Safewalk project
OverviewIn this project you will implement a server for the Purdue Safe Walk Program. The server you are going to write will handle requests and commands sent from the user.Safe Walk is a campus safety system (currently done manually) that allows people on campus to request that someone walk with them from one location to another on campus. For more details, refer to this document.DefinitionsHere are some definitions and terms that will be used throughout this project.LocationsA location is a building in Purdue campus. A location is identified by a unique acronym. First, for simplicity, the following locations will be defined in the system:CL50: Class of 1950 Lecture HallEE: Electrical Engineering BuildingLWSN: Lawson Computer Science BuildingPMU: Purdue Memorial UnionPUSH: Purdue University Student Health Center*: Any one of the location aboveYou may think of * as a wildcard that matches with any of the first five locations.As you will see later, a user message will contain two locations, FROM and TO. Locations not on the list above will be considered invalid.UserA user is anyone who sends content to the server.RequesterA requester is a user who asks for help (instead of sending commands). Again, as you will find later, not all users are requesters.PrerequisitesKnowledge of file I/O operations.Knowledge of Java List API.ObjectivesUnderstand and use the Java Socket API to implement an iterative server.More specifically, java.net.ServerSocket for a socket-based server program.Understand the similarities between files and sockets.Learn to implement a basic, text-based server-client protocol.Learn to write exhaustive JUnit tests.Learn to use simple network utilities telnet and netcat (nc).SpecificationsNow you are going to write your own server program.Command-Line ArgumentsName your program SafeWalkServer. To run it, use the command java SafeWalkServer port where the port argument should be an integer between1025 and 65535 inclusive. If the port argument is given but invalid, print an error message (any meaningful message) and exit gracefully. If the port argument is not provided, your program should use a port that is automatically allocated, in which case you must print this port number to stdout before the server startsaccepting requests. For example,Port not specified. Using free port 8888.where 8888 is the port allocated automatically. Note that 8888 is just an example.If the port is already used (the constructor of ServerSocket will throw an exception). Print an error message and exit gracefully.Class ConstructorsYour SafeWalkServer should have two constructors corresponding to the situations where port may or may not be given.Finish these two methods:/** * Construct the server, and create a server socket, * bound to the specified port. * * @throws IOException IO error when opening the socket. */public SafeWalkServer(int port) throws IOException { //TODO: finish the method} /** * Construct the server, and create a server socket, * bound to a port that is automatically allocated. * * @throws IOException IO error when opening the socket. */public SafeWalkServer() throws IOException { //TODO: finish the method}Note that the constructors may throw exceptions if any problem occurs during the execution of the constructor. If the object is successfully instantiated without exceptions then the server object is ready to run.To enable the socket to be reclaimed by the operating system when the program exits, be sure to set the address to reusable by callingsetReuseAddress(true). For more details, refer to setReuseAddress.Required MethodsYour SafeWalkServer class must extend ServerSocket class and implement the Runnable interface. Thus, you must provide a run method. You must also provide a method isPortValid. The following javadoc comments describe their functionality./** * Start a loop to accept incoming connections. */public void run() { //TODO: finish this method} /** * Return true if the port entered by the user is valid. Else return false. * Return false if you get a NumberFormatException while parsing the parameter port * Call this method from main() before creating SafeWalkServer object * Note that you do not have to check for validity of automatically assigned port */public static boolean isPortValid(String port) {//TODO: finish this method}Note that your server should not start accepting incoming requests before run() is called.To make the server run forever, your run() method may look something like:while (/* condition */) { Socket client = accept(); // i.e., do something with client}Note that accept() blocks the execution of the server until there is an incoming connection.Basic ProtocolIt is very difficult for two people to communicate if one does not understand the other’s language. Similarly, a server cannot talk to clients unless they conform to the same protocol. The