// SPDX-License-Identifier: BSD-3-Clause
// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
package org.xbill.DNS.tools;

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.InterruptedIOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
import org.xbill.DNS.Address;
import org.xbill.DNS.CNAMERecord;
import org.xbill.DNS.Cache;
import org.xbill.DNS.Credibility;
import org.xbill.DNS.DClass;
import org.xbill.DNS.DNAMERecord;
import org.xbill.DNS.ExtendedFlags;
import org.xbill.DNS.Flags;
import org.xbill.DNS.Header;
import org.xbill.DNS.Message;
import org.xbill.DNS.Name;
import org.xbill.DNS.NameTooLongException;
import org.xbill.DNS.OPTRecord;
import org.xbill.DNS.Opcode;
import org.xbill.DNS.RRset;
import org.xbill.DNS.Rcode;
import org.xbill.DNS.Record;
import org.xbill.DNS.Section;
import org.xbill.DNS.SetResponse;
import org.xbill.DNS.TSIG;
import org.xbill.DNS.TSIGRecord;
import org.xbill.DNS.Type;
import org.xbill.DNS.Zone;
import org.xbill.DNS.ZoneTransferException;

/**
 * A very basic implementation of a DNS server.
 *
 * @author Brian Wellington &lt;bwelling@xbill.org&gt;
 */
public class jnamed {

  static final int FLAG_DNSSECOK = 1;
  static final int FLAG_SIGONLY = 2;

  Map<Integer, Cache> caches;
  Map<Name, Zone> znames;
  Map<Name, TSIG> TSIGs;

  private static String addrport(InetAddress addr, int port) {
    return addr.getHostAddress() + "#" + port;
  }

  public jnamed(String conffile) throws IOException, ZoneTransferException {
    FileInputStream fs;
    InputStreamReader isr;
    BufferedReader br;
    List<Integer> ports = new ArrayList<>();
    List<InetAddress> addresses = new ArrayList<>();
    try {
      fs = new FileInputStream(conffile);
      isr = new InputStreamReader(fs);
      br = new BufferedReader(isr);
    } catch (Exception e) {
      System.out.println("Cannot open " + conffile);
      return;
    }

    try {
      caches = new HashMap<>();
      znames = new HashMap<>();
      TSIGs = new HashMap<>();

      String line;
      while ((line = br.readLine()) != null) {
        StringTokenizer st = new StringTokenizer(line);
        if (!st.hasMoreTokens()) {
          continue;
        }
        String keyword = st.nextToken();
        if (!st.hasMoreTokens()) {
          System.out.println("Invalid line: " + line);
          continue;
        }
        if (keyword.charAt(0) == '#') {
          continue;
        }
        switch (keyword) {
          case "primary":
            addPrimaryZone(st.nextToken(), st.nextToken());
            break;
          case "secondary":
            addSecondaryZone(st.nextToken(), st.nextToken());
            break;
          case "cache":
            Cache cache = new Cache(st.nextToken());
            caches.put(DClass.IN, cache);
            break;
          case "key":
            String s1 = st.nextToken();
            String s2 = st.nextToken();
            if (st.hasMoreTokens()) {
              addTSIG(s1, s2, st.nextToken());
            } else {
              addTSIG("hmac-md5", s1, s2);
            }
            break;
          case "port":
            ports.add(Integer.valueOf(st.nextToken()));
            break;
          case "address":
            String addr = st.nextToken();
            addresses.add(Address.getByAddress(addr));
            break;
          default:
            System.out.println("unknown keyword: " + keyword);
            break;
        }
      }

      if (ports.isEmpty()) {
        ports.add(53);
      }

      if (addresses.isEmpty()) {
        addresses.add(Address.getByAddress("0.0.0.0"));
      }

      for (InetAddress address : addresses) {
        for (Integer o : ports) {
          int port = o;
          addUDP(address, port);
          addTCP(address, port);
          System.out.println("jnamed: listening on " + addrport(address, port));
        }
      }
      System.out.println("jnamed: running");
    } finally {
      br.close();
    }
  }

  public void addPrimaryZone(String zname, String zonefile) throws IOException {
    Name origin = null;
    if (zname != null) {
      origin = Name.fromString(zname, Name.root);
    }
    Zone newzone = new Zone(origin, zonefile);
    znames.put(newzone.getOrigin(), newzone);
  }

  public void addSecondaryZone(String zone, String remote)
      throws IOException, ZoneTransferException {
    Name zname = Name.fromString(zone, Name.root);
    Zone newzone = new Zone(zname, DClass.IN, remote);
    znames.put(zname, newzone);
  }

  public void addTSIG(String algstr, String namestr, String key) throws IOException {
    Name name = Name.fromString(namestr, Name.root);
    TSIGs.put(name, new TSIG(algstr, namestr, key));
  }

