ArrayList<String> results = null;

            try {

                ctx = getTemporaryContext();

            } catch (NamingException nx) {

                throw new Error(nx);

            }

            if (addr.length == 4) { // IPv4 Address

                for (int i = addr.length-1; i >= 0; i--) {

                    literalip += (addr[i] & 0xff) +".";

                }

                literalip += "IN-ADDR.ARPA.";

                results = resolve(ctx, literalip, ids, 0);

                host = results.get(0);

            } else if (addr.length == 16) { // IPv6 Address

                /**

                 * 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

                 */

                for (int i = addr.length-1; i >= 0; i--) {

                    literalip += Integer.toHexString((addr[i] & 0x0f)) +"."

                        +Integer.toHexString((addr[i] & 0xf0) >> 4) +".";

                }

                String ip6lit = literalip + "IP6.ARPA.";

                try {

                    results = resolve(ctx, ip6lit, ids, 0);

                    host = results.get(0);

                } catch (UnknownHostException e) {

                    host = null;

                }

                if (host == null) {

                    // IP6.ARPA lookup failed, let's try the older IP6.INT

                    ip6lit = literalip + "IP6.INT.";

                    results = resolve(ctx, ip6lit, ids, 0);

                    host = results.get(0);

                }

            }

        } catch (Exception e) {

            throw new UnknownHostException(e.getMessage());

        }

        // Either we couldn't find it or the address was neither IPv4 or IPv6

        if (host == null)

            throw new UnknownHostException();

        // remove trailing dot

        if (host.endsWith(".")) {

            host = host.substring(0, host.length() - 1);

        }

        return host;

    }

    // ---------

    private static void appendIfLiteralAddress(String addr, StringBuilder sb) {

        if (IPAddressUtil.isIPv4LiteralAddress(addr)) {

            sb.append("dns://").append(addr).append(' ');

        } else {

            if (IPAddressUtil.isIPv6LiteralAddress(addr)) {

                sb.append("dns://[").append(addr).append("] ");

            }

        }

    }

    /*

     * @return String containing the JNDI-DNS provider URL

     *         corresponding to the supplied List of nameservers.

     */

    private static String createProviderURL(List<String> nsList) {

        StringBuilder sb = new StringBuilder();

        for (String s: nsList) {

            appendIfLiteralAddress(s, sb);

        }

        return sb.toString();

    }

    /*

     * @return String containing the JNDI-DNS provider URL

     *         corresponding to the list of nameservers

     *         contained in the provided str.

     */

    private static String createProviderURL(String str) {

        StringBuilder sb = new StringBuilder();

        StringTokenizer st = new StringTokenizer(str, ",");

        while (st.hasMoreTokens()) {

            appendIfLiteralAddress(st.nextToken(), sb);

        }

        return sb.toString();

    }

}