Advertise with short hostnames
Advertise with a shorter hostname by default (can be disabled via a
chicken bit), instead of "Android_[32 characters]" as the hostname.
This should allow decreasing the size of APF programs necessary for
advertising offload, and make the advertiser compatible with Matter
use-cases. Some Matter implementations (notably CHIP) interpreted
the example in "4.3.1.1. Host Name Construction" of the spec as
if only 16 character hostnames needed to be supported, despite not
following the rule to construct the hostname based on link-layer
addresses.
The hostname changed once in T when migrating from mdnsresponder to the
current advertiser implementation, so changing the format again is
unlikely to create problems, especially since this keeps the "Android_"
prefix.
Bug: 341141476
Test: atest
Change-Id: Ic8311f41a1a943ec8230203fcd74eda7a26a691c
diff --git a/service-t/src/com/android/server/NsdService.java b/service-t/src/com/android/server/NsdService.java
index 0adb290..fe1db3b 100644
--- a/service-t/src/com/android/server/NsdService.java
+++ b/service-t/src/com/android/server/NsdService.java
@@ -1943,6 +1943,8 @@
.setCachedServicesRetentionTime(mDeps.getDeviceConfigPropertyInt(
MdnsFeatureFlags.NSD_CACHED_SERVICES_RETENTION_TIME,
MdnsFeatureFlags.DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS))
+ .setIsShortHostnamesEnabled(mDeps.isTetheringFeatureNotChickenedOut(
+ mContext, MdnsFeatureFlags.NSD_USE_SHORT_HOSTNAMES))
.setOverrideProvider(new MdnsFeatureFlags.FlagOverrideProvider() {
@Override
public boolean isForceEnabledForTest(@NonNull String flag) {
diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsAdvertiser.java b/service-t/src/com/android/server/connectivity/mdns/MdnsAdvertiser.java
index 9c52eca..54f7ca3 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsAdvertiser.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsAdvertiser.java
@@ -46,6 +46,7 @@
import com.android.server.connectivity.ConnectivityResources;
import com.android.server.connectivity.mdns.util.MdnsUtils;
+import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
@@ -117,7 +118,7 @@
* Generates a unique hostname to be used by the device.
*/
@NonNull
- public String[] generateHostname() {
+ public String[] generateHostname(boolean useShortFormat) {
// Generate a very-probably-unique hostname. This allows minimizing possible conflicts
// to the point that probing for it is no longer necessary (as per RFC6762 8.1 last
// paragraph), and does not leak more information than what could already be obtained by
@@ -127,10 +128,24 @@
// Having a different hostname per interface is an acceptable option as per RFC6762 14.
// This hostname will change every time the interface is reconnected, so this does not
// allow tracking the device.
- // TODO: consider deriving a hostname from other sources, such as the IPv6 addresses
- // (reusing the same privacy-protecting mechanics).
- return new String[] {
- "Android_" + UUID.randomUUID().toString().replace("-", ""), LOCAL_TLD };
+ if (useShortFormat) {
+ // A short hostname helps reduce the size of APF mDNS filtering programs, and
+ // is necessary for compatibility with some Matter 1.0 devices which assumed
+ // 16 characters is the maximum length.
+ // Generate a hostname matching Android_[0-9A-Z]{8}, which has 36^8 possibilities.
+ // Even with 100 devices advertising the probability of collision is around 2E-9,
+ // which is negligible.
+ final SecureRandom sr = new SecureRandom();
+ final String allowedChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+ final StringBuilder sb = new StringBuilder(8);
+ for (int i = 0; i < 8; i++) {
+ sb.append(allowedChars.charAt(sr.nextInt(allowedChars.length())));
+ }
+ return new String[]{ "Android_" + sb.toString(), LOCAL_TLD };
+ } else {
+ return new String[]{
+ "Android_" + UUID.randomUUID().toString().replace("-", ""), LOCAL_TLD};
+ }
}
}
@@ -825,7 +840,7 @@
mCb = cb;
mSocketProvider = socketProvider;
mDeps = deps;
- mDeviceHostName = deps.generateHostname();
+ mDeviceHostName = deps.generateHostname(mDnsFeatureFlags.isShortHostnamesEnabled());
mSharedLog = sharedLog;
mMdnsFeatureFlags = mDnsFeatureFlags;
final ConnectivityResources res = new ConnectivityResources(context);
@@ -943,7 +958,7 @@
mRegistrations.remove(id);
// Regenerates host name when registrations removed.
if (mRegistrations.size() == 0) {
- mDeviceHostName = mDeps.generateHostname();
+ mDeviceHostName = mDeps.generateHostname(mMdnsFeatureFlags.isShortHostnamesEnabled());
}
}
diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java b/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
index c4a9110..1cf5e4d 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
@@ -81,6 +81,12 @@
public static final String NSD_CACHED_SERVICES_REMOVAL = "nsd_cached_services_removal";
/**
+ * A feature flag to control whether to use shorter (16 characters + .local) hostnames, instead
+ * of Android_[32 characters] hostnames.
