connectivity/mdns/MdnsFeatureFlags.java

/*
 * Copyright (C) 2021 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.annotation.Nullable;

/**
 * The class that contains mDNS feature flags;
 */
public class MdnsFeatureFlags {
    /**
     * A feature flag to control whether the mDNS offload is enabled or not.
     */
    public static final String NSD_FORCE_DISABLE_MDNS_OFFLOAD = "nsd_force_disable_mdns_offload";

    /**
     * A feature flag to control whether the probing question should include
     * InetAddressRecords or not.
     */
    public static final String INCLUDE_INET_ADDRESS_RECORDS_IN_PROBING =
            "include_inet_address_records_in_probing";
    /**
     * A feature flag to control whether expired services removal should be enabled.
     */
    public static final String NSD_EXPIRED_SERVICES_REMOVAL =
            "nsd_expired_services_removal";

    /**
     * A feature flag to control whether the label count limit should be enabled.
     */
    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";

    /**
     * A feature flag to control whether unicast replies should be enabled.
     *
     * <p>Enabling this feature causes replies to queries with the Query Unicast (QU) flag set to be
     * sent unicast instead of multicast, as per RFC6762 5.4.
     */
    public static final String NSD_UNICAST_REPLY_ENABLED = "nsd_unicast_reply_enabled";

    /**
     * A feature flag to control whether the aggressive query mode should be enabled.
     */
    public static final String NSD_AGGRESSIVE_QUERY_MODE = "nsd_aggressive_query_mode";

    /**
     * A feature flag to control whether the query with known-answer should be enabled.
     */
    public static final String NSD_QUERY_WITH_KNOWN_ANSWER = "nsd_query_with_known_answer";

    /**
     * A feature flag to avoid advertising empty TXT records, as per RFC 6763 6.1.
     */
    public static final String NSD_AVOID_ADVERTISING_EMPTY_TXT_RECORDS =
            "nsd_avoid_advertising_empty_txt_records";

    /**
     * A feature flag to control whether the cached services removal should be enabled.
     * The removal will be triggered if the retention time has elapsed after all listeners have been
     * unregistered from the service type client or the interface has been destroyed.
     */
    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.
     */
    public static final String NSD_CACHED_SERVICES_RETENTION_TIME =
            "nsd_cached_services_retention_time";
    public static final int DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS = 10000;

    /**
     * A feature flag to control whether the accurate delay callback should be enabled.
     */
    public static final String NSD_ACCURATE_DELAY_CALLBACK = "nsd_accurate_delay_callback";

    // Flag for offload feature
    public final boolean mIsMdnsOffloadFeatureEnabled;

    // Flag for including InetAddressRecords in probing questions.
    public final boolean mIncludeInetAddressRecordsInProbing;

    // Flag for expired services removal
    public final boolean mIsExpiredServicesRemovalEnabled;

    // Flag for label count limit
    public final boolean mIsLabelCountLimitEnabled;

    // Flag for known-answer suppression
    public final boolean mIsKnownAnswerSuppressionEnabled;

    // Flag to enable replying unicast to queries requesting unicast replies
    public final boolean mIsUnicastReplyEnabled;

    // Flag for aggressive query mode
    public final boolean mIsAggressiveQueryModeEnabled;

    // Flag for query with known-answer
    public final boolean mIsQueryWithKnownAnswerEnabled;

    // Flag for avoiding advertising empty TXT records
    public final boolean mAvoidAdvertisingEmptyTxtRecords;

    // Flag for cached services removal
    public final boolean mIsCachedServicesRemovalEnabled;

    // Retention Time for cached services
    public final long mCachedServicesRetentionTime;

    // 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;

    /**
     * A provider that can indicate whether a flag should be force-enabled for testing purposes.
     */
    public interface FlagOverrideProvider {
        /**
         * Indicates whether the flag should be force-enabled for testing purposes.
         */
        boolean isForceEnabledForTest(@NonNull String flag);


        /**
         * Get the int value of the flag for testing purposes.
         */
        int getIntValueForTest(@NonNull String flag, int defaultValue);
    }

    /**
     * Indicates whether the flag should be force-enabled for testing purposes.
     */
    private boolean isForceEnabledForTest(@NonNull String flag) {
        return mOverrideProvider != null && mOverrideProvider.isForceEnabledForTest(flag);
    }

