CIS 3931 - Java - Fall 1998 - Assignment # 8 Assignment # 8 Playing Network Ping Pong Due: Friday, December 4th by midnight. Deliverables: Email all files that you create to cis3931@cs.fsu.edu by the due date, including a journal/diary of the steps you went through during this assignment. Since many of the assignments involve writing Java applets it will greatly assist the grading of the assignments if you create HTML on your home page that includes the assignment's applets. Please include the web address of your applet in the journal/diary. Note that for assignments that require you to create source code yourself rather than type in existing code (like this one) you should take careful measures not to accidentally make your .java files world-readable within your HTML directory. When emailing your files it can be problematic to faithfully re-create the file names. Here are detailed instructions that you can use for this and future assignments. If you use xi.cs.fsu.edu (which is running Solaris) you can create a single compress "tar" file that can then be emailed to cis3931@cs.fsu.edu. cd location_of_P8_source
gnutar czvf ~/P8.tar.gz . If you use an email client that supports attachments then you can just attach the file P8.tar.gz to your email submission. If you do not use an email client that supports attachments you will first have to convert the binary compressed "tar" file into a format suitable for an email message, such as uuencoding. Here is an example of encoding the P8.tar.gz file and sending it via a UNIX pipe to a mail client: uuencode P8.tar.gz < P8.tar.gz | /usr/ucb/mail -s "P8.tar.gz" cis3931@cs.fsu.edu If you choose to use some other operating system, such as Windows '95, Windows NT or Windows '98 be careful that you use a compression agent that correctly preserves both case sensitivity and the entire file name length, such as WinZip. You will be asked to re-submit your assignment via email if the format you use is not correctly identified and/or formatted. Please do not email all the files separately. Assignment: This lesson uses the material in Lesson 24 (All About Sockets). Specifically, you are to write a Java network client applet (pongClient) and a Java network server application (pongServer). When completed, your program, along with a masterServer and other student's solutions, will interact in an exciting fashion. To understand what is required a discussion of the protocols needed for client to server and server to master server is presented, followed by specific requirements for the client and server. The Pong protocol was developed to allow you to interrogate a number of servers from a single client. It will be used by your pongClient to measure how long it takes to contact a list of Pong servers. One of the applet security manager rules enforced within typical browsers is that a network connection between an applet can only be made back to the host machine that served up the web pages containing the applet. For this reason you must develop a Pong server that runs as a standalone Java application on the same machine as the web server. Your Pong server will act as an intermediary, performing as a relay agent for the Pong protocol. You are provided a Java file containing all of the definitions you will need for the following protocols (you can find it here, in Pong.java). It is important that you use these values, otherwise your client and server will not properly interact with the other Pong servers and the master Pong server. In addition to the public constants, you need to use the pongIdentity class to correctly identify your pongServer to the masterServer. All communication between clients and servers is through the Socket and ServerSocket class. All data sent through the sockets is serialized. pongClient to pongServer Protocol pongClient request pongServer response Pong.CLIENT_LIST If OK, Hashtable of pongIdentitys, else Pong.CLIENT_NAK Pong.SERVER_PING, pongIdentity of server to ping IF OK, Pong.CLIENT_ACK, else Pong.CLIENT_NAK pongServer to masterServer Protocol pongServer request masterServer response Pong.SERVER_LOGIN, pongIdentity of this pongServer If successful, Pong.SERVER_ACK, else Pong.SERVER_ALREADY_LOGGED_IN Pong.SERVER_LOGOUT, pongIdentity of this pongServer If successful, Pong.SERVER_ACK, else Pong.SERVER_NOT_LOGGED_IN Pong.SERVER_LIST, pongIdentity of this pongServer If successful, Hashtable of pongIdentitys of all logged-in pongServers, else Pong.SERVER_NAK Pong.CLIENT_PING, pongIdentity of this pongServer If successful, Pong.CLIENT_ACK, else Pong.CLIENT_NAK Pong.SERVER_PING, pongIdentity of pongServer to ping If successful, Pong.CLIENT_ACK, else Pong.CLIENT_NAK To see the protocol in action, look at the pongClient applet. It will help to see how it runs before trying to figure out how the pongClient and pongServer are supposed to work. pongClient Specification Create a Java applet that uses the 1.1 event model. You can model it after the P6 solution as well as the network client on page 919 (the Knock Knock client). Create a start Button, a TextField to accept the pong server name, a TextField to accept the pong server port address, an extended Canvas to draw the Ping Circle and a non-editable TextArea to display the log of events. When the start Button is pressed, take the input from