changeset 47282:0feb93f627d2

8185072: network006 times out in many configs in JDK10-hs nightly Reviewed-by: chegar, rriggs
author vtewari
date Tue, 26 Sep 2017 20:34:10 +0530
parents 6e99a776ae76
children dc9b1da1314b
files src/java.base/unix/native/libnet/PlainSocketImpl.c test/jdk/java/net/HugeDataTransferTest.java
diffstat 2 files changed, 890 insertions(+), 7 deletions(-) [+]
line wrap: on
line diff
--- a/src/java.base/unix/native/libnet/PlainSocketImpl.c	Tue Sep 26 20:29:13 2017 +0530
+++ b/src/java.base/unix/native/libnet/PlainSocketImpl.c	Tue Sep 26 20:34:10 2017 +0530
@@ -679,14 +679,16 @@
         }
 
         /* ECONNABORTED or EWOULDBLOCK error so adjust timeout if there is one. */
-        currNanoTime = JVM_NanoTime(env, 0);
-        nanoTimeout -= (currNanoTime - prevNanoTime);
-        if (nanoTimeout < NET_NSEC_PER_MSEC) {
-            JNU_ThrowByName(env, JNU_JAVANETPKG "SocketTimeoutException",
-                    "Accept timed out");
-            return;
+        if (nanoTimeout >= NET_NSEC_PER_MSEC) {
+            currNanoTime = JVM_NanoTime(env, 0);
+            nanoTimeout -= (currNanoTime - prevNanoTime);
+            if (nanoTimeout < NET_NSEC_PER_MSEC) {
+                JNU_ThrowByName(env, JNU_JAVANETPKG "SocketTimeoutException",
+                        "Accept timed out");
+                return;
+            }
+            prevNanoTime = currNanoTime;
         }
-        prevNanoTime = currNanoTime;
     }
 
     if (newfd < 0) {
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/net/HugeDataTransferTest.java	Tue Sep 26 20:34:10 2017 +0530
@@ -0,0 +1,881 @@
+/*
+ * Copyright (c) 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.
+ *
+ * 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.
+ */
+
+/**
+ * @test
+ * @bug 8185072
+ * @summary network006 times out in many configs in JDK10-hs nightly
+ * @run main/othervm/manual HugeDataTransferTest 1
+ */
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.io.PrintStream;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.net.UnknownHostException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Random;
+
+/**
+ * This test makes huge number of data transfers between 2 Java virtual machines
+ * using the TCP/IP protocol, and checks if those data are transfered correctly.
+ * Both client and server VMs run on the same local computer and attach TCP/IP
+ * sockets to the local host, or to the loopback domain
+ * ``<code>localhost</code>'' (having IP address <code>127.0.0.1</code>).
+ *
+ * <p>
+ * In this test, 128 client/server connections are established. Once a
+ * connection is established, client passes a data parcel to server, and server
+ * reads that parcel and checks if it is same as expected (byte-to-byte equality
+ * is desired). Then server passes (some other) parcel to the client, and client
+ * reads and verifies those bytes. This ping-pong game is repeated 128 times;
+ * and after that each pair of sockets checks if there are no extra bytes
+ * accedentally passed through their connection.
+ *
+ * <p>
+ * Parcels lengths and contents are chosen randomly, and average parcel length
+ * is 128 bytes. So totally, each pair of sockets passes ~16Kb of data to each
+ * other, and thus ~32Kb of data are transfered by each sockets pair. Totally,
+ * ~4Mb of data are transfered by all client/server pairs.
+ *
+ * @author vtewari
+ */
+public class HugeDataTransferTest {
+
+    /**
+     * Timeout for TCP/IP sockets (currently set to 1 min).
+     */
+    private static int SO_TIMEOUT;// = 2*60*1000;
+
+    /**
+     * Maximal number of connections this test should open simultaneously.
+     */
+    private final static int MAX_CONNECTIONS = 128;
+
+    /**
+     * Check few more connections to make sure that MAX_CONNECTIONS are safe.