    /**
     * Get the int value of the flag for testing purposes.
     *
     * @return the test int value, or given default value if it is unset or the OverrideProvider
     * doesn't exist.
     */
    private int getIntValueForTest(@NonNull String flag, int defaultValue) {
        if (mOverrideProvider == null) {
            return defaultValue;
        }
        return mOverrideProvider.getIntValueForTest(flag, defaultValue);
    }

    /**
     * Indicates whether {@link #NSD_UNICAST_REPLY_ENABLED} is enabled, including for testing.
     */
    public boolean isUnicastReplyEnabled() {
        return mIsUnicastReplyEnabled || isForceEnabledForTest(NSD_UNICAST_REPLY_ENABLED);
    }

    /**
     * Indicates whether {@link #NSD_AGGRESSIVE_QUERY_MODE} is enabled, including for testing.
     */
    public boolean isAggressiveQueryModeEnabled() {
        return mIsAggressiveQueryModeEnabled || isForceEnabledForTest(NSD_AGGRESSIVE_QUERY_MODE);
    }

    /**
     * Indicates whether {@link #NSD_KNOWN_ANSWER_SUPPRESSION} is enabled, including for testing.
     */
    public boolean isKnownAnswerSuppressionEnabled() {
        return mIsKnownAnswerSuppressionEnabled
                || isForceEnabledForTest(NSD_KNOWN_ANSWER_SUPPRESSION);
    }

    /**
     * Indicates whether {@link #NSD_QUERY_WITH_KNOWN_ANSWER} is enabled, including for testing.
     */
    public boolean isQueryWithKnownAnswerEnabled() {
        return mIsQueryWithKnownAnswerEnabled
                || isForceEnabledForTest(NSD_QUERY_WITH_KNOWN_ANSWER);
    }

    /**
     * Indicates whether {@link #NSD_AVOID_ADVERTISING_EMPTY_TXT_RECORDS} is enabled, including for
     * testing.
     */
    public boolean avoidAdvertisingEmptyTxtRecords() {
        return mAvoidAdvertisingEmptyTxtRecords
                || isForceEnabledForTest(NSD_AVOID_ADVERTISING_EMPTY_TXT_RECORDS);
    }

    /**
     * Indicates whether {@link #NSD_CACHED_SERVICES_REMOVAL} is enabled, including for testing.
     */
    public boolean isCachedServicesRemovalEnabled() {
        return mIsCachedServicesRemovalEnabled
                || isForceEnabledForTest(NSD_CACHED_SERVICES_REMOVAL);
    }

    /**
     * Get the value which is set to {@link #NSD_CACHED_SERVICES_RETENTION_TIME}, including for
     * testing.
     */
    public long getCachedServicesRetentionTime() {
        return getIntValueForTest(
                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.
     */
    public boolean isAccurateDelayCallbackEnabled() {
        return mIsAccurateDelayCallbackEnabled
                || isForceEnabledForTest(NSD_ACCURATE_DELAY_CALLBACK);
    }

    /**
     * The constructor for {@link MdnsFeatureFlags}.
     */
    public MdnsFeatureFlags(boolean isOffloadFeatureEnabled,
            boolean includeInetAddressRecordsInProbing,
            boolean isExpiredServicesRemovalEnabled,
            boolean isLabelCountLimitEnabled,
            boolean isKnownAnswerSuppressionEnabled,
            boolean isUnicastReplyEnabled,
            boolean isAggressiveQueryModeEnabled,
            boolean isQueryWithKnownAnswerEnabled,
            boolean avoidAdvertisingEmptyTxtRecords,
            boolean isCachedServicesRemovalEnabled,
            long cachedServicesRetentionTime,
            boolean isAccurateDelayCallbackEnabled,
            boolean isShortHostnamesEnabled,
            @Nullable FlagOverrideProvider overrideProvider) {
        mIsMdnsOffloadFeatureEnabled = isOffloadFeatureEnabled;
        mIncludeInetAddressRecordsInProbing = includeInetAddressRecordsInProbing;
        mIsExpiredServicesRemovalEnabled = isExpiredServicesRemovalEnabled;
        mIsLabelCountLimitEnabled = isLabelCountLimitEnabled;
        mIsKnownAnswerSuppressionEnabled = isKnownAnswerSuppressionEnabled;
        mIsUnicastReplyEnabled = isUnicastReplyEnabled;
        mIsAggressiveQueryModeEnabled = isAggressiveQueryModeEnabled;
        mIsQueryWithKnownAnswerEnabled = isQueryWithKnownAnswerEnabled;
        mAvoidAdvertisingEmptyTxtRecords = avoidAdvertisingEmptyTxtRecords;
        mIsCachedServicesRemovalEnabled = isCachedServicesRemovalEnabled;
        mCachedServicesRetentionTime = cachedServicesRetentionTime;
        mIsAccurateDelayCallbackEnabled = isAccurateDelayCallbackEnabled;
        mIsShortHostnamesEnabled = isShortHostnamesEnabled;
        mOverrideProvider = overrideProvider;
    }


