Support mDns Known-Answer Suppression
Support the RFC 6762 section 7.1. Known-Answer Suppression.
If the response contains an answer that is also present in the
answer section and the known-answer's TTL is greater than half
of the original TTL, suppress the response.
Bug: 312657709
Test: atest FrameworksNetTests NsdManagerTest
Passed DUPLICAE SUPPRESSION test case of BCT
Change-Id: I1890e9fba068c1f59a1d93c3514f0e7d07da1814
diff --git a/service-t/src/com/android/server/NsdService.java b/service-t/src/com/android/server/NsdService.java
index 9c01dda..2ac2b18 100644
--- a/service-t/src/com/android/server/NsdService.java
+++ b/service-t/src/com/android/server/NsdService.java
@@ -1702,6 +1702,8 @@
mContext, MdnsFeatureFlags.NSD_EXPIRED_SERVICES_REMOVAL))
.setIsLabelCountLimitEnabled(mDeps.isTetheringFeatureNotChickenedOut(
mContext, MdnsFeatureFlags.NSD_LIMIT_LABEL_COUNT))
+ .setIsKnownAnswerSuppressionEnabled(mDeps.isFeatureEnabled(
+ mContext, MdnsFeatureFlags.NSD_KNOWN_ANSWER_SUPPRESSION))
.build();
mMdnsSocketClient =
new MdnsMultinetworkSocketClient(handler.getLooper(), mMdnsSocketProvider,
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 0a6d8c1..1ad47a3 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsFeatureFlags.java
@@ -41,6 +41,11 @@
*/
public static final String NSD_LIMIT_LABEL_COUNT = "nsd_limit_label_count";
+ /**
+ * A feature flag to control whether the known-answer suppression should be enabled.
+ */
+ public static final String NSD_KNOWN_ANSWER_SUPPRESSION = "nsd_known_answer_suppression";
+
// Flag for offload feature
public final boolean mIsMdnsOffloadFeatureEnabled;
@@ -53,17 +58,22 @@
// Flag for label count limit
public final boolean mIsLabelCountLimitEnabled;
+ // Flag for known-answer suppression
+ public final boolean mIsKnownAnswerSuppressionEnabled;
+
/**
* The constructor for {@link MdnsFeatureFlags}.
*/
public MdnsFeatureFlags(boolean isOffloadFeatureEnabled,
boolean includeInetAddressRecordsInProbing,
boolean isExpiredServicesRemovalEnabled,
- boolean isLabelCountLimitEnabled) {
+ boolean isLabelCountLimitEnabled,
+ boolean isKnownAnswerSuppressionEnabled) {
mIsMdnsOffloadFeatureEnabled = isOffloadFeatureEnabled;
mIncludeInetAddressRecordsInProbing = includeInetAddressRecordsInProbing;
mIsExpiredServicesRemovalEnabled = isExpiredServicesRemovalEnabled;
mIsLabelCountLimitEnabled = isLabelCountLimitEnabled;
+ mIsKnownAnswerSuppressionEnabled = isKnownAnswerSuppressionEnabled;
}
@@ -79,6 +89,7 @@
private boolean mIncludeInetAddressRecordsInProbing;
private boolean mIsExpiredServicesRemovalEnabled;
private boolean mIsLabelCountLimitEnabled;
+ private boolean mIsKnownAnswerSuppressionEnabled;
/**
* The constructor for {@link Builder}.
@@ -88,6 +99,7 @@
mIncludeInetAddressRecordsInProbing = false;
mIsExpiredServicesRemovalEnabled = false;
mIsLabelCountLimitEnabled = true; // Default enabled.
+ mIsKnownAnswerSuppressionEnabled = false;
}
/**
@@ -132,13 +144,24 @@
}
/**
+ * Set whether the known-answer suppression is enabled.
+ *
+ * @see #NSD_KNOWN_ANSWER_SUPPRESSION
+ */
+ public Builder setIsKnownAnswerSuppressionEnabled(boolean isKnownAnswerSuppressionEnabled) {
+ mIsKnownAnswerSuppressionEnabled = isKnownAnswerSuppressionEnabled;
+ return this;
+ }
+
+ /**
* Builds a {@link MdnsFeatureFlags} with the arguments supplied to this builder.
