Exercise 1: A Simple Mail User Agent in Java

In this exercise you will implement a mail user agent (mail client) that sends mail to remote hosts. Your task is to program the SMTP interaction between the Mail User Agent (MUA) and the remote SMTP server.

Working in pairs: allowed!

Command line syntax

java MailClient <sender> <”comma-separated-recipents-list”> <”body”> <”subject”> <port>

Example: java MailClient com1@cs.huji.ac.il ”daniel51@cs.huji.ac.il,adaliot@cs.huji.ac.il” ”Hello…” ”This is Ex1.” 25

You should implement only the commands HELO, MAIL FROM, RCPT TO, DATA, QUIT.

The implementation should be done in Java using TCP.

The program should return 0 when successful, and System.exit(1) on error.

You should implement the char stuffing algorithm we talked about in class. (See SMTP RFC section 4.5.2 http://www.faqs.org/rfcs/rfc821.html)

Example interaction:

S: 220 hamburger.edu

C: HELO crepes.fr

S: 250 Hello crepes.fr, pleased to meet you

C: MAIL FROM: <alice@crepes.fr>

S: 250 alice@crepes.fr... Sender ok

C: RCPT TO: <bob@hamburger.edu>

S: 250 bob@hamburger.edu ... Recipient ok

C: DATA

S: 354 Enter mail, end with "." on a line by itself

   C: Date: 23 Oct 81 11:22:33

   C: From: SMTP@HOSTY.ARPA

   C: To: JOE@HOSTW.ARPA

   C: Subject: Mail System Problem

C:

   C:   Sorry JOE, your message to SAM@HOSTZ.ARPA lost.

   C:   HOSTZ.ARPA said this:

   C:    "550 No Such User"

   C: .

S: 250 Message accepted for delivery

C: QUIT

S: 221 hamburger.edu closing connection

You should check the server error codes. In case of error, the program should System.exit(1)

Command	Reply Code
DATA	354
HELO	250
MAIL FROM	250
QUIT	221
RCPT TO	250

The above table also lists the accepted reply codes for each of the SMTP commands you need to implement. For simplicity, you can assume that any other reply from the server indicates a fatal error and abort the sending of the message. In reality, SMTP distinguishes between transient (reply codes 4xx) and permanent (reply codes 5xx) errors, and the sender is allowed to repeat commands that yielded in a transient error. See Appendix E of RFC 821 for more details.

In addition, when you open a connection to the server, it will reply with the code 220.

Testing your software:

Open a connection from inside HUJI CS network to mail.cs.huji.ac.il and send a message to yourself.

Submission

You should implement one file called MailClient.java . In a README file write on the first line the logins of the two students which submitted this exercise separate by comma. Next write the full names.

Submit a tar file using the course-admin submission system:

tar cvzf ex1.tgz MailClient.java README

You MUST check your tar file using the command "~com1/www/checkme_ex1.sh ex1.tgz" on a linux machine (either mangal or inferno)

Example output of this command is:


com1@beach:~/www/Exercises/Ex1# ~com1/www/checkme_ex1.sh ex1.tgz 

Running on host: beach

Please verify that you check the program on either mangal or inferno

Going to open tar file: ex1.tgz

README

MailClient.java

Found exercise submitted by logins: moshe,ofnik

Please verify that logins are correct and seperated by comma




Trying to compile exercise

Compilation OK

Tar file OK!

com1@beach:~/www/Exercises/Ex1#

Example tar file is found on: ~com1/www/ex1.tgz"

Grading

The exercises will be checked using uniform random sampling. Any mistake in creating the tar or README files, will result in 10 points penalty.

References

http://www.faqs.org/rfcs/rfc821.html

Tips

Remember to check every call to the Java socket API for exceptions. For example, InetAddress.getName() can throw exception in case of the DNS query failed.