Log Buffer System

/**
 * Manages log buffer pipelines, recovery, cleanup, and HTTP endpoint
 * Responsible for loading, starting and stopping log buffer pipelines, creating concurrent writers,
 * starting cleaner service, and recovering logs from buffer
 */
public class LogBufferService extends AbstractIdleService {
    /**
     * Start log buffer service including pipeline loading and recovery
     * @throws Exception if service startup fails
     */
    protected void startUp() throws Exception;
    
    /**
     * Stop log buffer service and cleanup resources
     * @throws Exception if service shutdown fails  
     */
    protected void shutDown() throws Exception;
}

/**
 * Appends logs to log buffer file with automatic rotation
 * File format: <length><log_event> where length is Avro encoded int32
 * Files are named with monotonically increasing numbers: (max_file_id + 1).buf
 */
public class LogBufferWriter implements Flushable, Closeable {
    /**
     * Create log buffer writer with specified configuration
     * @param logEventSerializer Serializer for log events
     * @param locationFactory Factory for creating file locations
     * @param maxFileSizeInBytes Maximum file size before rotation
     * @param cleaner Cleanup runnable for old files
     */
    public LogBufferWriter(LoggingEventSerializer logEventSerializer, LocationFactory locationFactory, 
                          long maxFileSizeInBytes, Runnable cleaner);
    
    /**
     * Append log event to buffer file
     * @param logEvent Log event to append
     * @throws IOException if write operation fails
     */
    public void append(LogBufferEvent logEvent) throws IOException;
    
    /**
     * Flush buffered data to file system
     * @throws IOException if flush operation fails
     */
    public void flush() throws IOException;
    
    /**
     * Close writer and cleanup resources
     * @throws IOException if close operation fails
     */
    public void close() throws IOException;
}

/**
 * Thread-safe wrapper for LogBufferWriter supporting concurrent writes
 * Provides synchronization for multiple threads writing to the same log buffer
 */
public class ConcurrentLogBufferWriter implements Flushable, Closeable {
    /**
     * Create concurrent log buffer writer
     * @param logBufferWriter Underlying writer to wrap
     */
    public ConcurrentLogBufferWriter(LogBufferWriter logBufferWriter);
    
    /**
     * Thread-safe append operation
     * @param logEvent Log event to append
     * @throws IOException if write operation fails
     */
    public synchronized void append(LogBufferEvent logEvent) throws IOException;
    
    /**
     * Thread-safe flush operation
     * @throws IOException if flush operation fails
     */
    public synchronized void flush() throws IOException;
    
    /**
     * Thread-safe close operation
     * @throws IOException if close operation fails
     */
    public synchronized void close() throws IOException;
}

/**
 * HTTP handler for log buffer requests
 * Processes incoming log events through HTTP endpoints
 */
public class LogBufferHandler extends AbstractHttpHandler {
    // Handles HTTP requests for log buffer operations
    // POST /logBuffer - Process log events through buffer
}

/**
 * Service for recovering logs from buffer files
 * Handles recovery operations after system restarts or failures
 */
public class LogBufferRecoveryService extends AbstractIdleService {
    /**
     * Start recovery service
     * @throws Exception if recovery startup fails
     */
    protected void startUp() throws Exception;
    
    /**
     * Stop recovery service
     * @throws Exception if recovery shutdown fails
     */
    protected void shutDown() throws Exception;
}

/**
 * Reader for recovering log events from buffer files
 * Provides sequential access to log events stored in buffer files
 */
public class LogBufferReader implements Closeable {
    /**
     * Create log buffer reader for specified file
     * @param bufferFile File containing buffered log events
     * @param serializer Serializer for deserializing log events
     */
    public LogBufferReader(File bufferFile, LoggingEventSerializer serializer);
    
    /**
     * Read next log event from buffer
     * @return Next log event, or null if end of file reached
     * @throws IOException if read operation fails
     */
    public LogBufferEvent readNext() throws IOException;
    
    /**
     * Close reader and cleanup resources
     * @throws IOException if close operation fails
     */
    public void close() throws IOException;
}

/**
 * Cleaner service for removing processed log buffer files
 * Automatically removes old buffer files that have been processed
 */
public class LogBufferCleaner {
    /**
     * Create log buffer cleaner with configuration
     * @param retentionPeriodMs Retention period for buffer files in milliseconds
     * @param cleanupIntervalMs Interval between cleanup runs in milliseconds
     */
    public LogBufferCleaner(long retentionPeriodMs, long cleanupIntervalMs);
    