  public Cache getCache(int dclass) {
    return caches.computeIfAbsent(dclass, Cache::new);
  }

  public Zone findBestZone(Name name) {
    Zone foundzone;
    foundzone = znames.get(name);
    if (foundzone != null) {
      return foundzone;
    }
    int labels = name.labels();
    for (int i = 1; i < labels; i++) {
      Name tname = new Name(name, i);
      foundzone = znames.get(tname);
      if (foundzone != null) {
        return foundzone;
      }
    }
    return null;
  }

  public RRset findExactMatch(Name name, int type, int dclass, boolean glue) {
    Zone zone = findBestZone(name);
    if (zone != null) {
      return zone.findExactMatch(name, type);
    } else {
      List<RRset> rrsets;
      Cache cache = getCache(dclass);
      if (glue) {
        rrsets = cache.findAnyRecords(name, type);
      } else {
        rrsets = cache.findRecords(name, type);
      }
      if (rrsets == null) {
        return null;
      } else {
        return rrsets.get(0); /* not quite right */
      }
    }
  }

  void addRRset(Name name, Message response, RRset rrset, int section, int flags) {
    for (int s = 1; s <= section; s++) {
      if (response.findRRset(name, rrset.getType(), s)) {
        return;
      }
    }
    if ((flags & FLAG_SIGONLY) == 0) {
      for (Record r : rrset.rrs()) {
        if (r.getName().isWild() && !name.isWild()) {
          r = r.withName(name);
        }
        response.addRecord(r, section);
      }
    }
    if ((flags & (FLAG_SIGONLY | FLAG_DNSSECOK)) != 0) {
      for (Record r : rrset.sigs()) {
        if (r.getName().isWild() && !name.isWild()) {
          r = r.withName(name);
        }
        response.addRecord(r, section);
      }
    }
  }

  private void addSOA(Message response, Zone zone) {
    response.addRecord(zone.getSOA(), Section.AUTHORITY);
  }

  private void addNS(Message response, Zone zone, int flags) {
    RRset nsRecords = zone.getNS();
    addRRset(nsRecords.getName(), response, nsRecords, Section.AUTHORITY, flags);
  }

  private void addCacheNS(Message response, Cache cache, Name name) {
    SetResponse sr = cache.lookupRecords(name, Type.NS, Credibility.HINT);
    if (!sr.isDelegation()) {
      return;
    }
    RRset nsRecords = sr.getNS();
    for (Record r : nsRecords.rrs()) {
      response.addRecord(r, Section.AUTHORITY);
    }
  }

  private void addGlue(Message response, Name name, int flags) {
    RRset a = findExactMatch(name, Type.A, DClass.IN, true);
    if (a == null) {
      return;
    }
    addRRset(name, response, a, Section.ADDITIONAL, flags);
  }

  private void addAdditional2(Message response, int section, int flags) {
    for (Record r : response.getSection(section)) {
      Name glueName = r.getAdditionalName();
      if (glueName != null) {
        addGlue(response, glueName, flags);
      }
    }
  }

  private void addAdditional(Message response, int flags) {
    addAdditional2(response, Section.ANSWER, flags);
    addAdditional2(response, Section.AUTHORITY, flags);
  }

  byte addAnswer(Message response, Name name, int type, int dclass, int iterations, int flags) {
    SetResponse sr;
    byte rcode = Rcode.NOERROR;

    if (iterations > 6) {
      return Rcode.NOERROR;
    }

    if (type == Type.SIG || type == Type.RRSIG) {
      type = Type.ANY;
      flags |= FLAG_SIGONLY;
    }

    Zone zone = findBestZone(name);
    if (zone != null) {
      sr = zone.findRecords(name, type);
    } else {
      Cache cache = getCache(dclass);
      sr = cache.lookupRecords(name, type, Credibility.NORMAL);
    }

    if (sr.isUnknown()) {
      addCacheNS(response, getCache(dclass), name);
    }
    if (sr.isNXDOMAIN()) {
      response.getHeader().setRcode(Rcode.NXDOMAIN);
      if (zone != null) {
        addSOA(response, zone);
        if (iterations == 0) {
          response.getHeader().setFlag(Flags.AA);
        }
      }
      rcode = Rcode.NXDOMAIN;
    } else if (sr.isNXRRSET()) {
      if (zone != null) {
        addSOA(response, zone);
        if (iterations == 0) {
          response.getHeader().setFlag(Flags.AA);
        }
      }
    } else if (sr.isDelegation()) {
      RRset nsRecords = sr.getNS();
      addRRset(nsRecords.getName(), response, nsRecords, Section.AUTHORITY, flags);
    } else if (sr.isCNAME()) {
      CNAMERecord cname = sr.getCNAME();
      RRset rrset = new RRset(cname);
      addRRset(name, response, rrset, Section.ANSWER, flags);
      if (zone != null && iterations == 0) {
        response.getHeader().setFlag(Flags.AA);
      }
      rcode = addAnswer(response, cname.getTarget(), type, dclass, iterations + 1, flags);
    } else if (sr.isDNAME()) {
      DNAMERecord dname = sr.getDNAME();
      RRset rrset = new RRset(dname);
      addRRset(name, response, rrset, Section.ANSWER, flags);
      Name newname;
      try {
        newname = name.fromDNAME(dname);
      } catch (NameTooLongException e) {
        return Rcode.YXDOMAIN;
      }

