services/core/java/com/android/server/am/SettingsToPropertiesMapper.java

/*
 * Copyright (C) 2018 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.am;

import android.content.ContentResolver;
import android.database.ContentObserver;
import android.net.Uri;
import android.os.Build;
import android.os.SystemProperties;
import android.provider.Settings;
import android.text.TextUtils;
import android.util.Slog;

import com.android.internal.annotations.VisibleForTesting;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashSet;

/**
 * Maps system settings to system properties.
 * <p>The properties are dynamically updated when settings change.
 */
class SettingsToPropertiesMapper {

    private static final String TAG = "SettingsToPropertiesMapper";

    private static final String SYSTEM_PROPERTY_PREFIX = "persist.device_config.";

    private static final String RESET_PERFORMED_PROPERTY = "device_config.reset_performed";

    private static final String RESET_RECORD_FILE_PATH =
            "/data/server_configurable_flags/reset_flags";

    private static final String SYSTEM_PROPERTY_VALID_CHARACTERS_REGEX = "^[\\w\\.\\-@:]*$";

    private static final String SYSTEM_PROPERTY_INVALID_SUBSTRING = "..";

    private static final int SYSTEM_PROPERTY_MAX_LENGTH = 92;

    // experiment flags added to Global.Settings(before new "Config" provider table is available)
    // will be added under this category.
    private static final String GLOBAL_SETTINGS_CATEGORY = "global_settings";

    // Add the global setting you want to push to native level as experiment flag into this list.
    //
    // NOTE: please grant write permission system property prefix
    // with format persist.experiment.[experiment_category_name]. in system_server.te and grant read
    // permission in the corresponding .te file your feature belongs to.
    @VisibleForTesting
    static final String[] sGlobalSettings = new String[] {
    };

    @VisibleForTesting
    static final String[] sDeviceConfigScopes = new String[] {
    };

    private final String[] mGlobalSettings;

    private final String[] mDeviceConfigScopes;

    private final ContentResolver mContentResolver;

    @VisibleForTesting
    protected SettingsToPropertiesMapper(ContentResolver contentResolver,
            String[] globalSettings,
            String[] deviceConfigScopes) {
        mContentResolver = contentResolver;
        mGlobalSettings = globalSettings;
        mDeviceConfigScopes = deviceConfigScopes;
    }

    @VisibleForTesting
    void updatePropertiesFromSettings() {
        for (String globalSetting : mGlobalSettings) {
            Uri settingUri = Settings.Global.getUriFor(globalSetting);
            String propName = makePropertyName(GLOBAL_SETTINGS_CATEGORY, globalSetting);
            if (settingUri == null) {
                log("setting uri is null for globalSetting " + globalSetting);
                continue;
            }
            if (propName == null) {
                log("invalid prop name for globalSetting " + globalSetting);
                continue;
            }

            ContentObserver co = new ContentObserver(null) {
                @Override
                public void onChange(boolean selfChange) {
                    updatePropertyFromSetting(globalSetting, propName, true);
                }
            };

            // only updating on starting up when no native flags reset is performed during current
            // booting.
            if (!isNativeFlagsResetPerformed()) {
                updatePropertyFromSetting(globalSetting, propName, true);
            }
            mContentResolver.registerContentObserver(settingUri, false, co);
        }

        // TODO: address sDeviceConfigScopes after DeviceConfig APIs are available.
    }

    public static SettingsToPropertiesMapper start(ContentResolver contentResolver) {
        SettingsToPropertiesMapper mapper =  new SettingsToPropertiesMapper(
                contentResolver, sGlobalSettings, sDeviceConfigScopes);
        mapper.updatePropertiesFromSettings();
        return mapper;
    }

    /**
     * If native level flags reset has been performed as an attempt to recover from a crash loop
     * during current device booting.
     * @return
     */
    public boolean isNativeFlagsResetPerformed() {
        String value = systemPropertiesGet(RESET_PERFORMED_PROPERTY);
        return "true".equals(value);
    }

