How to convert blog feed in Json API using php

Feed.php

<?php
header('Content-Type: application/json; Charset=UTF-8');
$feed = new DOMDocument();
$feed->load('http://androidstudiodevelop.blogspot.com/feeds/posts/default?alt=rss');// put your feed url here
$json = array();

$json['title'] = $feed->getElementsByTagName('channel')->item(0)->getElementsByTagName('title')->item(0)->firstChild->nodeValue;
$json['description'] = $feed->getElementsByTagName('channel')->item(0)->getElementsByTagName('description')->item(0)->firstChild->nodeValue;
$json['link'] = $feed->getElementsByTagName('channel')->item(0)->getElementsByTagName('link')->item(0)->firstChild->nodeValue;


$items = $feed->getElementsByTagName('channel')->item(0)->getElementsByTagName('item');

$json['item'] = array();
$i = 0;


foreach($items as $item) {
   $title = $item->getElementsByTagName('title')->item(0)->firstChild->nodeValue;
   $description = $item->getElementsByTagName('description')->item(0)->firstChild->nodeValue;
   $pubDate = $item->getElementsByTagName('pubDate')->item(0)->firstChild->nodeValue;
   $guid = $item->getElementsByTagName('guid')->item(0)->firstChild->nodeValue;
   
   $json['item'][$i++]['title'] = $title; 
   $json['item'][$i++]['description'] = $description;
   $json['item'][$i++]['pubdate'] = $pubDate;
   $json['item'][$i++]['guid'] = $guid;    
//create a new array out of it
file_put_contents('feed.json', json_encode($json));
$json_string = json_encode($json);
$file = 'feed.json';
file_put_contents($file, $json_string);
}

echo json_encode($json);
?>