+ */
+ public static final String NSD_USE_SHORT_HOSTNAMES = "nsd_use_short_hostnames";
+
+ /**
* A feature flag to control the retention time for cached services.
*
* <p> Making the retention time configurable allows for testing and future adjustments.
@@ -130,6 +136,9 @@
// Flag for accurate delay callback
public final boolean mIsAccurateDelayCallbackEnabled;
+ // Flag to use shorter (16 characters + .local) hostnames
+ public final boolean mIsShortHostnamesEnabled;
+
@Nullable
private final FlagOverrideProvider mOverrideProvider;
@@ -225,6 +234,10 @@
NSD_CACHED_SERVICES_RETENTION_TIME, (int) mCachedServicesRetentionTime);
}
+ public boolean isShortHostnamesEnabled() {
+ return mIsShortHostnamesEnabled || isForceEnabledForTest(NSD_USE_SHORT_HOSTNAMES);
+ }
+
/**
* Indicates whether {@link #NSD_ACCURATE_DELAY_CALLBACK} is enabled, including for testing.
*/
@@ -248,6 +261,7 @@
boolean isCachedServicesRemovalEnabled,
long cachedServicesRetentionTime,
boolean isAccurateDelayCallbackEnabled,
+ boolean isShortHostnamesEnabled,
@Nullable FlagOverrideProvider overrideProvider) {
mIsMdnsOffloadFeatureEnabled = isOffloadFeatureEnabled;
mIncludeInetAddressRecordsInProbing = includeInetAddressRecordsInProbing;
@@ -261,6 +275,7 @@
mIsCachedServicesRemovalEnabled = isCachedServicesRemovalEnabled;
mCachedServicesRetentionTime = cachedServicesRetentionTime;
mIsAccurateDelayCallbackEnabled = isAccurateDelayCallbackEnabled;
+ mIsShortHostnamesEnabled = isShortHostnamesEnabled;
mOverrideProvider = overrideProvider;
}
@@ -285,6 +300,7 @@
private boolean mIsCachedServicesRemovalEnabled;
private long mCachedServicesRetentionTime;
private boolean mIsAccurateDelayCallbackEnabled;
+ private boolean mIsShortHostnamesEnabled;
private FlagOverrideProvider mOverrideProvider;
/**
@@ -303,6 +319,7 @@
mIsCachedServicesRemovalEnabled = false;
mCachedServicesRetentionTime = DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS;
mIsAccurateDelayCallbackEnabled = false;
+ mIsShortHostnamesEnabled = true; // Default enabled.
mOverrideProvider = null;
}
@@ -439,6 +456,16 @@
}
/**
+ * Set whether the short hostnames feature is enabled.
+ *
+ * @see #NSD_USE_SHORT_HOSTNAMES
+ */
+ public Builder setIsShortHostnamesEnabled(boolean isShortHostnamesEnabled) {
+ mIsShortHostnamesEnabled = isShortHostnamesEnabled;
+ return this;
+ }
+
+ /**
* Builds a {@link MdnsFeatureFlags} with the arguments supplied to this builder.