    /**
     * return an array of native flag categories under which flags got reset during current device
     * booting.
     * @return
     */
    public String[] getResetNativeCategories() {
        if (!isNativeFlagsResetPerformed()) {
            return new String[0];
        }

        String content = getResetFlagsFileContent();
        if (TextUtils.isEmpty(content)) {
            return new String[0];
        }

        String[] property_names = content.split(";");
        HashSet<String> categories = new HashSet<>();
        for (String property_name : property_names) {
            String[] segments = property_name.split("\\.");
            if (segments.length < 3) {
                log("failed to extract category name from property " + property_name);
                continue;
            }
            categories.add(segments[2]);
        }
        return categories.toArray(new String[0]);
    }

    /**
     * system property name constructing rule: "persist.device_config.[category_name].[flag_name]".
     * If the name contains invalid characters or substrings for system property name,
     * will return null.
     * @param categoryName
     * @param flagName
     * @return
     */
    @VisibleForTesting
    static String makePropertyName(String categoryName, String flagName) {
        String propertyName = SYSTEM_PROPERTY_PREFIX + categoryName + "." + flagName;

        if (!propertyName.matches(SYSTEM_PROPERTY_VALID_CHARACTERS_REGEX)
                || propertyName.contains(SYSTEM_PROPERTY_INVALID_SUBSTRING)) {
            return null;
        }

        return propertyName;
    }

    private String getSetting(String name, boolean isGlobalSetting) {
        if (isGlobalSetting) {
            return Settings.Global.getString(mContentResolver, name);
        } else {
            // TODO: complete the code after DeviceConfig APIs implemented.
            return null;
        }
    }

    private void setProperty(String key, String value) {
        // Check if need to clear the property
        if (value == null) {
            // It's impossible to remove system property, therefore we check previous value to
            // avoid setting an empty string if the property wasn't set.
            if (TextUtils.isEmpty(systemPropertiesGet(key))) {
                return;
            }
            value = "";
        } else if (value.length() > SYSTEM_PROPERTY_MAX_LENGTH) {
            log(value + " exceeds system property max length.");
            return;
        }

        try {
            systemPropertiesSet(key, value);
        } catch (Exception e) {
            // Failure to set a property can be caused by SELinux denial. This usually indicates
            // that the property wasn't whitelisted in sepolicy.
            // No need to report it on all user devices, only on debug builds.
            log("Unable to set property " + key + " value '" + value + "'", e);
        }
    }

    private static void log(String msg, Exception e) {
        if (Build.IS_DEBUGGABLE) {
            Slog.wtf(TAG, msg, e);
        } else {
            Slog.e(TAG, msg, e);
        }
    }

    private static void log(String msg) {
        if (Build.IS_DEBUGGABLE) {
            Slog.wtf(TAG, msg);
        } else {
            Slog.e(TAG, msg);
        }
    }

    @VisibleForTesting
    protected String systemPropertiesGet(String key) {
        return SystemProperties.get(key);
    }

    @VisibleForTesting
    protected void systemPropertiesSet(String key, String value) {
        SystemProperties.set(key, value);
    }

    @VisibleForTesting
    protected String getResetFlagsFileContent() {
        String content = null;
        try {
            File reset_flag_file = new File(RESET_RECORD_FILE_PATH);
            BufferedReader br = new BufferedReader(new FileReader(reset_flag_file));
            content = br.readLine();

            br.close();
        } catch (IOException ioe) {
            log("failed to read file " + RESET_RECORD_FILE_PATH, ioe);
        }
        return content;
    }

    @VisibleForTesting
    void updatePropertyFromSetting(String settingName, String propName, boolean isGlobalSetting) {
        String settingValue = getSetting(settingName, isGlobalSetting);
        setProperty(propName, settingValue);
    }
}