/*

 * 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

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package jdk.dns.client.internal;

import jdk.dns.client.ex.DnsCommunicationException;

import jdk.dns.client.ex.DnsInvalidNameException;

import java.io.IOException;

import java.nio.charset.StandardCharsets;

/**

 * The ResourceRecord class represents a DNS resource record.

 * The string format is based on the master file representation in

 * RFC 1035.

 *

 * @author Scott Seligman

 */

public class ResourceRecord {

    /*

     * Resource record type codes

     */

    public static final int TYPE_A = 1;

    public static final int TYPE_CNAME = 5;

    public static final int TYPE_AAAA = 28;

    public static final int TYPE_PTR = 12;

    static final int QTYPE_STAR = 255;          // query type "*"

    private static final int TYPE_NS = 2;

    private static final int TYPE_SOA = 6;

    private static final int TYPE_HINFO = 13;

    private static final int TYPE_MX = 15;

    private static final int TYPE_TXT = 16;

    private static final int TYPE_SRV = 33;

    private static final int TYPE_NAPTR = 35;

    //static final int QTYPE_AXFR = 252;          // zone transfer //Do not want to support that

    /*

     * Mapping from resource record type codes to type name strings.

     */

    private static final String[] rrTypeNames = {

            null, "A", "NS", null, null,

            "CNAME", "SOA", null, null, null,

            null, null, "PTR", "HINFO", null,

            "MX", "TXT", null, null, null,

            null, null, null, null, null,

            null, null, null, "AAAA", null,

            null, null, null, "SRV", null,

            "NAPTR"

    };

    /*

     * Resource record class codes

     */

    public static final int CLASS_INTERNET = 1;

    static final int QCLASS_STAR = 255;      // query class "*"

    /*

     * Mapping from resource record type codes to class name strings.

     */

    private static final String[] rrClassNames = {

            null, "IN"

    };

    /*

     * Maximum number of compression references in labels.

     * Used to detect compression loops.

     */

    private static final int MAXIMUM_COMPRESSION_REFERENCES = 16;

    byte[] msg;                 // DNS message

    int msgLen;                 // msg size (in octets)

    boolean qSection;           // true if this RR is part of question section

    // and therefore has no ttl or rdata

    int offset;                 // offset of RR w/in msg

    int rrlen;                  // number of octets in encoded RR

    DnsName name;               // name field of RR, including root label

    int rrtype;                 // type field of RR

    String rrtypeName;          // name of rrtype

    int rrclass;                // class field of RR

    String rrclassName;         // name of rrclass

    int ttl = 0;                // ttl field of RR

    int rdlen = 0;              // number of octets of rdata

    Object rdata = null;        // rdata -- most are String, unknown are byte[]

    /*

     * Constructs a new ResourceRecord.  The encoded data of the DNS

     * message is contained in msg; data for this RR begins at msg[offset].

     * If qSection is true this RR is part of a question section.  It's

     * not a true resource record in that case, but is treated as if it

     * were a shortened one (with no ttl or rdata).  If decodeRdata is

     * false, the rdata is not decoded (and getRdata() will return null)

     * unless this is an SOA record.

     *

     * @throws CommunicationException if a decoded domain name isn't valid.

     * @throws ArrayIndexOutOfBoundsException given certain other corrupt data.

     */

    ResourceRecord(byte[] msg, int msgLen, int offset,

                   boolean qSection, boolean decodeRdata)

            throws DnsCommunicationException {

        this.msg = msg;

        this.msgLen = msgLen;

        this.offset = offset;

        this.qSection = qSection;

        decode(decodeRdata);

    }

    public String toString() {

        String text = name + " " + rrclassName + " " + rrtypeName;

        if (!qSection) {

            text += " " + ttl + " " +

                    ((rdata != null) ? rdata : "[n/a]");

        }

        return text;

    }

    /*

     * Returns the name field of this RR, including the root label.

     */

    public DnsName getName() {

        return name;

    }

    /*

     * Returns the number of octets in the encoded RR.

     */

    public int size() {

        return rrlen;

    }

    public int getType() {

        return rrtype;

    }

    public int getRrclass() {

        return rrclass;

    }

    public Object getRdata() {

        return rdata;

    }

    public static String getTypeName(int rrtype) {

        return valueToName(rrtype, rrTypeNames);

    }

    public static int getType(String typeName) {

        return nameToValue(typeName, rrTypeNames);

    }

    public static int getRrclass(String className) {

        return nameToValue(className, rrClassNames);

    }

    private static String valueToName(int val, String[] names) {

        String name = null;

        if ((val > 0) && (val < names.length)) {

            name = names[val];

        } else if (val == QTYPE_STAR) {         // QTYPE_STAR == QCLASS_STAR

            name = "*";

        }

        if (name == null) {

            name = Integer.toString(val);

        }

        return name;

    }

    private static int nameToValue(String name, String[] names) {

        if (name.isEmpty()) {

            return -1;                          // invalid name

        } else if (name.equals("*")) {

            return QTYPE_STAR;                  // QTYPE_STAR == QCLASS_STAR

        }

        if (Character.isDigit(name.charAt(0))) {

            try {

                return Integer.parseInt(name);

            } catch (NumberFormatException e) {

            }

        }

        for (int i = 1; i < names.length; i++) {

            if ((names[i] != null) &&

                    name.equalsIgnoreCase(names[i])) {

                return i;

            }

        }

        return -1;                              // unknown name

    }

    /*

     * Decodes the binary format of the RR.

