CodeIgniter/PHP : Remove empty lines above RSS or ATOM xml tag

Problem:

Your friend is complaining that your website RSS feed is busted and validating with https://validator.w3.org gives this error message :

Sorry

This feed does not validate.

line 3, column 0: XML parsing error: :3:0: XML or text declaration not at start of entity

Parsing the XML file manually seems to ok and you wonder why the w3.org's validator is not accepting the generated RSS xml? Upon closer inspection, you noticed that there are 2 empty lines above the <?xml tag. These empty lines caused the validator to mark the RSS or ATOM xml as invalid.

01.

02.

03. <?xml version="1.0" encoding="utf-8"?>

04. <rss version="2.0"

You scanned the PHP and CodeIgniter core files and still unable to discover what caused the empty lines.

Solution:

To remove the empty lines before <?xml tag, simply add the functions ob_start(); and ob_end_clean(); before generating the XML output.

Example:

 ob_start();
 ob_end_clean();
 header("Content-Type: application/rss+xml");

This should get rid the extra empty lines before the <?xml tag and validating the RSS/ATOM feed again should be ok now.