    /** Returns a {@link Builder} for {@link MdnsFeatureFlags}. */
    public static Builder newBuilder() {
        return new Builder();
    }

    /** A builder to create {@link MdnsFeatureFlags}. */
    public static final class Builder {

        private boolean mIsMdnsOffloadFeatureEnabled;
        private boolean mIncludeInetAddressRecordsInProbing;
        private boolean mIsExpiredServicesRemovalEnabled;
        private boolean mIsLabelCountLimitEnabled;
        private boolean mIsKnownAnswerSuppressionEnabled;
        private boolean mIsUnicastReplyEnabled;
        private boolean mIsAggressiveQueryModeEnabled;
        private boolean mIsQueryWithKnownAnswerEnabled;
        private boolean mAvoidAdvertisingEmptyTxtRecords;
        private boolean mIsCachedServicesRemovalEnabled;
        private long mCachedServicesRetentionTime;
        private boolean mIsAccurateDelayCallbackEnabled;
        private boolean mIsShortHostnamesEnabled;
        private FlagOverrideProvider mOverrideProvider;

        /**
         * The constructor for {@link Builder}.
         */
        public Builder() {
            mIsMdnsOffloadFeatureEnabled = false;
            mIncludeInetAddressRecordsInProbing = false;
            mIsExpiredServicesRemovalEnabled = true; // Default enabled.
            mIsLabelCountLimitEnabled = true; // Default enabled.
            mIsKnownAnswerSuppressionEnabled = true; // Default enabled.
            mIsUnicastReplyEnabled = true; // Default enabled.
            mIsAggressiveQueryModeEnabled = false;
            mIsQueryWithKnownAnswerEnabled = false;
            mAvoidAdvertisingEmptyTxtRecords = true; // Default enabled.
            mIsCachedServicesRemovalEnabled = true; // Default enabled.
            mCachedServicesRetentionTime = DEFAULT_CACHED_SERVICES_RETENTION_TIME_MILLISECONDS;
            mIsAccurateDelayCallbackEnabled = false;
            mIsShortHostnamesEnabled = true; // Default enabled.
            mOverrideProvider = null;
        }

        /**
         * Set whether the mDNS offload feature is enabled.
         *
         * @see #NSD_FORCE_DISABLE_MDNS_OFFLOAD
         */
        public Builder setIsMdnsOffloadFeatureEnabled(boolean isMdnsOffloadFeatureEnabled) {
            mIsMdnsOffloadFeatureEnabled = isMdnsOffloadFeatureEnabled;
            return this;
        }

        /**
         * Set whether the probing question should include InetAddressRecords.
         *
         * @see #INCLUDE_INET_ADDRESS_RECORDS_IN_PROBING
         */
        public Builder setIncludeInetAddressRecordsInProbing(
                boolean includeInetAddressRecordsInProbing) {
            mIncludeInetAddressRecordsInProbing = includeInetAddressRecordsInProbing;
            return this;
        }

        /**
         * Set whether the expired services removal is enabled.
         *
         * @see #NSD_EXPIRED_SERVICES_REMOVAL
         */
        public Builder setIsExpiredServicesRemovalEnabled(boolean isExpiredServicesRemovalEnabled) {
            mIsExpiredServicesRemovalEnabled = isExpiredServicesRemovalEnabled;
            return this;
        }

        /**
         * Set whether the label count limit is enabled.
         *
         * @see #NSD_LIMIT_LABEL_COUNT
         */
        public Builder setIsLabelCountLimitEnabled(boolean isLabelCountLimitEnabled) {
            mIsLabelCountLimitEnabled = isLabelCountLimitEnabled;
            return this;
        }

