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	/*
	* Copyright (c) 1996, 2014, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.rmi.transport;

	import java.io.IOException;
	import java.io.ObjectOutput;
	import java.rmi.MarshalException;
	import java.rmi.NoSuchObjectException;
	import java.rmi.Remote;
	import java.rmi.RemoteException;
	import java.rmi.server.LogStream;
	import java.rmi.server.ObjID;
	import java.rmi.server.RemoteCall;
	import java.rmi.server.RemoteServer;
	import java.rmi.server.ServerNotActiveException;
	import java.security.AccessControlContext;
	import java.security.AccessController;
	import java.security.Permissions;
	import java.security.PrivilegedAction;
	import java.security.ProtectionDomain;
	import sun.rmi.runtime.Log;
	import sun.rmi.server.Dispatcher;
	import sun.rmi.server.UnicastServerRef;

	/**
	* Transport abstraction for enabling communication between different
	* VMs.
	*
	* @author Ann Wollrath
	*/
	@SuppressWarnings("deprecation")
	public abstract class Transport {

	/** "transport" package log level */
	static final int logLevel = LogStream.parseLevel(getLogLevel());

	private static String getLogLevel() {
	return java.security.AccessController.doPrivileged(
	new sun.security.action.GetPropertyAction("sun.rmi.transport.logLevel"));
	}

	/* transport package log */
	static final Log transportLog =
	Log.getLog("sun.rmi.transport.misc", "transport", Transport.logLevel);

	/** References the current transport when a call is being serviced */
	private static final ThreadLocal<Transport> currentTransport = new ThreadLocal<>();

	/** ObjID for DGCImpl */
	private static final ObjID dgcID = new ObjID(ObjID.DGC_ID);

	/** AccessControlContext for setting context ClassLoader */
	private static final AccessControlContext SETCCL_ACC;
	static {
	Permissions perms = new Permissions();
	perms.add(new RuntimePermission("setContextClassLoader"));
	ProtectionDomain[] pd = { new ProtectionDomain(null, perms) };
	SETCCL_ACC = new AccessControlContext(pd);
	}

	/**
	* Returns a <I>Channel</I> that generates connections to the
	* endpoint <I>ep</I>. A Channel is an object that creates and
	* manages connections of a particular type to some particular
	* address space.
	* @param ep the endpoint to which connections will be generated.
	* @return the channel or null if the transport cannot
	* generate connections to this endpoint
	*/
	public abstract Channel getChannel(Endpoint ep);

	/**
	* Removes the <I>Channel</I> that generates connections to the
	* endpoint <I>ep</I>.
	*/
	public abstract void free(Endpoint ep);

	/**
	* Export the object so that it can accept incoming calls.
	*/
	public void exportObject(Target target) throws RemoteException {
	target.setExportedTransport(this);
	ObjectTable.putTarget(target);
	}

	/**
	* Invoked when an object that was exported on this transport has
	* become unexported, either by being garbage collected or by
	* being explicitly unexported.
	**/
	protected void targetUnexported() { }

	/**
	* Returns the current transport if a call is being serviced, otherwise
	* returns null.
	**/
	static Transport currentTransport() {
	return currentTransport.get();
	}

	/**
	* Verify that the current access control context has permission to accept
	* the connection being dispatched by the current thread. The current
	* access control context is passed as a parameter to avoid the overhead of
	* an additional call to AccessController.getContext.
	*/
	protected abstract void checkAcceptPermission(AccessControlContext acc);

	/**
	* Sets the context class loader for the current thread.
	*/
	private static void setContextClassLoader(ClassLoader ccl) {
	AccessController.doPrivileged((PrivilegedAction<Void>)() -> {
	Thread.currentThread().setContextClassLoader(ccl);
	return null;
	}, SETCCL_ACC);
	}

	/**
	* Service an incoming remote call. When a message arrives on the
	* connection indicating the beginning of a remote call, the
	* threads are required to call the <I>serviceCall</I> method of
	* their transport. The default implementation of this method
	* locates and calls the dispatcher object. Ordinarily a
	* transport implementation will not need to override this method.
	* At the entry to <I>tr.serviceCall(conn)</I>, the connection's
	* input stream is positioned at the start of the incoming
	* message. The <I>serviceCall</I> method processes the incoming
	* remote invocation and sends the result on the connection's
	* output stream. If it returns "true", then the remote
	* invocation was processed without error and the transport can
	* cache the connection. If it returns "false", a protocol error
	* occurred during the call, and the transport should destroy the
	* connection.
	*/
	public boolean serviceCall(final RemoteCall call) {
	try {
	/* read object id */
	final Remote impl;
	ObjID id;

	try {
	id = ObjID.read(call.getInputStream());
	} catch (java.io.IOException e) {
	throw new MarshalException("unable to read objID", e);
	}

	/* get the remote object */
	Transport transport = id.equals(dgcID) ? null : this;
	Target target =
	ObjectTable.getTarget(new ObjectEndpoint(id, transport));

	if (target == null \|\| (impl = target.getImpl()) == null) {
	throw new NoSuchObjectException("no such object in table");
	}

	final Dispatcher disp = target.getDispatcher();
	target.incrementCallCount();
	try {
	/* call the dispatcher */
	transportLog.log(Log.VERBOSE, "call dispatcher");

	final AccessControlContext acc =
	target.getAccessControlContext();
	ClassLoader ccl = target.getContextClassLoader();

	ClassLoader savedCcl = Thread.currentThread().getContextClassLoader();

	try {
	setContextClassLoader(ccl);
	currentTransport.set(this);
	try {
	java.security.AccessController.doPrivileged(
	new java.security.PrivilegedExceptionAction<Void>() {
	public Void run() throws IOException {
	checkAcceptPermission(acc);
	disp.dispatch(impl, call);
	return null;
	}
	}, acc);
	} catch (java.security.PrivilegedActionException pae) {
	throw (IOException) pae.getException();
	}
	} finally {
	setContextClassLoader(savedCcl);
	currentTransport.set(null);
	}

	} catch (IOException ex) {
	transportLog.log(Log.BRIEF,
	"exception thrown by dispatcher: ", ex);
	return false;
	} finally {
	target.decrementCallCount();
	}

	} catch (RemoteException e) {

	// if calls are being logged, write out exception
	if (UnicastServerRef.callLog.isLoggable(Log.BRIEF)) {
	// include client host name if possible
	String clientHost = "";
	try {
	clientHost = "[" +
	RemoteServer.getClientHost() + "] ";
	} catch (ServerNotActiveException ex) {
	}
	String message = clientHost + "exception: ";
	UnicastServerRef.callLog.log(Log.BRIEF, message, e);
	}

	/* We will get a RemoteException if either a) the objID is
	* not readable, b) the target is not in the object table, or
	* c) the object is in the midst of being unexported (note:
	* NoSuchObjectException is thrown by the incrementCallCount
	* method if the object is being unexported). Here it is
	* relatively safe to marshal an exception to the client
	* since the client will not have seen a return value yet.
	*/
	try {
	ObjectOutput out = call.getResultStream(false);
	UnicastServerRef.clearStackTraces(e);
	out.writeObject(e);
	call.releaseOutputStream();

	} catch (IOException ie) {
	transportLog.log(Log.BRIEF,
	"exception thrown marshalling exception: ", ie);
	return false;
	}
	}

	return true;
	}
	}

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