protocol that your server uses will be simple text messages.Client RequestsThere are two types of messages that your server needs to handle: request messages and commands.The request message is simple text in CSV (comma-separated value) form, with three fields: NAME,FROM,TO whereNAME is the human-friendly name of the user. You can assume it does not contain any commas.FROM is the location the user wants to move from (FROM cannot be *).TO is the destination of the user’s movement (TO cannot be the same as FROM).For example, a message Tom Riddle,LWSN,PUSH means the person named Tom Riddle wants to move from LWSN to PUSH, while the message Harry Potter,LWSN,* means that Harry Potter wants to move from LWSN to * location (perhaps to help someone as a volunteer).There are three commands that your server needs to handle. Note that they all start with a colon (:).:RESETFor each waiting request message, respond with ERROR: connection reset and close its socket, before discarding the request.For the client that originated the command, respond with RESPONSE: success and close its socket.:SHUTDOWNGracefully terminate the server (i.e., do what :RESET does, close the socket and whatever streams your server uses, and exit the run loop).:PENDING_REQUESTS,TASK,FROM,TOTASK refers to the information that the user is seeking. Valid values for TASK are # and *.Valid values for FROM and TO are one of the locations listed above.Refer to the following table to know the action that needs to performed for each combination of TASK, FROM and TO. Close the client socket after the write operation. While writing unpaired request messages, use the 3-tuple form (see example below)If a command from the client starts with a colon (:) but does not conform to the above specifications then respond to the client with ERROR: invalid command and close its socket.TASKFROMTOWrite to the client socket (Action)#**total number of pending requests#Any valid location other than **total number of pending requests starting at FROM#*Any valid location other than *total number of pending requests destined to TO***list all the pending requestsExample commands and their corresponding response messages are as shown below. Note that these are examples, you should not hard code values in your program. You should stick to the format of the response messages shown below.:PENDING_REQUESTS,#,LWSN,* // command RESPONSE: # of pending requests from LWSN = 1 // response :PENDING_REQUESTS,#,*,PUSH // command RESPONSE: # of pending requests to PUSH = 2 // response:PENDING_REQUESTS,#,*,* // command RESPONSE: # of pending requests = 2 // response:PENDING_REQUESTS,*,*,* // command [[Alicia, PMU, PUSH], [Riya, LWSN, EE]] // responseRequest/Command HandlingWhenever accept() returns a Socket object, your server has received a new request/command to handle. Your server should handle a request/command by doing the following steps: validity check, handle request/command, clean up.Validity CheckBefore performing a request/command, your server should first check if it is valid. The rules are as follows:If the text is a command (i.e., starting with :), make sure it is in the list of defined commands.If the text represents a request,make sure it contains all three tokens (i.e., NAME, FROM, TO), separated by commas; and thatFROM and TO are known locations;FROM cannot be *;TO must be different from FROM.If the request is invalid, respond with ERROR: invalid request to the client and close its socket. If the command is invalid, respond with ERROR: invalid command to the client and close its socket.Handle Request/CommandIf the message is a valid command, perform it as specified in the list of commands.If the message is a valid request, try to find a match for it:Try to find a pair for the client:The FROM location of paired clients must be the same;The TO location of paired clients must be the same, or, one and only one can have its TO be *.If there is no suitable pair for the requester, put it on hold:You will need a list structure to store outstanding user requests in which to search for matches.Do not close the client socket when storing them because you will need the connection later.For this project, you can assume the client will not close the socket by itself.If a matched pair is found, move the on-hold client out of the list, respond to each of the pair their match’s request message prefixed with RESPONSE: , and close their sockets.If a user (e.g., C) can form pairs with more than one user (e.g., A and B), then pair it with the oldest on-hand user (e.g., A, if A submitted its request first). That is, requests are handled in first-come, first-served order, sometimes also called First-In First-Out (FIFO).For example, givenTom Riddle,LWSN,PUSHVegeta,LWSN,EEHarry Potter,LWSN,*Andy,CL50,*Bella,CL50,*Cyndi,EE,*Woody,CL50,PMUGoku,LWSN,EEEdward,CL50,PUSHJohn