        /**
         * Set whether the known-answer suppression is enabled.
         *
         * @see #NSD_KNOWN_ANSWER_SUPPRESSION
         */
        public Builder setIsKnownAnswerSuppressionEnabled(boolean isKnownAnswerSuppressionEnabled) {
            mIsKnownAnswerSuppressionEnabled = isKnownAnswerSuppressionEnabled;
            return this;
        }

        /**
         * Set whether the unicast reply feature is enabled.
         *
         * @see #NSD_UNICAST_REPLY_ENABLED
         */
        public Builder setIsUnicastReplyEnabled(boolean isUnicastReplyEnabled) {
            mIsUnicastReplyEnabled = isUnicastReplyEnabled;
            return this;
        }

        /**
         * Set a {@link FlagOverrideProvider} to be used by {@link #isForceEnabledForTest(String)}.
         *
         * If non-null, features that use {@link #isForceEnabledForTest(String)} will use that
         * provider to query whether the flag should be force-enabled.
         */
        public Builder setOverrideProvider(@Nullable FlagOverrideProvider overrideProvider) {
            mOverrideProvider = overrideProvider;
            return this;
        }

        /**
         * Set whether the aggressive query mode is enabled.
         *
         * @see #NSD_AGGRESSIVE_QUERY_MODE
         */
        public Builder setIsAggressiveQueryModeEnabled(boolean isAggressiveQueryModeEnabled) {
            mIsAggressiveQueryModeEnabled = isAggressiveQueryModeEnabled;
            return this;
        }

        /**
         * Set whether the query with known-answer is enabled.
         *
         * @see #NSD_QUERY_WITH_KNOWN_ANSWER
         */
        public Builder setIsQueryWithKnownAnswerEnabled(boolean isQueryWithKnownAnswerEnabled) {
            mIsQueryWithKnownAnswerEnabled = isQueryWithKnownAnswerEnabled;
            return this;
        }

        /**
         * Set whether to avoid advertising empty TXT records.
         *
         * @see #NSD_AVOID_ADVERTISING_EMPTY_TXT_RECORDS
         */
        public Builder setAvoidAdvertisingEmptyTxtRecords(boolean avoidAdvertisingEmptyTxtRecords) {
            mAvoidAdvertisingEmptyTxtRecords = avoidAdvertisingEmptyTxtRecords;
            return this;
        }

        /**
         * Set whether the cached services removal is enabled.
         *
         * @see #NSD_CACHED_SERVICES_REMOVAL
         */
        public Builder setIsCachedServicesRemovalEnabled(boolean isCachedServicesRemovalEnabled) {
            mIsCachedServicesRemovalEnabled = isCachedServicesRemovalEnabled;
            return this;
        }

        /**
         * Set cached services retention time.
         *
         * @see #NSD_CACHED_SERVICES_RETENTION_TIME
         */
        public Builder setCachedServicesRetentionTime(long cachedServicesRetentionTime) {
            mCachedServicesRetentionTime = cachedServicesRetentionTime;
            return this;
        }

        /**
         * Set whether the accurate delay callback is enabled.
         *
         * @see #NSD_ACCURATE_DELAY_CALLBACK
         */
        public Builder setIsAccurateDelayCallbackEnabled(boolean isAccurateDelayCallbackEnabled) {
            mIsAccurateDelayCallbackEnabled = isAccurateDelayCallbackEnabled;
            return this;
        }

        /**
         * 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() {
            return new MdnsFeatureFlags(mIsMdnsOffloadFeatureEnabled,
                    mIncludeInetAddressRecordsInProbing,
                    mIsExpiredServicesRemovalEnabled,
                    mIsLabelCountLimitEnabled,
                    mIsKnownAnswerSuppressionEnabled,
                    mIsUnicastReplyEnabled,
                    mIsAggressiveQueryModeEnabled,
                    mIsQueryWithKnownAnswerEnabled,
                    mAvoidAdvertisingEmptyTxtRecords,
                    mIsCachedServicesRemovalEnabled,
                    mCachedServicesRetentionTime,
                    mIsAccurateDelayCallbackEnabled,
                    mIsShortHostnamesEnabled,
                    mOverrideProvider);
        }
    }
}