https://source.android.com/ 
/*
 * Copyright (C) 2007 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 android.util;

import android.annotation.SystemApi;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


Access to the system diagnostic event record.  System diagnostic events are
used to record certain system-level events (such as garbage collection,
activity manager state, system watchdogs, and other low level activity),
which may be automatically collected and analyzed during system development.

This is not the main "logcat" debugging log (Log)! These diagnostic events are for system integrators, not application authors. 
Events use integer tag codes corresponding to /system/etc/event-log-tags.
They carry a payload of one or more int, long, or String values.  The
event-log-tags file defines the payload contents for each type code.

/**
 * Access to the system diagnostic event record.  System diagnostic events are
 * used to record certain system-level events (such as garbage collection,
 * activity manager state, system watchdogs, and other low level activity),
 * which may be automatically collected and analyzed during system development.
 *
 * <p>This is <b>not</b> the main "logcat" debugging log ({@link android.util.Log})!
 * These diagnostic events are for system integrators, not application authors.
 *
 * <p>Events use integer tag codes corresponding to /system/etc/event-log-tags.
 * They carry a payload of one or more int, long, or String values.  The
 * event-log-tags file defines the payload contents for each type code.
 */
public class EventLog {
    
@hide
/** @hide */ public EventLog() {}

    private static final String TAG = "EventLog";

    private static final String TAGS_FILE = "/system/etc/event-log-tags";
    private static final String COMMENT_PATTERN = "^\\s*(#.*)?$";
    private static final String TAG_PATTERN = "^\\s*(\\d+)\\s+(\\w+)\\s*(\\(.*\\))?\\s*$";
    private static HashMap<String, Integer> sTagCodes = null;
    private static HashMap<Integer, String> sTagNames = null;

    
A previously logged event read from the logs. Instances are thread safe. 
/** A previously logged event read from the logs. Instances are thread safe. */
    public static final class Event {
        private final ByteBuffer mBuffer;
        private Exception mLastWtf;

        // Layout of event log entry received from Android logger.
        //  see system/core/include/log/log.h
        private static final int LENGTH_OFFSET = 0;
        private static final int HEADER_SIZE_OFFSET = 2;
        private static final int PROCESS_OFFSET = 4;
        private static final int THREAD_OFFSET = 8;
        private static final int SECONDS_OFFSET = 12;
        private static final int NANOSECONDS_OFFSET = 16;
        private static final int UID_OFFSET = 24;

        // Layout for event log v1 format, v2 and v3 use HEADER_SIZE_OFFSET
        private static final int V1_PAYLOAD_START = 20;
        private static final int DATA_OFFSET = 4;

        // Value types
        private static final byte INT_TYPE    = 0;
        private static final byte LONG_TYPE   = 1;
        private static final byte STRING_TYPE = 2;
        private static final byte LIST_TYPE   = 3;
        private static final byte FLOAT_TYPE = 4;

        
Params:
  • data – containing event, read from the system
/** @param data containing event, read from the system */
        /*package*/ Event(byte[] data) {
            mBuffer = ByteBuffer.wrap(data);
            mBuffer.order(ByteOrder.nativeOrder());
        }

        
Returns:the process ID which wrote the log entry
/** @return the process ID which wrote the log entry */
        public int getProcessId() {
            return mBuffer.getInt(PROCESS_OFFSET);
        }

        
Returns:the UID which wrote the log entry
@hide
/**
         * @return the UID which wrote the log entry
         * @hide
         */
        @SystemApi
        public int getUid() {
            try {
                return mBuffer.getInt(UID_OFFSET);
            } catch (IndexOutOfBoundsException e) {
                // buffer won't contain the UID if the caller doesn't have permission.
                return -1;
            }
        }

        
Returns:the thread ID which wrote the log entry
/** @return the thread ID which wrote the log entry */
        public int getThreadId() {
            return mBuffer.getInt(THREAD_OFFSET);
        }

        
Returns:the wall clock time when the entry was written
/** @return the wall clock time when the entry was written */
        public long getTimeNanos() {
            return mBuffer.getInt(SECONDS_OFFSET) * 1000000000l
                    + mBuffer.getInt(NANOSECONDS_OFFSET);
        }

