Phpmailer and async sending email - php

Question

I read some other question before ask here cause other answers don't response to my problem.
I've a custom made cms in php. For example if I insert a new payment, the script send to all admin user a notify:
function insert_payment() {
// CODE TO INSERT PAYMENT INSIDE MYSQL DB
$sql_payment = "INSERT INTO payments ($amount, ...) VALUES (?, ...);"
...
// NOTIFY ALL ADMINS
foreach ( $array_emails as $email ) {
send_email_to_admin($email, $subject, $body);
}
// redirect to dashboard
header("Location: " . $homepage);
}
This is an example of send_email_to_admin() function:
function send_email_to_admin($email, $subject, $body) {
// return example:
// $result = array(
// "Error" = true or false
// "DateTimeOfSent" = datetime
// "Email" = string
//)
// SAVE RESULTS IN MYSQL DB ( I need to register results to be sure email are sent without errors...table can be then seen to a specific pages under admin panel of cms)
$mail = new PHPMailer;
...
...
if(!$mail->send()) {
$result = array("Error" => true, "DateTimeOfSent" => date("Y-m-d"), "Email" => $mail);
} else {
$result = array("Error" => false, "DateTimeOfSent" => date("Y-m-d"), "Email" => $mail);
}
$sql_result = "INSERT INTO SentResult ("Error", "DateTimeSent", "Email", ...) VALUES ( $result['Error'], $result['DateTimeOfSent'], $result['Email'] )"
...
//end function
}
Now if I have 1 or 2 admins is ok...but if I have a lot of admins the time gap is not good for waiting a result for each sent.
I'd like to pass the foreach loop to a child process if it possible that can process async the entire loop of SENDING and SAVING inside MYSQL the results.
So header("Location: " . $homepage) can be executed immediately.
Some additional info:
I'm using hosted server so i can't install packages and libraries
I can use only function provided by default PHP config
I can't use a cronjob queue method cause my hosting not provide a free service
i'd like a solution working on IIS windows server and a Linux based server
I'd like an little script example based on my code cause i never used a async method in php and i don't know nothing about it :(
Sorry for my english

Answer 1

you could implement a queue and process this queue (asynchronously) with a curl call.
Instead of sending the emails directly from function send_email_to_admin(), insert a new dataset in a dedicated SQL table EmailQueue. Next you write a recursive function that processes this queue (all emails waiting to be send) until the table EmailQueue is empty.
insert payment:
...
// NOTIFY ALL ADMINS
foreach ( $array_emails as $email ) {
queue_email($email, $subject, $body);
}
curl_process_email_queue();
...
make CURL call, to detach from parent script (source):
function curl_process_email_queue() {
$c = curl_init();
curl_setopt($c, CURLOPT_URL, $url/send_queued_emails.php);
curl_setopt($c, CURLOPT_FOLLOWLOCATION, true); // Follow the redirects (needed for mod_rewrite)
curl_setopt($c, CURLOPT_HEADER, false); // Don't retrieve headers
curl_setopt($c, CURLOPT_NOBODY, true); // Don't retrieve the body
curl_setopt($c, CURLOPT_RETURNTRANSFER, true); // Return from curl_exec rather than echoing
curl_setopt($c, CURLOPT_FRESH_CONNECT, true); // Always ensure the connection is fresh
// Timeout super fast once connected, so it goes into async.
curl_setopt( $c, CURLOPT_TIMEOUT, 1 );
return curl_exec( $c );
}
queue email:
function queue_email($email, $subject, $body) {
$sql = "INSERT INTO emailQueue ("email", "subject", "body") VALUES ($email, $subject, $body)";
...
};
seperate PHP send_queued_emails.php script to be called via URL by cURL, that actualy sends the queued emails (recursively, until queue is empty):
<?php
// close connection early, but keep executing script
// https://stackoverflow.com/a/141026/5157195
ob_end_clean();
header("Connection: close");
ignore_user_abort(true);
ob_start();
echo('Some status message');
$size = ob_get_length();
header("Content-Length: $size");
header("Content-Encoding: none");
ob_end_flush();
flush();
// connection is closed at this point
// start actual processing here
send_queued_emails();
function send_queued_emails() {
// avoid concurrent access
$sql = 'START TRANSACTION';
mysqli_query($sql);
// read one item from the queue
$sql = 'SELECT "id", email", "subject", "body" FROM emailQueue LIMIT 1';
$result = mysqli_query($sql);
// if no more datasets are found, exit the function
if (!$result || (mysqli_num_rows($result) == 0))
return;
// mail the queried data
$mail = new PHPMailer;
...
// optionally write the result back to database
$sql_result = 'INSERT INTO SentResult ... ';
mysqli_query($sql);
// delete the email from the queue
$sql = 'DELETE FROM emailQueue WHERE "id"=...';
mysqli_query($sql);
// commit transaction
$sql = 'COMMIT';
mysqli_query($sql);
// recursively call the function
send_queued_emails();
};
To improve the reliability you may want to use transactions, to prevent issues for concurrent calls of the script send_queued_emails.php. For other options also see Methods for asynchronous processes in PHP 5.4.
EDIT: added "close connection early, but keep executing script" as proposed in this thread. This should enable you to even set a higher timeout for the cURL call.
EDIT2: added header("Content-Encoding: none"); as proposed by itajackass (refer to comments)