jquery - Google App Engine, AJAX is returning string of contents of PHP file insteasd of JSON

I have been trying to get working the datatable in GAE with PHP as a runtime but somehow it is returning the actual page content instead of json response. Following is the app.yaml file.

application: app353
version: 1
runtime: php
api_version: 1
threadsafe: yes

handlers:
- url: /favicon\.ico
static_files: favicon.ico
upload: favicon\.ico

- url: /css
static_dir: css

- url: /js
static_dir: js

- url: .*
script: index.php

- url: /php/genjson
script: php/genjsonphp.php
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PHP/HTML snippet

<?php

?> 
<script src="./js/jquery.js"></script>
<script type="text/javascript" language="javascript" src="./js/jquery.dataTables.js">     
</script>
<link rel="stylesheet" type="text/css" media="all" href="./css/jquery.dataTables.css" /> 


<script>
$(document).ready(function() 
{    
$('#example').dataTable( 
{  
 "ajax": './php/genjsonphp.php' 
 } );
} );
</script>


 <table class="display" id="example">
 <thead>
 <th>Dimensions</th>

 </thead>
 <tbody></tbody>
 </table> 
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directory structure are as follows

css/*.css
js/*.js
php/genjsonphp.php
app.yaml
index.php
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Content snippet from getjsonphp.phh

header('Content-Type: application/json');
var_dump(json_decode($strjSon));
header('Content-Type: application/json');
echo $strjSon;
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Log from google app engine.

default: "GET /css/jquery.dataTables.css HTTP/1.1" 304 -

default: "GET /php/genjsonphp.php HTTP/1.1" 200 675

Spent lots of time debugging but no luck Can someone point to the error or documentation please.

Thanks, Sachin