+     */
+    private final static int CONNECTIONS_RESERVE = 10;
+
+    /**
+     * The test used to fail with connection reset by peer set to 50. (and once
+     * in a three if it was set to 10). So now we set it to MAX_CONNECTIONS
+     * (128).
+     */
+    private final static int BACKLOG_QUEUE_LENGTH = MAX_CONNECTIONS;
+
+    /**
+     * Number of parcels to be sent/recieved.
+     */
+    private final static int DATA_PARCELS = 128;
+
+    /**
+     * Maximal length of data parcel to be sent/recieved (it equals to 256 bytes
+     * now).
+     */
+    private final static int MAX_PARCEL = 1 << 8;
+
+    /**
+     * Either actually display optional reports or not.
+     */
+    static private final boolean DEBUG_MODE = false;
+
+    /**
+     * How many IP sockets can we open simultaneously? Check if
+     * <code>MAX_CONNECTIONS</code> connections can be open simultaneously.
+     */
+    private static int detectOSLimitation() {
+        final int CONNECTIONS_TO_TRY = MAX_CONNECTIONS + CONNECTIONS_RESERVE;
+        display("--- Trying to open " + CONNECTIONS_TO_TRY + " connections:");
+
+        InetAddress address;
+        ServerSocket serverSocket;
+        try {
+            address = InetAddress.getLocalHost();
+            int anyPort = 0;
+            int defaultBacklog = BACKLOG_QUEUE_LENGTH;
+            serverSocket = new ServerSocket(anyPort, defaultBacklog, address);
+        } catch (IOException ioe) {
+            throw new Error("FATAL error while loading the test: " + ioe);
+        }
+        display(serverSocket.toString());
+
+        Socket server[] = new Socket[CONNECTIONS_TO_TRY];
+        Socket client[] = new Socket[CONNECTIONS_TO_TRY];
+
+        int i, port = serverSocket.getLocalPort();
+        for (i = 0; i < CONNECTIONS_TO_TRY; i++) {
+            try {
+                client[i] = new Socket(address, port);
+                display(">Open: client[" + i + "] = " + client[i]);
+                server[i] = serverSocket.accept();
+                display(">Open: server[" + i + "] = " + server[i]);
+            } catch (IOException ioe) {
+                display(">OOPS! -- failed to open connection #" + i);
+                break;
+            }
+        }
+        display("> Could open "
+                + (i < CONNECTIONS_TO_TRY ? "only " : "") + i + " connections.");
+        display(">Closing them:");
+        for (int j = 0; j < i; j++) {
+            try {
+                server[j].close();
+                client[j].close();
+            } catch (IOException ioe) {
+                throw new Error("FATAL error while loading the test: " + ioe);
+            }
+        }
+        display(">OK.");
+        int safeConnections = i - CONNECTIONS_RESERVE;
+        if (safeConnections < 1) {
+            safeConnections = 1;
+        }
+        if (safeConnections < MAX_CONNECTIONS) {
+            complain("------------------------- CAUTION: -------------------");
+            complain("While checking the OS limitations, the test found that");
+            complain("only " + i + " TCP/IP socket connections could be safely open");
+            complain("simultaneously. However, possibility to open at least");
+            complain("" + MAX_CONNECTIONS + "+" + CONNECTIONS_RESERVE
+                    + " connections were expected.");
+            complain("");
+            complain("So, the test will check only " + safeConnections + " connection"
+                    + (safeConnections == 1 ? "" : "s") + " which seem");
+            complain("safe to be open simultaneously.");
+            complain("------------------------------------------------------");
+        }
+        return safeConnections;
+    }
+
+    //----------------------------------------------------------------//
+    /**
+     * Re-calls to the method <code>run(args[],out)</code> actually performing
+     * the test. After <code>run(args[],out)</code> stops, follow JDK-like
+     * convention for exit codes. I.e.: stop with exit status 95 if the test has
+     * passed, or with status 97 if the test has failed.
+     *
+     * @see #run(String[],PrintStream)
+     */
+    public static void main(String args[]) {
+        int exitCode = run(args, System.out);
+        System.exit(exitCode + 95);
+        // JCK-like exit status.
