Question

I’m changing some Perl scripts in an existing solution. Due to some changes when upgrading the (Windows) server I’ve switched them from running ISAPI to CGI. This means I now have to send Content-Type manually or it will fail.

So I need to enable output buffering (print statements, so STDOUT), send Content-Type: text/html, but in the cases where it is a redirect I need to clear output buffer and send new header.

How do I do that?

Or is there another way? Note that the script is already using print for outputting HTML, and I can’t change that. (It was written in the early 90’s.)

select(STDOUT);
$| = 0;
print "Content-Type: text/html\n\n";
# somehow clear output
print "Location: login.pl\n\n";

Answer 1

You can’t “undo” a print to STDOUT. You need to decide whether you’re generating HTML output or a redirect before you send anything to STDOUT.

One way of doing that would be to select an in-memory buffer instead of STDOUT:

my $buffer = '';
open(my $out, '>', \$buffer) or die;
select($out);
print "Content-Type: text/html\n\n";

if (generate_redirect) {
  print STDOUT "Location: login.pl\n\n";
} else {
  print STDOUT $buffer;
}

As soon as you’re sure you won’t be generating a redirect, you can re-select STDOUT and output the buffer:

select STDOUT;
print $buffer;
print "<p>HTML now goes to client instead of \$buffer</p>\n";