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patch to support mDNS and multicast to servers #148

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504fe0d
Update SimpleResolver.java
ka2ddo Jan 6, 2021
fce0cf8
Update NioUdpClient.java
ka2ddo Jan 6, 2021
544182b
Update SimpleResolver.java
ka2ddo Jan 6, 2021
855b7be
reduce duplicate code in mDNS support changes
ka2ddo Jan 7, 2021
1cf8fb8
reduce duplicated code in mDNS changes
ka2ddo Jan 7, 2021
cc916e5
resolve format complaints in mDNS-modified code
ka2ddo Jan 7, 2021
e838df6
resolve format complaints in mDNS changes
ka2ddo Jan 7, 2021
92d98d5
resolve issues reported by dnsjava over regarding consistent behavior
ka2ddo Mar 13, 2021
80aa3cd
a few more bugfixes to the mDNS changes per dnsjava author's request.
ka2ddo Mar 13, 2021
31f2621
make the format checker happy (again!).
ka2ddo Mar 13, 2021
c1ce27b
more formatting issues that the online checker didn't report on the
ka2ddo Mar 13, 2021
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Update NioUdpClient.java 
Add support to wait for multiple answers to arrive if and only if the address of the DNS server is a multicast address.
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@ka2ddo
ka2ddo authored Jan 6, 2021
commit fce0cf8b18dbddc65b8613cdd319dd3c281fa7df
100 changes: 86 additions & 14 deletions src/main/java/org/xbill/DNS/NioUdpClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
import java.io.EOFException;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import java.nio.ByteBuffer;
Expand All @@ -12,6 +13,7 @@
import java.nio.channels.Selector;
import java.security.SecureRandom;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Queue;
import java.util.concurrent.CompletableFuture;
Expand Down Expand Up @@ -71,8 +73,7 @@ private static void checkTransactionTimeouts() {
for (Iterator<Transaction> it = pendingTransactions.iterator(); it.hasNext(); ) {
Transaction t = it.next();
if (t.endTime - System.nanoTime() < 0) {
t.silentCloseChannel();
t.f.completeExceptionally(new SocketTimeoutException("Query timed out"));
t.closeTransaction();
it.remove();
}
}
Expand All @@ -81,19 +82,20 @@ private static void checkTransactionTimeouts() {
@RequiredArgsConstructor
private static class Transaction implements KeyProcessor {
private final byte[] data;
private final int max;
final int max;
private final long endTime;
private final DatagramChannel channel;
private final CompletableFuture<byte[]> f;
private final SocketAddress remoteSocketAddress;
final CompletableFuture<Object> f;

void send() throws IOException {
ByteBuffer buffer = ByteBuffer.wrap(data);
verboseLog(
"UDP write",
channel.socket().getLocalSocketAddress(),
channel.socket().getRemoteSocketAddress(),
remoteSocketAddress,
data);
int n = channel.send(buffer, channel.socket().getRemoteSocketAddress());
int n = channel.send(buffer, remoteSocketAddress);
if (n <= 0) {
throw new EOFException();
}
Expand All @@ -109,10 +111,12 @@ public void processReadyKey(SelectionKey key) {

DatagramChannel channel = (DatagramChannel) key.channel();
ByteBuffer buffer = ByteBuffer.allocate(max);
SocketAddress source;
int read;
try {
read = channel.read(buffer);
if (read <= 0) {
source = channel.receive(buffer);
read = buffer.position();
if (read <= 0 || source == null) {
throw new EOFException();
}
} catch (IOException e) {
Expand All @@ -128,26 +132,88 @@ public void processReadyKey(SelectionKey key) {
verboseLog(
"UDP read",
channel.socket().getLocalSocketAddress(),
channel.socket().getRemoteSocketAddress(),
remoteSocketAddress,
data);
silentCloseChannel();
f.complete(data);
pendingTransactions.remove(this);
}

private void silentCloseChannel() {
void silentCloseChannel() {
try {
channel.disconnect();
channel.close();
} catch (IOException e) {
// ignore, we either already have everything we need or can't do anything
}
}

