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 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.rmi.server;

import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.lang.reflect.Proxy;
import java.net.MalformedURLException;
import java.net.URL;
import java.rmi.*;
import java.rmi.activation.*;
import java.rmi.server.Operation;
import java.rmi.server.RMIClassLoader;
import java.rmi.server.RemoteCall;
import java.rmi.server.RemoteObject;
import java.rmi.server.RemoteObjectInvocationHandler;
import java.rmi.server.RemoteRef;
import java.rmi.server.RemoteStub;

@SuppressWarnings("deprecation")
public class ActivatableRef implements RemoteRef {

    private static final long serialVersionUID = 7579060052569229166L;

    protected ActivationID id;
    protected RemoteRef ref;
    transient boolean force = false;

    private static final int MAX_RETRIES = 3;
    private static final String versionComplaint =
        "activation requires 1.2 stubs";

    
Create a new (empty) ActivatableRef
/**
     * Create a new (empty) ActivatableRef
     */
    public ActivatableRef()
    {}

    
Create a ActivatableRef with the specified id
/**
     * Create a ActivatableRef with the specified id
     */
    public ActivatableRef(ActivationID id, RemoteRef ref)
    {
        this.id = id;
        this.ref = ref;
    }

    
Returns the stub for the remote object whose class is
specified in the activation descriptor. The ActivatableRef
in the resulting stub has its activation id set to the
activation id supplied as the second argument.
/**
     * Returns the stub for the remote object whose class is
     * specified in the activation descriptor. The ActivatableRef
     * in the resulting stub has its activation id set to the
     * activation id supplied as the second argument.
     */
    public static Remote getStub(ActivationDesc desc, ActivationID id)
        throws StubNotFoundException
    {
        String className = desc.getClassName();

        try {
            Class<?> cl =
                RMIClassLoader.loadClass(desc.getLocation(), className);
            RemoteRef clientRef = new ActivatableRef(id, null);
            return Util.createProxy(cl, clientRef, false);

        } catch (IllegalArgumentException e) {
            throw new StubNotFoundException(
                "class implements an illegal remote interface", e);

        } catch (ClassNotFoundException e) {
            throw new StubNotFoundException("unable to load class: " +
                                            className, e);
        } catch (MalformedURLException e) {
            throw new StubNotFoundException("malformed URL", e);
        }
    }

    
Invoke method on remote object. This method delegates remote
method invocation to the underlying ref type.  If the
underlying reference is not known (is null), then the object
must be activated first.  If an attempt at method invocation
fails, the object should force reactivation.  Method invocation
must preserve "at most once" call semantics.  In RMI, "at most
once" applies to parameter deserialization at the remote site
and the remote object's method execution.  "At most once" does
not apply to parameter serialization at the client so the
parameters of a call don't need to be buffered in anticipation
of call retry. Thus, a method call is only be retried if the
initial method invocation does not execute at all at the server
(including parameter deserialization).
/**
     * Invoke method on remote object. This method delegates remote
     * method invocation to the underlying ref type.  If the
     * underlying reference is not known (is null), then the object
     * must be activated first.  If an attempt at method invocation
     * fails, the object should force reactivation.  Method invocation
     * must preserve "at most once" call semantics.  In RMI, "at most
     * once" applies to parameter deserialization at the remote site
     * and the remote object's method execution.  "At most once" does
     * not apply to parameter serialization at the client so the
     * parameters of a call don't need to be buffered in anticipation
     * of call retry. Thus, a method call is only be retried if the
     * initial method invocation does not execute at all at the server
     * (including parameter deserialization).
     */
    public Object invoke(Remote obj,
                         java.lang.reflect.Method method,
                         Object[] params,
                         long opnum)
        throws Exception
    {

        boolean force = false;
        RemoteRef localRef;
        Exception exception = null;