    /**
     * Start cleanup operations
     * Begins periodic cleanup of old buffer files
     */
    public void start();
    
    /**
     * Stop cleanup operations
     * Stops periodic cleanup and cleans up resources
     */
    public void stop();
}

/**
 * Represents a log event in the buffer system
 * Wrapper for log events with buffer-specific metadata
 */
public class LogBufferEvent {
    /**
     * Get the underlying log event
     * @return ILoggingEvent containing the actual log data
     */
    public ILoggingEvent getLoggingEvent();
    
    /**
     * Get the timestamp of the event
     * @return Timestamp in milliseconds since epoch
     */
    public long getTimestamp();
}

/**
 * Request structure for log buffer operations
 * Contains log events and metadata for buffer processing
 */
public class LogBufferRequest {
    /**
     * Get log events in this request
     * @return List of log events to be buffered
     */
    public List<LogBufferEvent> getLogEvents();
    
    /**
     * Get request metadata
     * @return Map of metadata key-value pairs
     */
    public Map<String, String> getMetadata();
}

/**
 * Represents pending log buffer request awaiting processing
 * Used for managing queued requests in the buffer system
 */
public class PendingLogBufferRequest {
    /**
     * Get the underlying request
     * @return LogBufferRequest that is pending processing
     */
    public LogBufferRequest getRequest();
    
    /**
     * Get the submission timestamp
     * @return When this request was submitted for processing
     */
    public long getSubmissionTime();
}

/**
 * File offset information for log buffer files
 * Tracks position information for reading/writing buffer files
 */
public class LogBufferFileOffset {
    /**
     * Get the file identifier
     * @return Unique identifier for the buffer file
     */
    public String getFileId();
    
    /**
     * Get the offset within the file
     * @return Byte offset within the buffer file
     */
    public long getOffset();
}

/**
 * Pipeline configuration for log buffer processing
 * Defines how log buffer integrates with logging pipelines
 */
public class LogBufferPipelineConfig {
    /**
     * Get buffer directory path
     * @return Directory path where buffer files are stored
     */
    public String getBufferDir();
    
    /**
     * Get maximum file size for buffer files
     * @return Maximum size in bytes before file rotation
     */
    public long getMaxFileSize();
    
    /**
     * Get retention period for buffer files
     * @return Retention period in milliseconds
     */
    public long getRetentionPeriod();
}

/**
 * Log processor pipeline specifically for buffer processing
 * Integrates buffer operations with CDAP logging pipeline framework
 */
public class LogBufferProcessorPipeline extends LogProcessorPipelineContext {
    /**
     * Create buffer processor pipeline with configuration
     * @param config Pipeline configuration
     * @param checkpointManager Manager for tracking processing checkpoints
     */
    public LogBufferProcessorPipeline(LogBufferPipelineConfig config, CheckpointManager<LogBufferFileOffset> checkpointManager);
    
    /**
     * Start pipeline processing
     * @throws Exception if pipeline startup fails
     */
    public void start() throws Exception;
    
    /**
     * Stop pipeline processing
     * @throws Exception if pipeline shutdown fails
     */
    public void stop() throws Exception;
}

import io.cdap.cdap.logging.logbuffer.*;
import io.cdap.cdap.logging.serialize.LoggingEventSerializer;
import org.apache.twill.filesystem.LocalLocationFactory;

// Create log buffer writer
LoggingEventSerializer serializer = new LoggingEventSerializer();
LocalLocationFactory locationFactory = new LocalLocationFactory();
long maxFileSize = 64 * 1024 * 1024; // 64MB

LogBufferWriter writer = new LogBufferWriter(
    serializer, 
    locationFactory, 
    maxFileSize, 
    () -> System.out.println("Cleanup triggered")
);

// Create concurrent wrapper for multi-threaded access
ConcurrentLogBufferWriter concurrentWriter = new ConcurrentLogBufferWriter(writer);

// Append log events
LogBufferEvent event = // ... create log event
concurrentWriter.append(event);
concurrentWriter.flush();

// Cleanup
concurrentWriter.close();

// Recovery example
LogBufferRecoveryService recoveryService = // ... obtain recovery service
recoveryService.startUp(); // Recover any pending logs

// Cleanup configuration
LogBufferCleaner cleaner = new LogBufferCleaner(
    24 * 60 * 60 * 1000L, // 24 hour retention
    60 * 60 * 1000L       // 1 hour cleanup interval
);
cleaner.start();