Add MdnsProber
MdnsProber is an implementation of MdnsPacketRepeater that will be used
to send probes for service names before advertising them, to know if
they are already in use.
Bug: 241738458
Test: atest
Change-Id: I4e5f779b891e2c665ba7f752fb5fbd4255070725
diff --git a/service/mdns/com/android/server/connectivity/mdns/MdnsProber.java b/service/mdns/com/android/server/connectivity/mdns/MdnsProber.java
new file mode 100644
index 0000000..db7049e
--- /dev/null
+++ b/service/mdns/com/android/server/connectivity/mdns/MdnsProber.java
@@ -0,0 +1,156 @@
+/*
+ * Copyright (C) 2022 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.server.connectivity.mdns;
+
+import android.annotation.NonNull;
+import android.os.Looper;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.net.module.util.CollectionUtils;
+
+import java.net.SocketAddress;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.Supplier;
+
+/**
+ * Sends mDns probe requests to verify service records are unique on the network.
+ *
+ * TODO: implement receiving replies and handling conflicts.
+ */
+public class MdnsProber extends MdnsPacketRepeater<MdnsProber.ProbingInfo> {
+ @NonNull
+ private final String mLogTag;
+
+ public MdnsProber(@NonNull String interfaceTag, @NonNull Looper looper,
+ @NonNull MdnsReplySender replySender,
+ @NonNull PacketRepeaterCallback<ProbingInfo> cb) {
+ // 3 packets as per https://datatracker.ietf.org/doc/html/rfc6762#section-8.1
+ super(looper, replySender, cb);
+ mLogTag = MdnsProber.class.getSimpleName() + "/" + interfaceTag;
+ }
+
+ static class ProbingInfo implements Request {
+
+ private final int mServiceId;
+ @NonNull
+ private final MdnsPacket mPacket;
+ @NonNull
+ private final Supplier<Iterable<SocketAddress>> mDestinationsSupplier;
+
+ /**
+ * Create a new ProbingInfo
+ * @param serviceId Service to probe for.
+ * @param probeRecords Records to be probed for uniqueness.
+ * @param destinationsSupplier Supplier for the probe destinations. Will be called on the
+ * probe handler thread for each probe.
+ */
+ ProbingInfo(int serviceId, @NonNull List<MdnsRecord> probeRecords,
+ @NonNull Supplier<Iterable<SocketAddress>> destinationsSupplier) {
+ mServiceId = serviceId;
+ mPacket = makePacket(probeRecords);
+ mDestinationsSupplier = destinationsSupplier;
+ }
+
+ public int getServiceId() {
+ return mServiceId;
+ }
+
+ @NonNull
+ @Override
+ public MdnsPacket getPacket(int index) {
+ return mPacket;
+ }
+
+ @NonNull
+ @Override
+ public Iterable<SocketAddress> getDestinations(int index) {
+ return mDestinationsSupplier.get();
+ }
+
+ @Override
+ public long getDelayMs(int nextIndex) {
+ // As per https://datatracker.ietf.org/doc/html/rfc6762#section-8.1
+ return 250L;
+ }
+
+ @Override
+ public int getNumSends() {
+ // 3 packets as per https://datatracker.ietf.org/doc/html/rfc6762#section-8.1
+ return 3;
+ }
+
+ private static MdnsPacket makePacket(@NonNull List<MdnsRecord> records) {
+ final ArrayList<MdnsRecord> questions = new ArrayList<>(records.size());
+ for (final MdnsRecord record : records) {
+ if (containsName(questions, record.getName())) {
+ // Already added this name
+ continue;
+ }
+
+ // TODO: legacy Android mDNS used to send the first probe (only) as unicast, even
+ // though https://datatracker.ietf.org/doc/html/rfc6762#section-8.1 says they
+ // SHOULD all be. rfc6762 15.1 says that if the port is shared with another
+ // responder unicast questions should not be used, and the legacy mdnsresponder may
+ // be running, so not using unicast at all may be better. Consider using legacy
+ // behavior if this causes problems.
