DefaultDnsRecordDecoder Class — netty Architecture

Source Code

codec-dns/src/main/java/io/netty/handler/codec/dns/DefaultDnsRecordDecoder.java lines 27–155

public class DefaultDnsRecordDecoder implements DnsRecordDecoder {

    static final String ROOT = ".";

    /**
     * Creates a new instance.
     */
    protected DefaultDnsRecordDecoder() { }

    @Override
    public final DnsQuestion decodeQuestion(ByteBuf in) throws Exception {
        String name = decodeName(in);
        DnsRecordType type = DnsRecordType.valueOf(in.readUnsignedShort());
        int qClass = in.readUnsignedShort();
        return new DefaultDnsQuestion(name, type, qClass);
    }

    @Override
    public final <T extends DnsRecord> T decodeRecord(ByteBuf in) throws Exception {
        final int startOffset = in.readerIndex();
        final String name = decodeName(in);

        final int endOffset = in.writerIndex();
        if (endOffset - in.readerIndex() < 10) {
            // Not enough data
            in.readerIndex(startOffset);
            return null;
        }

        final DnsRecordType type = DnsRecordType.valueOf(in.readUnsignedShort());
        final int aClass = in.readUnsignedShort();
        final long ttl = in.readUnsignedInt();
        final int length = in.readUnsignedShort();
        final int offset = in.readerIndex();

        if (endOffset - offset < length) {
            // Not enough data
            in.readerIndex(startOffset);
            return null;
        }

        @SuppressWarnings("unchecked")
        T record = (T) decodeRecord(name, type, aClass, ttl, in, offset, length);
        in.readerIndex(offset + length);
        return record;
    }

    /**
     * Decodes a record from the information decoded so far by {@link #decodeRecord(ByteBuf)}.
     *
     * @param name the domain name of the record
     * @param type the type of the record
     * @param dnsClass the class of the record
     * @param timeToLive the TTL of the record
     * @param in the {@link ByteBuf} that contains the RDATA
     * @param offset the start offset of the RDATA in {@code in}
     * @param length the length of the RDATA
     *
     * @return a {@link DnsRawRecord}. Override this method to decode RDATA and return other record implementation.
     */
    protected DnsRecord decodeRecord(
            String name, DnsRecordType type, int dnsClass, long timeToLive,
            ByteBuf in, int offset, int length) throws Exception {

        // DNS message compression means that domain names may contain "pointers" to other positions in the packet
        // to build a full message. This means the indexes are meaningful and we need the ability to reference the
        // indexes un-obstructed, and thus we cannot use a slice here.
        // See https://www.ietf.org/rfc/rfc1035 [4.1.4. Message compression]
        if (type == DnsRecordType.PTR) {
            return new DefaultDnsPtrRecord(
                    name, dnsClass, timeToLive, decodeName0(in.duplicate().setIndex(offset, offset + length)));
        }
        if (type == DnsRecordType.CNAME || type == DnsRecordType.NS) {
            return new DefaultDnsRawRecord(name, type, dnsClass, timeToLive,
                                           DnsCodecUtil.decompressDomainName(
                                                   in.duplicate().setIndex(offset, offset + length)));
        }
        if (type ==  DnsRecordType.MX) {
            // MX RDATA: 16-bit preference + exchange (domain name, possibly compressed)
            if (length < 3) {
                throw new CorruptedFrameException("MX record RDATA is too short: " + length);