services/usb/java/com/android/server/usb/UsbDeviceLogger.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.usb;

import android.util.Log;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.util.dump.DualDumpOutputStream;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.LinkedList;

/**
* Constructor UsbDeviceLogger class
*/
public class UsbDeviceLogger {
    private final Object mLock = new Object();

    // ring buffer of events to log.
    @GuardedBy("mLock")
    private final LinkedList<Event> mEvents;

    private final String mTitle;

    // the maximum number of events to keep in log
    private final int mMemSize;

    /**
     * Constructor for Event class.
     */
    public abstract static class Event {
        // formatter for timestamps
        private static final SimpleDateFormat sFormat = new SimpleDateFormat("MM-dd HH:mm:ss:SSS");

        private final Calendar mCalendar;

        Event() {
            mCalendar = Calendar.getInstance();
        }

    /**
     * Convert event to String
     * @return StringBuilder
     */
        public String toString() {
            return (new StringBuilder(String.format("%tm-%td %tH:%tM:%tS.%tL",
                    mCalendar, mCalendar, mCalendar, mCalendar, mCalendar, mCalendar)))
                    .append(" ").append(eventToString()).toString();
        }

        /**
         * Causes the string message for the event to appear in the logcat.
         * Here is an example of how to create a new event (a StringEvent), adding it to the logger
         * (an instance of UsbDeviceLoggerr) while also making it show in the logcat:
         * <pre>
         *     myLogger.log(
         *         (new StringEvent("something for logcat and logger")).printLog(MyClass.TAG) );
         * </pre>
         * @param tag the tag for the android.util.Log.v
         * @return the same instance of the event
         */
        public Event printLog(String tag) {
            Log.i(tag, eventToString());
            return this;
        }

        /**
         * Convert event to String.
         * This method is only called when the logger history is about to the dumped,
         * so this method is where expensive String conversions should be made, not when the Event
         * subclass is created.
         * Timestamp information will be automatically added, do not include it.
         * @return a string representation of the event that occurred.
         */
        public abstract String eventToString();
    }

    /**
    * Constructor StringEvent class
    */
    public static class StringEvent extends Event {
        private final String mMsg;

        public StringEvent(String msg) {
            mMsg = msg;
        }

        @Override
        public String eventToString() {
            return mMsg;
        }
    }

    /**
     * Constructor for logger.
     * @param size the maximum number of events to keep in log
     * @param title the string displayed before the recorded log
     */
    public UsbDeviceLogger(int size, String title) {
        mEvents = new LinkedList<Event>();
        mMemSize = size;
        mTitle = title;
    }

    /**
     * Constructor for logger.
     * @param evt the maximum number of events to keep in log
     */
    public synchronized void log(Event evt) {
        synchronized (mLock) {
            if (mEvents.size() >= mMemSize) {
                mEvents.removeFirst();
            }
            mEvents.add(evt);
        }
    }

    /**
     * Constructor for logger.
     * @param dump the maximum number of events to keep in log
     * @param id the category of events
     */
    public synchronized void dump(DualDumpOutputStream dump, long id) {
        dump.write("USB Event Log", id, mTitle);
        for (Event evt : mEvents) {
            dump.write("USB Event", id, evt.toString());
        }
    }
}