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Proxy.java

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/**************************************************************************
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package org.hebe.mps;

import java.io.*;
import java.net.*;

/**
 * This is the base class of all client-side MPS object handles. It
 * maintains a Connection object and an InputStream and an
 * OutputStream. There is very little behaviour on this object - the
 * automatically-generated subclasses provide all the functionality by
 * making use of this object's protected member variables.
 *
 * @author Tony Garnock-Jones <tonyg@kcbbs.gen.nz>
 * @see org.hebe.mps.Connection
 * @see org.hebe.mps.InputStream
 * @see org.hebe.mps.OutputStream
 */
public class Proxy {
    /** The connection to the remote object server. */
    private org.hebe.mps.Connection _connection;
    /** Pipe used when sending messages to the remote server. */
    private org.hebe.mps.OutputStream _output;
    /** Pipe used when receiving messages from the remote server. */
    private org.hebe.mps.InputStream _input;

    /**
     * Only invoked by subclass constructors. Creates a connection to
     * the named object, possibly using the naming service passed in,
     * if it is not null.
     *
     * @param resolvedName the name of the server to create a proxy for
     * @exception MPSException if anything goes wrong
     */
    protected Proxy(String resolvedName)
        throws MPSException
    {
        _connection = new Connection(resolvedName);
        _input = new InputStream(_connection);
        _output = new OutputStream(_connection);
    }

    /**
     * Disconnects this client proxy from the server. Closes the
     * socket. It'd be nice if eventually this was reversible -
     * subsequent calls to methods on the proxy should transparently
     * reconnect and succeed, but currently once the connection is
     * gone, it's gone.
     *
     * @exception MPSException if anything goes wrong
     */
    public void _disconnect_proxy() throws MPSException {
        _connection.close();
    }

    /**
     * Retrieve the canonical name of the server this proxy is
     * connected to. Used (occasionally) to pass references to MPS
     * objects around between MPS interfaces.
     *
     * @return the canonical name of the connected server
     * @see org.hebe.mps.OutputStream#writeReference
     */
    protected String getReference() {
        return _connection.getResolvedName();
    }

    /**
     * Returns a handle on this proxy's output stream for
     * communication with the server.
     */
    protected org.hebe.mps.OutputStream getOutputStream() {
        _output.writeint(_connection.getOid());
        return _output;
    }

    /**
     * Returns a handle on this proxy's input stream for
     * communication from the server.
     */
    protected org.hebe.mps.InputStream getInputStream()
        throws MPSException
    {
        if (_input.readint() != _connection.getOid()) {
            throw new MPSException("OID mismatch in Proxy.getInputStream");
        }
        return _input;
    }
}

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