Description
1) Introduction
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 Python 3.7 (to
avoid decompiling to Java source code to use in the assignment) is provided for you to test
your program. The goal of the assignment is to make you familiar with the application layer and TCP
sockets. You must implement your program using the Java Socket API of the JDK. If you
have 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 in the
grading; while you will not get a zero from your project, you may need to have an
appointment 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 top of TCP. There is a .txt file provided to you with the server source code. Several clients (in your case, multiple clients can be run on different consoles at the same host) should be able to edit the
text file together. Several operations and specifications are present for this case. In
program lifecycle, first an authentication check will be done. A specific username and
password 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 (Client
A) cannot change the text file without getting an update first, since the file may already
been changed by another client (Client B) after the last update of Client A. If a new version
of the file is present for Client A, that file should be seen as “version conflict” by Client A
using the version information associated to the file. Each change by either of the clients
results in an increment to the file version. If the client side version does NOT match with
that 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 APND or
WRTE operation. UPDT operation doesn’t change the file version. Upon connecting to the
server, a client should first download the text file by using the UPDT command. As already
mentioned, in order to modify an already modified document, a preliminary UPDT
operation must be made. 3) Connection Formats
i) Commands
In order to fulfill the program specifications, your client will need to use specific
commands to communicate with the server. Commands should be strings encoded in US- ASCII. The format is below:
is the name of the command. For all possible commands and their
explanations, 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\n
PASS Send the password for
authentication
PASS cs421s2020\r\n
WRTE
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 “The Dark
Side of the Moon”\r\n
APND
Append a new line to the file. is the last
value for the version of the
file known by the client . APND 12 “Train of
Thought”\r\n
UPDT Get up-to-date file. is the last
value for the version of the
file known by the client . UPDT 12\r\n
EXIT – 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 have
the following format:
is either OK (success) or INVALID (failure), for the sake of simplicity. You
should check the part if is INVALID or the response belongs to
UPDT 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 discrepancy
between the server and the local version is observed by the client, then an update is
required at the client side. is the response message. Detailed responses to erroneous operations as
well 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” status
when 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 the
server 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 program
and the server program on your own machine you should use 127.0.0.1 or localhost
for this argument. The control port to which the server will bind. Your program should
connect 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 main
method should be TextEditor). Your program should run with the command
java TextEditor
where “< >” denotes command-line arguments. These arguments must be the same as the
arguments 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, on port
60000. 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) from multiple command
prompts. Same source code can be used as clients. 6) Final Remarks
Please contact your teaching assistant if you have any doubt about the
assignment. Do not forget to check the response message after sending each command to
see 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 a bit to
correct 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 ports by
waiting for them to timeout, restarting the machine, etc.
Remember that all the commands must be constructed as strings and encoded with
US-ASCII encoding. Use big-endian format if it is necessary to use. Please put the folder containing the images under the same directory with the
server and client codes. 7) Submission rules
You need to apply all the following rules in your submission. You will lose points if you do
not obey the submission rules below or your program does not run as described in the
assignment 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], and include
your name and student ID. For example, the subject line must be
[CS421_2020SPRING_PA1]AliVelioglu20141222 if your name and ID are Ali Velioglu
and 20141222, respectively. If you are submitting an assignment done by two
students, the subject line should include the names and IDs of both group members. The subject of the e-mail should be
[CS421_2020SPRING_PA1]AliVelioglu20141222AyseFatmaoglu20255666 if group
members 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 .rar
file, 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. The
archive 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, Idea or
NetBeans, etc.). You may, and are encouraged to, use these programs while
developing, 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 be
taken in case of plagiarism.
