Java tutorial
/* * Copyright (c) 2013 The Netty Project * ------------------------------------ * All rights reserved. This program and the accompanying materials * are made available under the terms of the Eclipse Public License v1.0 * and Apache License v2.0 which accompanies this distribution. * * The Eclipse Public License is available at * http://www.eclipse.org/legal/epl-v10.html * * The Apache License v2.0 is available at * http://www.opensource.org/licenses/apache2.0.php * * You may elect to redistribute this code under either of these licenses. */ package io.vertx.core.dns.impl.decoder; import io.netty.buffer.ByteBuf; import io.netty.handler.codec.DecoderException; import io.netty.handler.codec.dns.DnsPtrRecord; import io.netty.handler.codec.dns.DnsRawRecord; import io.netty.handler.codec.dns.DnsRecord; import io.netty.handler.codec.dns.DnsRecordType; import io.netty.util.CharsetUtil; import io.vertx.core.dns.impl.MxRecordImpl; import io.vertx.core.dns.impl.SrvRecordImpl; import java.net.InetAddress; import java.net.UnknownHostException; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.function.Function; /** * Handles the decoding of resource records. Some default decoders are mapped to * their resource types in the map {@code decoders}. */ public class RecordDecoder { /** * Decodes MX (mail exchanger) resource records. */ public static final Function<DnsRecord, MxRecordImpl> MX = record -> { ByteBuf packet = ((DnsRawRecord) record).content(); int priority = packet.readShort(); String name = RecordDecoder.readName(packet); return new MxRecordImpl(priority, name); }; /** * Decodes any record that simply returns a domain name, such as NS (name * server) and CNAME (canonical name) resource records. */ public static final Function<DnsRecord, String> DOMAIN = record -> { if (record instanceof DnsPtrRecord) { String val = ((DnsPtrRecord) record).hostname(); if (val.endsWith(".")) { val = val.substring(0, val.length() - 1); } return val; } else { ByteBuf content = ((DnsRawRecord) record).content(); return RecordDecoder.getName(content, content.readerIndex()); } }; /** * Decodes A resource records into IPv4 addresses. */ public static final Function<DnsRecord, String> A = address(4); /** * Decodes AAAA resource records into IPv6 addresses. */ public static final Function<DnsRecord, String> AAAA = address(16); /** * Decodes SRV (service) resource records. */ public static final Function<DnsRecord, SrvRecordImpl> SRV = record -> { ByteBuf packet = ((DnsRawRecord) record).content(); int priority = packet.readShort(); int weight = packet.readShort(); int port = packet.readUnsignedShort(); String target = RecordDecoder.readName(packet); String[] parts = record.name().split("\\.", 3); String service = parts[0]; String protocol = parts[1]; String name = parts[2]; return new SrvRecordImpl(priority, weight, port, name, protocol, service, target); }; /** * Decodes SOA (start of authority) resource records. */ public static final Function<DnsRecord, StartOfAuthorityRecord> SOA = record -> { ByteBuf packet = ((DnsRawRecord) record).content(); String mName = RecordDecoder.readName(packet); String rName = RecordDecoder.readName(packet); long serial = packet.readUnsignedInt(); int refresh = packet.readInt(); int retry = packet.readInt(); int expire = packet.readInt(); long minimum = packet.readUnsignedInt(); return new StartOfAuthorityRecord(mName, rName, serial, refresh, retry, expire, minimum); }; public static final Function<DnsRecord, List<String>> TXT = record -> { List<String> list = new ArrayList<>(); ByteBuf data = ((DnsRawRecord) record).content(); int index = data.readerIndex(); while (index < data.writerIndex()) { int len = data.getUnsignedByte(index++); list.add(data.toString(index, len, CharsetUtil.UTF_8)); index += len; } return list; }; static Function<DnsRecord, String> address(int octets) { return record -> { ByteBuf data = ((DnsRawRecord) record).content(); int size = data.writerIndex() - data.readerIndex(); if (size != octets) { throw new DecoderException("Invalid content length, or reader index when decoding address [index: " + data.readerIndex() + ", expected length: " + octets + ", actual: " + size + "]."); } byte[] address = new byte[octets]; data.getBytes(data.readerIndex(), address); try { return InetAddress.getByAddress(address).getHostAddress(); } catch (UnknownHostException e) { throw new DecoderException("Could not convert address " + data.toString(data.readerIndex(), size, CharsetUtil.UTF_8) + " to InetAddress."); } }; } /** * Retrieves a domain name given a buffer containing a DNS packet. If the * name contains a pointer, the position of the buffer will be set to * directly after the pointer's index after the name has been read. * * @param buf the byte buffer containing the DNS packet * @return the domain name for an entry */ static String readName(ByteBuf buf) { int position = -1; StringBuilder name = new StringBuilder(); for (int len = buf.readUnsignedByte(); buf.isReadable() && len != 0; len = buf.readUnsignedByte()) { boolean pointer = (len & 0xc0) == 0xc0; if (pointer) { if (position == -1) { position = buf.readerIndex() + 1; } buf.readerIndex((len & 0x3f) << 8 | buf.readUnsignedByte()); } else { name.append(buf.toString(buf.readerIndex(), len, CharsetUtil.UTF_8)).append("."); buf.skipBytes(len); } } if (position != -1) { buf.readerIndex(position); } if (name.length() == 0) { return null; } return name.substring(0, name.length() - 1); } /** * Retrieves a domain name given a buffer containing a DNS packet without * advancing the readerIndex for the buffer. * * @param buf the byte buffer containing the DNS packet * @param offset the position at which the name begins * @return the domain name for an entry */ static String getName(ByteBuf buf, int offset) { StringBuilder name = new StringBuilder(); for (int len = buf.getUnsignedByte(offset++); buf.writerIndex() > offset && len != 0; len = buf.getUnsignedByte(offset++)) { boolean pointer = (len & 0xc0) == 0xc0; if (pointer) { offset = (len & 0x3f) << 8 | buf.getUnsignedByte(offset++); } else { name.append(buf.toString(offset, len, CharsetUtil.UTF_8)).append("."); offset += len; } } if (name.length() == 0) { return null; } return name.substring(0, name.length() - 1); } private static final Map<DnsRecordType, Function<DnsRecord, ?>> decoders = new HashMap<>(); static { decoders.put(DnsRecordType.A, RecordDecoder.A); decoders.put(DnsRecordType.AAAA, RecordDecoder.AAAA); decoders.put(DnsRecordType.MX, RecordDecoder.MX); decoders.put(DnsRecordType.TXT, RecordDecoder.TXT); decoders.put(DnsRecordType.SRV, RecordDecoder.SRV); decoders.put(DnsRecordType.NS, RecordDecoder.DOMAIN); decoders.put(DnsRecordType.CNAME, RecordDecoder.DOMAIN); decoders.put(DnsRecordType.PTR, RecordDecoder.DOMAIN); decoders.put(DnsRecordType.SOA, RecordDecoder.SOA); } /** * Decodes a resource record and returns the result. * * @param record * @return the decoded resource record */ @SuppressWarnings("unchecked") public static <T> T decode(DnsRecord record) { DnsRecordType type = record.type(); Function<DnsRecord, ?> decoder = decoders.get(type); if (decoder == null) { throw new IllegalStateException("Unsupported resource record type [id: " + type + "]."); } T result = null; try { result = (T) decoder.apply(record); } catch (Exception e) { e.printStackTrace(); } return result; } }