+ questions.add(new MdnsAnyRecord(record.getName(), false /* unicast */));
+ }
+
+ return new MdnsPacket(
+ MdnsConstants.FLAGS_QUERY,
+ questions,
+ Collections.emptyList() /* answers */,
+ records /* authorityRecords */,
+ Collections.emptyList() /* additionalRecords */);
+ }
+
+ /**
+ * Return whether the specified name is present in the list of records.
+ */
+ private static boolean containsName(@NonNull List<MdnsRecord> records,
+ @NonNull String[] name) {
+ return CollectionUtils.any(records, r -> Arrays.equals(name, r.getName()));
+ }
+ }
+
+ @NonNull
+ @Override
+ protected String getTag() {
+ return mLogTag;
+ }
+
+ @VisibleForTesting
+ protected long getInitialDelay() {
+ // First wait for a random time in 0-250ms
+ // as per https://datatracker.ietf.org/doc/html/rfc6762#section-8.1
+ return (long) (Math.random() * 250);
+ }
+
+ /**
+ * Start sending packets for probing.
+ */
+ public void startProbing(@NonNull ProbingInfo info) {
+ startProbing(info, getInitialDelay());
+ }
+
+ private void startProbing(@NonNull ProbingInfo info, long delay) {
+ startSending(info.getServiceId(), info, delay);
+ }
+}
diff --git a/service/mdns/com/android/server/connectivity/mdns/MdnsRecord.java b/service/mdns/com/android/server/connectivity/mdns/MdnsRecord.java
index 10b8825..00871ea 100644
--- a/service/mdns/com/android/server/connectivity/mdns/MdnsRecord.java
+++ b/service/mdns/com/android/server/connectivity/mdns/MdnsRecord.java
@@ -201,6 +201,17 @@
protected abstract void readData(MdnsPacketReader reader) throws IOException;
/**
+ * Write the first fields of the record, which are common fields for questions and answers.
+ *
+ * @param writer The writer to use.
+ */
+ public final void writeHeaderFields(MdnsPacketWriter writer) throws IOException {
+ writer.writeLabels(name);
+ writer.writeUInt16(type);
+ writer.writeUInt16(cls);
+ }
+
+ /**
* Writes the record to a packet.
*
* @param writer The writer to use.
@@ -208,9 +219,7 @@
*/
@VisibleForTesting
public final void write(MdnsPacketWriter writer, long now) throws IOException {
- writer.writeLabels(name);
- writer.writeUInt16(type);
- writer.writeUInt16(cls);
+ writeHeaderFields(writer);
writer.writeUInt32(MILLISECONDS.toSeconds(getRemainingTTL(now)));
diff --git a/service/mdns/com/android/server/connectivity/mdns/MdnsReplySender.java b/service/mdns/com/android/server/connectivity/mdns/MdnsReplySender.java
index 2acd789..1fdbc5c 100644
--- a/service/mdns/com/android/server/connectivity/mdns/MdnsReplySender.java
+++ b/service/mdns/com/android/server/connectivity/mdns/MdnsReplySender.java
@@ -67,7 +67,8 @@
writer.writeUInt16(packet.additionalRecords.size()); // additional records count
for (MdnsRecord record : packet.questions) {
- record.write(writer, 0L);
+ // Questions do not have TTL or data
+ record.writeHeaderFields(writer);
}
for (MdnsRecord record : packet.answers) {
record.write(writer, 0L);
diff --git a/tests/unit/Android.bp b/tests/unit/Android.bp
index 8ed735a..209430a 100644
--- a/tests/unit/Android.bp
+++ b/tests/unit/Android.bp
@@ -74,6 +74,7 @@
"java/com/android/server/connectivity/VpnTest.java",
"java/com/android/server/net/ipmemorystore/*.java",
"java/com/android/server/connectivity/mdns/**/*.java",
+ "java/com/android/server/connectivity/mdns/**/*.kt",
]
}
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt
new file mode 100644
index 0000000..cc75191
--- /dev/null
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt
