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Article: 1056 of comp.lang.perl
Path: lightnin!rwsys!trsvax!utacfd.uta.edu!news.oc.com!lgc.com!cs.utexas.edu!uunet!usc!rpi!scott.skidmore.edu!psinntp!psinntp!internet!sbi!zeuswtc!cyclone!bet
From: [email protected] (Bennett E. Todd @ Salomon Brothers Inc., NY )
Newsgroups: comp.lang.perl
#Subject: Re: a perl program which is run from inetd
Message-ID: <[email protected]>
Date: 30 Sep 92 21:10:05 GMT
References: <[email protected]> <[email protected]>
Sender: [email protected]
Organization: Salomon Brothers, Inc.
Lines: 223


Here's an example daemon. I continue to twiddle and tweak it periodically.

#/usr/bin/perl

# Location of hosts DBM database
$hosts = '/usr/local/etc/hosts';

# Smtpd: SMTP daemon
#
# Install with a line like so in /etc/inetd.conf:
#  smtp stream tcp nowait root .../smtpd %A

# If we print anything, let's make it look like Internet goop.
$\="\r\n"; # output line delimiter


# Save hostname for a zillion messages; date is needed for mail header
$hostname=`hostname`;
chop $hostname;
$date = `date`;
chop $date;

# Parse arg. The %A above cause $ARGV[0] to be something like 810e5850.2569
$ARGV[0] =~ s/^([0-9a-e][0-9a-e])// || die "500 bad address\r\n221 $hostname stopped";
$o1 = hex($1);
$ARGV[0] =~ s/^([0-9a-e][0-9a-e])// || die "500 bad address\r\n221 $hostname stopped";
$o2 = hex($1);
$ARGV[0] =~ s/^([0-9a-e][0-9a-e])// || die "500 bad address\r\n221 $hostname stopped";
$o3 = hex($1);
$ARGV[0] =~ s/^([0-9a-e][0-9a-e])// || die "500 bad address\r\n221 $hostname stopped";
$o4 = hex($1);
$ARGV[0] =~ s/^\.([0-9][0-9][0-9][0-9])// || die "500 bad address\r\n221 $hostname stopped";
$port = $1;
$via="$o1.$o2.$o3.$o4";

# Try to translate ``via'' IP address into hostname. Don't sweat it if you can't.
#open(HOSTS,'</etc/hosts') || die "500 cannot open /etc/hosts\r\n221 $hostname stopped";
#lookup: while (<HOSTS>) {
#       /^$via[         ]*([^   ]*)/ && do { $via=$1; last lookup;};
#};
#close(HOSTS) || die "500 cannot close /etc/hosts\r\n221 $hostname stopped";
dbmopen(%hosts,$hosts,undef) && do {
       ($_ = $hosts{$via}) && ($via = $_);
       dbmclose(%hosts);
};

# Suck up passwd file. There are other ways this could be implemented....
open(PASSWD, '</etc/passwd') || die "500 cannot open /etc/passwd\r\n221 $hostname stopped";
while(<PASSWD>) {
       chop;
       ($pw_logname, $pw_passwd, $pw_uid, $pw_gid, $pw_gcos, $pw_home, $pw_shell) = split(/:/);
       $pw_passwd{$pw_logname} = $pw_passwd;
       $pw_uid{$pw_logname} = $pw_uid;
       $pw_gid{$pw_logname} = $pw_gid;
       $pw_gcos{$pw_logname} = $pw_gcos;
       $pw_home{$pw_logname} = $pw_home;
       if ($pw_shell eq '') {
               $pw_shell{$pw_logname} = '/bin/sh';
       } else {
               $pw_shell{$pw_logname} = $pw_shell;
       };
};