void closeTransaction() {
silentCloseChannel();
f.completeExceptionally(new SocketTimeoutException("Query timed out"));
}
}

private static class MultiAnswerTransaction extends Transaction {
MultiAnswerTransaction(byte[] query, int max, long endTime, DatagramChannel channel,
SocketAddress remoteSocketAddress,
CompletableFuture<Object> f) {
super(query, max, endTime, channel, remoteSocketAddress, f);
}

public void processReadyKey(SelectionKey key) {
if (!key.isReadable()) {
silentCloseChannel();
f.completeExceptionally(new EOFException("channel not readable"));
pendingTransactions.remove(this);
return;
}

DatagramChannel channel = (DatagramChannel) key.channel();
ByteBuffer buffer = ByteBuffer.allocate(max);
SocketAddress source;
int read;
try {
source = channel.receive(buffer);
read = buffer.position();
if (read <= 0 || source == null) {
return; // ignore this datagram
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@ibauersachs ibauersachs Mar 14, 2021

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This is a lot of code duplication. The return here vs. EOFException could be:

if (remoteSocketAddress.getAddress().isMulticast()) {
  return;
}
throw new EOFException();

}
} catch (IOException e) {
silentCloseChannel();
f.completeExceptionally(e);
pendingTransactions.remove(this);
return;
}

buffer.flip();
byte[] data = new byte[read];
System.arraycopy(buffer.array(), 0, data, 0, read);
verboseLog(
"UDP read",
channel.socket().getLocalSocketAddress(),
source,
data);
answers.add(data);
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@ibauersachs ibauersachs Mar 14, 2021

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This is the only other line in this method that differs for mDNS. Instead of duplicating everything, move the processing of the data byte-array into a separate method, e.g.

// in Transaction:
...
  System.arraycopy(buffer.array(), 0, data, 0, read);
  verboseLog("UDP read", channel.socket().getLocalSocketAddress(), source, data);
  processAnswer(data);
}

processAnswer(byte[] data) {
  silentCloseChannel();
  f.complete(Collections.singletonList(data));
  pendingTransactions.remove(this);
}

// in MultiAnswerTransaction:
processAnswer(byte[] data) {
  answers.add(data);
}

}

private ArrayList<byte[]> answers = new ArrayList<>();
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@ibauersachs ibauersachs Mar 14, 2021

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Move this to the top of the class definition and make it final, fields randomly in the middle of classes is weird.


@Override
void closeTransaction() {
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@ibauersachs ibauersachs Mar 14, 2021

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closeTransaction is only triggered when the timeout has expired. Is this really the only condition on which you want to return answers? What about the case where one is only interested in the first answer, as fast as possible?

The timeout processing currently only runs every second. Is that still sufficient?

if (answers.size() > 0) {
silentCloseChannel();
f.complete(answers);
} else {
// we failed, no answers
super.closeTransaction();
}
}
}

static CompletableFuture<byte[]> sendrecv(
static CompletableFuture<Object> sendrecv(
InetSocketAddress local, InetSocketAddress remote, byte[] data, int max, Duration timeout) {
CompletableFuture<byte[]> f = new CompletableFuture<>();
CompletableFuture<Object> f = new CompletableFuture<>();
try {
final Selector selector = selector();
DatagramChannel channel = DatagramChannel.open();
Expand Down Expand Up @@ -185,9 +251,15 @@ static CompletableFuture<byte[]> sendrecv(
}
}

channel.connect(remote);
long endTime = System.nanoTime() + timeout.toNanos();
Transaction t = new Transaction(data, max, endTime, channel, f);
Transaction t;
if (!remote.getAddress().isMulticastAddress()) {
channel.connect(remote);
t = new Transaction(data, max, endTime, channel, f);
} else {
// stop this a little before the timeout so we can report what answers we did get
t = new MultiAnswerTransaction(data, max, endTime - 1000000000L, channel, f);
}
pendingTransactions.add(t);
registrationQueue.add(t);
selector.wakeup();
Expand Down