/*
* Copyright 2003-2006 Sun Microsystems, Inc. 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. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
package com.sun.jdi.connect.spi;
import java.io.IOException;
/**
* A connection between a debugger and a target VM which it debugs.
*
* <p> A Connection represents a bi-directional communication channel
* between a debugger and a target VM. A Connection is created when
* {@link com.sun.jdi.connect.spi.TransportService TransportService}
* establishes a connection and successfully handshakes with a target
* VM. A TransportService implementation provides a reliable
* JDWP packet transportation service and consequently a Connection
* provides a reliable flow of JDWP packets between the debugger
* and the target VM. A Connection is stream oriented, that is, the
* JDWP packets written to a connection are read by the target VM
* in the order in which they were written. Similiarly packets written
* to a Connection by the target VM are read by the debugger in the
* order in which they were written.
*
* <p> A connection is either open or closed. It is open upon creation,
* and remains open until it is closed. Once closed, it remains closed,
* and any attempt to invoke an I/O operation upon it will cause a
* {@link ClosedConnectionException} to be thrown. A connection can
* be tested by invoking the {@link #isOpen isOpen} method.
*
* <p> A Connection is safe for access by multiple concurrent threads,
* although at most one thread may be reading and at most one thread may
* be writing at any given time. </p>
*
* @since 1.5
*/
public abstract class Connection {
/**
* Reads a packet from the target VM.
*
* <p> Attempts to read a JDWP packet from the target VM.
* A read operation may block indefinitely and only returns
* when it reads all bytes of a packet, or in the case of a
* transport service that is based on a stream-oriented
* communication protocol, the end of stream is encountered.
*
* <p> Reading a packet does not do any integrity checking on
* the packet aside from a check that the length of the packet
* (as indicated by the value of the <tt>length</tt> field, the
* first four bytes of the packet) is 11 or more bytes.
* If the value of the <tt>length</tt> value is less then 11
* then an <tt>IOException</tt> is thrown.
*
* <p> Returns a byte array of a length equal to the length
* of the received packet, or a byte array of length 0 when an
* end of stream is encountered. If end of stream is encountered
* after some, but not all bytes of a packet, are read then it
* is considered an I/O error and an <tt>IOException</tt> is
* thrown. The first byte of the packet is stored in element
* <tt>0</tt> of the byte array, the second in element <tt>1</tt>,
* and so on. The bytes in the byte array are laid out as per the
* <a href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
* JDWP specification</a>. That is, all fields in the packet
* are in big endian order as per the JDWP specification.
*
* <p> This method may be invoked at any time. If another thread has
* already initiated a {@link #readPacket readPacket} on this
* connection then the invocation of this method will block until the
* first operation is complete. </p>
*
* @return the packet read from the target VM
*
* @throws ClosedConnectionException
* If the connection is closed, or another thread closes
* the connection while the readPacket is in progress.
*
* @throws java.io.IOException
* If the length of the packet (as indictaed by the first
* 4 bytes) is less than 11 bytes, or an I/O error occurs.
*
*
*/
public abstract byte[] readPacket() throws IOException;
/**
* Writes a packet to the target VM.
*
* <p> Attempts to write, or send, a JDWP packet to the target VM.
* A write operation only returns after writing the entire packet
* to the target VM. Writing the entire packet does not mean
* the entire packet has been transmitted to the target VM
* but rather that all bytes have been written to the
* transport service. A transport service based on a TCP/IP connection
* may, for example, buffer some or all of the packet before
* transmission on the network.
*
* <p> The byte array provided to this method should be laid out
* as per the <a
* href="../../../../../../../../../technotes/guides/jpda/jdwp-spec.html">
* JDWP specification</a>. That is, all fields in the packet
* are in big endian order. The first byte, that is element
* <tt>pkt[0]</tt>, is the first byte of the <tt>length</tt> field.
* <tt>pkt[1]</tt> is the second byte of the <tt>length</tt> field,
* and so on.
*
* <p> Writing a packet does not do any integrity checking on
* the packet aside from checking the packet length. Checking
* the packet length requires checking that the value of the
* <tt>length</tt> field (as indicated by the first four bytes
* of the packet) is 11 or greater. Consequently the length of
* the byte array provided to this method, that is
* <tt>pkt.length</tt>, must be 11 or more, and must be equal
* or greater than the value of the <tt>length</tt> field. If the
* length of the byte array is greater than the value of
* the <tt>length</tt> field then all bytes from element
* <tt>pkt[length]</tt> onwards are ignored. In other words,
* any additional bytes that follow the packet in the byte
* array are ignored and will not be transmitted to the target
* VM.
*
* <p> A write operation may block or may complete immediately.
* The exact circumstances when an operation blocks depends on
* the transport service. In the case of a TCP/IP connection to
* the target VM, the writePacket method may block if there is
* network congestion or there is insufficient space to buffer
* the packet in the underlying network system.
*
* <p> This method may be invoked at any time. If another thread has
* already initiated a write operation upon this Connection then
* a subsequent invocation of this method will block until the first
* operation is complete. </p>
*
* @param pkt
* The packet to write to the target VM.
*
* @throws ClosedConnectionException
* If the connection is closed, or another thread closes
* the connection while the write operation is in progress.
*
* @throws java.io.IOException
* If an I/O error occurs.
*
* @throws IllegalArgumentException
* If the value of the <tt>length</tt> field is invalid,
* or the byte array is of insufficient length.
*/
public abstract void writePacket(byte pkt[]) throws IOException;
/**
* Closes this connection.
*
* <p> If the connection is already closed then invoking this method
* has no effect. After a connection is closed, any further attempt
* calls to {@link #readPacket readPacket} or {@link #writePacket
* writePacket} will throw a {@link ClosedConnectionException}.
*
* <p> Any thread currently blocked in an I/O operation ({@link
* #readPacket readPacket} or {@link #writePacket writePacket})
* will throw a {@link ClosedConnectionException}).
*
* <p> This method may be invoked at any time. If some other thread has
* already invoked it, however, then another invocation will block until
* the first invocation is complete, after which it will return without
* effect. </p>
*
* @throws java.io.IOException
* If an I/O error occurs
*/
public abstract void close() throws IOException;
/**
* Tells whether or not this connection is open. </p>
*
* @return <tt>true</tt> if, and only if, this connection is open
*/
public abstract boolean isOpen();
}