Re: Exceptions and Return Codes

[Henri Icarus]

This is a great question, and I look forward to others replies to it. The big problem is that there is no one size fits all answer to this question. If your perl is a CGI script you don't want to die before you've printed out some error message. In other cases die is just fine. If you've got a database connection open you may want to clean up so an eval block is crucial. For the purposes of simple CGI's I've used the following general purpose "bomb" routine:

#---------------------------------------------------
# subroutine bomb
#        a somewhat ungracefull way to end the execution of the cgi
sub bomb
{
    my $error_text = shift;

    print "\n<B>Ho Boy! A nasty error has occured:</B> "; 
        #extra \n to close off the HTTP header
    print $error_text;
    print "\n";
    my @mail;

    if ($MAIL_BOMB_LIST ne '') {
        &printbomb(\@mail,$error_text);
        @BombRecipients = split (/,/, $MAIL_BOMB_LIST);

        my $submission = join '',@mail;
        $submission = "\n\n".$submission;
        $sent = &send_mail ($BombSMTPServer, $submission, 'CGI_Bomber@
+acme.com', "CGI $ENV{'SCRIPT_NAME'} bombed.", $BombReplyto, @BombReci
+pients);
    }
    exit;
}

# load error message and backtrace into @$array
sub printbomb
{
    my $array = shift;
    my $message = shift;
    
    my($syserror) = $!; 
    
    push @$array, <<"EOM";
The CGI script $ENV{'SCRIPT_NAME'} seems to be having trouble!

Error Message: $message
Sys Error is: $syserror

EOM

    my $i = 2;    # start back 2 so as not to print bomb & printbomb s
+tack frames.
    push @$array, "Backtrace:\n";
    push @$array, "    Subroutine name   | Line |                     
+  File                      \n";
    push @$array, "----------------------|------|---------------------
+----------------------------\n";
    while(($pack,$file,$line,$subname) = caller($i++)) {
        push @$array, sprintf("%21s |%5s |%50s\n",$subname,$line,$file
+);
    }
}

This code is obviously not the neatest, but it's very nice for debugging. It simply prints out the error message, but then e-mails the stack backtrace to the emails in the global $MAIL_BOMB_LIST

-I went outside... and then I came back in!!!!

[Abigail]

The disadvantage of using a bomb function is that it only performs the intended task if you use bomb. No CPAN module will do so. If you use a __DIE__ handler, you will catch all dies, including those from modules.

And it has the added benefit that if someone else has to maintain the code, she won't be wondering what this bomb function is for.

-- Abigail