      CNAMERecord cname = new CNAMERecord(name, dclass, 0, newname);
      RRset cnamerrset = new RRset(cname);
      addRRset(name, response, cnamerrset, Section.ANSWER, flags);
      if (zone != null && iterations == 0) {
        response.getHeader().setFlag(Flags.AA);
      }
      rcode = addAnswer(response, newname, type, dclass, iterations + 1, flags);
    } else if (sr.isSuccessful()) {
      List<RRset> rrsets = sr.answers();
      for (RRset rrset : rrsets) {
        addRRset(name, response, rrset, Section.ANSWER, flags);
      }
      if (zone != null) {
        addNS(response, zone, flags);
        if (iterations == 0) {
          response.getHeader().setFlag(Flags.AA);
        }
      } else {
        addCacheNS(response, getCache(dclass), name);
      }
    }
    return rcode;
  }

  byte[] doAXFR(Name name, Message query, TSIG tsig, TSIGRecord qtsig, Socket s) {
    Zone zone = znames.get(name);
    boolean first = true;
    if (zone == null) {
      return errorMessage(query, Rcode.REFUSED);
    }
    try {
      DataOutputStream dataOut;
      dataOut = new DataOutputStream(s.getOutputStream());
      int id = query.getHeader().getID();
      Iterator<RRset> it = zone.AXFR();
      while (it.hasNext()) {
        RRset rrset = it.next();
        Message response = new Message(id);
        Header header = response.getHeader();
        header.setFlag(Flags.QR);
        header.setFlag(Flags.AA);
        addRRset(rrset.getName(), response, rrset, Section.ANSWER, FLAG_DNSSECOK);
        if (tsig != null) {
          tsig.apply(response, qtsig, first);
          qtsig = response.getTSIG();
        }
        first = false;
        byte[] out = response.toWire();
        dataOut.writeShort(out.length);
        dataOut.write(out);
      }
    } catch (IOException ex) {
      System.out.println("AXFR failed");
    }
    try {
      s.close();
    } catch (IOException ex) {
      // ignore
    }
    return null;
  }

  /*
   * Note: a null return value means that the caller doesn't need to do
   * anything.  Currently this only happens if this is an AXFR request over
   * TCP.
   */
  byte[] generateReply(Message query, byte[] in, Socket s) {
    Header header;
    int maxLength;
    int flags = 0;

    header = query.getHeader();
    if (header.getFlag(Flags.QR)) {
      return null;
    }
    if (header.getRcode() != Rcode.NOERROR) {
      return errorMessage(query, Rcode.FORMERR);
    }
    if (header.getOpcode() != Opcode.QUERY) {
      return errorMessage(query, Rcode.NOTIMP);
    }

    Record queryRecord = query.getQuestion();

    TSIGRecord queryTSIG = query.getTSIG();
    TSIG tsig = null;
    if (queryTSIG != null) {
      tsig = TSIGs.get(queryTSIG.getName());
      if (tsig == null || tsig.verify(query, in, null) != Rcode.NOERROR) {
        return formerrMessage(in);
      }
    }

    OPTRecord queryOPT = query.getOPT();
    if (s != null) {
      maxLength = 65535;
    } else if (queryOPT != null) {
      maxLength = Math.max(queryOPT.getPayloadSize(), 512);
    } else {
      maxLength = 512;
    }

    if (queryOPT != null && (queryOPT.getFlags() & ExtendedFlags.DO) != 0) {
      flags = FLAG_DNSSECOK;
    }

    Message response = new Message(query.getHeader().getID());
    response.getHeader().setFlag(Flags.QR);
    if (query.getHeader().getFlag(Flags.RD)) {
      response.getHeader().setFlag(Flags.RD);
    }
    response.addRecord(queryRecord, Section.QUESTION);