@@ -0,0 +1,201 @@
+/*
+ * Copyright (C) 2022 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.server.connectivity.mdns
+
+import android.os.Build
+import android.os.Handler
+import android.os.HandlerThread
+import android.os.Looper
+import com.android.internal.util.HexDump
+import com.android.server.connectivity.mdns.MdnsProber.ProbingInfo
+import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo
+import com.android.testutils.DevSdkIgnoreRunner
+import java.net.DatagramPacket
+import java.net.InetSocketAddress
+import java.net.MulticastSocket
+import java.util.concurrent.CompletableFuture
+import java.util.concurrent.TimeUnit
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.ArgumentCaptor
+import org.mockito.Mockito.any
+import org.mockito.Mockito.atLeast
+import org.mockito.Mockito.mock
+import org.mockito.Mockito.never
+import org.mockito.Mockito.timeout
+import org.mockito.Mockito.times
+import org.mockito.Mockito.verify
+
+private val destinationsSupplier = {
+ listOf(InetSocketAddress(MdnsConstants.getMdnsIPv6Address(), MdnsConstants.MDNS_PORT)) }
+
+private const val TEST_TIMEOUT_MS = 10_000L
+private const val SHORT_TIMEOUT_MS = 200L
+
+private val TEST_SERVICE_NAME_1 = arrayOf("testservice", "_nmt", "_tcp", "local")
+private val TEST_SERVICE_NAME_2 = arrayOf("testservice2", "_nmt", "_tcp", "local")
+
+@RunWith(DevSdkIgnoreRunner::class)
+@IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class MdnsProberTest {
+ private val thread = HandlerThread(MdnsProberTest::class.simpleName)
+ private val socket = mock(MulticastSocket::class.java)
+ @Suppress("UNCHECKED_CAST")
+ private val cb = mock(MdnsPacketRepeater.PacketRepeaterCallback::class.java)
+ as MdnsPacketRepeater.PacketRepeaterCallback<ProbingInfo>
+ private val buffer = ByteArray(1500)
+
+ @Before
+ fun setUp() {
+ thread.start()
+ }
+
+ @After
+ fun tearDown() {
+ thread.quitSafely()
+ }
+
+ private class TestProbeInfo(probeRecords: List<MdnsRecord>, private val delayMs: Long = 1L) :
+ ProbingInfo(1 /* serviceId */, probeRecords, destinationsSupplier) {
+ // Just send the packets quickly. Timing-related tests for MdnsPacketRepeater are already
+ // done in MdnsAnnouncerTest.
+ override fun getDelayMs(nextIndex: Int) = delayMs
+ }
+
+ private class TestProber(
+ looper: Looper,
+ replySender: MdnsReplySender,
+ cb: PacketRepeaterCallback<ProbingInfo>
+ ) : MdnsProber("testiface", looper, replySender, cb) {
+ override fun getInitialDelay() = 0L
+ }
+
+ private fun assertProbesSent(probeInfo: TestProbeInfo, expectedHex: String) {
+ repeat(probeInfo.numSends) { i ->
+ verify(cb, timeout(TEST_TIMEOUT_MS)).onSent(i, probeInfo)
+ // If the probe interval is short, more than (i+1) probes may have been sent already
+ verify(socket, atLeast(i + 1)).send(any())
+ }
+
+ val captor = ArgumentCaptor.forClass(DatagramPacket::class.java)
+ // There should be exactly numSends probes sent at the end
+ verify(socket, times(probeInfo.numSends)).send(captor.capture())
+
+ captor.allValues.forEach {
+ assertEquals(expectedHex, HexDump.toHexString(it.data))
+ }
+ verify(cb, timeout(TEST_TIMEOUT_MS)).onFinished(probeInfo)
+ }
+
+ private fun makeServiceRecord(name: Array<String>, port: Int) = MdnsServiceRecord(
+ name,
+ 0L /* receiptTimeMillis */,
+ false /* cacheFlush */,
+ 120_000L /* ttlMillis */,
+ 0 /* servicePriority */,
+ 0 /* serviceWeight */,
+ port,
+ arrayOf("myhostname", "local"))
+
+ @Test
+ fun testProbe() {