the server name and port fields and initiate a connection to that pongServer: Create a Socket connection to the server name & port. Log the success/failure of the connection in the log TextArea. Use Pong.CLIENT_LIST to get a Hashtable of pongIdentitys for each of the other pongServers that are running. Walk through the hash table, issuing a Pong.SERVER_PING for each pongIdentity, logging the progress of the ping in the TextArea. Send the pongIdentity of the pongServer with each SERVER_PING. Keep track of the number of milliseconds it takes for each Pong.SERVER_PING (you may find a Vector useful, as well as System.currentTimeMillis()), as well as the minimum and maximum milliseconds for any one ping. Plot the ping time in a unit circle, using the circle origin as time zero and the line segment length as a ratio of the millisecond time. Notice that you will need the maximum ping time to correctly scale your lines. Spread the lines evenly around the unit circle (two lines would be 180 degrees apart, three lines would be 120, etc.). Print the clientName of the server at the end of the line. If while contacting a pongServer you are unable to receive a Pong.CLIENT_ACK, report that the host is "dead" in the log window and discard the timing for that server (don't draw it's line, since it was never ping'ed). Your paint() method must be capable of redrawing the last Ping Circle whenever it is called, rather than just when the data is initially created. Use a Canvas preferred size of 300 by 300. pongServer Specification Create a multi-threaded network server Java application. It must accept two command-line arguments: the name of the server and the port number that this server will listen on. A good starting point for figuring out the structure of the program can be found on page 920 (the Knock Knock Joke Multiclient Server). Open a Socket to the masterServer (it is listening on host Pong.MASTERHOST, port Pong.MASTERPORT). Create a pongIdentity and fill out the fields with the correct values (clientName, myIP and myPort). Send the masterServer a Pong.SERVER_LOGIN, followed by your pongIdentity. If you do not get back a Pong.SERVER_ACK, print out an error message and exit. Create an idle time monitoring thread that will be used to kill your pongServer whenever enough time has elapsed without receiving any requests from a client. Use Pong.MAX_IDLE_TIME (the value is in seconds -- it's set to 5 minutes) as your maximum idle time. Your idle thread will sleep at some reasonable time interval (wake up once very 5 seconds) and then determine if more than Pong.MAX_IDLE_TIME seconds have elapsed between the last accept() call from the server's main loop and now. If so, your idle thread will shut down your pongServer. Create a ServerSocket and use accept() to listen for a client request. If a request comes in, spawn a thread to handle that client's request: If Pong.CLIENT_LIST received, send a Pong.SERVER_LIST to the masterServer along with your pongIdentity. You will receive back a Hashtable of all the pongIdentitys known by the masterServer or you will receive one of the error values (Pong.SERVER_NAK, etc.). Return to the client a Pong.CLIENT_NAK if you receive an error, else pass the Hashtable back to the client. If Pong.CLIENT_PING received, send a Pong.CLIENT_ACK back to the client. If Pong.SERVER_PING received, read in the pongIdentity of the pongServer to ping. Open a Socket to that pongServer's name and port (retrieved from the pongIdentity) and issue a Pong.CLIENT_PING. If a Pong.CLIENT_ACK is received, send back a Pong.CLIENT_ACK to the client, else send a Pong.CLIENT_NAK. Continue reading client requests within this thread until either an invalid request is sent or your server's idle timer expires. Note that the masterServer will remove any pongServers from it's internal list one hour from the last received masterServer request. You will either have to stop and restart your server manually or attempt to Pong.SERVER_LOGIN again. Notes You must select a pongServer name and a port number that are unique. As a suggestion, your server name can be simply your first and last name. If you prefer anonymity, select a catchy pseudonym. As for the port numbers, you must select one that is unused on the machine that you choose to run your server on (more than likely you'll choose xi.cs.fsu.edu, since that's where the departmental web server runs). You can use a number unique to you that is any unused random number between 1024 and 65535 (I suggest you don't use any private numbers, such as a part of your SSN or a credit card :). You don't have to tell anybody else your number, as it is passed to all other pongServers via the protocol. Note that the Computer Science firewall machinery will ONLY let "officially-blessed" Socket traffic into and out of the department (email, FTP, web traffic, etc.). This means you cannot run your server on a machine outside of the department and expect it to work. Proxy solutions are available, but complex. MAKE SURE you write your server so that it does NOT get into any tight CPU loops or hangs around idle for more than 5 minutes. If your server abuses the system, it will be killed by members of the System group and noted for future use by the grader. If written correctly your server will have minimal impact on the system.