+    }
+
+    public static int run(String args[], PrintStream out) {
+        HugeDataTransferTest.out = out;
+
+        //
+        // Get the Internet address of the local machine.
+        //
+        InetAddress address = null;
+        try {
+            address = InetAddress.getLocalHost();
+        } catch (UnknownHostException exception) {
+            complain(exception.toString());
+            return 2; // FAILED
+        }
+        display("Host: " + address);
+
+        //
+        // Detect if it is safe to open MAX_CONNETIONS simultaneously:
+        //
+        final int CONNECTIONS = detectOSLimitation();
+
+        //
+        // Assign ServerSocket, and start client VM which should open
+        // the prescribed number of CONNECTIONS to that ServerSocket.
+        //
+        ServerSocket serverSocket;
+        try {
+            final int anyPort = 0;
+            final int defaultBacklog = BACKLOG_QUEUE_LENGTH;
+            serverSocket = new ServerSocket(anyPort, defaultBacklog, address);
+        } catch (IOException exception) {
+            complain("Cannot assign a ServerSocket on: " + address);
+            return 2;
+        }
+
+        //
+        // Start the client process on different VM.
+        //
+        String jdkPath = System.getProperty("test.jdk");
+        Path toolName = Paths.get("bin", "java" + (isWindows() ? ".exe" : ""));
+        Path jdkTool = Paths.get(jdkPath, toolName.toString());
+
+        String IPAddress = address.getHostAddress();
+        int localPort = serverSocket.getLocalPort();
+        String arguments = " " + CONNECTIONS + " " + IPAddress + " " + localPort;
+        //String command = args[0] + " " + network006.class.getName() + "$Client " + arguments;
+        String command = jdkTool.toAbsolutePath().toString() + " " + Client.class.getName() + " " + arguments;
+        try {
+            SO_TIMEOUT = Integer.parseInt(args[0]) * 60 * 1000;
+        } catch (NumberFormatException e) {
+            complain("Wrong timeout argument: " + e);
+            return 2;
+        }
+
+        Runtime runtime = Runtime.getRuntime();
+
+        Process client = null;
+        IORedirector redirectOut = null;
+        IORedirector redirectErr = null;
+
+        try {
+            // Start clients on different JVM:
+            client = runtime.exec(command);
+
+            // Provide clients with access to stderr and stdout:
+            InputStream clientOut = client.getInputStream();
+            InputStream clientErr = client.getErrorStream();
+            redirectOut = new IORedirector(clientOut, DEBUG_MODE ? out : null);
+            redirectErr = new IORedirector(clientErr, out);
+            redirectOut.start();
+            redirectErr.start();
+
+        } catch (IOException exception) {
+            complain("Failed to start client: " + exception);
+            return 2;
+        }
+        //
+        // Start the server threads (and let them establish connections):
+        //
+
+        Server server[] = new Server[CONNECTIONS];
+        for (int i = 0; i < CONNECTIONS; i++) {
+            server[i] = new Server(serverSocket);
+            display("Server #" + i + ": " + server[i]);
+            server[i].start();
+        }
+
+        //
+        // Wait for the servers and the clients:
+        //
+        boolean testFailed = false;
+
+        try {
+            client.waitFor();
+            int clientStatus = client.exitValue();
+            display("Client VM exitCode=" + clientStatus);
+
+            // Let I/O redirectors to flush:
+            if (redirectOut.isAlive()) {
+                redirectOut.join();
+            }
+            if (redirectErr.isAlive()) {
+                redirectErr.join();
+            }
+
+            // If client has crashed, also terminate the server (to avoid hangup).
+            if (clientStatus != 95) {
+                complain("Client VM has crashed: exit status=" + clientStatus);
+                testFailed = true;
+            }
+
+            // Client has finished OK; wait for the server.
