Description
In this programming assignment, you are asked to implement a program in Java. You should code a client that can collaboratively edit a text (.txt) file, which is located at a server, together with other clients. The server program written and tested in Python3.7(toavoid decompiling to Java source code to use in the assignment) is provided for youtotest
your program. The goal of the assignment is to make you familiar with the application layer andTCPsockets. You must implement your program using the Java Socket API of the JDK. If youhave any doubt about what to use or not to use, please contact your teaching assistant. When preparing your project please keep in mind that your projects will be auto- graded by a computer program. Any problems in the formatting can create problems inthegrading; while you will not get a zero from your project, you may need to have anappointment with your teaching assistant for a manual grading. Errors caused by
incorrectly naming the project files and folder structure will result in point deductions. 2) Specifications
“TextEditor” uses a custom application level protocol which is built on topof TCP. There is a .txt file provided to you with the server source code. Several clients (inyour case, multiple clients can be run on different consoles at the same host) should be able toedit thetext file together. Several operations and specifications are present for this case. Inprogram lifecycle, first an authentication check will be done. A specific username andpassword will be looked after by the server. Authenticated clients can then edit the text by
using several commands that are described below. It is very important that a client (ClientA) cannot change the text file without getting an update first, since the file may alreadybeen changed by another client (Client B) after the last update of Client A. If a newversionof the file is present for Client A, that file should be seen as “version conflict” by Client Ausing the version information associated to the file. Each change by either of the clientsresults in an increment to the file version. If the client side version does NOT matchwiththat of the server, the client can deduce that a change has been made in the file. Initially, server program sets the file version to 0 and increments it after each successful APNDorWRTE operation. UPDT operation doesn’t change the file version. Upon connecting totheserver, a client should first download the text file by using the UPDT command. As alreadymentioned, in order to modify an already modified document, a preliminary UPDToperation must be made. 3) Connection Formats
i) Commands
In order to fulfill the program specifications, your client will need to use specificcommands to communicate with the server. Commands should be strings encodedinUS- ASCII. The format is below:
is the name of the command. For all possible commands andtheirexplanations, see Figure 2. is a single space character. Can be omitted if is empty. is the argument specific to the command. All arguments include
version of client side. See Figure 1 for more information. is a carriage return character followed by a line feed character, i.e., “\r\n”. MessageType Arguments Definition Example
USER Send the username for
authentication
USER bilkentstu\r\nPASS Send the password for
authentication
PASS cs421s2020\r\nWRTE
Write arbitrary text on the
specific line
in the file. is the last
value for the version of the
file known by the client .
WRTE 12 5“TheDarkSide of theMoon”\r\nAPND
Append a new line to the file. is the last
value for the version of the
file known by the client . APND 12 “TrainofThought”\r\nUPDT Get up-to-date file. is the last
value for the version of the
file known by the client . UPDT 12\r\nEXIT – Terminate the program EXIT\r\n
Figure 1 List of commands with examples ii) Responses
The response messages sent by the server are also encoded in US-ASCII. Responses havethe following format:
is either OK (success) or INVALID (failure), for the sake of simplicity. Youshould check the part if is INVALID or the response belongstoUPDT which contains the current state of the file.
is the number specifying the current version of the document. is incremented by the server after each change in the document. If a discrepancybetween the server and the local version is observed by the client, then anupdateisrequired at the client side. is the response message. Detailed responses to erroneous operationsaswell as the up-to-date file at the server are returned within this part. is a carriage return character followed by a line feed character, i.e., “\r\n”. For example, for “WRTE” command, the response might report the “Version Conflict” statuswhen the version reported by the client does NOT match with that of the server. 4) Running the server program
The server program we provide is written and tested in Python 3.7. You should start theserver program before running your client program using the following command:
python Server.py
where “” denotes command-line arguments. These command-line arguments are: The IP address of the server. Since you will be running both your programand the server program on your own machine you should use 127.0.0.1 or localhostfor this argument. The control port to which the server will bind. Your programshouldconnect to the server from this port to send the control commands. Example:
The command above starts the server with IP 127.0.0.1, i.e., localhost, which uses port
60000 for the control commands. 5) Running the TextEditor
Your program must be a console application (no graphical user interface, GUI, is allowed)and should be named as TextEditor.java (i.e., the name of the class that includes the mainmethod should be TextEditor). Your program should run with the command
java TextEditor
where “” denotes command-line arguments. These arguments must be the same as thearguments for the server program, which are explained above. Example:
In this example, the program connects to the server with IP 127.0.0.1, i.e., localhost, onport60000. Please note that you must run your program after you start the server program. Do not forget to run more than one client (two is enough) frommultiple commandprompts. Same source code can be used as clients. 6) Final Remarks
Please contact your teaching assistant if you have any doubt about theassignment. Do not forget to check the response message after sending each commandtosee if your code is working and debug it if it is not. Note that the server cannot
detect all the errors that you make; therefore, you might have to experiment abit tocorrect all your errors. You can modify the source code of the server for experimental purposes. However, do not forget that your projects will be evaluated based on the version we provide. You might receive some socket exceptions if your program fails to close sockets
from its previous instance. In that case, you can manually shut down those portsbywaiting for them to timeout, restarting the machine, etc.
Remember that all the commands must be constructed as strings and encodedwithUS-ASCII encoding. Use big-endian format if it is necessary to use. Please put the folder containing the images under the same directory withtheserver and client codes. 7) Submission rules
You need to apply all the following rules in your submission. You will lose points if youdonot obey the submission rules below or your program does not run as described intheassignment above. The assignment should be submitted as an e-mail attachment sent to
mehmet.sakaoglu[at]bilkent.edu.tr. Any other methods (Disk/CD/DVD) of
submission will not be accepted. The subject of the e-mail should start with [CS421_2020SPRING_PA1], andincludeyour name and student ID. For example, the subject line must be
[CS421_2020SPRING_PA1]AliVelioglu20141222 if your name and ID are Ali Veliogluand 20141222, respectively. If you are submitting an assignment done by twostudents, the subject line should include the names and IDs of both group members. The subject of the e-mail should be
[CS421_2020SPRING_PA1]AliVelioglu20141222AyseFatmaoglu20255666if groupmembers are Ali Velioglu and Ayse Fatmaoglu with IDs 20141222 and 20255666, respectively. All the files must be submitted in a zip file whose name is the same as the subject
line except the [CS421_2020SPRING_PA1] part. The file must be a .zip file, not a.rarfile, or any other compressed file. All the files must be in the root of the zip file; directory structures are not allowed. Please note that this also disallows organizing your code into Java packages. Thearchive should not contain any file other than the source code(s) with .java
extension. The archive should not contain these:
o Any class files or other executables, o Any third-party library archives (i.e., jar files), o Project files used by IDEs (e.g., JCreator, JBuilder, SunOne, Eclipse, IdeaorNetBeans, etc.). You may, and are encouraged to, use these programs whiledeveloping, but the end result must be a clean, IDE-independent program. The standard rules for plagiarism and academic honesty apply. Your
submitted codes will be carefully checked and disciplinary actions will betaken in case of plagiarism.
