Alternative for echo in sending header plugin

Question

I'm getting the following PHP error's from Wordpress:

Warning: Cannot modify header information - headers already sent by (output started at domain/public_html/sdapi/wp-content/plugins/testpost/testpost.php:74) in domain/public_html/sdapi/wp-admin/post.php on line 235

Warning: Cannot modify header information - headers already sent by (output started at domain/public_html/sdapi/wp-content/plugins/testpost/testpost.php:74) in domain/public_html/sdapi/wp-includes/pluggable.php on line 1196

With this code:

    <?php
/**
 * Plugin Name: testpost
 */
add_action( 'publish_post', 'testpost', 10, 1 );
function testpost( $post ) {

// ***** Get variables *****
$post_id = $post;
$post_object = get_post( $post_id );
$post_object->post_content;

$title = $post_object->post_title;
$source_url = get_permalink( $post_id );
$body = $post_object->post_content;

$titleprint = preg_replace("/\r?\n/", "\\n", addslashes($title));    
$bodyprint = preg_replace("/\r?\n/", "\\n", addslashes($body));
$posturlprint = preg_replace("/\r?\n/", "\\n", addslashes($source_url));




// ***** Run script *****
echo "<script>

var Request = new XMLHttpRequest();

Request.open('POST', '****POSTURL****');

Request.setRequestHeader('Content-Type', 'application/json');
Request.setRequestHeader('Accept', 'application/json');
Request.setRequestHeader('Authorization', '****TOKEN****');

Request.onreadystatechange = function () {
if (this.readyState === 4) {
}
};

var body = {
'article': {
'uuid': '090bda74-b021-4c7c-a44a-44f33bba32142',
'title': '". $titleprint ."',
'source_url': '". $posturlprint ."',
'body': '". $bodyprint ."'
}
};

Request.send(JSON.stringify(body));


</script>";




}
?>

*Whitespace before <?php is added by pasting here, cannot get rid of it :(

At first I thought it was the Whitespace problem as explained extensively here: How to fix "Headers already sent" error in PHP.

Unfortunately that's not it (easy to fix) and I'm thinking it's the "Print, echo issue" as described in the same answer.

Unfortunately I need to use echo, otherwise my plugin doesn't work at all.

Is there an alternative for using echo here, or perhaps some way around this? Hope someone can help.

Answer 1

Try to use ob_start(); to prevent headers already sent problem. this problem is mostly due to extra spaces in php code or and also you have too much spaces before closing the ?> tag , you can also avoid to use this closing tag and please remove these spaces.

<?php
 ob_start();
/**
 * Plugin Name: testpost
 */
add_action( 'publish_post', 'testpost', 10, 1 );
function testpost( $post ) {

// ***** Get variables *****
$post_id = $post;
$post_object = get_post( $post_id );
$post_object->post_content;

$title = $post_object->post_title;
$source_url = get_permalink( $post_id );
$body = $post_object->post_content;

$titleprint = preg_replace("/\r?\n/", "\\n", addslashes($title));    
$bodyprint = preg_replace("/\r?\n/", "\\n", addslashes($body));
$posturlprint = preg_replace("/\r?\n/", "\\n", addslashes($source_url));

// ***** Run script *****
echo "<script>

var Request = new XMLHttpRequest();

Request.open('POST', '****POSTURL****');

Request.setRequestHeader('Content-Type', 'application/json');
Request.setRequestHeader('Accept', 'application/json');
Request.setRequestHeader('Authorization', '****TOKEN****');

Request.onreadystatechange = function () {
if (this.readyState === 4) {
}
};

var body = {
'article': {
'uuid': '090bda74-b021-4c7c-a44a-44f33bba32142',
'title': '". $titleprint ."',
'source_url': '". $posturlprint ."',
'body': '". $bodyprint ."'
}
};

Request.send(JSON.stringify(body));

</script>";
}
?>

Answer 2

It seems like whitespace exists in the start of your code. That's why you are getting this warning. There should not be any space in the beginning and end of the php tags.