        
Returns:the type tag code of the entry
/** @return the type tag code of the entry */
        public int getTag() {
            int offset = mBuffer.getShort(HEADER_SIZE_OFFSET);
            if (offset == 0) {
                offset = V1_PAYLOAD_START;
            }
            return mBuffer.getInt(offset);
        }

        
Returns:one of Integer, Long, Float, String, null, or Object[] of same.
/** @return one of Integer, Long, Float, String, null, or Object[] of same. */
        public synchronized Object getData() {
            try {
                int offset = mBuffer.getShort(HEADER_SIZE_OFFSET);
                if (offset == 0) {
                    offset = V1_PAYLOAD_START;
                }
                mBuffer.limit(offset + mBuffer.getShort(LENGTH_OFFSET));
                if ((offset + DATA_OFFSET) >= mBuffer.limit()) {
                    // no payload
                    return null;
                }
                mBuffer.position(offset + DATA_OFFSET); // Just after the tag.
                return decodeObject();
            } catch (IllegalArgumentException e) {
                Log.wtf(TAG, "Illegal entry payload: tag=" + getTag(), e);
                mLastWtf = e;
                return null;
            } catch (BufferUnderflowException e) {
                Log.wtf(TAG, "Truncated entry payload: tag=" + getTag(), e);
                mLastWtf = e;
                return null;
            }
        }

        
Returns:the loggable item at the current position in mBuffer.
/** @return the loggable item at the current position in mBuffer. */
        private Object decodeObject() {
            byte type = mBuffer.get();
            switch (type) {
            case INT_TYPE:
                return mBuffer.getInt();

            case LONG_TYPE:
                return mBuffer.getLong();

            case FLOAT_TYPE:
                return mBuffer.getFloat();

            case STRING_TYPE:
                try {
                    int length = mBuffer.getInt();
                    int start = mBuffer.position();
                    mBuffer.position(start + length);
                    return new String(mBuffer.array(), start, length, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    Log.wtf(TAG, "UTF-8 is not supported", e);
                    mLastWtf = e;
                    return null;
                }

            case LIST_TYPE:
                int length = mBuffer.get();
                if (length < 0) length += 256;  // treat as signed byte
                Object[] array = new Object[length];
                for (int i = 0; i < length; ++i) array[i] = decodeObject();
                return array;

            default:
                throw new IllegalArgumentException("Unknown entry type: " + type);
            }
        }

        
@hide
/** @hide */
        public static Event fromBytes(byte[] data) {
            return new Event(data);
        }

        
@hide
/** @hide */
        public byte[] getBytes() {
            byte[] bytes = mBuffer.array();
            return Arrays.copyOf(bytes, bytes.length);
        }

        
Retreive the last WTF error generated by this object.

@hide
/**
         * Retreive the last WTF error generated by this object.
         * @hide
         */
        //VisibleForTesting
        public Exception getLastError() {
            return mLastWtf;
        }

        
Clear the error state for this object.

@hide
/**
         * Clear the error state for this object.
         * @hide
         */
        //VisibleForTesting
        public void clearError() {
            mLastWtf = null;
        }

        
@hide
/**
         * @hide
         */
        @Override
        public boolean equals(Object o) {
            // Not using ByteBuffer.equals since it takes buffer position into account and we
            // always use absolute positions here.
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Event other = (Event) o;
            return Arrays.equals(mBuffer.array(), other.mBuffer.array());
        }

        
@hide
/**
         * @hide
         */
        @Override
        public int hashCode() {
            // Not using ByteBuffer.hashCode since it takes buffer position into account and we
            // always use absolute positions here.
            return Arrays.hashCode(mBuffer.array());
        }
    }

    // We assume that the native methods deal with any concurrency issues.

    
Record an event log message.

Params:
  • tag – The event type tag code
  • value – A value to log
Returns:The number of bytes written
/**
     * Record an event log message.
     * @param tag The event type tag code
     * @param value A value to log
     * @return The number of bytes written
     */
    public static native int writeEvent(int tag, int value);

    
Record an event log message.

Params:
  • tag – The event type tag code
  • value – A value to log
Returns:The number of bytes written
/**
     * Record an event log message.
     * @param tag The event type tag code
     * @param value A value to log
     * @return The number of bytes written
     */
    public static native int writeEvent(int tag, long value);

    
Record an event log message.