*/
public MdnsFeatureFlags build() {
@@ -454,6 +481,7 @@
mIsCachedServicesRemovalEnabled,
mCachedServicesRetentionTime,
mIsAccurateDelayCallbackEnabled,
+ mIsShortHostnamesEnabled,
mOverrideProvider);
}
}
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsAdvertiserTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/MdnsAdvertiserTest.kt
index df48f6c..ba62114 100644
--- a/tests/unit/java/com/android/server/connectivity/mdns/MdnsAdvertiserTest.kt
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsAdvertiserTest.kt
@@ -42,17 +42,20 @@
import java.util.Objects
import java.util.concurrent.CompletableFuture
import java.util.concurrent.TimeUnit
+import kotlin.test.assertTrue
import org.junit.After
import org.junit.Assert.assertEquals
import org.junit.Before
import org.junit.Test
import org.junit.runner.RunWith
import org.mockito.ArgumentCaptor
+import org.mockito.ArgumentMatchers.anyBoolean
import org.mockito.ArgumentMatchers.eq
import org.mockito.Mockito.any
import org.mockito.Mockito.anyInt
import org.mockito.Mockito.argThat
import org.mockito.Mockito.atLeastOnce
+import org.mockito.Mockito.doCallRealMethod
import org.mockito.Mockito.doReturn
import org.mockito.Mockito.mock
import org.mockito.Mockito.never
@@ -185,12 +188,12 @@
@Before
fun setUp() {
thread.start()
- doReturn(TEST_HOSTNAME).`when`(mockDeps).generateHostname()
+ doReturn(TEST_HOSTNAME).`when`(mockDeps).generateHostname(anyBoolean())
doReturn(mockInterfaceAdvertiser1).`when`(mockDeps).makeAdvertiser(eq(mockSocket1),
- any(), any(), any(), any(), eq(TEST_HOSTNAME), any(), any()
+ any(), any(), any(), any(), any(), any(), any()
)
doReturn(mockInterfaceAdvertiser2).`when`(mockDeps).makeAdvertiser(eq(mockSocket2),
- any(), any(), any(), any(), eq(TEST_HOSTNAME), any(), any()
+ any(), any(), any(), any(), any(), any(), any()
)
doReturn(true).`when`(mockInterfaceAdvertiser1).isProbing(anyInt())
doReturn(true).`when`(mockInterfaceAdvertiser2).isProbing(anyInt())
@@ -578,11 +581,59 @@
fun testRemoveService_whenAllServiceRemoved_thenUpdateHostName() {
val advertiser =
MdnsAdvertiser(thread.looper, socketProvider, cb, mockDeps, sharedlog, flags, context)
- verify(mockDeps, times(1)).generateHostname()
+ verify(mockDeps, times(1)).generateHostname(anyBoolean())
postSync { advertiser.addOrUpdateService(SERVICE_ID_1, SERVICE_1,
DEFAULT_ADVERTISING_OPTION, TEST_CLIENT_UID_1) }
postSync { advertiser.removeService(SERVICE_ID_1) }
- verify(mockDeps, times(2)).generateHostname()
+ verify(mockDeps, times(2)).generateHostname(anyBoolean())
+ }
+
+ private fun doHostnameGenerationTest(shortHostname: Boolean): Array<String> {
+ doCallRealMethod().`when`(mockDeps).generateHostname(anyBoolean())
+ val flags = MdnsFeatureFlags.newBuilder().setIsShortHostnamesEnabled(shortHostname).build()
+ val advertiser =
+ MdnsAdvertiser(thread.looper, socketProvider, cb, mockDeps, sharedlog, flags, context)
+ postSync { advertiser.addOrUpdateService(SERVICE_ID_1, SERVICE_1,
+ DEFAULT_ADVERTISING_OPTION, TEST_CLIENT_UID_1) }
+
+ val socketCbCaptor = ArgumentCaptor.forClass(SocketCallback::class.java)
+ verify(socketProvider).requestSocket(eq(TEST_NETWORK_1), socketCbCaptor.capture())
+
+ val socketCb = socketCbCaptor.value
+ postSync { socketCb.onSocketCreated(TEST_SOCKETKEY_1, mockSocket1, listOf(TEST_LINKADDR)) }
+
+ val hostnameCaptor = ArgumentCaptor.forClass(Array<String>::class.java)
+ verify(mockDeps).makeAdvertiser(
+ eq(mockSocket1),
+ eq(listOf(TEST_LINKADDR)),
+ eq(thread.looper),
+ any(),
+ any(),
+ hostnameCaptor.capture(),
+ any(),
+ any()
+ )
+ return hostnameCaptor.value
+ }
+
+ @Test
+ fun testShortHostnameGeneration() {
+ val hostname = doHostnameGenerationTest(shortHostname = true)
+ // Short hostnames are [8 uppercase letters or digits].local
+ assertEquals(2, hostname.size)
+ assertTrue(Regex("Android_[A-Z0-9]{8}").matches(hostname[0]),
+ "Unexpected hostname: ${hostname.contentToString()}")
+ assertEquals("local", hostname[1])
+ }
+
+ @Test
+ fun testLongHostnameGeneration() {
+ val hostname = doHostnameGenerationTest(shortHostname = false)
+ // Long hostnames are Android_[32 lowercase hex characters].local
+ assertEquals(2, hostname.size)
+ assertTrue(Regex("Android_[a-f0-9]{32}").matches(hostname[0]),
+ "Unexpected hostname: ${hostname.contentToString()}")
+ assertEquals("local", hostname[1])
}
private fun postSync(r: () -> Unit) {