     * May throw ArrayIndexOutOfBoundsException given corrupt data.

     */

    private void decode(boolean decodeRdata) throws DnsCommunicationException {

        int pos = offset;       // index of next unread octet

        name = new DnsName();                           // NAME

        pos = decodeName(pos, name);

        rrtype = getUShort(pos);                        // TYPE

        rrtypeName = (rrtype < rrTypeNames.length)

                ? rrTypeNames[rrtype]

                : null;

        if (rrtypeName == null) {

            rrtypeName = Integer.toString(rrtype);

        }

        pos += 2;

        rrclass = getUShort(pos);                       // CLASS

        rrclassName = (rrclass < rrClassNames.length)

                ? rrClassNames[rrclass]

                : null;

        if (rrclassName == null) {

            rrclassName = Integer.toString(rrclass);

        }

        pos += 2;

        if (!qSection) {

            ttl = getInt(pos);                          // TTL

            pos += 4;

            rdlen = getUShort(pos);                     // RDLENGTH

            pos += 2;

            rdata = (decodeRdata ||                     // RDATA

                    (rrtype == TYPE_SOA))

                    ? decodeRdata(pos)

                    : null;

            if (rdata instanceof DnsName) {

                rdata = rdata.toString();

            }

            pos += rdlen;

        }

        rrlen = pos - offset;

        msg = null;     // free up for GC

    }

    /*

     * Returns the 1-byte unsigned value at msg[pos].

     */

    private int getUByte(int pos) {

        return (msg[pos] & 0xFF);

    }

    /*

     * Returns the 2-byte unsigned value at msg[pos].  The high

     * order byte comes first.

     */

    private int getUShort(int pos) {

        return (((msg[pos] & 0xFF) << 8) |

                (msg[pos + 1] & 0xFF));

    }

    /*

     * Returns the 4-byte signed value at msg[pos].  The high

     * order byte comes first.

     */

    private int getInt(int pos) {

        return ((getUShort(pos) << 16) | getUShort(pos + 2));

    }

    /*

     * Returns the 4-byte unsigned value at msg[pos].  The high

     * order byte comes first.

     */

    private long getUInt(int pos) {

        return (getInt(pos) & 0xffffffffL);

    }

    /*

     * Returns the name encoded at msg[pos], including the root label.

     */

    private DnsName decodeName(int pos) throws DnsCommunicationException {

        DnsName n = new DnsName();

        decodeName(pos, n);

        return n;

    }

    /*

     * Prepends to "n" the domain name encoded at msg[pos], including the root

     * label.  Returns the index into "msg" following the name.

     */

    private int decodeName(int pos, DnsName n) throws DnsCommunicationException {

        int endPos = -1;

        int level = 0;

        try {

            while (true) {

                if (level > MAXIMUM_COMPRESSION_REFERENCES)

                    throw new IOException("Too many compression references");

                int typeAndLen = msg[pos] & 0xFF;

                if (typeAndLen == 0) {                  // end of name

                    ++pos;

                    n.add(0, "");

                    break;

                } else if (typeAndLen <= 63) {          // regular label

                    ++pos;

                    n.add(0, new String(msg, pos, typeAndLen,

                            StandardCharsets.ISO_8859_1));

                    pos += typeAndLen;

                } else if ((typeAndLen & 0xC0) == 0xC0) { // name compression

                    ++level;

                    // cater for the case where the name pointed to is itself

                    // compressed: we don't want endPos to be reset by the second

                    // compression level.

                    int ppos = pos;

                    if (endPos == -1) endPos = pos + 2;

                    pos = getUShort(pos) & 0x3FFF;

                    if (debug) {

                        dprint("decode: name compression at " + ppos

                                + " -> " + pos + " endPos=" + endPos);

                        assert endPos > 0;

                        assert pos < ppos;

                        assert pos >= Header.HEADER_SIZE;

                    }

                } else

                    throw new IOException("Invalid label type: " + typeAndLen);

            }

        } catch (IOException | DnsInvalidNameException e) {

            DnsCommunicationException ce = new DnsCommunicationException(

                    "DNS error: malformed packet");

            ce.initCause(e);

            throw ce;

        }

        if (endPos == -1)

            endPos = pos;

        return endPos;

    }

    /*

     * Returns the rdata encoded at msg[pos].  The format is dependent

     * on the rrtype and rrclass values, which have already been set.

     * The length of the encoded data is rdlen, which has already been

     * set.

     * The rdata of records with unknown type/class combinations is

     * returned in a newly-allocated byte array.