+            for (int i = 0; i < CONNECTIONS; i++) {
+                display("Server: waiting for #" + i);
+                if (server[i].isAlive()) {
+                    display("Server #" + i + ": (joining...)" + server[i]);
+                    server[i].join();
+                }
+                if (server[i].exception != null) {
+                    if (server[i].message != null) {
+                        complain("Server #" + i + "(finished): with message:" + server[i].message);
+                    }
+
+                    complain("Server #" + i + "(finished): " + server[i].exception);
+                    server[i].exception.printStackTrace(out);
+                    out.flush();
+//                    complain("Server #"+i+": "+server[i].exception.getStackTrace());
+                    testFailed = true;
+                }
+            }
+
+        } catch (InterruptedException exception) {
+            complain("Test interrupted: " + exception);
+            testFailed = true;
+        }
+
+        if (testFailed) {
+            complain("Test failed.");
+        } else {
+            display("Test passed.");
+        }
+        return testFailed ? 2 : 0;
+    }
+
+    private static boolean isWindows() {
+        return System.getProperty("os.name").toLowerCase().startsWith("win");
+    }
+    //----------------------------------------------------------------//
+    /**
+     * Log stream for error messages and/or (optional) execution trace.
+     */
+    private static PrintStream out;
+
+    /**
+     * Print error message.
+     */
+    private static synchronized void complain(Object message) {
+        out.println("# " + message);
+        out.flush();
+    }
+
+    ;
+
+    /**
+     * Display optional report: comment ca va?
+     */
+    private static synchronized void display(Object report) {
+        if (DEBUG_MODE) {
+            out.println(report.toString());
+        }
+        out.flush(); //todo shouldn't this be inside if??
+    }
+
+    ;
+
+    //----------------------------------------------------------------//
+
+    /**
+     * Server thread should reply to data parcels sent by Client VM.
+     */
+    private static class Server extends Thread {
+
+        /**
+         * The socket is assigned at the Server instantiation.
+         */
+        private ServerSocket serverSocket;
+
+        /**
+         * The socket is assigned at the Server runtime.
+         */
+        private Socket socket;
+
+        /**
+         * Display the server socket.
+         */
+        @Override
+        public String toString() {
+
+            return "ServerSocket: " + serverSocket.toString();
+//                    + " socket: " + socket.toString();
+        }
+
+        /**
+         * Which port is this socket listening?
+         */
+        int getPort() {
+            return serverSocket.getLocalPort();
+        }
+
+        /**
+         * Find some free port at the given <code>address</code> and attach new
+         * server to hear that port. // lidsten to??
+         */
+        public Server(ServerSocket serverSocket) {
+            this.serverSocket = serverSocket;
+        }
+
+        /**
+         * Exception just arisen while the server was working, or
+         * <code>null</code> if it was OK with the server.
+         */
+        Exception exception = null;
+        String message = null;
+
+        /**
+         * Accept connection, then reply to client's parcels.
+         */
+        @Override
+        public void run() {
+            try {
+                socket = serverSocket.accept();
+                socket.setSoTimeout(SO_TIMEOUT);
+
+                InputStream istream = socket.getInputStream();
+                OutputStream ostream = socket.getOutputStream();
+
+                Random random = new Random(getPort());
+
+                for (int i = 0; i < DATA_PARCELS; i++) {
+                    Parcel etalon = new Parcel(random);
+                    message = "reading parcel number " + i;
+                    Parcel sample = new Parcel(istream); // read
+                    if (!sample.equals(etalon)) {
+                        complain("Server thread for port #"
+                                + getPort() + " got unexpected parcel:\n"
+                                + "sample=" + sample + "\n"
+                                + "etalon=" + etalon);
+                        throw new TestFailure( //received??
+                                "server has read unexpected parcel");
+                    }
+                    message = "sending parcel number " + i;
+                    etalon.send(ostream);
+                    ostream.flush();
+                }
+
+                int datum = istream.read(); // wait for client close()
+                if (datum >= 0) {
+                    throw new TestFailure(
+                            "server has read ambigous byte: " + datum);
+                }
+
+                ostream.close(); // implies: socket.close();
+
+            } catch (Exception oops) {
+                exception = oops;
+            }
+        }
+    }
+
+    //----------------------------------------------------------------//
+    /**
+     * Client VM should send data parcels to Server VM and recieve and verify
+     * the server's replies.