Params:
  • tag – The event type tag code
  • value – A value to log
Returns:The number of bytes written
/**
     * Record an event log message.
     * @param tag The event type tag code
     * @param value A value to log
     * @return The number of bytes written
     */
    public static native int writeEvent(int tag, float value);

    
Record an event log message.

Params:
  • tag – The event type tag code
  • str – A value to log
Returns:The number of bytes written
/**
     * Record an event log message.
     * @param tag The event type tag code
     * @param str A value to log
     * @return The number of bytes written
     */
    public static native int writeEvent(int tag, String str);

    
Record an event log message.

Params:
  • tag – The event type tag code
  • list – A list of values to log
Returns:The number of bytes written
/**
     * Record an event log message.
     * @param tag The event type tag code
     * @param list A list of values to log
     * @return The number of bytes written
     */
    public static native int writeEvent(int tag, Object... list);

    
Read events from the log, filtered by type.

Params:
  • tags – to search for
  • output – container to add events into
Throws:
/**
     * Read events from the log, filtered by type.
     * @param tags to search for
     * @param output container to add events into
     * @throws IOException if something goes wrong reading events
     */
    public static native void readEvents(int[] tags, Collection<Event> output)
            throws IOException;

    
Read events from the log, filtered by type, blocking until logs are about to be overwritten.

Params:
  • tags – to search for
  • timestamp – timestamp allow logs before this time to be overwritten.
  • output – container to add events into
Throws:
@hide
/**
     * Read events from the log, filtered by type, blocking until logs are about to be overwritten.
     * @param tags to search for
     * @param timestamp timestamp allow logs before this time to be overwritten.
     * @param output container to add events into
     * @throws IOException if something goes wrong reading events
     * @hide
     */
    @SystemApi
    public static native void readEventsOnWrapping(int[] tags, long timestamp,
            Collection<Event> output)
            throws IOException;

    
Get the name associated with an event type tag code.

Params:
  • tag – code to look up
Returns:the name of the tag, or null if no tag has that number
/**
     * Get the name associated with an event type tag code.
     * @param tag code to look up
     * @return the name of the tag, or null if no tag has that number
     */
    public static String getTagName(int tag) {
        readTagsFile();
        return sTagNames.get(tag);
    }

    
Get the event type tag code associated with an event name.

Params:
  • name – of event to look up
Returns:the tag code, or -1 if no tag has that name
/**
     * Get the event type tag code associated with an event name.
     * @param name of event to look up
     * @return the tag code, or -1 if no tag has that name
     */
    public static int getTagCode(String name) {
        readTagsFile();
        Integer code = sTagCodes.get(name);
        return code != null ? code : -1;
    }

    
Read TAGS_FILE, populating sTagCodes and sTagNames, if not already done.

/**
     * Read TAGS_FILE, populating sTagCodes and sTagNames, if not already done.
     */
    private static synchronized void readTagsFile() {
        if (sTagCodes != null && sTagNames != null) return;

        sTagCodes = new HashMap<String, Integer>();
        sTagNames = new HashMap<Integer, String>();

        Pattern comment = Pattern.compile(COMMENT_PATTERN);
        Pattern tag = Pattern.compile(TAG_PATTERN);
        BufferedReader reader = null;
        String line;

        try {
            reader = new BufferedReader(new FileReader(TAGS_FILE), 256);
            while ((line = reader.readLine()) != null) {
                if (comment.matcher(line).matches()) continue;

                Matcher m = tag.matcher(line);
                if (!m.matches()) {
                    Log.wtf(TAG, "Bad entry in " + TAGS_FILE + ": " + line);
                    continue;
                }

                try {
                    int num = Integer.parseInt(m.group(1));
                    String name = m.group(2);
                    sTagCodes.put(name, num);
                    sTagNames.put(num, name);
                } catch (NumberFormatException e) {
                    Log.wtf(TAG, "Error in " + TAGS_FILE + ": " + line, e);
                }
            }
        } catch (IOException e) {
            Log.wtf(TAG, "Error reading " + TAGS_FILE, e);
            // Leave the maps existing but unpopulated
        } finally {
            try { if (reader != null) reader.close(); } catch (IOException e) {}
        }
    }
}