V22.0480-005 Lab 2: Fingerd server

Due date: Thursday Feb. 5, 3:30 pm.



In this lab assignment you will write a finger server (fingerd). Your fingerd will answer finger requests from clients.

You'll be writing this server to learn about how to use the server-side of the socket abstraction, as well as the fork and execve system calls. As in the first lab, we use client to mean an application program that establishes connections for the purpose of sending data. We use server to mean an application program that accepts connections in order to service requests by sending back responses, e.g., the finger daemon, the Apache web server, the SSH daemon, etc. For this lab, all network communication will continue to occur over TCP.

For more information about sockets and the various system calls we will use throughout the lab, please see the IPC Tutorial, as well as following man pages:

% man bind
% man listen
% man accept
% man fork
% man execve

Design Requirements

Your finger server will create a blocking TCP socket, either on a specified port or allowing the kernel to assign the port. (Although fingerd normally runs on port 79, you will be using a port above 1024, that you will subsequently specify in your client request. Port numbers below 1024 require root permissions to bind.)

The server will then listen on this socket, accepting connections from clients. Recall that accept returns a new socket that is connected to the client. You should read the client's request (of some user's name) from the socket, and then fork a new process and execve the finger command locally on this username. You should return the output from the local execution of finger to the client.

Your server application should be run in the following way:

% ./fingerd [port]

where the first optional argument is the port on which the server listens on its host. If it is not included, the kernel should assign a port.

Getting Started

We have provided a skeleton sc project directory. It is available in ~class/src/fingerd.tar.gz. Start by unpacking the source code in your home directory. On the class machines, you can do so with the following commands:

% tar xzf ~class/src/fingerd.tar.gz
% cd fingerd
% setenv AUTOCONF_VERSION 2.13
% sh ./setup
automake: configure.in: installing `./install-sh'
automake: configure.in: installing `./mkinstalldirs'
automake: configure.in: installing `./missing'
configure.in: 22: required file `./ltconfig' not found
automake: Makefile.am: installing `./INSTALL'
automake: Makefile.am: installing `./COPYING'
+ autoconf
+ set +x

The skeleton source tree contains source file fingerd.c, where you need to implement your echo server.

Next, you must configure the software and generate a Makefile--a set of instructions for how to compile the software. For this class, we will use the GNU autoconf and automake tools to generate Makefiles. On the class machines, generate the Makefile with the following commands:
% setenv DEBUG -g
% ./configure
creating cache ./config.cache
checking for a BSD compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
creating Makefile
creating config.h

Once the software is configured, you can build fingerd by running gmake. (Note that this is gmake with a g, and not make.)

% gmake
gcc -DHAVE_CONFIG_H -I. -I. -I.     -g -O2 -c fingerd.c
/bin/sh ./libtool --mode=link gcc  -g -O2 -static -o fingerd  fingerd.o  
mkdir .libs
gcc -g -O2 -o fingerd fingerd.o
That's it! You've now built fingerd.

You might wish to test your server using the netcat utility, as shown in class. On the same machine as your server,

% nc localhost [port]

Now, type in your username at the client and press return. It should be sent to the server, which should reply with your finger information. any data typed into stdin at the client should be output at your server, and echoed back to the client.

For example, using the system fingerd running on port 79:
101 class-serv:~> nc localhost 79
mfreed ^R
Login: mfreed                           Name: Michael Freedman
Directory: /home/c/mfreed               Shell: /usr/local/bin/tcsh
On since Tue Jan 27 13:35 (EST) on ttyp1 from ludlow.scs.cs.nyu.edu
Mail last read Fri Jan 23 03:58 2004 (EST)
No Plan.


You should make sure your client satisfies these requirements:

Collaboration policy

You must write all the code you hand in for the programming assignments, except for code that we give you as part of the assigment. You are not allowed to look at anyone else's solution (and you're not allowed to look at solutions from previous years). You may discuss the assignments with other students, but you may not look at or copy each others' code.

How/What to hand in

You must submit two files: To build a software distribution, run the command:
% gmake distcheck
rm -rf fingerd-0.0
mkdir fingerd-0.0
chmod 777 fingerd-0.0
here=`cd . && pwd`; \
top_distdir=`cd fingerd-0.0 && pwd`; \
distdir=`cd fingerd-0.0 && pwd`; \
cd /home/c/dm/sc \
  && automake-1.4 --include-deps --build-dir=$here --srcdir-name=/home/c/dm/sc --output-dir=$top_distdir --gnu Makefile
chmod -R a+r fingerd-0.0
gmake[1]: Leaving directory `/disk/c3/scratch/dm/fingerd-0.0/=build'
rm -rf fingerd-0.0
fingerd-0.0.tar.gz is ready for distribution
To turn in your distribution, copy it to the directory ~class/handin/lab2/username where username is your username:
% cp fingerd-0.0.tar.gz ~class/handin/lab2/`logname`/
To create a script file, use the script command. When you run script, everything you type gets saved in a file called typescript. Press CTRL-D to finish the script. The typescript should be copied to the same directory as the software distribution. For example:
% script
Script started, output file is typescript
% testfingerd ./fingerd
fingerd: connect test: passed
fingerd: server read test: passed
fingerd: server send known test: passed
fingerd: server send unknown test: passed
fingerd: multiple connect test: passed
fingerd: server read at multiple connect test: passed
fingerd: server write at multiple connect test: passed
test-fingerd: passed 7 failed 0

% ^D Script done, output file is typescript
% cp typescript ~class/handin/lab2/`logname`/
If you have any problems about submission, please contact the TA or instructor.