Also use other compressed names in DNS compression
The previous implementation of writeLabels would not include a
compressed name in the label dictionary, so if a packet had
"something.local", "a.service.local" and "b.service.local",
"service.local" would not be compressed because "a.service.local"
already used compression (for .local).
Fix this and add a test.
Bug: 254166302
Test: atest
Change-Id: I41c557d6debd11acb4c0813735ef7af7323f45d7
diff --git a/service/mdns/com/android/server/connectivity/mdns/MdnsPacketWriter.java b/service/mdns/com/android/server/connectivity/mdns/MdnsPacketWriter.java
index 1f22fa9..c0f9b8b 100644
--- a/service/mdns/com/android/server/connectivity/mdns/MdnsPacketWriter.java
+++ b/service/mdns/com/android/server/connectivity/mdns/MdnsPacketWriter.java
@@ -192,22 +192,31 @@
}
}
+ final int[] offsets;
if (suffixLength > 0) {
- for (int i = 0; i < (labels.length - suffixLength); ++i) {
- writeString(labels[i]);
- }
+ offsets = writePartialLabelsNoCompression(labels, labels.length - suffixLength);
writePointer(suffixPointer);
} else {
- int[] offsets = writeLabelsNoCompression(labels);
-
- // Add entries to the label dictionary for each suffix of the label list, including
- // the whole list itself.
- for (int i = 0, len = labels.length; i < labels.length; ++i, --len) {
- String[] value = new String[len];
- System.arraycopy(labels, i, value, 0, len);
- labelDictionary.put(offsets[i], value);
- }
+ offsets = writeLabelsNoCompression(labels);
}
+
+ // Add entries to the label dictionary for each suffix of the label list, including
+ // the whole list itself.
+ // Do not replace the last suffixLength suffixes that already have dictionary entries.
+ for (int i = 0, len = labels.length; i < labels.length - suffixLength; ++i, --len) {
+ String[] value = new String[len];
+ System.arraycopy(labels, i, value, 0, len);
+ labelDictionary.put(offsets[i], value);
+ }
+ }
+
+ private int[] writePartialLabelsNoCompression(String[] labels, int count) throws IOException {
+ int[] offsets = new int[count];
+ for (int i = 0; i < count; ++i) {
+ offsets[i] = getWritePosition();
+ writeString(labels[i]);
+ }
+ return offsets;
}
/**
@@ -216,11 +225,7 @@
* @return The offsets where each label was written to.
*/
public int[] writeLabelsNoCompression(String[] labels) throws IOException {
- int[] offsets = new int[labels.length];
- for (int i = 0; i < labels.length; ++i) {
- offsets[i] = getWritePosition();
- writeString(labels[i]);
- }
+ final int[] offsets = writePartialLabelsNoCompression(labels, labels.length);
writeUInt8(0); // NUL terminator
return offsets;
}
@@ -246,4 +251,4 @@
public DatagramPacket getPacket(SocketAddress destAddress) throws IOException {
return new DatagramPacket(data, pos, destAddress);
}
-}
\ No newline at end of file
+}
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsPacketWriterTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/MdnsPacketWriterTest.kt
new file mode 100644
index 0000000..5c9c294
--- /dev/null
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsPacketWriterTest.kt
@@ -0,0 +1,55 @@
+/*
+ * 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.net.InetAddresses
+import android.os.Build
+import com.android.testutils.DevSdkIgnoreRule.IgnoreUpTo
+import com.android.testutils.DevSdkIgnoreRunner
+import java.net.InetSocketAddress
+import kotlin.test.assertContentEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(DevSdkIgnoreRunner::class)
+@IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class MdnsPacketWriterTest {
+ @Test
+ fun testNameCompression() {
+ val writer = MdnsPacketWriter(ByteArray(1000))
+ writer.writeLabels(arrayOf("my", "first", "name"))
+ writer.writeLabels(arrayOf("my", "second", "name"))
+ writer.writeLabels(arrayOf("other", "first", "name"))
+ writer.writeLabels(arrayOf("my", "second", "name"))
+ writer.writeLabels(arrayOf("unrelated"))
+
+ val packet = writer.getPacket(
+ InetSocketAddress(InetAddresses.parseNumericAddress("2001:db8::123"), 123))
+
+ // Each label takes length + 1. So "first.name" offset = 3, "name" offset = 9
+ val expected = "my".label() + "first".label() + "name".label() + 0x00.toByte() +
+ // "my.second.name" offset = 15
+ "my".label() + "second".label() + byteArrayOf(0xC0.toByte(), 9) +
+ "other".label() + byteArrayOf(0xC0.toByte(), 3) +
+ byteArrayOf(0xC0.toByte(), 15) +
+ "unrelated".label() + 0x00.toByte()
+
+ assertContentEquals(expected, packet.data.copyOfRange(0, packet.length))
+ }
+}
+
+private fun String.label() = byteArrayOf(length.toByte()) + encodeToByteArray()
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt
index cc75191..419121c 100644
--- a/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsProberTest.kt
@@ -160,14 +160,11 @@
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"
+ "000000094020A6D79686F73746E616D65C022C02D00210001000000780008000000009403C052C00" +
+ "C0010000100000078001211746573744B65793D7465737456616C7565"
assertProbesSent(probeInfo, expected)
}