Question

My colleagues and I are maintaining and developing a Perl web-project that works via mod_perl.

Now we are going through a major legacy code refactoring in which we have implemented some sort of an MVC pattern.

Among other things, my task is to make sure that all HTTP response headers are processed and sent back to the browser inside the main controller. For example, if a redirect is required, a page handler throws an exception, then the main controller catches it and generates the corresponding headers.

It all looked well until I started to implement cookie handling. Before that our code just printed cookie headers to output when it was required, like so:

# $response is an instance of the CGI class
print $response->redirect(
    -uri => "/some_uri/",
    -cookie => $response->cookie(
         -name => 'user_id',
         -value => $user->{'id'},
         -path => '/', -expires => '+1M'));

And now I want the $response object to store that information, so I can later send all headers together. I thought that it would go something like that:

sub page_handler {
    # ...
    $response->cookie(-name => 'user_id',
         -value => $user->{'id'},
         -path => '/', -expires => '+1M');
    return;
}

# And then, inside the controller

sub controller {
    # ...
    # the same $response instance 
    print $response->header();
    print $output;
    # ....
    exit();
}

But it seems that the CGI class object doesn’t store all headers that it creates with the header method. Some headers seem to persist, while others do not, here is what I get in re.pl:

$ use CGI;        
$ my $response = CGI->new();
$CGI1 = CGI=HASH(0xa6efba0);
$ $response->header();
Content-Type: text/html; charset=ISO-8859-1

$ $response->header(-type => 'text/plain', -charset => 'UTF-8', -status => '200 OK');
Status: 200 OK
Content-Type: text/plain; charset=UTF-8

$ $response->header();
Content-Type: text/html; charset=UTF-8 

I expected the last output to be either the same as the previous one, or the same as the first one, where I have not yet set any headers. I did not expect it to change partially.

That is why I ask my question: Why does some header information in a CGI.pm object persist while another does not?

Am I using the object incorrectly? Is there a way I could use it the way I intended to?

PS: Sorry for the long question, I wanted to make sure you understand what I want to do.

PPS: Also, I know that many people around here recommend going away from CGI and using Catalyst. This is, I am afraid, not an option right now, because we have too much legacy code, and we are hoping to get away from mod_perl altogether. This is required only for a certain feature.

Answer 1

To answer your question, the header method doesn’t store any information, nothing is persistent.

With your example of the header ‘object’ persisting, reading TFM helps:

The -charset parameter can be used to control the character set sent to the browser. If not provided, defaults to ISO-8859-1. As a side effect, this sets the charset() method as well. [emphasis mine]

After you call header with some parameters, then call it as default, the only thing to ‘persist’ is the character set.

For your cookie problem, i think you’d have to store $response->cookie(); somewhere. TFM doesn’t say that the cookie() sub stores the data anywhere, it just says that it creates a cookie.

I agree with Sinan though – throwing exceptions is crazy talk, especially to cover CGI.pm’s redirect sub. I’d rethink that one. Or go completely the other way and write the whole webapp only using exception handling – there’s be some good laughs along the way :o)