Doe,PUSH,PMU:PENDING_REQUESTS,*,*,*the server will do the following:Tom Riddle is put on hold (added to the list)Vegeta gets put on holdHarry Potter is matched with Tom Riddle from LWSN to PUSHHarry Potter receives RESPONSE: Tom Riddle,LWSN,PUSHTom Riddle receives RESPONSE: Harry Potter,LWSN,*Tom Riddle is removed from the listAndy is put on holdBella is put on hold. She cannot be matched with Andy because they are both going to * (they are volunteers)Cyndi is put on holdWoody is matched with Andy from CL50 to PMUWoody receives RESPONSE: Andy,CL50,*Andy receives RESPONSE: Woody,CL50,PMUAndy is removed from the listGoku is matched with Vegeta from LWSN to EEVegeta receives RESPONSE: Goku,LWSN,EEGoku receives RESPONSE: Vegeta,LWSN,EEVegeta is removed from the listEdward is matched with Bella (sparkle, sparkle!) from CL50 to PUSHJohn Doe is put on holdCyndi is still in the queue, waiting on a user to advertise EE to anywhere except *The client who sends :PENDING_REQUESTS,*,*,* will get[[Cyndi, EE, *], [John Doe, PUSH, PMU]]If the server then receives command :RESET then Cyndi and John Doe will get the response ERROR: connection reset and have their connections closed.Use the readLine method of BufferedReader when reading from input streams, and the println method of PrintWriter when writing to output streams. Refer to textbook or lecture slides from week 10 (External Communication) for more details.Clean UpAfter a client has been served (paired with another client, or connection reset), close its streams and socket gracefully so that Java garbage collector knows to reclaim the resources.Self-TestingFor testing the server you can either write JUnit tests or use networking tools. We strongly suggest that you write JUnit tests as it can automate the testing process.Writing Junit TestsDownload Client.java. Use this class to start a client from your test method.Do not make any modifications to the Client class.If you are clueless at this point then refer toOfficial JUnit websiteLecture handout on JUnit. You can download the corresponding programs from PiazzaClient.javaimport java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.Socket;import java.net.SocketTimeoutException; /** * Client class for SafeWalkServer */public class Client implements Runnable {private final String host;private final int port;private final String message;private boolean timeout;private String result; /** * Used to create Client socket without timeout */public Client(String host, int port, String msg) {this.host = host;this.port = port;this.message = msg;} /** * Necessary for JUnit testing (and otherwise) * Used to create Client socket with timeout */public Client(String host, int port, String msg, boolean value) {this.host = host;this.port = port;this.message = msg;timeout = value;} public String getResult() {return result;} public void run() {// try with resource block is used heretry (Socket s = new Socket(host, port);PrintWriter out = new PrintWriter(s.getOutputStream(), true);BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));) {if (timeout) s.setSoTimeout(1000);out.println(message);result = in.readLine();} catch (SocketTimeoutException e) {/* During testing the following message might get printed. * It does not always mean that there is an error in the program */System.out.println(“Connection timed out”); } catch (IOException e) {System.err.println(e);}} public static void main(String[] args) {Client c = new Client(args[0], Integer.parseInt(args[1]), args[2]);Thread t = new Thread(c);t.start();try {t.join();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(c.getResult());}}Networking Tools UNIX Or Mac OS XUsing the lab computers, or a personal computer running Linux or Mac OS X, you will have access to two simple UNIX networking tools that may help you in the initial testing, and are described below.One is telnet. To use telnet to send messages to your server, issue the following command in your terminal:$ telnet HOST_NAME PORT_NUMBERwhere HOST_NAME and PORT_NUMBER are the host and port on which your server program is running. Here, you can use 127.0.0.1 or localhost as the host name if you wish to connect to a port on the local machine.If the connection is established, you can send text by typing it.The other is netcat, which prints the content in its stdin to a remote socket, and prints the response to stdout. An example command may be$ nc data.cs.purdue.edu 14180 < client_msg.txtwhich assumes your server runs on data.cs.purdue.edu:14180 and the request message is stored in client_msg.txt.WindowsIf you are developing on a Windows computer, you may or may not have access to the telnet command by default. You can test this by opening the command prompt and trying to run it. If you don't have access, an alternative is to use ncat, an implementation of netcat for Windows. Download fromhere. Use it with the form$ ncat