        /*
         * Attempt object activation if active ref is unknown.
         * Throws a RemoteException if object can't be activated.
         */
        synchronized (this) {
            if (ref == null) {
                localRef = activate(force);
                force = true;
            } else {
                localRef = ref;
            }
        }

        for (int retries = MAX_RETRIES; retries > 0; retries--) {

            try {
                return localRef.invoke(obj, method, params, opnum);
            } catch (NoSuchObjectException e) {
                /*
                 * Object is not active in VM; retry call
                 */
                exception = e;
            } catch (ConnectException e) {
                /*
                 * Failure during connection setup; retry call
                 */
                exception = e;
            } catch (UnknownHostException e) {
                /*
                 * Failure during connection setup; retry call.
                 */
                exception = e;
            } catch (ConnectIOException e) {
                /*
                 * Failure reusing cached connection; retry call
                 */
                exception = e;
            } catch (MarshalException e) {
                /*
                 * Failure during parameter serialization; call may
                 * have reached server, so call retry not possible.
                 */
                throw e;
            } catch (ServerError e) {
                /*
                 * Call reached server; propagate remote exception.
                 */
                throw e;
            } catch (ServerException e) {
                /*
                 * Call reached server; propagate remote exception
                 */
                throw e;
            } catch (RemoteException e) {
                /*
                 * This is a catch-all for other RemoteExceptions.
                 * UnmarshalException being the only one relevant.
                 *
                 * StubNotFoundException should never show up because
                 * it is generally thrown when attempting to locate
                 * a stub.
                 *
                 * UnexpectedException should never show up because
                 * it is only thrown by a stub and would be wrapped
                 * in a ServerException if it was propagated by a
                 * remote call.
                 */
                synchronized (this) {
                    if (localRef == ref) {
                        ref = null;     // this may be overly conservative
                    }
                }

                throw e;
            }

            if (retries > 1) {
                /*
                 * Activate object, since object could not be reached.
                 */
                synchronized (this) {
                    if (localRef.remoteEquals(ref) || ref == null) {
                        RemoteRef newRef = activate(force);

                        if (newRef.remoteEquals(localRef) &&
                            exception instanceof NoSuchObjectException &&
                            force == false) {
                            /*
                             * If last exception was NoSuchObjectException,
                             * then old value of ref is definitely wrong,
                             * so make sure that it is different.
                             */
                            newRef = activate(true);
                        }

                        localRef = newRef;
                        force = true;
                    } else {
                        localRef = ref;
                        force = false;
                    }
                }
            }
        }

        /*
         * Retries unsuccessful, so throw last exception
         */
        throw exception;
    }

    
private method to obtain the ref for a call.
/**
     * private method to obtain the ref for a call.
     */
    private synchronized RemoteRef getRef()
        throws RemoteException
    {
        if (ref == null) {
            ref = activate(false);
        }

        return ref;
    }

    
private method to activate the remote object.
NOTE: the caller must be synchronized on "this" before
calling this method.
/**
     * private method to activate the remote object.
     *
     * NOTE: the caller must be synchronized on "this" before
     * calling this method.
     */
    private RemoteRef activate(boolean force)
        throws RemoteException
    {
        assert Thread.holdsLock(this);

        ref = null;
        try {
            /*
             * Activate the object and retrieve the remote reference
             * from inside the stub returned as the result. Then
             * set this activatable ref's internal ref to be the
             * ref inside the ref of the stub. In more clear terms,
             * the stub returned from the activate call contains an
             * ActivatableRef. We need to set the ref in *this*
             * ActivatableRef to the ref inside the ActivatableRef
             * retrieved from the stub. The ref type embedded in the
             * ActivatableRef is typically a UnicastRef.
             */

            Remote proxy = id.activate(force);
            ActivatableRef newRef = null;

            if (proxy instanceof RemoteStub) {
                newRef = (ActivatableRef) ((RemoteStub) proxy).getRef();
            } else {
                /*
                 * Assume that proxy is an instance of a dynamic proxy
                 * class.  If that assumption is not correct, or either of
                 * the casts below fails, the resulting exception will be
                 * wrapped in an ActivateFailedException below.
                 */
                RemoteObjectInvocationHandler handler =
                    (RemoteObjectInvocationHandler)
                    Proxy.getInvocationHandler(proxy);
                newRef = (ActivatableRef) handler.getRef();
            }
            ref = newRef.ref;
            return ref;

