Hello

I came across some code and I am grateful please, for some explanation on what the code is doing (for want of a better phrase). I am not understanding how it 'works', but it does. It is a cgi script. Opinions on the quality of it is not as important to me as is the desire to understand the principle of it.

The original is here: http://www.onlamp.com/2008/02/19/library; some code extract is below.

My initial ignorant questions are I suppose:

• How does the code in the 'eval' block get linked up with the related sub routines above ?
• How does the cgi process know which method to call ?
• Is it all related to the CGI module and if so how and where are these sub routines/calls passed to the CGI module object to get called when it (or the cgi process/env) needs for each http method ?

Generally an overview of what is 'going on' would help me a great deal, as I am struggling (apologies) to understand it.

Thank you. Habs.

extract code:

....

use CGI '3.30', ();
my $q = CGI->new;


.....

sub GET($$) {
    my ($path, $code) = @_;
    return unless $q->request_method eq 'GET' or $q->request_method eq
+ 'HEAD';
    return unless $q->path_info =~ $path;
    $code->();
    exit;
}

sub POST($$) {
    my ($path, $code) = @_;
    return unless $q->request_method eq 'POST';
    return unless $q->path_info =~ $path;
    $code->();
    exit;
}

sub PUT($$) {
    my ($path, $code) = @_;
    return unless $q->request_method eq 'PUT';
    return unless $q->path_info =~ $path;
    $code->();
    exit;
}

sub DELETE($$) {
    my ($path, $code) = @_;
    return unless $q->request_method eq 'DELETE';
    return unless $q->path_info =~ $path;
    $code->();
    exit;
}

.....

eval {

....

    GET qr{^/=$} => sub {
        print $q->header('text/html');

        print $q->h1('REST API Documentation');

        print $q->p('Here is a list of what you can do:');

        ......
    };

....

    GET qr{^/=/model/book/id/([\d-]+)$} => sub {
        my $id = $1;

        # Look up the resource file
        my $filename = get_local_path($id);
        if (-f $filename) {

            # Open and slurp up the file and output the resource

    .....

    };

....

    DELETE qr{^/=/model/book/id/([\d-]+)$} => sub {
        my $id = $1;

        # Make sure the book actually exists
        my $resource_path = get_local_path($id);
        unless (-f $resource_path) {
            barf 404, 'Where is What?',
                'Nothing here to delete.';
        }

    ....

    };
};

if ($@) {

    # Handle barfing
    if (ref $@ and reftype $@ eq 'HASH') {
        my $ERROR = $@;
        print $q->header( -status => $ERROR->{status}, -type => 'text/
+html' );
        print $q->h1( $ERROR->{title} );
        print $q->p( $ERROR->{message} ) if $ERROR->{message};
    }

    # Handle anything else
    else {
        my $ERROR = $@;
        print $q->header( -status => 500, -type => 'text/html' );
        print $q->title('Server Error');
        print $q->p( $ERROR );
    }

    exit;
}

# Nothing handles this, throw back a standard 404
print $q->header(-status => 404, -type => 'text/html');
print $q->h1('Resource Not Found');
[download]

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