+     */
+    private static class Client extends Thread {
+
+        /**
+         * This thread uses the single client socket.
+         */
+        private Socket socket;
+
+        /**
+         * Address and port of this socket.
+         */
+        @Override
+        public String toString() {
+            return socket.toString();
+        }
+
+        /**
+         * Did the thread failed? If yes, what is the failure's reason.
+         */
+        Exception exception = null;
+        String message = null;
+
+        public static java.io.PrintStream complainStream = System.out;
+        public static java.io.PrintStream displayStream = System.err;
+
+        /**
+         * Connect client socket on the given <code>address</code> and
+         * <code>port</code>.
+         */
+        Client(InetAddress address, int port) throws IOException {
+            socket = new Socket(address, port);
+            socket.setSoTimeout(SO_TIMEOUT);
+        }
+
+        /**
+         * What is the port number this socket is listening for?
+         */
+        int getPort() {
+            return socket.getPort();
+        }
+
+        /**
+         * Establish connection, then read/respond <code>DATA_PARCELS</code>
+         * parcels of random data. Set initial seed for pseudo-random numbers
+         * generator to the value of the local port number.
+         *
+         * @see #DATA_PARCELS
+         * @see #getPort()
+         */
+        @Override
+        public void run() {
+            try {
+                InputStream istream = socket.getInputStream();
+                OutputStream ostream = socket.getOutputStream();
+
+                Random random = new Random(getPort());
+                // suggested by Oleg -- to avoid race conditions
+                /* try{
+                    Thread.sleep(500);
+                }
+                catch (java.lang.InterruptedException e)
+                {
+                }*/
+
+                for (int i = 0; i < DATA_PARCELS; i++) {
+                    Parcel etalon = new Parcel(random);
+                    message = "sending parcel number: " + i;
+                    etalon.send(ostream);
+                    ostream.flush();
+
+                    message = "reading parcel number: " + i;
+                    Parcel sample = new Parcel(istream); // read
+                    if (!sample.equals(etalon)) {
+                        complain("Client thread for port #"
+                                + getPort() + " got unexpected parcel:\n"
+                                + "sample=" + sample + "\n"
+                                + "etalon=" + etalon);
+                        throw new TestFailure(
+                                "parcel context is unexpected to client");
+                    }
+                }
+
+                if (istream.available() > 0) {
+                    int datum = istream.read();
+                    throw new TestFailure(
+                            "client has read ambigous byte: " + datum);
+                }
+                ostream.close(); // implies: socket.close()
+
+            } catch (Exception oops) {
+                exception = oops;
+            }
+        }
+
+        /**
+         * Establish lots of connections to server socket, attack servers with
+         * huge data parcels, and check if they reply correctly. The number of
+         * connections to try, the address and port number for the server socket
+         * are passed through <code>args[]</code>, like:
+         * <pre>
+         *    java network006$Client connections_to_try address port
+         * </pre>
+         */
+        public static void main(String args[]) {
+            if (DEBUG_MODE) {
+                try {
+                    String filename = "Client" + ((args.length == 3) ? args[2] : "new");
+                    displayStream = new PrintStream(filename + ".out");
+                    complainStream = new PrintStream(filename + ".err");
+                } catch (FileNotFoundException exception) {
+                    complain(exception);
+                }
+
+            }
+
+            if (args.length != 3) {
+                complain("Client expects 3 paramenets:");
+                complain("    java " + Client.class.getName() + " connections_to_try address port");
+                exit(1); // FAILED
+            }
+
+            int CONNECTIONS = Integer.parseInt(args[0]);
+            display("Client VM: will try " + CONNECTIONS + " connections.");
+            InetAddress address;
+            try {
+                address = InetAddress.getByName(args[1]);
+            } catch (UnknownHostException exception) {
+                address = null;
+                complain("Client: cannot find host: \"" + args[1] + "\"");
+                exit(4);
+            }
+            display("Client: host to contact: " + address);
+            int port = Integer.parseInt(args[2]);
+            display("Client: port to contact: " + port);
+
+            //
