Assignment 1: Simple Mail Client/Server Application Implementation

CS3205 ­ Computer Networks
Assignment 1: Simple Mail Client/Server Application Implementation

1 Assignment description
The objective of this assignment is to implement a simple email client, and a mail server using the Socket Interface.
We will be implementing a minimal client and server in this assignment. The objective of the assignment is to
familiarize yourself with writing a network server and a client.
There are two major components to the software: (i) the email server, and (ii) the email client. The communication will be based on a TCP socket.
1.1 Email server
The purpose of the email server is to respond to the requests generated by the client. The server is expected to be up
and running on the remote machine, listening to a specific port.
The server software contains these major components:
(i) NETWORK INTERFACE: This piece is responsible for receiving requests from the client, and passing it to
the COMMAND PROCESSOR.
(ii) COMMAND PROCESSOR: This is responsible for processing the request from the client, running appropriate system commands and passing the output generated to the NETWORK INTERFACE.
When the server is started, the default directory is called the “root” directory of the server. The user’s mail spool
files will be stored in this directory.
The server one spool file to each user, for storing the mails delivered to the specified user.
The user’s spool file consists of multiple email records. The email record format for userC is as given below.
Each email record is terminated by ###.
From: userA
To: userC
Date: Sat Jan 28 21:38:48 IST 2017
Subject: Hello
...
Contents
...
###
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From: userB
To: userC
Date: Sat Jan 28 21:39:16 IST 2017
Subject: Hello again
...
Contents
...
###
From: userD
To: userC
Date: Sat Jan 28 22:39:16 IST 2017
Subject: Congrats
...
Contents
...
###
The commands that the server will support are as follows:
• LSTU
Semantics: The server will send a list of users (separated by spaces) to the client, which then prints the
message.
• ADDU <userid>
Semantics: The server will create an empty mail spool file if the specified userid is not present; otherwise, the
server will reply with a message, “Userid already present” to the client.
• USER <userid>
Semantics: If the userid is valid, the server sends an ack message to client (to be printed) that the specified
user exists and has XY number of messages in his/her spool file. Also, the server will next respond to mail
item requests from the specified user’s file. The current user is set to this specified user.
The mail read pointer is set to the first mail item in the user’s spool file.
If the userid is invalid, the server sends an error message to client (to be printed) that specified user does not
exist.
• READM
Semantics: If the current mail pointer of the current user is INVALID, the server sends a message “No More
Mail” to the client.
The server sends the current mail item (being pointed to) in the spool file, to the client (that prints it). The
spool file’s mail pointer will then move forward to the next item. If this is the last item in the spool file, then
the mail pointer will go back to the first item, if exists. Otherwise, it will be set to INVALID.
To terminate each mail message, use three special characters (###). Assume that this pattern does not appear
in each mail message.
• DELM
Semantics: If the current mail pointer of the current user is INVALID, the server sends a message “No More
Mail” to the client.
The server deletes the current mail item (being pointed to) in the spool file, and sends a confirmation message
“Message Deleted”. The spool file’s mail pointer will then move forward to the next item. If this is the last
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item in the spool file, then the mail pointer will be go back to first item, if exists. Otherwise it will be set to
INVALID.
This can be verified by checking the user’s spool mail file in the server directory.
• SEND <userid>
Semantics:
If the userid is valid, copy the message contents to the specified receiver’s userid (as sent from the current
user). The server will store from and To fields, and contents accordingly. The mail will be appended at the
end of the receiver’s spool file.
If the userid is invalid, the server sends an error message to the client (to be printed) that the specified user
does not exist.
• DONEU
Semantics: The current user’s mail spool reading activity is stopped. Any subsequent READM and DELM
commands will result in error messages being sent from the server to the client. The next current user has to
be set using the USER command.
• QUIT
Semantics: The current session with the client ends. The server closes the connection with the client.
1.2 Email Client
An end user will be running the email client to communicate with the server. The client software can be partitioned
into these major pieces:
(i) USER INPUT INTERFACE: The user­input interface accepts user commands, processes them, and passes
appropriate data to the network interface.
