I've been using the JSON header via CGI::Application::Plugin::JSON to send data from a CGI::Application webapp. Say you have a runmode called "blackout". Here's an untested sketch:

sub blackout {
    my $self = shift;
    my $message = 'hi!';
    $self->header_add(-type=>"text/plain");
    my $query = $self->query();
    my $output =  $query->start_html();
    $output .= $query->span($message);
    $self->add_json_header(boStatus=>'OK');
    $self->add_json_header(boError=>'SUCCESS');
    $self->add_json_header(boMessage=>$message);
    $output .= $query->end_html;
    return $output;
}
[download]

Notice the span tag: I couldn't find a way to get it working without putting someting in the body of the page, so I just stuck the message in there. Figured it would at least mean something if it ever got displayed by a browser.

Now on the other end, I'm using the prototype library to get the JSON out of the header.

I don't know how to do Ajax without prototype, so this is the best I can give you.

function tryJSON(app) {
    var url = '/cgi-bin/TryCGIApp.cgi';
    var params = "mode=blackout";
    new Ajax.Request(url, {
        onSuccess : function(resp,jsonheader) {
            var foo = jsonheader.boStatus;
            var funk = jsonheader.boError;
            alert("The response from the server is: " + foo + " and " 
++ funk);
        },
        onFailure : function(resp) {
            alert("Oops, there's been an error.");
        },
        parameters : params
    });
}
[download]

I assume there's some way to reverse this process, with the javascript adding the JSON headers, but I haven't gotten that far yet...If you get it, please post!

Update:  explicitly mention CGI::Application::Plugin::JSON

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