GitHub - superfrink/genserv: A Generic Network Server Program

Branches Tags

Name		Name	Last commit message	Last commit date
Latest commit History 3 Commits
Makefile		Makefile
README.html		README.html
genserv.c		genserv.c

Repository files navigation

<html>
  <head>
    <title>genserv (a generic server program) : SuperFrink.Net</title>
  </head>
  
  <h2>genserv : A Generic Network Server Program</h2>
  <br>
  &nbsp; by Chad Clark  &nbsp; &nbsp;
  <hr>
  <br>
  <br>
  <h4>The Beginning</h4>
  Supose you have a program written in a language where you don't want to
  learn how to deal with network sockets or maybe a language that doesn't
  support sockets directly such as Bash.  What if you want to make this
  program available on a network?  Well you could write a web based front
  end.  I chose to write genserv (from Generic or General Server).<br>
  <br>
  <br>
  <h4>The Idea</h4>
  <ul>
    <li>There is a C program that listens for a network connect.
    <li>When a connection is made a child process is forked to deal with
        the new connection.
    <li>The child process sets the standard file descriptors (STDIN, STDOUT
        and STDERR) to all point to the network file descriptor.
    <li>The child then executes the application we want to connect to the
        network.
    <li>The application runs and deals with all I/O on the three standard
        file descriptors as normal.
  </ul>
  This works because of the way Linux handles network connections as files.<br>
  The application doesn't need to even know the network connection exists.<br>
  <br>
  <br>
  <h4>The Code</h4>
  The code is all in one C file.<br>
  There is also a makefile> but it's really simple
  and is only used because I like make.<br>
  Just put both files in one directory and type <tt>make</tt>.<br>
  <br>
  <br>
  <h4>Using genserv</h4>
  From the program's usage description:
    <blockquote> <pre>
usage:
         ./genserv port_num program_name args
where:
  "port_num" is a valid TCP port number.
  "program_name" is a program to be run when a client connects.
  "args" is an optional list of arguments to the program to be executed.

eg: ./genserv 12345 /usr/bin/uptime
    will listen on port 12345 and print the uptime string then exit.

eg: ./genserv 12345 /usr/bin/uptime -V
    will listen on port 12345 and print the uptime version then exit.
    </pre> </blockquote>
  <br>
  In the future I want to add some sort of basic authentication scheme.<br>
  Most likely just a password that is set when genserv is started.<br>
  Currently there is no authentication build into genserv so any programs<br>
  which get run from genserv need to either do their own authentications <br>
  or be open to the network.<br>
  <br>
  It may also be usefull/interesting to read the
  <a href="http://www.dwheeler.com/secure-programs/">Secure Programming
  for Linux and Unix HOWTO</a> <br>
  if you have to write programs which other people will be running.<br>
  <br>
  <br>
  <h4>Testing</h4>
  All of my work was done a stock
  <a href="http://www.slackware.com">Slackware Linux</a> 8.1 machine.<br>
  <br>
  To test the program run <b><tt>./genserv 12321 ls -l </tt></b>.<br>
  From another TTY telnet to port 12321 (eg <b><tt>telnet 127.0.0.1 12321</tt>
  </b>).<br>
  You should see something like:
    <pre> <blockquote>
[frink@thepurplebuffalo ~/code/cxx/genserv]$telnet 127.0.0.1 12321
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
total 32
drwx------    2 frink    users        4096 May 17 18:00 CVS
-rw-r--r--    1 frink    users          94 May 17 21:46 Makefile
-rwx------    1 frink    users       16693 May 17 21:46 genserv
-rw-r--r--    1 frink    users        3887 May 17 21:46 genserv.c
-rw-------    1 frink    users           0 May 17 21:47 typescript
Connection closed by foreign host.
[frink@thepurplebuffalo ~/code/cxx/genserv]$
    </blockquote> </pre>

  <br>
  <br>
  <h4>Known Bugs</h4>
  <ul>
    <li>ioctl() causes an issue on "who am i" but not on "who".<br>
        I belive this is because STDIN is mapped to a network file
        descriptor and not to a tty.<br><br>
        In particular ioctl sets errno for "Request or argp is not valid."
        who then exits with status zero.<br>
        <pre>
        ioctl(0, SNDCTL_TMR_TIMEBASE, 0xbffff598) = -1 EINVAL (Invalid argument)
        _exit(0) 
        </pre>
  </ul>
  <br>
  <br>


  </body>
</html>