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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.net.module.util;
import android.annotation.NonNull;
import android.annotation.Nullable;
import com.android.net.module.util.DnsPacketUtils.DnsRecordParser;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;
/**
* Defines basic data for DNS protocol based on RFC 1035.
* Subclasses create the specific format used in DNS packet.
*
* @hide
*/
public abstract class DnsPacket {
/**
* Thrown when parsing packet failed.
*/
public static class ParseException extends RuntimeException {
public String reason;
public ParseException(@NonNull String reason) {
super(reason);
this.reason = reason;
}
public ParseException(@NonNull String reason, @NonNull Throwable cause) {
super(reason, cause);
this.reason = reason;
}
}
/**
* DNS header for DNS protocol based on RFC 1035.
*/
public class DnsHeader {
private static final String TAG = "DnsHeader";
public final int id;
public final int flags;
public final int rcode;
private final int[] mRecordCount;
/* If this bit in the 'flags' field is set to 0, the DNS message corresponding to this
* header is a query; otherwise, it is a response.
*/
private static final int FLAGS_SECTION_QR_BIT = 15;
/**
* Create a new DnsHeader from a positioned ByteBuffer.
*
* The ByteBuffer must be in network byte order (which is the default).
* Reads the passed ByteBuffer from its current position and decodes a DNS header.
* When this constructor returns, the reading position of the ByteBuffer has been
* advanced to the end of the DNS header record.
* This is meant to chain with other methods reading a DNS response in sequence.
*/
DnsHeader(@NonNull ByteBuffer buf) throws BufferUnderflowException {
id = Short.toUnsignedInt(buf.getShort());
flags = Short.toUnsignedInt(buf.getShort());
rcode = flags & 0xF;
mRecordCount = new int[NUM_SECTIONS];
for (int i = 0; i < NUM_SECTIONS; ++i) {
mRecordCount[i] = Short.toUnsignedInt(buf.getShort());
}
}
/**
* Determines if the DNS message corresponding to this header is a response, as defined in
* RFC 1035 Section 4.1.1.
*/
public boolean isResponse() {
return (flags & (1 << FLAGS_SECTION_QR_BIT)) != 0;
}
/**
* Get record count by type.
*/
public int getRecordCount(int type) {
return mRecordCount[type];
}
}
/**
* Superclass for DNS questions and DNS resource records.
*
* DNS questions (No TTL/RDATA)
* DNS resource records (With TTL/RDATA)
*/
public class DnsRecord {
private static final int MAXNAMESIZE = 255;
public static final int NAME_NORMAL = 0;
public static final int NAME_COMPRESSION = 0xC0;
private static final String TAG = "DnsRecord";
public final String dName;
public final int nsType;
public final int nsClass;
public final long ttl;
private final byte[] mRdata;
/**
* Create a new DnsRecord from a positioned ByteBuffer.
*
* Reads the passed ByteBuffer from its current position and decodes a DNS record.
* When this constructor returns, the reading position of the ByteBuffer has been
* advanced to the end of the DNS header record.
* This is meant to chain with other methods reading a DNS response in sequence.
*
* @param buf ByteBuffer input of record, must be in network byte order
* (which is the default).
*/
DnsRecord(int recordType, @NonNull ByteBuffer buf)
throws BufferUnderflowException, ParseException {
dName = DnsRecordParser.parseName(buf, 0 /* Parse depth */,
/* isNameCompressionSupported= */ true);
if (dName.length() > MAXNAMESIZE) {
throw new ParseException(
"Parse name fail, name size is too long: " + dName.length());
}
nsType = Short.toUnsignedInt(buf.getShort());
nsClass = Short.toUnsignedInt(buf.getShort());
if (recordType != QDSECTION) {
ttl = Integer.toUnsignedLong(buf.getInt());
final int length = Short.toUnsignedInt(buf.getShort());
mRdata = new byte[length];
buf.get(mRdata);
} else {
ttl = 0;
mRdata = null;
}
}
/**
* Get a copy of rdata.
*/
@Nullable
public byte[] getRR() {
return (mRdata == null) ? null : mRdata.clone();
}
}
public static final int QDSECTION = 0;
public static final int ANSECTION = 1;
public static final int NSSECTION = 2;
public static final int ARSECTION = 3;
private static final int NUM_SECTIONS = ARSECTION + 1;
private static final String TAG = DnsPacket.class.getSimpleName();
protected final DnsHeader mHeader;
protected final List<DnsRecord>[] mRecords;
protected DnsPacket(@NonNull byte[] data) throws ParseException {
if (null == data) {
throw new ParseException("Parse header failed, null input data");
}
final ByteBuffer buffer;
try {
buffer = ByteBuffer.wrap(data);
mHeader = new DnsHeader(buffer);
} catch (BufferUnderflowException e) {
throw new ParseException("Parse Header fail, bad input data", e);
}
mRecords = new ArrayList[NUM_SECTIONS];
for (int i = 0; i < NUM_SECTIONS; ++i) {
final int count = mHeader.getRecordCount(i);
if (count > 0) {
mRecords[i] = new ArrayList(count);
}
for (int j = 0; j < count; ++j) {
try {
mRecords[i].add(new DnsRecord(i, buffer));
} catch (BufferUnderflowException e) {
throw new ParseException("Parse record fail", e);
}
}
}
}
}
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