Add attachments for create_post

Fixed. May be this will help someone looking for the same.

I wrote my own function in controllers/core.php:

public function ux_publish_post() {
    global $wpdb;

    global $json_api;
    $json = file_get_contents('php://input');
    $request_data = json_decode($json);

    global $user_ID;

    $new_post = array(
        'post_title'    => $request_data->post_title,
        'post_content'  => $request_data->post_content,
        'post_status'   => 'publish',
        'post_date'     => date( 'Y-m-d H:i:s' ),
        'post_author'   => $user_ID,
        'post_type'     => 'post',
        'post_category' => array(0)
        );

    $post_id = wp_insert_post( $new_post );

    $postId = $post_id;//$_REQUEST['postId'];
    $image = $request_data->post_image_attachment;

    $directory = "/".date(Y)."/".date(m)."/";
    $wp_upload_dir = wp_upload_dir();
    $data = base64_decode($image);
    $filename = "IMG_".time().".png";
    $fileurl = "../wp-content/uploads".$directory.$filename;

    $filetype = wp_check_filetype( basename( $fileurl), null );

     $upload_dir = wp_upload_dir();

    $upload_path = str_replace( '/', DIRECTORY_SEPARATOR, $upload_dir['path'] ) . DIRECTORY_SEPARATOR;

	// upload
    $image_upload = file_put_contents( $upload_path . $filename, $data );

    $attachment = array(
        'guid' => $wp_upload_dir['url'] . '/' . basename( $fileurl ),
        'post_mime_type' => $filetype['type'],
        'post_title' => preg_replace('/\.[^.]+$/', '', basename($fileurl)),
        'post_content' => '',
        'post_status' => 'inherit'
        );

    $attach_id = wp_insert_attachment( $attachment, $fileurl ,$postId);
    require_once(ABSPATH . 'wp-admin/includes/image.php');

	// Generate the metadata for the attachment, and update the database record.
    $attach_data = wp_generate_attachment_metadata( $attach_id,$fileurl );
    wp_update_attachment_metadata( $attach_id,$attach_data );

    return array('post_id' => $post_id);
}

https://localhost/website/?json=ux_publish_post

Parameters:

{
“post_title”:”New Title”,
“post_content”:”This is description”,
“post_image_attachment”:”/9j/4AAQSkZ…”
}

(Image is encoded)