2012 twenty-four merry days of Perl Feed

Reindeer Games

Dancer - 2012-12-05

Dancer is a Perl micro-web framework originally based on Ruby's Sinatra. Its status as a micro-framework means, amongst other things, that it is a very nimble creature, and can be thus showed many nifty tricks.

Have Your Party MC'ed by One of Santa's Close Collaborator

It doesn't take a lot of boilerplate to create a minimalistic web service with Dancer. For example, want to have a web service returning a random song in the current directory to help the party's DJ? There we go:


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#!/usr/bin/perl
use strict;
use warnings;

use autodie;

use Dancer;

use List::Util qw/ shuffle /;
use MP3::Info;

get '/song' => sub {
    opendir my $dir, '.';

    my ( $file ) = shuffle grep { /\.mp3$/ } readdir $dir;

    my $song = MP3::Info->new($file);

    return sprintf "%s (%s)", $song->title, $song->artist;
};

dance;
 

The result is bare-bone, but oh-so-wonderfully functional:

    $ perl next_song.pl
    >> Dancer 1.311 server 6046 listening on http://0.0.0.0:3000
    == Entering the development dance floor ...

    # meanwhile, on the DJ side
    $ curl http://localhost:3000/song
    01 A Tap Dancer's Dilemma (DIABLO SWING ORCHESTRA)

Shorter!

Can we make this shorter? You bet we can. For example, to be able to create mini-web services that only answer to their index route, we can create the module C.pm:


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package C;

use Dancer;

{ package ::main; use Dancer ':syntax'; }

END {
    get '/' => \&::index if defined &::index;
    dance;
}

1;
 

And voilà, make room for your new MC:

    $ perl -MC -MMP3::Info -e'sub index{@s=<*.mp3>;$s[rand@s];}'
    >> Dancer 1.311 server 6046 listening on http://0.0.0.0:3000
    == Entering the development dance floor ...

    # meanwhile, on the DJ side
    $  curl http://localhost:3000/
    01 - 01 A Tap Dancer's Dilemma.mp3

Even shorter!

Can we make this even shorter? Maybe slurp on simple scripts present in sub-directories and convert them into web service routes? My, but of course:


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package C;

use 5.10.0;

use Dancer;
use Path::Class qw/ dir /;

{ package ::main; use Dancer ':syntax'; }

dir('.')->traverse( sub{
    my( $child, $cont ) = @_;

    return $cont->() if -d $child;

    my( $route, $method ) = $child =~ /^(.*)\.(get|post|put)$/ or return;

    $route =~ s/^\.// or $route =~ s#^#/#;
    $route =~ s/SPLAT/*/g;

    say "adding route '$route'";

    eval <<"END_ROUTE";
$method '$route' => sub {
    \@_ = \@ARGV = splat;
    local \*STDOUT;
    open STDOUT, '>', \\my \$output;

    { @{[ $child->slurp ]} };

    return \$output;
};
END_ROUTE

    die "couldn't compile route '$child': $@" if $@;
});

END { dance; }

1;
 

And with that MC on steroid, we can now have auto-web-serviceable perl scripts:

    $ cat song.get
    use List::Util qw/ shuffle /;
    use MP3::Info;

    opendir my $dir, '.';
    my ( $file ) = shuffle grep { /\.mp3$/ } readdir $dir;
    my $song = MP3::Info->new($file);

    printf "%s (%s)", $song->title, $song->artist;

    $ cat request/SPLAT.put
    use 5.10.0;

    open my $request_fh, '>>', 'requests';

    my $song = shift;

    say {$request_fh} $song;

    say "song '$song' added to the list";

which can be used from the command-line:

    $ perl song.get
    01 A Tap Dancer's Dilemma (DIABLO SWING ORCHESTRA)

    $ perl request/SPLAT.put "Rudoplh The Red-Nosed Reindeer"
    song 'Rudoplh The Red-Nosed Reindeer' added to the list

and, once the MC is roused,

    $ perl -MC -e1
    adding route '/request/*'
    adding route '/song'
    >> Dancer 1.311 server 6586 listening on http://0.0.0.0:3000
    == Entering the development dance floor ...

the Holidays are suddenly all Web 2.0-ified:

    $ curl http://localhost:3000/song
    01 A Tap Dancer's Dilemma (DIABLO SWING ORCHESTRA)

    $ curl -X PUT http://localhost:3000/request/Rudolf_the_red_nosed_reindeer
    song 'Rudolf_the_red_nosed_reindeer' added to the list

See Also

Gravatar Image This article contributed by: Yanick Champoux <yanick@cpan.org>