プログラミングの小石・大石

以下のプログラムはメイル・クライアントからメイルを SMTP によってうけとって SMTP サーバにリレーするが，"viagra" というキーワードがみつかると転送しない． 動作させるためには 'smtp.server.address' のかわりに実際に使用する SMTP サーバのアドレス / ドメイン名を指定する． (ポートが既定の 25 でなければ，それもかきかえる必要がある.)

############################################################################
#
#	Simple Mail Proxy
#
############################################################################

use Carp;
use Net::SMTP;
use Net::SMTP::Server;
use Mail::Message;
use Sys::Hostname;

use strict;

my $debug = 0;


## SMTP server address and port ##
#
my $SMTP_Server_Address = 'smtp.server.address';
my $SMTP_Server_Port = 25;


### Mail proxy (this server) address and port ##
#
my $Proxy_Port = 25;


#===========================================================================
#	Mail client connection service
#===========================================================================

### Constants ###

my $SUCCEEDED = 0;

my %commands = (DATA => \&cmd_data,
		EXPN => \&cmd_dummy,
		HELO => \&cmd_helo,
		HELP => \&cmd_help,
		MAIL => \&cmd_mail,
		NOOP => \&cmd_noop,
		QUIT => \&cmd_quit,
		RCPT => \&cmd_rcpt,
		RSET => \&cmd_rset,
		VRFY => \&cmd_dummy);

### Variables ###

my $client_socket;
my $from;
my @to;
my $message;


sub client_put ($) {
    my ($message) = @_;
    print "Sent:     $message\n" if ($debug);
    print $client_socket $message, "\r\n";
}

sub cmd_data () {
    if (!defined($from)) {
	client_put("503 5.5.1 Sender address not yet specified");
	return 1;
    };
    if (!@to) {
	client_put("503 5.5.1 Recepient address not yet specified");
	return 1;
    };
    client_put("354 Start mail input; end with .");

    my $done = 0;
    while (<$client_socket>) {
	# print "Received: $_" if ($debug);
	if (/^\.\r\n$/) {
	    $done = 1;
	    last;
	};
	s/^\.\./\./;
	$message .= $_;
    };
    if (!$done) {
	client_put("451 5.6.0 Message input failed");
	return 1;
    };
    return 0;
}

sub cmd_helo () {
    client_put("250-Action completed, okay");
    client_put("250 ENHANCEDSTATUSCODES");
}

sub cmd_help () {
    my $out = "214-Commands\r\n";
    my $total = keys %commands;
    my $i = 0;
    foreach my $cmd (keys %commands) {
	$out .= "\r\n214";
	if ($i++ % 5 != 0) {
	    $out .= $total - $i < 5 ? " " : "-";
	} else {
	    $out .= " ";
	};
    };
    client_put($out);
}

sub cmd_noop () {
    client_put("252 Unknown status, but attempting delivery");
}

sub cmd_quit () {
    client_put("221 Service closing");
    $client_socket->close();
    return 0;
}

sub cmd_mail ($) {
    my ($arg)  = @_;
    $arg =~ /FROM:\s*(\S+)$/i;
    $from = $1;
    client_put("250 Mail sender okay");
}

sub cmd_rcpt ($) {
    my ($arg) = @_;
    $arg =~ /TO:\s*(\S+)$/i;
    my $to = $1;
    push(@to, $to);
    client_put("250 Mail recepient okay");
}

sub cmd_rset () {
    $from = undef;
    @to = ();
    client_put("250 Reset action okay");
}

sub cmd_dummy () {
}



#===========================================================================
#	SMTP server connection service
#===========================================================================

### relay ($from, @to, $msg) ###
#   forward a mail to specified SMTP server
#
sub relay ($\@$) {
    my ($from, $to, $msg) = @_;
    
    $from =~ /<.*@(.*)>/;
    my $domain = $1;
    print "Domain: $domain\n" if ($debug);
    my $client = new Net::SMTP($SMTP_Server_Address, Port => $SMTP_Server_Port,
			       Hello => $domain, Timeout => 30, Debug => $debug) ||
	croak "Unable to connect to mail server: $!\n";
    if ($client) {
	$client->mail($from);
	foreach my $recipient (@$to) {
	    $client->to($recipient);
	};
	$client->data($msg);
	$client->quit() || croak "Relay failed: $!\n";
    };
}


#===========================================================================
#	Main
#===========================================================================

my $server = new Net::SMTP::Server(hostname(), $Proxy_Port) ||
    croak "Unable to create a new mail proxy: $!\n";

while ($client_socket = $server->accept()) {

    $from = undef;
    @to = ();
    $message = undef;
    my $accepted;

    client_put("220 Service ready");

    while (<$client_socket>) {
	print "Received: $_" if ($debug);
	chomp;
	my ($cmd, $arg);
	/^\s*(\S+)(\s+(.*\S))?\s*$/;
	$cmd = $1;
	$arg = $3;
	$cmd =~ tr/a-z/A-Z/;
	if (!defined($commands{$cmd})) {
	    client_put("500 5.5.2 Syntax error, command unrecognized");
	    next;
	};

	&{$commands{$cmd}}($arg);

	if ($cmd eq 'DATA') {
	    my $msg = Mail::Message->read($message);
	    my $body = $msg->body;
	    if ($body =~ /viagra/i) {
		client_put("554 5.6.0 Invalid keyword included: viagra");
		$accepted = 0;
	    } else {
		client_put("250 2.0.0 Message accepted for delivery");
		$accepted = 1;
	    };
	};
    };

    $client_socket->close();

    if ($accepted) {
	relay($from, @to, $message);
    };
}