+            // Establish connections, and start client processes:
+            //
+            Client client[] = new Client[CONNECTIONS];
+            for (int i = 0; i < CONNECTIONS; i++) {
+                try {
+                    client[i] = new Client(address, port);
+                    display("Client #" + i + ": " + client[i]);
+
+                } catch (IOException ioe) {
+                    complain("Client #" + i + "(creation): " + ioe);
+                    ioe.printStackTrace(complainStream);
+                    complainStream.flush();
+//                    complain("Client #" + i + "(creation): " + ioe.getStackTrace());
+                    exit(3);
+                }
+            }
+
+            for (int i = 0; i < CONNECTIONS; i++) {
+                client[i].start();
+            }
+
+            //
+            // Wait until testing is not finished:
+            //
+            int status = 0;
+            for (int i = 0; i < CONNECTIONS; i++) {
+                display("Client: waiting for #" + i);
+                if (client[i].isAlive()) {
+                    display("Client #" + i + ": (joining...)" + client[i]);
+
+                    try {
+                        client[i].join();
+                    } catch (InterruptedException ie) {
+                        complain("Client #" + i + ": " + ie);
+                        status = 3;
+                    }
+                }
+                if (client[i].exception != null) {
+                    if (client[i].message != null) {
+                        complain("Client #" + i + "(finished) with message: " + client[i].message);
+                    }
+                    complain("Client #" + i + "(finished): " + client[i].exception);
+                    client[i].exception.printStackTrace(complainStream);
+                    complainStream.flush();
+                    if (status == 0) {
+                        status = 2;
+                    }
+                }
+            }
+
+            exit(status);
+        }
+
+        /**
+         * Print error message.
+         */
+        private static synchronized void complain(Object message) {
+            complainStream.println("# " + message);
+            complainStream.flush();
+        }
+
+        /**
+         * Display execution trace.
+         */
+        private static synchronized void display(Object message) {
+            if (!DEBUG_MODE) {
+                return;
+            }
+            displayStream.println(message.toString());
+            displayStream.flush();
+        }
+
+        /**
+         * Exit with JCK-like status.
+         */
+        private static void exit(int exitCode) {
+            int status = exitCode + 95;
+//          display("Client: exiting with code=" + status);
+            System.exit(status);
+        }
+    }
+
+    /**
+     * Two of such threads should redirect <code>out</code> and <code>err</code>
+     * streams of client VM.
+     */
+    private static class IORedirector extends Thread {
+
+        /**
+         * Source stream.
+         */
+        InputStream in;
+        /**
+         * Destination stream.
+         */
+        OutputStream out;
+
+        /**
+         * Redirect <code>in</code> to <code>out</code>.
+         */
+        public IORedirector(InputStream in, OutputStream out) {
+            this.in = in;
+            this.out = out;
+        }
+
+        /**
+         * Read input stream until the EOF, and write everithing to output
+         * stream. If output stream is assigned to <code>null</code>, do not
+         * print anything, but read the input stream anywhere.
+         */
+        @Override
+        public void run() {
+            try {
+                for (;;) {
+                    int symbol = in.read();
+                    if (symbol < 0) {
+                        break; // EOF
+                    }
+                    if (out != null) {
+                        out.write(symbol);
+                    }
+                }
+
+                if (out != null) {
+                    out.flush();
+                }
+
+            } catch (IOException exception) {
+                throw new TestFailure("IORedirector exception: " + exception);
+            }
+        }
+    }
+
+    //----------------------------------------------------------------//
+    /**
+     * A data parcel to be sent/recieved between Client VM and Server thread.
+     * When data parcel is sent, first 4 bytes are transfered which encode the
+     * <code>int</code> number equal to size of the parcel minus 1. I.e.: if
+     * number of data bytes in the parcel's contents is <code>N</code>, then the
+     * first 4 bytes encode the number <code>N-1</code>. After that, the
+     * parcel's contents bytes are transered.
+     */
+    static class Parcel {
+
+        private final byte[] parcel;
+
+        /**
+         * Display all bytes as integer values from 0 to 255; or return
+         * ``<tt>null</tt>'' if this Parcel is not yet initialized.
