Programming Assignment I TextEditor: Client for Collaborative Text Editing

1) Introduction

In this programming assignment, you are asked to implement a program in Java or Python. You should code a client that can collaboratively edit a text (.txt) =ile, which is located at a server, together with other clients. The server program is written and tested in Python 3.7 and 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 or socket module of Python. If you have any doubt about what to use or not to use, please contact your teaching assistant.

2) SpeciOications

“TextEditor” uses a custom application-level protocol which is built on top of TCP. There is a .txt =ile 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 =ile together. Several operations and speci=ications are present for this case. In program lifecycle, =irst an authentication check will be done. A speci=ic username (bilkentstu) and password (cs421f2022) 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 =ile without getting an update =irst, since the =ile may have already been changed by another client (Client B) after the last update of Client A. If a new version of the =ile is present for Client A, that =ile should be seen as “version con=lict” by Client A using the version information associated to the =ile. Each change by either of the clients results in an increment to the =ile 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 =ile. Initially, server program sets the =ile version to 0 and increments it after each successful APND or WRTE operation. UPDT operation doesn’t change the =ile version. Upon connecting to the server, a client should =irst download the text =ile by using the UPDT command. As already mentioned, in order to modify an already modi=ied document, a preliminary UPDT operation must be made.

3) Connection Formats

    i) Commands

In order to ful=ill the program speci=ications, your client will need to use speci=ic commands to communicate with the server. Commands should be strings encoded in US-ASCII. The format is below:

<MessageType><Space><Arguments><CR><LF>

    • <MessageType> is the name of the command. For all possible commands and their explanations, see Figure 2.

    • <Space> is a single space character. Can be omitted if <Argument> is empty.

    • <Argument> is the argument speci=ic to the command. All arguments include version of client side. See Figure 1 for more information.

    • <CR><LF> is a carriage return character followed by a line feed character, i.e., “\r\n”.
MessageTy
Arguments
DeOinition
Example




USER
<username>
Send the username for
USER bilkentstu\r\n


authentication





PASS
<password>
Send the password for
PASS cs421f2022\r\n


authentication





WRTE
<version><Spac
Write arbitrary text on
WRTE 12 5 “The Dark

e><linenumber>
the speci=ic line
Side of the Moon”

<Space><text>
<linenumber> in the
\r\n


=ile. <version> is the



last value for the version



of the =ile known by the





APND
<version><Spac
Append a new line to the
APND 12 “Train of

e><text>
=ile. <version> is the
Thought”\r\n


last value for the version



of the =ile known by the





UPDT
<version>
Get up-to-date =ile.
UPDT 12\r\n


<version> is the last



value for the version of



the =ile known by the





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:

<Code><Space><version><Space><Response><CR><LF>
    • <Code> is either OK (success) or INVALID (failure), for the sake of simplicity. You should check the <Response> part if <Code> is INVALID or the response belongs to UPDT which contains the current state of the =ile.

    • <version> is the number specifying the current version of the document. <version> 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.

    • <Response> is the response message. Detailed responses to erroneous operations as well as the up-to-date =ile at the server are returned within this part.

    • <CR><LF> 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 Con=lict” 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 <Addr> <ControlPort>

where “< >” denotes command-line arguments. These command-line arguments are:

    • <Addr> 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.

    • <ControlPort> 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 or TextEditor.py. Your program should run with one of the following commands:

java TextEditor <Addr> <ControlPort>

python3 TextEditor.py <Addr> <ControlPort>

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.

To gain bonus points, you can add additional features and mechanisms to TextEditor (to client or server side, or you can perform analysis with Wireshark). We will evaluate these features based on creativity and implementational complexity. The grading of this part is separate from the original grading scheme, and it is not mandatory. The bonus points that you will get from this part will be added to the original grade.

6) Report
Prepare a brief report to explain how your code works. Put screenshots of your console while at least 2 clients performing updates to the =ile. The report cannot be more than 5 pages, otherwise you will lose points. Indicate your operating system in the report. Mention what you have done for the bonus points, if you have done any.

        7) 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, clearing them using command-line 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.




        8) Important Rules


General Submission Rules:

1- ) Your submission should include source code(s) (.java/.py) and the report.
2- ) The format of the report should be PDF. (Do not upload .doc, .docx or any other types).

The number of pages should not exceed 5.

4- ) Your submission should not contain any other =iles other than the source code(s) (.java/.py), report (.pdf) and optional README. No .txt =iles, no folders, no IDE related =iles should be included.

5-) Compress these =iles with .zip format. (.rar, .7z or any other compressing types will not be accepted.)

6-) Make sure to follow rules in the “Submission Rules” section like name of the zip =ile, method of the submission etc.






For Python Submissions:

1-) The code should run with the “python3 TextEditor.py <Addr> <ControlPort> “command.

2-) Python version should be 3.7 or higher. Other versions (like Python 2) are not accepted.

For Java Submissions:

1-) The code should run with the following commands:

Compile: “javac *.java”

Run: “java TextEditor <Addr> <ControlPort>”

2-) Java version should be 8 or higher.

3-) The JDK should be Oracle JDK (not OpenJDK).

9) 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 uploaded to the Moodle in a zip =ile. Any other methods (Disk/CD/DVD) of submission will not be accepted.

    • The name of the submission should start with [CS421_PA1], and include your name and student ID. For example, the name must be

[CS421_PA1]AliVelioglu20111222

if your name and ID are Ali Velioglu and 20111222. You can complete this assignment either individullay or together with a classmate. In the latter case, you need to make a single submission with the names and IDs included in the submitted zip =ile name as well as inside the report =ile.

    • All the =iles must be submitted in a zip =ile whose name is described above. The =ile must be a .zip =ile, not a .rar =ile or any other compressed =ile.

    • All of the =iles must be in the root of the zip =ile; directory structures are not allowed. Please note that this also disallows organizing your code into Java packages. The archive should not contain any class =iles or other executables, any third-party library archives (i.e. jar =iles), any text =iles (other than optional README), project =iles 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.

    •