source: gli/trunk/src/org/greenstone/gatherer/util/PortFinder.java@ 18987

package org.greenstone.gatherer.util;

/** Verbatim copy of what's in GS3's org.greenstone.server */

import java.io.IOException;
import java.net.ServerSocket;
import java.net.BindException;

// When needing to use sockets, this class can be used to find an available port
public class PortFinder {

    // Port numbers range from 0 to 65,535. RESERVED PORTS are below 1025
    // see http://www.gnu.org/software/hello/manual/libc/Ports.html
    public static final int MAX_PORT = 65535;
    public static final int PORTS_RESERVED = 1024;

    // Considering a limited range of ports that will be reused (circular buffer)
    public final int PORT_BASE;
    public final int PORT_BLOCK_SIZE;

    // Keep track of what port numbers we have checked for availability
    private int nextFreePort;

    // The socket port number that we will use
    private int port = -1;


    public PortFinder() {
    this( PORTS_RESERVED+1, (MAX_PORT - PORTS_RESERVED) );
    }

    public PortFinder(int base, int blocksize) {
    PORT_BASE = base;
    PORT_BLOCK_SIZE = blocksize;

    nextFreePort = PORT_BASE;
    }

    /** Circular buffer. Modifies the value of nextFreePort (the buffer index). */
    private void incrementNextFreePort() {
    int offset = nextFreePort - PORT_BASE;
    offset = (offset + 1) % PORT_BLOCK_SIZE;
    nextFreePort = PORT_BASE + offset;
    } 

    /** Finds the first available port in the range specified during Constructor call.
     *  @return the number of an available port.    
     */
    public int findPortInRange() throws Exception { 
    try {
        boolean foundFreePort = false;
        for(int i = 0; i < PORT_BLOCK_SIZE; i++) {
        
        if(isPortAvailable(nextFreePort)) {
            foundFreePort = true;
            break;
            
        } else {
            incrementNextFreePort();
        }
        }
        
        if(foundFreePort) {
        // Free port number currently found becomes the port number of the socket
        // that will be used
        this.port = nextFreePort;
        incrementNextFreePort();
        
        } else {
        throw new Exception("Cannot find an available port in the range " 
                    + PORT_BASE + "-" + (PORT_BASE+PORT_BLOCK_SIZE)
                    + "\nwhich is necessary for forcibly terminating wget.");
        }
        
    }catch(IOException e) {
        System.err.println("Error when trying to find an available port. In PortFinder.findPort() " + e);
    }
    return port;
    }

    /** @return true if the portnumber is in the valid range. */
    public static boolean isValidPortNumber(int portNum) {
    return (portNum >= 0 && portNum <= MAX_PORT);
    }

    /** @return true if the portnumber is in the useable range. */
    public static boolean isAssignablePortNumber(int portNum) {
    return (portNum > PORTS_RESERVED && portNum <= MAX_PORT);
    }

    /** Finds an available port.
     * @return the number of an available port.
     */
    public static int findAnyFreePort() throws Exception {  
    ServerSocket tmpSocket = null;
    int portNumber = -1;
    try {
        // Creates a server socket, bound to the specified port.
        // A port of 0 creates a socket on any free port. 
        tmpSocket = new ServerSocket(0);
        portNumber = tmpSocket.getLocalPort();
        tmpSocket.close();
    } catch(Exception e) {
        System.err.println("Unable to find a free port or close it. Got Exception: " + e);
        tmpSocket = null;
    }
    return portNumber;
    }

    /** @return true if the portnum is available for use */
    public static boolean isPortAvailable(int portnum) {
    ServerSocket tmpSocket = null;
    try {
        tmpSocket = new ServerSocket(portnum);
        tmpSocket.close();
        //System.err.println("Port " + portnum + " not yet in use.");
        return true;
        
    } catch(BindException ex){
        // "Signals that an error occurred while attempting to bind a 
        // socket to a local address and port. Typically, the port is 
        // in use, or the requested local address could not be assigned."
        System.err.println("Port " + portnum + " already in use or can't be assigned.");
        tmpSocket = null;
        return false;       
    } catch(Exception ex) { 
        // Some other problem creating or closing the server socket
        System.err.println("Problem creating or closing server socket at port " + portnum);
        tmpSocket = null;
        return false;
    }
    }
}