+         */
+        @Override
+        public String toString() {
+            if (parcel == null) {
+                return "null";
+            }
+            String s = "{";
+            for (int i = 0; i < parcel.length; i++) {
+                s += (i > 0 ? ", " : "") + ((int) parcel[i] & 0xFF);
+            }
+            return s + "}";
+        }
+
+        /**
+         * Generate new <code>parcel[]</code> array using the given
+         * <code>random</code> numbers generator. Client and Server threads
+         * should use identical <code>random</code> generators, so that those
+         * threads could generate equal data parcels and check the parcel just
+         * transfered.
+         */
+        public Parcel(Random random) {
+            int size = random.nextInt(MAX_PARCEL) + 1;
+            parcel = new byte[size];
+            for (int i = 0; i < size; i++) {
+                parcel[i] = (byte) random.nextInt(256);
+            }
+        }
+
+        ;
+
+        /**
+         * Read exactly <code>size</code> bytes from the <code>istream</code>
+         * if possible, or throw <code>TestFailure</code> if unexpected end of
+         * <code>istream</code> occurs.
+         */
+        private static byte[] readBytes(int size, InputStream istream)
+                throws IOException {
+
+            byte data[] = new byte[size];
+            for (int i = 0; i < size; i++) {
+                int datum = istream.read();
+                if (datum < 0) {
+                    throw new TestFailure(
+                            "unexpected EOF: have read: " + i + " bytes of " + size);
+                }
+                data[i] = (byte) datum;
+            }
+            return data;
+        }
+
+        /**
+         * Read 4 bytes from <code>istream</code> and threat them to encode size
+         * of data parcel following these 4 bytes.
+         */
+        private static int getSize(InputStream istream) throws IOException {
+            byte data[] = readBytes(4, istream);
+            int data0 = (int) data[0] & 0xFF;
+            int data1 = (int) data[1] & 0xFF;
+            int data2 = (int) data[2] & 0xFF;
+            int data3 = (int) data[3] & 0xFF;
+            int sizeWord = data0 + (data1 << 8) + (data2 << 16) + (data3 << 24);
+            int size = sizeWord + 1;
+            if (size <= 0) {
+                throw new TestFailure("illegal size: " + size);
+            }
+            return size;
+        }
+
+        /**
+         * Send 4 bytes encoding actual size of the parcel just to be
+         * transfered.
+         */
+        private static void putSize(OutputStream ostream, int size)
+                throws IOException {
+
+            if (size <= 0) {
+                throw new TestFailure("illegal size: " + size);
+            }
+
+            int sizeWord = size - 1;
+            byte data[] = new byte[4];
+            data[0] = (byte) sizeWord;
+            data[1] = (byte) (sizeWord >> 8);
+            data[2] = (byte) (sizeWord >> 16);
+            data[3] = (byte) (sizeWord >> 24);
+            ostream.write(data);
+        }
+
+        /**
+         * Recieve data parcel.
+         */
+        public Parcel(InputStream istream) throws IOException {
+            int size = getSize(istream);
+            parcel = readBytes(size, istream);
+        }
+
+        /**
+         * Send <code>this</code> data parcel.
+         */
+        public void send(OutputStream ostream) throws IOException {
+            int size = parcel.length;
+            putSize(ostream, size);
+            ostream.write(parcel);
+        }
+
+        /**
+         * Check byte-to-byte equality between <code>this</code> and the
+         * <code>other</code> parcels.
+         */
+        public boolean equals(Parcel other) {
+            if (this.parcel.length != other.parcel.length) {
+                return false;
+            }
+            int size = parcel.length;
+            for (int i = 0; i < size; i++) {
+                if (this.parcel[i] != other.parcel[i]) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+
+    /**
+     * Server or Client may throw this exception to report the test failure.
+     */
+    static class TestFailure extends RuntimeException {
+
+        /**
+         * Report particular <code>purpose</code> of the test failure.
+         */
+        public TestFailure(String purpose) {
+            super(purpose);
+        }
+    }
+}