     */

    private Object decodeRdata(int pos) throws DnsCommunicationException {

        if (rrclass == CLASS_INTERNET) {

            switch (rrtype) {

                case TYPE_A:

                    return decodeA(pos);

                case TYPE_AAAA:

                    return decodeAAAA(pos);

                case TYPE_CNAME:

                case TYPE_NS:

                case TYPE_PTR:

                    return decodeName(pos);

                case TYPE_MX:

                    return decodeMx(pos);

                case TYPE_SOA:

                    return decodeSoa(pos);

                case TYPE_SRV:

                    return decodeSrv(pos);

                case TYPE_NAPTR:

                    return decodeNaptr(pos);

                case TYPE_TXT:

                    return decodeTxt(pos);

                case TYPE_HINFO:

                    return decodeHinfo(pos);

            }

        }

        // Unknown RR type/class

        if (debug) {

            dprint("Unknown RR type for RR data: " + rrtype + " rdlen=" + rdlen

                    + ", pos=" + pos + ", msglen=" + msg.length + ", remaining="

                    + (msg.length - pos));

        }

        byte[] rd = new byte[rdlen];

        System.arraycopy(msg, pos, rd, 0, rdlen);

        return rd;

    }

    /*

     * Returns the rdata of an MX record that is encoded at msg[pos].

     */

    private String decodeMx(int pos) throws DnsCommunicationException {

        int preference = getUShort(pos);

        pos += 2;

        DnsName name = decodeName(pos);

        return (preference + " " + name);

    }

    /*

     * Returns the rdata of an SOA record that is encoded at msg[pos].

     */

    private String decodeSoa(int pos) throws DnsCommunicationException {

        DnsName mname = new DnsName();

        pos = decodeName(pos, mname);

        DnsName rname = new DnsName();

        pos = decodeName(pos, rname);

        long serial = getUInt(pos);

        pos += 4;

        long refresh = getUInt(pos);

        pos += 4;

        long retry = getUInt(pos);

        pos += 4;

        long expire = getUInt(pos);

        pos += 4;

        long minimum = getUInt(pos);    // now used as negative TTL

        pos += 4;

        return (mname + " " + rname + " " + serial + " " +

                refresh + " " + retry + " " + expire + " " + minimum);

    }

    /*

     * Returns the rdata of an SRV record that is encoded at msg[pos].

     * See RFC 2782.

     */

    private String decodeSrv(int pos) throws DnsCommunicationException {

        int priority = getUShort(pos);

        pos += 2;

        int weight = getUShort(pos);

        pos += 2;

        int port = getUShort(pos);

        pos += 2;

        DnsName target = decodeName(pos);

        return (priority + " " + weight + " " + port + " " + target);

    }

    /*

     * Returns the rdata of an NAPTR record that is encoded at msg[pos].

     * See RFC 2915.

     */

    private String decodeNaptr(int pos) throws DnsCommunicationException {

        int order = getUShort(pos);

        pos += 2;

        int preference = getUShort(pos);

        pos += 2;

        StringBuffer flags = new StringBuffer();

        pos += decodeCharString(pos, flags);

        StringBuffer services = new StringBuffer();

        pos += decodeCharString(pos, services);

        StringBuffer regexp = new StringBuffer(rdlen);

        pos += decodeCharString(pos, regexp);

        DnsName replacement = decodeName(pos);

        return (order + " " + preference + " " + flags + " " +

                services + " " + regexp + " " + replacement);

    }

    /*

     * Returns the rdata of a TXT record that is encoded at msg[pos].

     * The rdata consists of one or more <character-string>s.

     */

    private String decodeTxt(int pos) {

        StringBuffer buf = new StringBuffer(rdlen);

        int end = pos + rdlen;

        while (pos < end) {

            pos += decodeCharString(pos, buf);

            if (pos < end) {

                buf.append(' ');

            }

        }

        return buf.toString();

    }

    /*

     * Returns the rdata of an HINFO record that is encoded at msg[pos].

     * The rdata consists of two <character-string>s.

     */

    private String decodeHinfo(int pos) {

        StringBuffer buf = new StringBuffer(rdlen);

        pos += decodeCharString(pos, buf);

        buf.append(' ');

        pos += decodeCharString(pos, buf);

        return buf.toString();

    }

    /*

     * Decodes the <character-string> at msg[pos] and adds it to buf.

     * If the string contains one of the meta-characters ' ', '\\', or

     * '"', then the result is quoted and any embedded '\\' or '"'

     * chars are escaped with '\\'.  Empty strings are also quoted.

     * Returns the size of the encoded string, including the initial

     * length octet.

     */

    private int decodeCharString(int pos, StringBuffer buf) {

        int start = buf.length();       // starting index of this string

        int len = getUByte(pos++);      // encoded string length

        boolean quoted = (len == 0);    // quote string if empty

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

            int c = getUByte(pos++);

            quoted |= (c == ' ');

            if ((c == '\\') || (c == '"')) {

                quoted = true;

                buf.append('\\');

            }

            buf.append((char) c);

        }

        if (quoted) {

            buf.insert(start, '"');

            buf.append('"');

        }

        return (len + 1);       // size includes initial octet

    }

    /*

     * Returns the rdata of an A record, in dotted-decimal format,

     * that is encoded at msg[pos].