+ val replySender = MdnsReplySender(thread.looper, socket, buffer)
+ val prober = TestProber(thread.looper, replySender, cb)
+ val probeInfo = TestProbeInfo(
+ listOf(makeServiceRecord(TEST_SERVICE_NAME_1, 37890)))
+ prober.startProbing(probeInfo)
+
+ // Inspect with python3:
+ // import scapy.all as scapy; scapy.DNS(bytes.fromhex('[bytes]')).show2()
+ val expected = "0000000000010000000100000B7465737473657276696365045F6E6D74045F746370056C" +
+ "6F63616C0000FF0001C00C002100010000007800130000000094020A6D79686F73746E616D65C022"
+ assertProbesSent(probeInfo, expected)
+ }
+
+ @Test
+ fun testProbeMultipleRecords() {
+ val replySender = MdnsReplySender(thread.looper, socket, buffer)
+ val prober = TestProber(thread.looper, replySender, cb)
+ val probeInfo = TestProbeInfo(listOf(
+ makeServiceRecord(TEST_SERVICE_NAME_1, 37890),
+ makeServiceRecord(TEST_SERVICE_NAME_2, 37891),
+ MdnsTextRecord(
+ // Same name as the first record; there should not be 2 duplicated questions
+ TEST_SERVICE_NAME_1,
+ 0L /* receiptTimeMillis */,
+ false /* cacheFlush */,
+ 120_000L /* ttlMillis */,
+ listOf(MdnsServiceInfo.TextEntry("testKey", "testValue")))))
+ prober.startProbing(probeInfo)
+
+ /*
+ Expected data obtained with:
+ scapy.raw(scapy.dns_compress(scapy.DNS(rd=0,
+ qd =
+ scapy.DNSQR(qname='testservice._nmt._tcp.local.', qtype='ALL') /
+ scapy.DNSQR(qname='testservice2._nmt._tcp.local.', qtype='ALL'),
+ ns=
+ scapy.DNSRRSRV(rrname='testservice._nmt._tcp.local.', type='SRV', ttl=120,
+ port=37890, target='myhostname.local.') /
+ scapy.DNSRRSRV(rrname='testservice2._nmt._tcp.local.', type='SRV', ttl=120,
+ port=37891, target='myhostname.local.') /
+ scapy.DNSRR(type='TXT', ttl=120, rrname='testservice._nmt._tcp.local.',
+ rdata='testKey=testValue'))
+ )).hex().upper()
+ // NOTE: due to a bug the second "myhostname" is not getting DNS compressed in the current
+ // actual probe, so data below is slightly different. Fix compression so it gets compressed.
+ */
+ val expected = "0000000000020000000300000B7465737473657276696365045F6E6D74045F746370056C6" +
+ "F63616C0000FF00010C746573747365727669636532C01800FF0001C00C002100010000007800130" +
+ "000000094020A6D79686F73746E616D65C0220C746573747365727669636532C0180021000100000" +
+ "07800130000000094030A6D79686F73746E616D65C022C00C0010000100000078001211746573744" +
+ "B65793D7465737456616C7565"
+ assertProbesSent(probeInfo, expected)
+ }
+
+ @Test
+ fun testStopProbing() {
+ val replySender = MdnsReplySender(thread.looper, socket, buffer)
+ val prober = TestProber(thread.looper, replySender, cb)
+ val probeInfo = TestProbeInfo(
+ listOf(makeServiceRecord(TEST_SERVICE_NAME_1, 37890)),
+ // delayMs is the delay between each probe, so does not apply to the first one
+ delayMs = SHORT_TIMEOUT_MS)
+ prober.startProbing(probeInfo)
+
+ // Expect the initial probe
+ verify(cb, timeout(TEST_TIMEOUT_MS)).onSent(0, probeInfo)
+
+ // Stop probing
+ val stopResult = CompletableFuture<Boolean>()
+ Handler(thread.looper).post { stopResult.complete(prober.stop(probeInfo.serviceId)) }
+ assertTrue(stopResult.get(TEST_TIMEOUT_MS, TimeUnit.MILLISECONDS),
+ "stop should return true when probing was in progress")
+
+ // Wait for a bit (more than the probe delay) to ensure no more probes were sent
+ Thread.sleep(SHORT_TIMEOUT_MS * 2)
+ verify(cb, never()).onSent(1, probeInfo)
+ verify(cb, never()).onFinished(probeInfo)
+
+ // Only one sent packet
+ verify(socket, times(1)).send(any())
+ }
+}