        } catch (ConnectException e) {
            throw new ConnectException("activation failed", e);
        } catch (RemoteException e) {
            throw new ConnectIOException("activation failed", e);
        } catch (UnknownObjectException e) {
            throw new NoSuchObjectException("object not registered");
        } catch (ActivationException e) {
            throw new ActivateFailedException("activation failed", e);
        }
    }

    
This call is used by the old 1.1 stub protocol and is
unsupported since activation requires 1.2 stubs.
/**
     * This call is used by the old 1.1 stub protocol and is
     * unsupported since activation requires 1.2 stubs.
     */
    public synchronized RemoteCall newCall(RemoteObject obj,
                                           Operation[] ops,
                                           int opnum,
                                           long hash)
        throws RemoteException
    {
        throw new UnsupportedOperationException(versionComplaint);
    }

    
This call is used by the old 1.1 stub protocol and is
unsupported since activation requires 1.2 stubs.
/**
     * This call is used by the old 1.1 stub protocol and is
     * unsupported since activation requires 1.2 stubs.
     */
    public void invoke(RemoteCall call) throws Exception
    {
        throw new UnsupportedOperationException(versionComplaint);
    }

    
This call is used by the old 1.1 stub protocol and is
unsupported since activation requires 1.2 stubs.
/**
     * This call is used by the old 1.1 stub protocol and is
     * unsupported since activation requires 1.2 stubs.
     */
    public void done(RemoteCall call) throws RemoteException {
        throw new UnsupportedOperationException(versionComplaint);
    }

    
Returns the class of the ref type to be serialized
/**
     * Returns the class of the ref type to be serialized
     */
    public String getRefClass(ObjectOutput out)
    {
        return "ActivatableRef";
    }

    
Write out external representation for remote ref.
/**
     * Write out external representation for remote ref.
     */
    public void writeExternal(ObjectOutput out) throws IOException
    {
        RemoteRef localRef = ref;

        out.writeObject(id);
        if (localRef == null) {
            out.writeUTF("");
        } else {
            out.writeUTF(localRef.getRefClass(out));
            localRef.writeExternal(out);
        }
    }

    
Read in external representation for remote ref.
Throws:
ClassNotFoundException – If the class for an object
being restored cannot be found./**
     * Read in external representation for remote ref.
     * @exception ClassNotFoundException If the class for an object
     * being restored cannot be found.
     */
    public void readExternal(ObjectInput in)
        throws IOException, ClassNotFoundException
    {
        id = (ActivationID)in.readObject();
        ref = null;
        String className = in.readUTF();

        if (className.equals("")) return;

        try {
            Class<?> refClass = Class.forName(RemoteRef.packagePrefix + "." +
                                              className);
            ref = (RemoteRef)refClass.newInstance();
            ref.readExternal(in);
        } catch (InstantiationException e) {
            throw new UnmarshalException("Unable to create remote reference",
                                         e);
        } catch (IllegalAccessException e) {
            throw new UnmarshalException("Illegal access creating remote reference");
        }
    }

    //----------------------------------------------------------------------;
    
Method from object, forward from RemoteObject
/**
     * Method from object, forward from RemoteObject
     */
    public String remoteToString() {
        return Util.getUnqualifiedName(getClass()) +
                " [remoteRef: " + ref + "]";
    }

    
default implementation of hashCode for remote objects
/**
     * default implementation of hashCode for remote objects
     */
    public int remoteHashCode() {
        return id.hashCode();
    }

    
default implementation of equals for remote objects
/** default implementation of equals for remote objects
     */
    public boolean remoteEquals(RemoteRef ref) {
        if (ref instanceof ActivatableRef)
            return id.equals(((ActivatableRef)ref).id);
        return false;
    }
}