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Islas, Sean (Capt) authoredIslas, Sean (Capt) authored
UnicastUdpSender.java 7.09 KiB
package MV3500Cohort2023MarchJune.homework2.Islas;
import java.io.*;
import java.net.*;
/**
* An example of sending UDP packets. The sending and receiving programs
* use different UDP ports; there can be problems getting this to work
* if both the sending and receiving sockets try to use the same port
* on the same host.
*
* Start this before launching UdpReceiver.
*
* @see <a href="https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html">https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html</a>
* @see <a href="https://en.wikipedia.org/wiki/User_Datagram_Protocol">https://en.wikipedia.org/wiki/User_Datagram_Protocol</a>
* @see <a href="https://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html">System properties</a>
* @author mcgredo
* @author brutzman@nps.edu
*/
public class UnicastUdpSender
{
/** Default constructor */
public UnicastUdpSender()
{
// default constructor
}
private static final String MY_NAME = System.getProperty("user.name"); // guru incantation 8)
// public static final int SENDING_PORT = 1414; // not needed, can let system choose an open local port
/** socket value of shared interest */
public static final int UDP_PORT = UnicastUdpReceiver.UDP_PORT; // 1415; ensure consistent
private static final int TOTAL_PACKETS_TO_SEND = 25;
/** socket value of shared interest */
public static final String DESTINATION_HOST = "localhost";
// here is what we need for lab comms
// public static final String DESTINATION_HOST = "10.1.105.16"; // localhost 127.0.0.1 or argon 10.1.105.1 or 10.1.105.1 or whatever
/**
* Program invocation, execution starts here
* @param args command-line arguments
*/
@SuppressWarnings("SleepWhileInLoop")
public static void main(String[] args)
{
DatagramSocket udpSocket = null;
DataOutputStream dos = null;
int packetID = 0; // counter variable to send in packet
float value = -1.0f; // unreachable value is good sentinel to ensure expected changes occur
String message = MY_NAME + " says Hello MV3500"; // no really
// String padding = new String();
try
{
System.out.println(UnicastUdpSender.class.getName() + " shows how to send simple-type values via DataOutputStream");
System.out.println(UnicastUdpSender.class.getName() + " started...");
// Create a UDP socket
udpSocket = new DatagramSocket(); // let system assign output port, then SENDING_PORT not needed
// Put together a message with binary content. "ByteArrayOutputStream"
// is a java.io utility that lets us put together an array of binary
// data, which we put into the UDP packet.
ByteArrayOutputStream baos = new ByteArrayOutputStream(1500); // how many bytes are in buffer? MTU=1500 is good
dos = new DataOutputStream(baos); // wrapper for writing values, connects both streams
// Put together a packet to send
// these types and order of variables must match on sender and receiver
byte[] byteArray = baos.toByteArray();
// ID of the host we are sending to
InetAddress destinationAddress = InetAddress.getByName(DESTINATION_HOST);
// ID of the host we are sending from
// InetAddress sourceAddress = InetAddress.getByName("localhost"); // possibly identical if source not modified
DatagramPacket datagramPacket = new DatagramPacket(byteArray, byteArray.length, destinationAddress, UDP_PORT);
System.out.println("UdpSender address/port: " + destinationAddress.getHostAddress() + "/" + UDP_PORT);
// Hmmm, how fast does UDP stream go? Does UDP effectively slow packets down, or does
// this cause network problems? (hint: yes for an unlimited send rate, unlike TCP).
// How do you know on the receiving side that you haven't received a
// duplicate UDP packet, out-of-order packet, or dropped packet? your responsibility.
for (int index = 1; index <= TOTAL_PACKETS_TO_SEND; index++) // avoid infinite send loops in code, they can be hard to kill!
{
packetID++; // increment counter, prefer using explicit value to index
value = TOTAL_PACKETS_TO_SEND - packetID; // countdown
boolean isPacketIdEvenParity = ((packetID % 2) == 0); // % is modulo operator; result 0 is even parity, 1 is odd parity
// values of interest follow. order and types of what was sent must match what you are reading!
dos.writeInt (packetID);
dos.writeFloat (value);
dos.writeUTF (message); // string value with guaranteed encoding, matches UTF-8 is 8 bit
dos.writeBoolean(isPacketIdEvenParity);
dos.flush(); // sends DataOutputStream to ByteArrayOutputStream
byteArray = baos.toByteArray(); // OK so go get the flushed result...
datagramPacket.setData(byteArray); // and put it in the packet...
udpSocket.send(datagramPacket); // and send it away. boom gone, nonblocking.
// System.out.println("udpSocket output port=" + udpSocket.getLocalPort()); // diagnostic tells what port was chosen by system
// if (isPacketIdEvenParity)
// padding = " ";
// else padding = "";
Thread.sleep(100); // Send packets at rate of one per second
System.out.println(" My guess is: " + packetID + "m/s");
// System.out.println("[" + UnicastUdpSender.class.getName() + "] " + MY_NAME + " " + sourceAddress +
// " port=" + UDP_PORT +
// " has sent values (" + packetID + "," + value + ",\"" + message + "\"," + isPacketIdEvenParity +
// ")" + padding + " as packet #" + index + " of " + TOTAL_PACKETS_TO_SEND);
baos.reset(); // clear the output stream after sending
} // end for loop
}
catch (IOException | InterruptedException e)
{
System.err.println("Problem with UdpSender, see exception trace:");
System.err.println(e);
}
finally // clean up prior to exit, don't want to leave behind zombies
{
if (udpSocket != null)
udpSocket.close();
try
{
if (dos != null)
dos.close();
}
catch (IOException e)
{
System.err.println("Problem with UdpSender, see exception trace:");
System.err.println(e);
}
System.out.println(UnicastUdpSender.class.getName() + " complete."); // all done
}
}
}