Dancer not displaying Template

nathaniels has asked for the wisdom of the Perl Monks concerning the following question:

I've recently been toying with moving some Perl code into a web setting using Dancer. Below is some code to generate a list of files in a specific folder and then take in the user's selection. However, when run through the browser it simply generates a blank page. What's confusing for me is that the unrelated code following the template determines whether or not it will generate the page.

This works:

any ['get', 'post'] => '/parsescript' => sub {
    
    template 'test.tt';
};
[download]

This doesn't:

any ['get', 'post'] => '/parsescript' => sub {
    
    template 'test.tt';
    
    my @filelist;
    my $rawtext;
    my $rootdir = 'C:\\Users\\Nathaniel\\Corpus\\';

    opendir (DIR, $rootdir) or die $!;

    while (my $file = readdir(DIR) ) { 

        next unless (-f "$rootdir/$file");
        next unless ($file =~ /\.txt$/);
    
        push @filelist, $file ;
    }
};
[download]

Thanks for your help!

UPDATE:Thank you to everyone for their help. As always, one of the best results of posting on here is learning about all the other small mistakes or inefficiencies in your code unrelated to the code-breaking problem. Special thanks to CountZero, it would probably have taken me months to realize template must go at the end of the sub. Turns out my biggest mistake (which I omitted in my post as it seemed irrelevant) was trying to pass a list (rather than a reference to a list) to the template. Thank you all!

Comment on Dancer not displaying Template Select or Download Code

Replies are listed 'Best First'.
Re: Dancer not displaying Template by Corion (Patriarch) on Sep 21, 2013 at 07:53 UTC
I found Dancer to swallow error messages and `die` messages, and also to swallow output when warnings are issued during the runtime. The workaround I've used in anger is to wrap my code in my own `eval` and the output the caught information myself. Which defeats the point of using a framework. In your case, I would look closely at whether the code could `die` (maybe `$rootdir` doesn't exist, etc.) or whether it could output warnings (which doesn't seem to be likely). Update: See CountZeros reply, which is the more propable cause I guess - your handler needs to return the proper content through `template`, so `template` should be mostly called as `return template ...;` [download]	[reply] [d/l] [select]
Re: Dancer not displaying Template by choroba (Cardinal) on Sep 21, 2013 at 08:27 UTC
You should call `template` as the last command in a sub. Also, you are not giving any parameters to the template - you probably need to pass @filelist to it. لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re: Dancer not displaying Template by CountZero (Bishop) on Sep 21, 2013 at 18:57 UTC
From the Dancer docs about the `template` function: Returns the response of processing the given template with the given parameters In other words, whatever the sub returns goes to the client's browser, which is not necessarily what was returned by `template`. Hence in your first example you indeed see a webpage and in the second example you "see" the value of the while loop once it ends. As that is unlikely to be a properly formed web-page there is nothing to see. So put the call to `template` at the very end of the sub. And don't forget to pass `@filelist` to the `template` function (read the docs on how to do this). CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James My blog: Imperial Deltronics	[reply] [d/l] [select]
Re: Dancer not displaying Template by CountZero (Bishop) on Sep 21, 2013 at 18:43 UTC
Nothing to do with your problem, but you do not need to double-up the backslashes and even don't need to use back-slashes in the filepath. `my $rootdir = 'C:/Users/Nathaniel/Corpus/';` [download] works equally well and is less typing. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James My blog: Imperial Deltronics	[reply] [d/l]