在没有cron的外部Web服务器上的特定时间执行脚本

Question

I've got a website which is hosted on an external web hosting service which amongst other things, allows users to subscribe to events and be added to a registration list.

I'd like to be able to remind these users via email one day before the event occurs, to remind them with updated information about location, etc..

Currently, my hosting service doesn't support cron jobs, something I thought would provide the means to achieve this.

I've had an idea of executing the function when any user visits the front page nearest to the time when I would send the emails, but it seems like a bad option and left me thinking that there must be a better way.

I know of some companies which will execute your scripts at a specific time for a fee, but I would like more flexibility with being able to configure it directly on my website.

I'm wondering if there is any API in PHP which could allow me to do this, or if my idea is the best way of achieving my goal, or am I missing something obvious..

Any help appreciated.

Answer 1

Take a look at mcrypt_encrypt and mcrypt_decrypt functions. You can set up a PHP script on your external page with get parameter as input. That input will be used as authentication so noone unauthorized runs the script. Use above functions to encrypt and decrypt authorization key. That could be anything you like, but I suggest you to create something random, for example:

$authMessage = 'yourMessage' . date('Y-m-d', time());

and encode it, then send it through get. Encrypted message will change every day, so it will be noticeably harder to break in.

On the remote server, you read encrypted message from get. Decode it using the same key you used to encode and check if everything's fine (that means, if string is decoded properly and date is today's date). If everything is ok, you can start up script.

You can do that also using simplier method, like involving md5():

On your primary server call your page with get parameter like this:

$get = md5('your secret phrase, the longer the better'.date('Y-m-d', time()));

on your remote server, when request with get parameter comes, do the same, and check if md5 you generated is equal to one that came from get. If it is, run the script.

Of course you will have to call your remote server remotely somehow... But I assume, that you're able to run cron on your primary server, so that won't be an issue.