WordPress API REST send mail with attachement send in HTTP request - php

Question

I'm trying to send an email from the WordPress REST API. This email has some file attached to it, that are sent from a JavaScript front end. I can get the data and the file, but I can't attach those files to the mail, it returns me this error :
Fatal error: Uncaught TypeError: preg_match(): Argument #2 ($subject) must be of type string, array given in /var/www/html/wp-includes/PHPMailer/PHPMailer.php:1853
Stack trace:
#0 /var/www/html/wp-includes/PHPMailer/PHPMailer.php(1853): preg_match('#^[a-z][a-z\\d+....', Array)
#1 /var/www/html/wp-includes/PHPMailer/PHPMailer.php(1865): PHPMailer\PHPMailer\PHPMailer::isPermittedPath(Array)
#2 /var/www/html/wp-includes/PHPMailer/PHPMailer.php(3193): PHPMailer\PHPMailer\PHPMailer::fileIsAccessible(Array)
#3 /var/www/html/wp-includes/pluggable.php(522): PHPMailer\PHPMailer\PHPMailer->addAttachment(Array)
#4 /var/www/html/wp-content/plugins/my-project/views/API/email.php(100): wp_mail(Array, 'Demande de fina...', '\n\t<h1>Demande d...', Array, Array)
#5 /var/www/html/wp-includes/rest-api/class-wp-rest-server.php(1171): financement_email(Object(WP_REST_Request))
#6 /var/www/html/wp-includes/rest-api/class-wp-rest-server.php(1018): WP_REST_Server->respond_to_request(Object(WP_REST_Request), '/my-project/fin...', Array, NULL)
#7 /var/www/html/wp-includes/rest-api/class-wp-rest-server.php(442): WP_REST_Server->dispatch(Object(WP_REST_Request))
#8 /var/www/html/wp-includes/rest-api.php(410): WP_REST_Server->serve_request('/my-project/fin...')
#9 /var/www/html/wp-includes/class-wp-hook.php(308): rest_api_loaded(Object(WP))
#10 /var/www/html/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters('', Array)
#11 /var/www/html/wp-includes/plugin.php(565): WP_Hook->do_action(Array)
#12 /var/www/html/wp-includes/class-wp.php(399): do_action_ref_array('parse_request', Array)
#13 /var/www/html/wp-includes/class-wp.php(780): WP->parse_request('')
#14 /var/www/html/wp-includes/functions.php(1332): WP->main('')
#15 /var/www/html/wp-blog-header.php(16): wp()
#16 /var/www/html/index.php(17): require('/var/www/html/w...')
#17 {main}
thrown in /var/www/html/wp-includes/PHPMailer/PHPMailer.php on line 1853
I get the files like this :
$files = $request->get_file_params();
I call the wp_mail function like this :
wp_mail( $to, $subject, $body, $headers, $files)

Answer 1

The fifth parameter to wp_mail expects only an array of absolute file paths.
get_file_params() is basically a pass-through to the global $_FILES which contains an array of arrays with known keys, including tmp_name, which should be the absolute path on disk that the file temporarily lives.
You should be able to use array_column to get an array of just absolute paths.
$cleanFiles = array_column($files, 'tmp_name');
Demo: https://3v4l.org/FS1kV