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MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections written in Java. The big version is a fork of the original MG4J that can handle more than 2^31 terms and documents.
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package it.unimi.dsi.big.mg4j.index.remote;

/*		 
 * MG4J: Managing Gigabytes for Java
 *
 * Copyright (C) 2006-2011 Sebastiano Vigna 
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 3 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, see .
 *
 */

import it.unimi.dsi.Util;
import it.unimi.dsi.fastutil.objects.AbstractObject2ObjectFunction;
import it.unimi.dsi.fastutil.objects.Object2ObjectFunction;
import it.unimi.dsi.lang.MutableString;
import it.unimi.dsi.util.LongInterval;
import it.unimi.dsi.util.LongIntervals;
import it.unimi.dsi.big.util.PrefixMap;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.net.Socket;
import java.net.SocketAddress;

import org.apache.log4j.Logger;

/** A remote prefix map.
 * 
 * @author Alessandro Arrabito
 * @author Sebastiano Vigna
 */

public class RemotePrefixMap extends RemoteTermMap implements PrefixMap, Serializable {
	public final static byte GET_INTERVAL = 3;
	public final static byte GET_PREFIX = 4;
	public final static byte HAS_PREFIXES = 5;

	static final long serialVersionUID = 1;
	/** Whether the remote map implements {@link PrefixMap#prefixMap()}. */
	private Boolean hasPrefixes;
	private AbstractObject2ObjectFunction prefixMap;
	private Object2ObjectFunction rangeMap;
	
	public RemotePrefixMap( final SocketAddress address, final long size ) {
		super( address, size );
	}
	
	private void ensureConnection() throws IOException {
		if ( remoteConnection == null ) remoteConnection = new RemoteIndexServerConnection( address, IndexServer.GET_PREFIX_MAP );
	}

	private boolean hasPrefixes() {
        if (hasPrefixes == null) {
            try {
                ensureConnection();
                remoteConnection.outputStream.writeByte( RemotePrefixMap.HAS_PREFIXES );
                remoteConnection.outputStream.flush();
                hasPrefixes = Boolean.valueOf( remoteConnection.inputStream.readBoolean() );
            }
            catch ( Exception e ) {
                    throw new RuntimeException( e );
            }
        }
        return hasPrefixes.booleanValue();
	}
	

	public static class ServerThread extends it.unimi.dsi.big.mg4j.index.remote.ServerThread {
		private static final boolean DEBUG = false;
		private final static Logger LOGGER = Util.getLogger( ServerThread.class );
		
		/** The remoted term map. */
		private final PrefixMap prefixMap;
		
		public ServerThread( final Socket socket, final PrefixMap prefixMap ) throws IOException {
			super( socket );
			this.prefixMap = prefixMap;
		}
		
		public void run() {
			try {
				final MutableString s = new MutableString();
				int command;
				LongInterval interval;

				for ( ;; ) {
					command = inputStream.readByte();
					if ( DEBUG ) LOGGER.debug( "Received remote command: " + command );

					switch ( command ) {
					case RemoteTermMap.GET_NUMBER:
						outputStream.writeLong( prefixMap.getLong( s.readSelfDelimUTF8( (InputStream)inputStream ) ) );
						outputStream.flush();
						break;

					case RemoteTermMap.GET_TERM:
						new MutableString( prefixMap.list().get( inputStream.readLong() ) ).writeSelfDelimUTF8( (OutputStream)outputStream );
						outputStream.flush();
						break;

					case RemoteTermMap.HAS_TERMS:
						outputStream.writeBoolean( prefixMap.list() != null );
						outputStream.flush();
						break;

					case RemotePrefixMap.GET_INTERVAL:
						interval = prefixMap.rangeMap().get( s.readSelfDelimUTF8( (InputStream)inputStream ) );
						outputStream.writeLong( interval.left );
						outputStream.writeLong( interval.right );
						outputStream.flush();
						break;

					case RemotePrefixMap.GET_PREFIX:
						new MutableString( prefixMap.prefixMap().get( LongInterval.valueOf( inputStream.readLong(), inputStream.readLong() ) ) ).writeSelfDelimUTF8( (OutputStream)outputStream );
						outputStream.flush();
						break;

					case RemotePrefixMap.HAS_PREFIXES:
						outputStream.writeBoolean( prefixMap.prefixMap() != null );
						outputStream.flush();
						break;

					default:
						LOGGER.error( "Unknown remote command: " + command );
					}
				}
			}
			catch ( EOFException e ) {
				LOGGER.warn( "The socket has been closed" );
			}
			catch ( Exception e ) {
				LOGGER.fatal( e, e );
			}
		}
	}


	public Object2ObjectFunction prefixMap() {
		if ( hasPrefixes() && prefixMap == null ) prefixMap = new AbstractObject2ObjectFunction() {
			private static final long serialVersionUID = 1L;

			public boolean containsKey( Object o ) {
				LongInterval interval = (LongInterval)o;
				return interval != LongIntervals.EMPTY_INTERVAL && interval.left >= 0 && interval.right < RemotePrefixMap.this.size64();
			}

			public MutableString get( Object o ) {
				final LongInterval interval = (LongInterval)o;
				try {
					ensureConnection();
					remoteConnection.outputStream.writeByte( RemotePrefixMap.GET_PREFIX );
					remoteConnection.outputStream.writeLong( interval.left );
					remoteConnection.outputStream.writeLong( interval.right );
					remoteConnection.outputStream.flush();
					return new MutableString().readSelfDelimUTF8( (InputStream)remoteConnection.inputStream );
				}
				catch ( Exception e ) {
						throw new RuntimeException( e );
				}
			}

			public int size() {
				return -1;
			}
			
		};
		
		return prefixMap;
	}

	public Object2ObjectFunction rangeMap() {
		if ( rangeMap == null ) rangeMap = new AbstractObject2ObjectFunction() {
			private static final long serialVersionUID = 1L;

			public boolean containsKey( Object o ) {
				return get( o ) != LongIntervals.EMPTY_INTERVAL;
			}

			public LongInterval get( Object o ) {
				CharSequence prefix = (CharSequence)o;
				try {
					ensureConnection();
					remoteConnection.outputStream.writeByte( RemotePrefixMap.GET_INTERVAL );
					new MutableString( prefix ).writeSelfDelimUTF8( (OutputStream)remoteConnection.outputStream );
					remoteConnection.outputStream.flush();
					return LongInterval.valueOf( remoteConnection.inputStream.readLong(), remoteConnection.inputStream.readLong() );
				}
				catch ( Exception e ) {
					throw new RuntimeException( e );
				}
			}

			public int size() {
				return -1;
			}
			
		};
		
		return rangeMap;
	}
}