That's a feature of CGI - it's treating your post data as an ISINDEX script. Definitely not something you want to rely on:

#!/usr/local/bin/perl

use strict;
use warnings;

use CGI;
use Data::Dumper;

my $cgi = CGI->new(  '{
      "Image": {
          "Width":  800,
          "Height": 600,
          "Title":  "View from 15th Floor",
          "Thumbnail": {
              "Url":    "http://www.example.com/image/481989943",
              "Height": 125,
              "Width":  "100"
          },
          "IDs": [116, 943, 234, 38793]
        }
   }'
);

print Dumper( $cgi );


$cgi = CGI->new(  '{
      "Image": {
          "Width=":  800,
          "Height": 600,
          "Title":  "View from 15th Floor",
          "Thumbnail": {
              "Url":    "http://www.example.com/image/481989943",
              "Height": 125,
              "Width":  "100"
          },
          "IDs": [116, 943, 234, 38793]
        }
   }'
);

print Dumper( $cgi );
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Your best bet is to provide a cgi_get_query method that deals with the data how you want to deal with it (as outlined in the docs for CGI::Application).

To get at the raw data of a post request, use CGI::Applications internal CGI objects special POSTDATA parameter like so:

my $data = $self->query->param('POSTDATA');
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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;
}
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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
    });
}
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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

++ and thanks for the clue about CGI::Application::Plugin::JSON (I hadn't seen that). I've been using JSON but instead of header type text/plain, I've been using application/json (which is outlined in the rfc).

-derby

Quick solution <if anybody still needed on sending json for runmode>

sub send_json_data: Runmode {
  my $self = shift;
  $self->header_add(-type=>"application/json");
  ...
}
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OR refer this inside of CGI::Application::Plugin::JSON import() >> _send_headers() should take care of it.. though, its not taking care of for above runmode to return json data.

sub _send_headers {
    my $self = shift;
    my $private = $self->param('__CAP_JSON') || {};

    if( defined $private->{header} ) {
        $self->header_add( '-x-json' => $self->json_header_string );
    }

    if( defined $private->{json_body} ) {
        $self->header_add('-type' => 'application/json');
    } elsif ( defined $private->{json_callback} ) {
        $self->header_add('-type' => 'text/javascript');
    }
}
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