Add DnsSvcbPacket

DnsSvcbPacket will be used to parse DNS packet of type SVCB.

Bug: 240259333
Test: will add some tests in a follow-up change
Change-Id: Icb13d50f2d95a898b3b7ea373db876f41690723a

staticlibs/Android.bp

@@ -96,6 +96,7 @@ java_library {
     srcs: [
     "framework/**/DnsPacket.java",
     "framework/**/DnsPacketUtils.java",
+    "framework/**/DnsSvcbPacket.java",
     "framework/**/DnsSvcbRecord.java",
     "framework/**/HexDump.java",
     "framework/**/NetworkStackConstants.java",

staticlibs/framework/com/android/net/module/util/DnsSvcbPacket.java

@@ -0,0 +1,182 @@
+/*
+ * Copyright (C) 2023 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.net.module.util;
+
+import static android.net.DnsResolver.TYPE_A;
+import static android.net.DnsResolver.TYPE_AAAA;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.text.TextUtils;
+import android.util.Log;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.StringJoiner;
+
+/**
+ * A class for a DNS SVCB response packet.
+ *
+ * @hide
+ */
+public class DnsSvcbPacket extends DnsPacket {
+    public static final int TYPE_SVCB = 64;
+
+    private static final String TAG = DnsSvcbPacket.class.getSimpleName();
+
+    /**
+     * Creates a DnsSvcbPacket object from the given wire-format DNS packet.
+     */
+    private DnsSvcbPacket(@NonNull byte[] data) throws DnsPacket.ParseException {
+        // If data is null, ParseException will be thrown.
+        super(data);
+
+        final int questions = mHeader.getRecordCount(QDSECTION);
+        if (questions != 1) {
+            throw new DnsPacket.ParseException("Unexpected question count " + questions);
+        }
+        final int nsType = mRecords[QDSECTION].get(0).nsType;
+        if (nsType != TYPE_SVCB) {
+            throw new DnsPacket.ParseException("Unexpected query type " + nsType);
+        }
+    }
+
+    /**
+     * Returns true if the DnsSvcbPacket is a DNS response.
+     */
+    public boolean isResponse() {
+        return mHeader.isResponse();
+    }
+
+    /**
+     * Returns whether the given protocol alpn is supported.
+     */
+    public boolean isSupported(@NonNull String alpn) {
+        return findSvcbRecord(alpn) != null;
+    }
+
+    /**
+     * Returns the TargetName associated with the given protocol alpn.
+     * If the alpn is not supported, a null is returned.
+     */
+    @Nullable
+    public String getTargetName(@NonNull String alpn) {
+        final DnsSvcbRecord record = findSvcbRecord(alpn);
+        return (record != null) ? record.getTargetName() : null;
+    }
+
+    /**
+     * Returns the TargetName that associated with the given protocol alpn.
+     * If the alpn is not supported, -1 is returned.
+     */
+    public int getPort(@NonNull String alpn) {
+        final DnsSvcbRecord record = findSvcbRecord(alpn);
+        return (record != null) ? record.getPort() : -1;
+    }
+
+    /**
+     * Returns the IP addresses that support the given protocol alpn.
+     * If the alpn is not supported, an empty list is returned.
+     */
+    @NonNull
+    public List<InetAddress> getAddresses(@NonNull String alpn) {
+        final DnsSvcbRecord record = findSvcbRecord(alpn);
+        if (record == null) return Collections.EMPTY_LIST;
+
+        // As per draft-ietf-dnsop-svcb-https-10#section-7.4 and draft-ietf-add-ddr-10#section-4,
+        // if A/AAAA records are available in the Additional section, use the IP addresses in
+        // those records instead of the IP addresses in ipv4hint/ipv6hint.
+        final List<InetAddress> out = getAddressesFromAdditionalSection();
+        if (out.size() > 0) return out;
+
+        return record.getAddresses();
+    }
+
+    /**
+     * Returns the value of SVCB key dohpath that associated with the given protocol alpn.
+     * If the alpn is not supported, a null is returned.
+     */
+    @Nullable
+    public String getDohPath(@NonNull String alpn) {
+        final DnsSvcbRecord record = findSvcbRecord(alpn);
+        return (record != null) ? record.getDohPath() : null;
+    }
+
+    /**
+     * Returns the DnsSvcbRecord associated with the given protocol alpn.
+     * If the alpn is not supported, a null is returned.
+     */
+    @Nullable
+    private DnsSvcbRecord findSvcbRecord(@NonNull String alpn) {
+        for (final DnsRecord record : mRecords[ANSECTION]) {
+            if (record instanceof DnsSvcbRecord) {
+                final DnsSvcbRecord svcbRecord = (DnsSvcbRecord) record;
+                if (svcbRecord.getAlpns().contains(alpn)) {
+                    return svcbRecord;
+                }
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns the IP addresses in additional section.
+     */
+    @NonNull
+    private List<InetAddress> getAddressesFromAdditionalSection() {
+        final List<InetAddress> out = new ArrayList<InetAddress>();
+        if (mHeader.getRecordCount(ARSECTION) == 0) {
+            return out;
+        }
+        for (final DnsRecord record : mRecords[ARSECTION]) {
+            if (record.nsType != TYPE_A && record.nsType != TYPE_AAAA) {
+                Log.d(TAG, "Found type other than A/AAAA in Additional section: " + record.nsType);
+                continue;
+            }
+            try {
+                out.add(InetAddress.getByAddress(record.getRR()));
+            } catch (UnknownHostException e) {
+                Log.w(TAG, "Failed to parse address");
+            }
+        }
+        return out;
+    }
+
+    @Override
+    public String toString() {
+        final StringJoiner out = new StringJoiner(" ");
+        out.add("QUERY: [" + TextUtils.join(", ", mRecords[QDSECTION]) + "]");
+        out.add("ANSWER: [" + TextUtils.join(", ", mRecords[ANSECTION]) + "]");
+        out.add("AUTHORITY: [" + TextUtils.join(", ", mRecords[NSSECTION]) + "]");
+        out.add("ADDITIONAL: [" + TextUtils.join(", ", mRecords[ARSECTION]) + "]");
+        return out.toString();
+    }
+
+    /**
+     * Creates a DnsSvcbPacket object from the given wire-format DNS answer.
+     */
+    public static DnsSvcbPacket fromResponse(@NonNull byte[] data) throws DnsPacket.ParseException {
+        DnsSvcbPacket out = new DnsSvcbPacket(data);
+        if (!out.isResponse()) {
+            throw new DnsPacket.ParseException("Not an answer packet");
+        }
+        return out;
+    }
+}