(ii) NETWORK INTERFACE: The network interface is responsible for establishing the required socket(s) with
the remote server. It is responsible for accepting the data provided by the USER INPUT INTERFACE above and
transmitting it over the socket. It is responsible for reading the responses transmitted by the server, and either storing
the data on file locally, or displaying it to the screen.
Client will wait at a prompt:
Main­Prompt>
The client software interface will then accept the following commands:
• Listusers
The client will send the message LSTU userid to the server, and print the server’s response.
• Adduser <userid>
The client will send the message ADDU userid to the server, and print the server’s response.
• SetUser <userid>
The client sends the message USER userid to the server, and prints the server’s response.
The client will then print a sub­prompt as follows:
Sub­Prompt <userid>
and wait for subsequent commands, specific to this user. These commands are:
1. Read
The client will send the message READM to the server, and print the server’s response.
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2. Delete
The client will send the message DELM to the server, and print the server’s response.
3. Send <receiverid>
The client prints a prompt, “Type Message:”. The user will type a mail message terminated by###. The
client then sends the message SEND receiverid <message>to the server, and prints the server’s
response.
4. Done
The client will send the message DONEU to the server, and print the server’s response.
• Quit
The client will send the message QUIT to the server, print the server’s response, and close the TCP session.
The role of the client interface is thus to accept the user commands, parse the commands, and generate the
appropriate Email Server commands that will be passed to the server.
2 Sample Session
Assume that you have created the files emailclient.c and emailserver.c and the corresponding executables in your Assignment1 directory. Please use a suitable unique port number for your server. The directory Assignment1/MAILSERVER
will be the “root” directory for the server purposes.
(Note: You can test for the following cases – (i) server and client running on the same machine. You can invoke
the client as: emailclient localhost <port>; (ii) server and client running on different machines.)
% cd Assignment1
% ./emailserver 25678 & ­­ Server is running on say, dcf15
% cd Assignment1
% ./emailclient dcf15 25678 ­­ Client running on another host
.... Server’s initial response.
Main­Prompt> Listusers
.... Server’s response.
Main­Prompt> Adduser UserA
...
Main­Prompt> Adduser UserB
...
Main­Prompt> Adduser UserC
...
Main­Prompt> Listusers
.... Server’s response.
Main­Prompt> SetUser UserA
...
Sub­Prompt­UserA>Read
... (Error)
Sub­Prompt­UserA>Send UserB
Type Message: How do you do?###
Sub­Prompt­UserA>Send UserC
Type Message: What is the time?###
Sub­Prompt­UserA>Send UserB
Type Message: Is the ATM working?###
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Sub­Prompt­UserA>Send UserC
Type Message: Are you studying?###
Sub­Prompt­UserA>Done
Main­Prompt> SetUser UserB
...
Sub­Prompt­UserB> Read
...
Sub­Prompt­UserB> Send UserA
Type Message: Where are you now?###
...
Sub­Prompt­UserB> Delete
...
Sub­Prompt­UserB> Done
...
Main­Prompt> SetUser UserA
...
Sub­Prompt­UserA>Read
...
Sub­Prompt­UserA>Done
...
Main­Prompt> Quit
...
%
3 What to Submit
Name your assignment directory as Assignment1 (Note: ALL UPPERCASE)
Once you are ready to submit, change directory to the directory above Assignment1, and tar all files in the
directory with the command:
tar czf XYxyBabc­Assignment1.tgz Assignment1
where XYxyBabc refers to your roll number.
The directory should contain the following files:
• Client Software Files
• Server Software files
• Makefile
Typing command ‘make’ at the UNIX command prompt, should generate all the required executables.
• a README file containing what port number to use, and instructions to compile, run and test your program.
README file should be written such that a TA must be able to run your code without your presence/help.
• a REPORT which consists snapshots (or copy pasted) of different sessions that are carried out. This can also
include extra/new things that you tried during the experiment (This gives you extra points). And, give a brief
summary as to what you learnt in this experiment and how much beneficial you feel the experiment was.
Make sure that all files have been correctly tar­red with the appropriate command. Then, submit the tgz file via
Moodle.
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5 Grading
• Server: 30 points
• Client: 30 points
• Report: 20 points
• Viva voce: 20 points
NO MAKE FILE: ­10 points;
NO README: ­10 points;
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