    Name name = queryRecord.getName();
    int type = queryRecord.getType();
    int dclass = queryRecord.getDClass();
    if (type == Type.AXFR && s != null) {
      return doAXFR(name, query, tsig, queryTSIG, s);
    }
    if (!Type.isRR(type) && type != Type.ANY) {
      return errorMessage(query, Rcode.NOTIMP);
    }

    byte rcode = addAnswer(response, name, type, dclass, 0, flags);
    if (rcode != Rcode.NOERROR && rcode != Rcode.NXDOMAIN) {
      return errorMessage(query, rcode);
    }

    addAdditional(response, flags);

    if (queryOPT != null) {
      int optflags = (flags == FLAG_DNSSECOK) ? ExtendedFlags.DO : 0;
      OPTRecord opt = new OPTRecord((short) 4096, rcode, (byte) 0, optflags);
      response.addRecord(opt, Section.ADDITIONAL);
    }

    response.setTSIG(tsig, Rcode.NOERROR, queryTSIG);
    return response.toWire(maxLength);
  }

  byte[] buildErrorMessage(Header header, int rcode, Record question) {
    Message response = new Message();
    response.setHeader(header);
    for (int i = 0; i < 4; i++) {
      response.removeAllRecords(i);
    }
    if (rcode == Rcode.SERVFAIL) {
      response.addRecord(question, Section.QUESTION);
    }
    header.setRcode(rcode);
    return response.toWire();
  }

  public byte[] formerrMessage(byte[] in) {
    Header header;
    try {
      header = new Header(in);
    } catch (IOException e) {
      return null;
    }
    return buildErrorMessage(header, Rcode.FORMERR, null);
  }

  public byte[] errorMessage(Message query, int rcode) {
    return buildErrorMessage(query.getHeader(), rcode, query.getQuestion());
  }

  public void TCPclient(Socket s) {
    try (InputStream is = s.getInputStream()) {
      int inLength;
      DataInputStream dataIn;
      DataOutputStream dataOut;
      byte[] in;

      dataIn = new DataInputStream(is);
      inLength = dataIn.readUnsignedShort();
      in = new byte[inLength];
      dataIn.readFully(in);

      Message query;
      byte[] response;
      try {
        query = new Message(in);
        response = generateReply(query, in, s);
        if (response == null) {
          return;
        }
      } catch (IOException e) {
        response = formerrMessage(in);
      }
      dataOut = new DataOutputStream(s.getOutputStream());
      dataOut.writeShort(response.length);
      dataOut.write(response);
    } catch (IOException e) {
      System.out.println(
          "TCPclient(" + addrport(s.getLocalAddress(), s.getLocalPort()) + "): " + e);
    }
  }

  public void serveTCP(InetAddress addr, int port) {
    try (ServerSocket sock = new ServerSocket(port, 128, addr)) {
      while (true) {
        final Socket s = sock.accept();
        Thread t;
        t = new Thread(() -> TCPclient(s));
        t.start();
      }
    } catch (IOException e) {
      System.out.println("serveTCP(" + addrport(addr, port) + "): " + e);
    }
  }

  public void serveUDP(InetAddress addr, int port) {
    try (DatagramSocket sock = new DatagramSocket(port, addr)) {
      final short udpLength = 512;
      byte[] in = new byte[udpLength];
      DatagramPacket indp = new DatagramPacket(in, in.length);
      DatagramPacket outdp = null;
      while (true) {
        indp.setLength(in.length);
        try {
          sock.receive(indp);
        } catch (InterruptedIOException e) {
          continue;
        }
        Message query;
        byte[] response;
        try {
          query = new Message(in);
          response = generateReply(query, in, null);
          if (response == null) {
            continue;
          }
        } catch (IOException e) {
          response = formerrMessage(in);
        }
        if (outdp == null) {
          outdp = new DatagramPacket(response, response.length, indp.getAddress(), indp.getPort());
        } else {
          outdp.setData(response);
          outdp.setLength(response.length);
          outdp.setAddress(indp.getAddress());
          outdp.setPort(indp.getPort());
        }
        sock.send(outdp);
      }
    } catch (IOException e) {
      System.out.println("serveUDP(" + addrport(addr, port) + "): " + e);
    }
  }

  public void addTCP(final InetAddress addr, final int port) {
    Thread t = new Thread(() -> serveTCP(addr, port));
    t.start();
  }

  public void addUDP(final InetAddress addr, final int port) {
    Thread t = new Thread(() -> serveUDP(addr, port));
    t.start();
  }

  public static void main(String[] args) {
    if (args.length > 1) {
      System.out.println("usage: jnamed [conf]");
      System.exit(0);
    }

    try {
      String conf;
      if (args.length == 1) {
        conf = args[0];
      } else {
        conf = "jnamed.conf";
      }
      new jnamed(conf);
    } catch (IOException | ZoneTransferException e) {
      System.out.println(e);
    }
  }
}