# Prepare for dialogue.
$|=1;      # Unbuffered writes
$/="\r\n"; # input line delimiter

# Opening greetings
print "220 $hostname Smtpd";

# This is the SMTP protocol, deduced by experimenting against a sendmail.
# Sure, I could have busted it up into subroutines. With lables on the blocks
# I think this is just as clear. It is certainly one hell of a big loop, though.
parse_command: while (<STDIN>) {
       chop;chop;
       /^helo *(.*)/i && do {
               $claim=$1;
               print "250 $hostname Hello $claim ($via), pleased to meet you";
               next parse_command;
       };
       /^help$/i && do {
               print '214-Commands:';
               print '214-     HELO    MAIL    RCPT    DATA    RSET';
               print '214-     NOOP    QUIT    HELP    VRFY    EXPN';
               print '214-For more info use "HELP <topic>".';
               print '214-smtp';
               print '214-Report bugs in the implementation to Bent.';
               print '214 End of HELP info';
               next parse_command;
       };
       s/^help *(.*)/\1/i && do {
         helpswitch: {
               /helo/i && do {
                       print '214-HELO <hostname>';
                       print '214-     Introduce yourself.  I am a boor, so I really don\'t';
                       print '214-     care if you do.';
                       last helpswitch;
               };
               /mail/i && do {
                       print '214-MAIL FROM: <sender>';
                       print '214-     Specifies the sender.';
                       last helpswitch;
               };
               /rcpt/i && do {
                       print '214-RCPT TO: <recipient>';
                       print '214-     Specifies the recipient.  Can be used any number of times.';
                       last helpswitch;
               };
               /data/i && do {
                       print '214-DATA';
                       print '214-     Following text is collected as the message.';
                       print '214-     End with a single dot.';
                       last helpswitch;
               };
               /rset/i && do {
                       print '214-RSET';
                       print '214-     Resets the system.';
                       last helpswitch;
               };
               /noop/i && do {
                       print '214-NOOP';
                       print '214-     Do nothing.';
                       last helpswitch;
               };
               /quit/i && do {
                       print '214-QUIT';
                       print '214-     Exit smtpd (SMTP).';
                       last helpswitch;
               };
               /help/i && do {
                       print '214-HELP [ <topic> ]';
                       print '214-     The HELP command gives help info.';
                       last helpswitch;
               };
               /vrfy/i && do {
                       print '214-VRFY <recipient>';
                       print '214-     Not implemented to protocol.  Gives some sexy';
                       print '214-     information.';
                       last helpswitch;
               };
               /expn/i && do {
                       print '214-EXPN <recipient>';
                       print '214-     Same as VRFY in this implementation.';
                       last helpswitch;
               };
               print '504 HELP topic unknown';
               next parse_command;
         };
         print '214 End of HELP info';
         next parse_command;
       };
       /^mail from: *(.*)/i && do {
               $from=$1;
               print "250 $from... Sender ok";
               next parse_command;
       };
       /^noop/ && do {
               print "200 OK";
               next parse_command;
       };
       /^quit/i && do {
               print "221 $hostname closing connection";
               exit(0);
       };
       /^rset/i && do {
               print '250 Reset state';
               next parse_command;
       };
       s/^(vrfy|expn) *(.*)/\2/i && do {
               s/@$hostname//;
               if ($pw_uid{$_} eq '') {
                       print "550 $_... User unknown";
                       next parse_command;
               };
               print "250 $pw_gcos{$_} <$_>";
               next parse_command;
       };
       s/^rcpt to: *(.*)/\1/i && do {
               s/^.*<([^>]*)>.*$/\1/;
               s/@$hostname//;
               if ($pw_uid{$_} eq '') {
                       print "550 $_... User unknown";
                       next parse_command;
               };
               push(@recipients,$_);
               print "250 $_... Recipient ok";
               next parse_command;
       };
       /^data/i && do {
               if ($from eq '') {
                       print '503 Need MAIL command';
                       next parse_command;
               };
               if ($#recipients < 0) {
                       print '503 Need RCPT (recipient)';
                       next parse_command;
               }
               open(BINMAIL,"|/bin/mail @recipients") || die "500 cannot call /bin/mail\r\n221 $hostname stopped";
               $sender = $from;
               $sender =~ s/^.*<([^>]*)>.*$/\1/;
               $sender =~ s/@.*$//;
               print BINMAIL "From $sender $date" || die "500 cannot send data to /bin/mail\r\n221 $hostname stopped";
               print BINMAIL "From: $from" || die "500 cannot send data to /bin/mail\r\n221 $hostname stopped";
               print BINMAIL "Received: $via ($claim)" || die "500 cannot send data to /bin/mail\r\n221 $hostname stopped";
               print BINMAIL "To: @recipients" || die "500 cannot send data to /bin/mail\r\n221 $hostname stopped";
               print '354 Enter mail, end with "." on a line by itself';
               while (<STDIN>) {
                       chop;chop;
                       /^\.$/ && do {
                               close BINMAIL || die "500 cannot close /bin/mail pipe\r\n221 $hostname stopped";
                               print '250 Mail accepted';
                               $#recipients = 0;
                               $from = '';
                               next parse_command;
                       };
                       print BINMAIL || die "500 cannot send data to /bin/mail\r\n221 $hostname stopped";
               }
               close BINMAIL;
               exit 0;
       };
       print "500 Command unrecognized";
};

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