services/core/java/com/android/server/ExtconStateObserver.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;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.os.FileUtils;
import android.util.Slog;

import java.io.File;
import java.io.IOException;

/**
 * A specialized ExtconUEventObserver that on receiving a {@link UEvent} calls {@link
 * #updateState(ExtconInfo, String, S)} with the value of{@link #parseState(ExtconInfo, String)}.
 *
 * @param <S> the type of state to parse and update
 * @hide
 */
public abstract class ExtconStateObserver<S> extends ExtconUEventObserver {
    private static final String TAG = "ExtconStateObserver";
    private static final boolean LOG = false;

    /**
     * Parses the current state from the state file for {@code extconInfo}.
     *
     * @param extconInfo the extconInfo to parse state for
     * @see #parseState(ExtconInfo, String)
     * @see ExtconInfo#getStatePath()
     */
    @Nullable
    public S parseStateFromFile(ExtconInfo extconInfo) throws IOException {
        String statePath = extconInfo.getStatePath();
        return parseState(
                extconInfo,
                FileUtils.readTextFile(new File(statePath), 0, null).trim());
    }

    @Override
    public void onUEvent(ExtconInfo extconInfo, UEvent event) {
        if (LOG) Slog.d(TAG, extconInfo.getName() + " UEVENT: " + event);
        String name = event.get("NAME");
        S state = parseState(extconInfo, event.get("STATE"));
        if (state != null) {
            updateState(extconInfo, name, state);
        }
    }

    /**
     * Subclasses of ExtconStateObserver should override this method update state for {@code
     * exconInfo} from an {@code UEvent}.
     *
     * @param extconInfo the external connection
     * @param eventName the {@code NAME} of the {@code UEvent}
     * @param state the{@code STATE} as parsed by {@link #parseState(ExtconInfo, String)}.
     */
    public abstract void updateState(ExtconInfo extconInfo, String eventName, @NonNull S state);

    /**
     * Subclasses of ExtconStateObserver should override this method to parse the {@code STATE} from
     * an UEvent.
     *
     * @param extconInfo that matches the {@code DEVPATH} of {@code event}
     * @param state the {@code STATE} from a {@code UEvent}.
     * @return the parsed state. Return null if the state can not be parsed.
     */
    @Nullable
    public abstract S parseState(ExtconInfo extconInfo, String state);
}