*/
public MdnsFeatureFlags build() {
return new MdnsFeatureFlags(mIsMdnsOffloadFeatureEnabled,
mIncludeInetAddressRecordsInProbing,
mIsExpiredServicesRemovalEnabled,
- mIsLabelCountLimitEnabled);
+ mIsLabelCountLimitEnabled,
+ mIsKnownAnswerSuppressionEnabled);
}
}
}
diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsRecordRepository.java b/service-t/src/com/android/server/connectivity/mdns/MdnsRecordRepository.java
index 1909208..d46a7b5 100644
--- a/service-t/src/com/android/server/connectivity/mdns/MdnsRecordRepository.java
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsRecordRepository.java
@@ -90,6 +90,7 @@
private final Looper mLooper;
@NonNull
private final String[] mDeviceHostname;
+ @NonNull
private final MdnsFeatureFlags mMdnsFeatureFlags;
public MdnsRecordRepository(@NonNull Looper looper, @NonNull String[] deviceHostname,
@@ -502,7 +503,7 @@
// Add answers from general records
addReplyFromService(question, mGeneralRecords, null /* servicePtrRecord */,
null /* serviceSrvRecord */, null /* serviceTxtRecord */, replyUnicast, now,
- answerInfo, additionalAnswerRecords);
+ answerInfo, additionalAnswerRecords, Collections.emptyList());
// Add answers from each service
for (int i = 0; i < mServices.size(); i++) {
@@ -510,7 +511,7 @@
if (registration.exiting || registration.isProbing) continue;
if (addReplyFromService(question, registration.allRecords, registration.ptrRecords,
registration.srvRecord, registration.txtRecord, replyUnicast, now,
- answerInfo, additionalAnswerRecords)) {
+ answerInfo, additionalAnswerRecords, packet.answers)) {
registration.repliedServiceCount++;
registration.sentPacketCount++;
}
@@ -563,6 +564,15 @@
return new MdnsReplyInfo(answerRecords, additionalAnswerRecords, delayMs, dest);
}
+ private boolean isKnownAnswer(MdnsRecord answer, @NonNull List<MdnsRecord> knownAnswerRecords) {
+ for (MdnsRecord knownAnswer : knownAnswerRecords) {
+ if (answer.equals(knownAnswer) && knownAnswer.getTtl() > (answer.getTtl() / 2)) {
+ return true;
+ }
+ }
+ return false;
+ }
+
/**
* Add answers and additional answers for a question, from a ServiceRegistration.
*/
@@ -572,7 +582,8 @@
@Nullable RecordInfo<MdnsServiceRecord> serviceSrvRecord,
@Nullable RecordInfo<MdnsTextRecord> serviceTxtRecord,
boolean replyUnicast, long now, @NonNull List<RecordInfo<?>> answerInfo,
- @NonNull List<MdnsRecord> additionalAnswerRecords) {
+ @NonNull List<MdnsRecord> additionalAnswerRecords,
+ @NonNull List<MdnsRecord> knownAnswerRecords) {
boolean hasDnsSdPtrRecordAnswer = false;
boolean hasDnsSdSrvRecordAnswer = false;
boolean hasFullyOwnedNameMatch = false;
@@ -601,6 +612,20 @@
}
hasKnownAnswer = true;
+
+ // RFC6762 7.1. Known-Answer Suppression:
+ // A Multicast DNS responder MUST NOT answer a Multicast DNS query if
+ // the answer it would give is already included in the Answer Section
+ // with an RR TTL at least half the correct value. If the RR TTL of the
+ // answer as given in the Answer Section is less than half of the true
+ // RR TTL as known by the Multicast DNS responder, the responder MUST
+ // send an answer so as to update the querier's cache before the record
+ // becomes in danger of expiration.
+ if (mMdnsFeatureFlags.mIsKnownAnswerSuppressionEnabled
+ && isKnownAnswer(info.record, knownAnswerRecords)) {
+ continue;
+ }
+
hasDnsSdPtrRecordAnswer |= (servicePtrRecords != null
&& CollectionUtils.any(servicePtrRecords, r -> info == r));
hasDnsSdSrvRecordAnswer |= (info == serviceSrvRecord);
@@ -612,8 +637,6 @@
continue;
}
- // TODO: Don't reply if in known answers of the querier (7.1) if TTL is > half
-
answerInfo.add(info);
}