Create the 404 template

The PSGI skeleton still has the code sending a plain 404 Not Found page for every other request:

return [ '404', [ 'Content-Type' => 'text/html' ], ['404 Not Found'], ];

The 404 page should look just like any other page on search.cpan.org, it even has the cpanstats at the bottom we worked so hard to try to replicate.

First thing is to create the template with the unique content of the 404 page.

We can visit a page that does not exists, for example http://search.cpan.org/xyz and click on view-source. There we can find the content specific to this page and copy it tot a file called tt/404.tt. That was quite easy. Now we need to use that template to create the HTML file.

We can just replace

return [ '404', [ 'Content-Type' => 'text/html' ], ['404 Not Found'], ];

by

template('404');

and visit any not existing page to see the results.

Change the HTTP response code

That looks good. The only problem is that the template() function returns all the pages with a 200 Success code and in the case of the 404 page, we would like the HTTP status code to be 404.

In order to see what HTTP status code a page returns try curl -I (that's an upper case i)

Main page:

$ curl -I http://search.cpan.org/
HTTP/1.1 200 OK
Date: Wed, 19 Nov 2014 09:17:39 GMT
Server: Plack/Starman (Perl)
Content-Length: 3643
Content-Type: text/html
Connection: close

Not existing page on search.cpan.org:

$ curl -I http://search.cpan.org/abc
HTTP/1.1 404 Not Found
Date: Wed, 19 Nov 2014 09:17:42 GMT
Server: Plack/Starman (Perl)
Content-Length: 4006
Content-Type: text/html
Connection: close

Not existing page on the clone:

$ curl -I http://localhost:5000/abc

We could change the template function to accept a value for the status code, but in almost every other page this should be 200. So making all other places pass 200 seemed like a waste of clarity. Making the parameter optional and then setting it to default to 200 would work, but seemed a bit complex to implement.

Finally I settled with just calling template(), capturing its output, and replacing the HTTP status code before returning the value to be displayed by the browser.

We know that template() will return a 3-element array reference in which the first value is the status code, the second is the header, and the third is the content of the page.

So I wrote this:

   my $reply = template('404');
   return [ '404', [ 'Content-Type' => 'text/html' ], $reply->[2], ];

Instead of the hard-coded '404 Not Found' string I put in the content returned by the template() function in the 3rd place.

Actually, looking at the code now, it might be cleaner to write this:

   my $reply = template('404');
   $reply->[0] = '404';
   return $reply;

but I Am not sure in that.

That is, replacing the status-code in the reply we received from the template() function. We can visit the page again to make sure it still works and we can look at its header:

$ curl -I http://localhost:5000/abc

That brings us to the next commit

$ git add .
$ git commit -m "add 404 Not Found page based on the content on sco. Use template for it"